Production controls and commercial regulations
Regulations on the technical and operational aspects of nursery plant production (certification and marketing) have recently come into force in the olive sector. These have evolved to respond to the demand for plant material of certified genetic provenance and phytosanitary status and to protect the sector by preventing the market release of heterogeneous olives that are reservoirs or carriers for infections which could jeopardise orchard yields .
The first regulation covering trade in nursery plants was the 1968 EC Directive No 68/193/EC, which laid down the minimum quality requirements (genetic and sanitary) of plants. Directives 92/34/EC, 93/64/EC and 93/79/EC are more specific in regulating fruit plant propagating material (including olive) and in laying down provisions for the inspection of nurseries and for the creation of lists of fruit plant varieties and propagating material held by suppliers.
Directive No 92/34/EC also introduced CAC material ( Conformitas agraria communitatis ) as the minimum quality standard of propagating material. Under this scheme, nurseries guarantee that plants are true to variety and free from quarantine pests and other agents of disease that could alter the quality standards of the material .
Further details about these categories can be found in the specific EC directives .
More recently, a number of countries have promoted a voluntary control scheme based on the requirements for CAC production conformity. This step was driven by a desire to set up and regulate a certification service specific to olive nursery production that is able to provide the necessary guarantees for the development of the sector ( Barba M., Mainolfi P. 1996; Ismaili Alaoui M., Dogse P. 2005; Martelli P., Prota U. 1997; Rotondi A., et al., 2003; Ouzzani N., et al., 2001).
Chapter 7 outlines a certification process for nursery-raised olives while Chapter 8 deals with pests and diseases that lower plant quality standards, alter certification goals and jeopardise nursery product sales .
 Chapter 7. Certification of plant production processes |
Certification has two goals: to protect the rights of end users (farmers) to buy a top-quality product and to allow nurseries to protect themselves from unfair competition by accrediting their production .
Genetic and sanitary certification is a process which controls and accredits the entire plant production process by guaranteeing clonal propagation from parent stock (foundation stock) and ensuring its phytosanitary suitability .
Process inspections are carried out by certification bodies (official, designated research institutes) which supervise the activities and methods implemented along the production chain. They accredit procedure and product suitability by analysing specific “critical points” such as: genetic and health compliance of foundation stock (cultivars and clones); certification of motherstock collections and shoot production; stages of propagation; nursery accreditation; procedures for purchase of plant material and for the sale of permanently labelled “certified” material.
Certification bodies are designated by the accreditation agency, which assesses their capabilities and objectivity and issues ‘specific regulations' approved by the National Certification Board, which is made up of experts and representatives.
All certification activities are carried out in cooperation with accredited centres, which check process stages on site and provide the National Certification Board with annual reports. Figure 7 outlines the roles of the accreditation agency, the certification body and the National Certification Board involved in this process.
The foundation stock (cultivar or clone) is identified by the plant breeder, who testifies to its genetic trueness and phytosanitary status and sees that these characteristics are properly maintained.
The entry of the foundation stock in the Pre-propagation Conservation Centre (PCC) is the first stage in the certification process. This centre may be public or private and is recognised by the National Phytosanitary Service which supervises its proficiency .
The task of the PCC is to evaluate the genetic and plant health compliance of the foundation stock received from the breeder, as well as to manage and conserve it as pre-basic (or super-elite) propagating material. At least two plants of this material are conserved in a screen house ( Photo 59 ) to isolate them from sources of contamination (health control ).
The PCC is also responsible for supplying the Pre-propagation Centres (PPCs) with the shoots for producing the “motherstock trees”.
The PPCs are managed by specialised laboratories or producer consortia and are recognised by the National Phytosanitary Service, which supervises their work (production of motherstock trees) and certifies this basic plant material after checking that the biometric characteristics of the olive trees comply with National Certification Board regulations . Besides conserving two or more basic-category plants in the screen house or field, the PPCs apply a specific protocol to produce and supply authorised bodies represented by nursery consortia or individual nurseries [Propagation Centres, PCs] with suitable certified plant material (seeds, scions, cuttings, rootstock, plants ) for setting up the motherstock collections. PCs are also supervised by the National Phytosanitary Service.
Nurseries subscribing to the certification scheme obtain “certified” plant material straight from the propagation fields as the sole source of supplies for propagation work (by grafting and cuttings). According to the working regulations and protocols, nurseries have to declare the number of shoots received, the grafts performed and the number of cuttings planted for rooting. Moreover, to reduce the critical points in the working stages and to facilitate controls, they must identify the cultivars and clones they intend to propagate in the mist propagation benches and graft houses.
“Certified” olive plants are sold under specific labels. At the time of sale, the nursery is responsible for ensuring that the characteristics of the plant comply with the declarations on its label (health status and trueness to variety) and with the production procedures specified in the regulations.
Nursery returns depend largely on the skill displayed during the critical points when creating and managing the motherstock collections and properly applying the procedures during the different stages of olive plant propagation and growing.
Correct management of the motherstock collections includes making sure that the area available is sufficient to house all the plants needed for scheduled production. Section B (Chapter 1 – Part I) specifies the analyses, checks and preventive measures required to protect the motherstock trees from contamination by pathogens and so ensure the health and agronomic suitability of this area. The procedures require all the motherstock trees to be marked and identified on a map to facilitate field checks, and nurseries have to document the quantity and intended purpose of the plant material taken from the motherstock trees.
Nursery activity is checked and supervised through the different stages of the process to control the genetic correspondence to variety and phytosanitary status of the propagated plants as well as to authorise their suitability for use. Table 3 summarises the types of checks carried out.
It is important to check periodically that the motherstock trees are true to the foundation stock by using morphological markers. Serological or biological assays are recommended for regular checks of plant phytosanitary status .
If implemented scientifically according to simple, efficient procedures, certification is an important tool for accrediting and diversifying nursery production. It results in the release of prime quality plants on the marketplace and helps to modernise the olive sector to make it sustainable.
The commercial success of nurseries can vary depending on the measures taken to curb pest and disease development during the stages of plant production ( Table 4 ).
Some adverse biotic conditions are hard to control and persist in the foundation stock used for plant propagation ( Martelli G.P. 1998) . This stock plays an important epidemiological role because it is a dangerous carrier for their dissemination ( Photo 60 ) . Other adverse conditions caused by insects are easy to identify ( Civantos M. 1999; Ricciolini M., Guidotti A. 2001 ) and to eliminate by simple treatment.
Pests and diseases should be diagnosed straight away and eradicated so that quality plants complying with certification requirements are produced.
Before describing symptoms, damage and preventive action, a list is provided of the chief sources of plant and animal infestation.
Plant diseases
Bacterial diseases. Pathogenic plant bacteria fall into two genera – Xanthomonas and Pseudomonas – and are generally less harmful than fungi. The weaker virulence of bacteria probably has to do with the characteristics of these micro-organisms: phytopathogenic bacteria do not form resistance mechanisms and find it harder to survive. They do not have the specific ability to penetrate the plant directly, only entering the internal tissues through natural openings or wounds. Plant cell liquids have an acid pH whereas bacteria prefer a subalkaline environment. They cannot be carried any distance by the wind because they aggregate in small jelly-like masses. The most hazardous bacterium is Pseudomonas Savastanoi pv. Savastanoi.
Fungal diseases. Fungi are the chief source of infestation in olive. The most common infections found in nurseries are caused by: Alternaria - Armillaria mellea - Botrytis cinerea - Spilocaea oleagina - Cylindrocarpon destructans - Gloesporium olivarum - Leivellula taurica - Mycocentrospora cladosporioides – Pythium - Stictis panizzei, Verticillium dahliae. In some cases correct cultural practices can contain the development of the disease, the biological cycle of which is closely linked to the taxonomic classification of the fungus concerned.
Viruses and phytoplasmas. Unlike other adverse conditions, viral diseases have been somewhat disregarded in olive propagation management. More recently, however, viruses and phytoplasmas have come to the forefront to corroborate phytosanitary certification ( Barba M. 1992; Bertolini E., et al., 1998; Clara M.I.H., et al., 1997; Felix, M.R., et al., 2001, 2005; Gallitelli, D., Savino, V., 1985; Henriques M.I.C., et al., 1992; Lavee S., and Tanne E., 1984; Saponari, M. Savino,V. 2003; Saponari, M., et al., 2002; Triolo E., et al., 1996) . The olive too has been found to be an unsuspected host to numerous viruses (12) and phytoplasmas (5), most of which have been isolated in asymptomatic plants and identified as the source of damage in only some cases. A list follows of those reported in the literature: SRLV( Strawberry latent ringspot ); ArMV ( Arabis mosaic ); CLRV ( Cherry leafroll ); CMV (Cucumber mosaic ); OLRSV ( Olive latent ringspot ); OLV 1 OLV 1 ( Olive latent 1 ); OLV 2 ( Olive latent 2 ); OVYaV ( Olive vein yellowing associated ); OYMDaV ( Olive yellow mottling and decline associated ); TMV ( Tobacco mosaic ); OSLV (Olive semilatent ); OLYaV ( Olive leaf yellowing associated ); Spherosis ( Olive micro spheroblasts ).
Viruses are carried passively through small wounds or by insects and the symptoms are often non-specific. Consequently, nursery producers should be vigilant and should contact technical experts at the first suspicion of viral symptoms.
Animal pests
Insects. This group includes a large number of species capable of damaging olive plants: Eriophyes oleae - Hylesinus oleiperda - Otiorrhynchus cribricollis -Liothrips oleae - Metcalfa pruinosa - Palpita unionalis - Resseliella oleisuga - Saissetia oleae .
Photo 61 illustrates some of the most common damage observed during the stages of olive nursery production listed in Table 4 .
I. Symptoms, plant damage and preventive action during the certification process
I.I. Conservation of plant stock (cultivars and clones) in the motherstock collection ( Photo 62 )
Olive plants of differing ages grown in the field can be attacked by different insects. Besides damaging the plants, these can transmit infections to the shoots collected for grafting or for rooting cuttings ( Table 5).
I.II. Propagation
Phytosanitary problems are linked to infections already present in the motherstock trees as well as to pathogens in the ground of the seed and graft facilities or in the soil of the mist propagation rooting benches .
During grafting, the biggest possibility of infection is when the scions have been taken from infected motherstock trees. The risk is greater if the plant material has been lifted arbitrarily from olive trees on private orchards. In mist propagation, the sudden development of fungi can alter the rooting performance of cuttings. Environmental conditions of high temperatures, near-saturation relative humidity, excessive watering of the rooting medium (perlite) and leaves and poor hygiene in the rooting benches and mist propagation greenhouses can all facilitate the development of fungi that can cause leaf drop and so harm root formation. Table 6 lists the insect pests most likely to infest olive plants during propagation .
I.III. Hardening of rooted cuttings or growing of plantlets
Rooted cuttings and grafted olive plants are placed in containers ( Photo 63 ) and transferred to greenhouses or tunnels for about six months in the wintertime. The development of some fungal diseases is limited in these environments, but some plant-eating pests pose more of a hazard ( Table 7 ).
I.IV. Growing the olive plants in the shade house
Growing conditions inside the shade house ( Photo 64 ) should be optimal to ensure a balanced ratio between the root system and aerial portion of the trees and so obtain marketable trees; the plants should also be checked for pests and diseases that could limit canopy development ( Table 8 ).
Generally, the pests and diseases that occur in nurseries are handled by chemical treatments, which are capable of combating most harmful agents. Nevertheless, preventive agricultural techniques are fundamental to reduce the risk of contamination in the new plants.
In practice, this means paying special attention to working choices. During the different stages of production nurseries must implement a series of measures, now listed, which are essential for containing the development of pests and diseases.
If viral disorders, dieback or death occur as a result of fungal infections it is absolutely essential to remove and destroy the infected plants to stop the infection from spreading. Work tools should be ‘sterilised' with disinfectant solutions to avoid fungal and bacterial contamination; grafting wounds should likewise be disinfected and covered with grafting wax or mastic.
Shoots should be taken solely from healthy plants and the rooting medium in the rooting benches should be used for one growing cycle only; it should be kept as clear as possible of plant debris which, during rooting, could contaminate it and encourage the development of rot.
Water management is also very important. Drip irrigation is preferable, applying short, frequent watering. The motherstock collections should have optimal drainage and effective drainage channels to remove excess water. Overhead irrigation should also be avoided because it is conducive to the development of fungal diseases.
Because plants are kept in the nursery greenhouses for lengthy periods of time, it is advisable to cover the roof and side openings with extremely fine-meshed nets to stop insects from entering.
I.V. Chief pests and diseases
A list follows of the pests and diseases of various origins that can damage nursery olive production. For ease of reading, each is described in the same order: symptoms, damage and any preventive action.
Alternaria
Symptoms: Irregular crust on plants, which is black, sooty and almost oily.
Damage : By damaging the leaves, it heavily restricts plant photosynthesis and alters gas exchange.
Prevention: Control scale insects and let air into the canopy.
Armillaria mellea
Symptoms and damage : Responsible for root rot, this pathogen resides in dead wood lying in very damp soil. It develops on debilitated trees and can cause considerable economic damage.
Botrytis cinerea
Symptoms and damage: Heavy growth of mould on the leaf blades leading to extensive necrotic lesions, or on petioles and shoots leading to the appearance of dry lesions. As a result, the vegetative parts dry out.
Prevention : This disease develops at a temperature of around 25 °C and in conditions of high relative humidity. The greenhouses should therefore be heated or opened for brief periods at night and the plants should be watered regularly.
Spilocaea oleagina
Symptoms : Round blotches of varying diameter appear on the green organs of the plant, especially the leaves; they range in colour from brown to yellow and green on the upper surface of the leaves.
Damage : This disease does the most damage to the leaves. The lesions cause defoliation and debilitate the plant. Premature leaf drop may occur even before the symptoms become fully apparent. Persistent rain (two or three days) and a temperature of between 5 and 25 °C are conducive to its development. Most infections occur in spring and autumn.
Prevention: Prune in December and January to open up the canopy and prevent excess internal humidity.
Cylindrocarpon destructans
Symptoms and damage : Leaves turn yellow and rapidly wilt and become desiccated.
This pathogen is rarely observed in young nursery plants. Promoted by transplant shock, it appears suddenly after the trees are planted out in the field. It can be considered an ‘opportunistic' disease that is active mainly in cold, heavy soils with a low acidity.
Prevention: Pay close attention to re-potting lesions.
Eriophyes oleae
Symptoms and damage : These mites make feeding bites in the shoots, which cause deformations similar to those caused by thrips and typical, yellowish-green hollows on the lower surface of the leaves and matching chlorotic bumps on the upper surface. When they attack the inflorescences, the flowers or whole inflorescences drop off.
Gloesporium olivarum
Symptoms : Initially, isolated ochre spots appear; they then grow and may join up. Attacks normally begin at the apex of the fruit, where rainwater accumulates. As the disease progresses, the attacked fruits display a round, dark depression; they later turn grey, become mummified and fall off.
Damage : The negative effects of olive anthracnose primarily affect the colour, acidity and organoleptic characteristics of the oil obtained from the olives.
Otiorrhynchus cribricollis
Symptoms and damage : These are usually mild in mature olives. In young olive plants, however, they lead to heavy debilitation and very poor growth (short internodes) of the trees affected; sometimes they may even kill the tree.
Hylesinus oleiperda
Symptoms : External symptoms on the wood are reddish–brown notches with roundish edges with the female entry hole at the centre. The symptoms only become noticeable after the trees are planted out.
Damage : The maternal and larval feeding galleries damage the woody structures of the plant.
Leivellula taurica
Symptoms and damage : This endoparasitic pathogen penetrates through the stomata. Chlorotic blotches covered with a floury mould appear on the upper surface and subsequently become necrotic.
Liothrips oleae
Symptoms and damage : The adults and greenish larvae puncture and suck the sap of the buds, leaves, flowers and young fruitlets, causing shoot, leaf and fruit deformation and flower drop.
Metcalfa pruinosa
Damage : The damage this insect causes to olive plants – honeydew on the leaves, with layers of mould and abundant, very visible wax – is very evident, but often well tolerated.
Direct damage in the form of sap sucking and fruit deformation is only reported sporadically.
Mycocentrospora cladosporioides
Symptoms : Irregularly shaped blotches appear on the lower surface of the leaves, with a very thin layer of lead–grey conidiophores. The matching areas on the upper surface of the leaves are marked with blotches, which are initially yellowish and then turn necrotic. Irregular, greyish blotches can appear on herbaceous shoots, leaf stalks and fruit stems.
Damage : Damage is primarily to one-year-old leaves, shoots and fruits.
Prevention : Motherstock trees whose canopy has been continually renewed owing to the collection of plant material are less affected by this pathogen. When the motherstock trees are container-raised and sheltered in the greenhouse in the colder months of the year, there is very little risk of exposure to the weather conditions necessary for its development.
Palpita unionalis
Symptoms and damage : The larvae are a particular hazard in young olive orchards because they can strip the leaf apparatus completely; they feed on leaves and fruit. The damage to mature olive orchards is not generally of economic importance. Conversely, in the nursery and in young orchards, the larvae can affect up to 90% of plant shoots and leaf surface.
In September, when the larvae attack the fruit, the damage can cut crop production by up to 30%.
Pythium
Symptoms and damage : This basically causes damping off in seedlings, as well as other diseases. The seeds may be affected pre- and post-emergence. In the first case, the seeds are attacked when they have just started to swell or they have germinated; in the second, infections develop in the crown area and make the plantlets bend and wither. Infection of the seedbeds causes patches where seeding has failed.
Prevention: Attacks are promoted by high soil moisture and relatively high temperatures. Waterlogging does not aggravate infections but does encourage the dispersal of the zoospores. The soil in the seedbeds should be partially or fully disinfected and the seeds and soil should be applied mixes of specific fungicides. Damage is often observed in conjunction with damage by other fungal species such as Rhizoctonia and Phytophtora .
Pseudomonas Savastanoi pv. Savastanoi
Symptoms: Rough galls develop on all the plant organs. The disease is very likely to spread because infection is heightened by the presence of wounds (hail, temperature drops, pruning cuts, harvesting wounds, early leaf drop) as well as by high humidity conditions and mild temperatures.
Damage: Damage severity is linked to the extent of organ necrosis and poor product characteristics, especially when the olive fruits are also affected.
Prevention: Disinfect pruning cuts and work tools.
Resseliella oleisuga
Symptoms and damage : Olive stems and shoots under 5 cm in diameter which have wounds come under attack the most. Localised cortical necrosis develops around the oviposition site and varies in size. In spring and summertime damage takes the form of hollows, cracking and changes in the colour of the bark, which turns yellow or reddish. The attacked areas may be desiccated partially or fully, so compromising plant growth. In nurseries, plants propagated by grafting are primarily sensitive to attacks by this dipteran because if the graft wound is not properly protected it can be an optimal site for it to lay its eggs.
Saissetia oleae
Damage : Damage is caused by sap extraction but is only serious when the population is very high. Indirect damage is due to the production of the sugary honeydew and subsequent development of sooty mould which reduces photosynthetic activity.
Prevention : Pest activity is contained at high temperatures (35 °C).
Stictis panizzei
Symptoms and damage: Reddish–brown blotches appear on the leaves; the edges stand out clearly and corpuscles are evident in the middle. Leaf drop occurs when attack is heavy .
Verticillium dahliae
Symptoms : These are seen on woody and fruiting shoots, on suckers and on the tips of branches with all their lateral branching. The first symptoms can be seen on the leaves of apical shoots, which turn a bronze colour; they start to curl and wither suddenly if the temperature conditions are favourable. They remain for a long time on shoots attacked by this pathogen. During this stage of rapid decline, the woody tissues of the attacked organs start to darken; this darkening intensifies until necrosis occurs. In the summertime the plants often send out new shoots below the attacked areas.
Damage : This may be limited to a few shoots on a single small branch or it may affect whole branches.
Prevention: Use certified plant stock.
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Figure 7 . Diagram of professional bodies involved in the certification process.
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The sequence of stages begins with the identification of the foundation stock (cultivars and clones). Next, ( Fig. 8 ) the foundation stock (original plant stock for certification ) enters the Pre-propagation Conservation Centre (PCC); then it is handled in the Pre-propagation Centre (PPC) and transferred to the Propagation Centre (PC).
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Figure 8 . Diagram of the certification process from the entry of the foundation stock until the production of the plants at the nursery.
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The foundation stock (cultivar or clone) is identified by the plant breeder, who testifies to its genetic trueness and phytosanitary status and sees that these characteristics are properly maintained.
The entry of the foundation stock in the Pre-propagation Conservation Centre (PCC) is the first stage in the certification process. This centre may be public or private and is recognised by the National Phytosanitary Service which supervises its proficiency .
The task of the PCC is to evaluate the genetic and plant health compliance of the foundation stock received from the breeder, as well as to manage and conserve it as pre-basic (or super-elite) propagating material. At least two plants of this material are conserved in a screen house ( Photo 59 ) to isolate them from sources of contamination (health control ).
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Photo 59 . Olive motherstock trees in the screen house.
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The PCC is also responsible for supplying the Pre-propagation Centres (PPCs) with the shoots for producing the “motherstock trees”.
The PPCs are managed by specialised laboratories or producer consortia and are recognised by the National Phytosanitary Service, which supervises their work (production of motherstock trees) and certifies this basic plant material after checking that the biometric characteristics of the olive trees comply with National Certification Board regulations . Besides conserving two or more basic-category plants in the screen house or field, the PPCs apply a specific protocol to produce and supply authorised bodies represented by nursery consortia or individual nurseries [Propagation Centres, PCs] with suitable certified plant material (seeds, scions, cuttings, rootstock, plants ) for setting up the motherstock collections. PCs are also supervised by the National Phytosanitary Service.
Nurseries subscribing to the certification scheme obtain “certified” plant material straight from the propagation fields as the sole source of supplies for propagation work (by grafting and cuttings). According to the working regulations and protocols, nurseries have to declare the number of shoots received, the grafts performed and the number of cuttings planted for rooting. Moreover, to reduce the critical points in the working stages and to facilitate controls, they must identify the cultivars and clones they intend to propagate in the mist propagation benches and graft houses.
“Certified” olive plants are sold under specific labels. At the time of sale, the nursery is responsible for ensuring that the characteristics of the plant comply with the declarations on its label (health status and trueness to variety) and with the production procedures specified in the regulations.
Nursery returns depend largely on the skill displayed during the critical points when creating and managing the motherstock collections and properly applying the procedures during the different stages of olive plant propagation and growing.
Correct management of the motherstock collections includes making sure that the area available is sufficient to house all the plants needed for scheduled production. Section B (Chapter 1 – Part I) specifies the analyses, checks and preventive measures required to protect the motherstock trees from contamination by pathogens and so ensure the health and agronomic suitability of this area. The procedures require all the motherstock trees to be marked and identified on a map to facilitate field checks, and nurseries have to document the quantity and intended purpose of the plant material taken from the motherstock trees.
Nursery activity is checked and supervised through the different stages of the process to control the genetic correspondence to variety and phytosanitary status of the propagated plants as well as to authorise their suitability for use. Table 3 summarises the types of checks carried out.
CERTIFICATION PROCESS CONTROLS
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STAGES
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GENETIC CORRESPONDENCE TO VARIETY
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HEALTH CONTROLS
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Conservation for Pre-propagation
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Phenological
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Assays
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Pre-propagation
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Phenological
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Assays
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multiplication
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Phenological
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Visual inspections (10%)
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propagation
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Biometric characteristics
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Visual
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Table 3 . Stages in the certification and control of trueness to variety and phytosanitary status.
It is important to check periodically that the motherstock trees are true to the foundation stock by using morphological markers. Serological or biological assays are recommended for regular checks of plant phytosanitary status .
If implemented scientifically according to simple, efficient procedures, certification is an important tool for accrediting and diversifying nursery production. It results in the release of prime quality plants on the marketplace and helps to modernise the olive sector to make it sustainable.
| Chapter 8. Olive pests and diseases in the nursery |
The commercial success of nurseries can vary depending on the measures taken to curb pest and disease development during the stages of plant production ( Table 4 ).
(I) Plant stock conservation
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(II) Propagation
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(III) Plant hardening & growing
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(IV) Plant growing
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Motherstock trees
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Seed germination
Grafting
Rooting
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Plant growth
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Shade (screen)
house
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Table 4 . Summary of the four stages of nursery plant production.
Some adverse biotic conditions are hard to control and persist in the foundation stock used for plant propagation ( Martelli G.P. 1998) . This stock plays an important epidemiological role because it is a dangerous carrier for their dissemination ( Photo 60 ) . Other adverse conditions caused by insects are easy to identify ( Civantos M. 1999; Ricciolini M., Guidotti A. 2001 ) and to eliminate by simple treatment.
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Photo 60 . When in the nursery, olive trees can be attacked by bacteria, fungi, viruses, cytoplasms and insects . The photo shows damage by Spilocaea oleagina andPseudomonas Savastanoi.
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Pests and diseases should be diagnosed straight away and eradicated so that quality plants complying with certification requirements are produced.
Before describing symptoms, damage and preventive action, a list is provided of the chief sources of plant and animal infestation.
Plant diseases
Bacterial diseases. Pathogenic plant bacteria fall into two genera – Xanthomonas and Pseudomonas – and are generally less harmful than fungi. The weaker virulence of bacteria probably has to do with the characteristics of these micro-organisms: phytopathogenic bacteria do not form resistance mechanisms and find it harder to survive. They do not have the specific ability to penetrate the plant directly, only entering the internal tissues through natural openings or wounds. Plant cell liquids have an acid pH whereas bacteria prefer a subalkaline environment. They cannot be carried any distance by the wind because they aggregate in small jelly-like masses. The most hazardous bacterium is Pseudomonas Savastanoi pv. Savastanoi.
Fungal diseases. Fungi are the chief source of infestation in olive. The most common infections found in nurseries are caused by: Alternaria - Armillaria mellea - Botrytis cinerea - Spilocaea oleagina - Cylindrocarpon destructans - Gloesporium olivarum - Leivellula taurica - Mycocentrospora cladosporioides – Pythium - Stictis panizzei, Verticillium dahliae. In some cases correct cultural practices can contain the development of the disease, the biological cycle of which is closely linked to the taxonomic classification of the fungus concerned.
Viruses and phytoplasmas. Unlike other adverse conditions, viral diseases have been somewhat disregarded in olive propagation management. More recently, however, viruses and phytoplasmas have come to the forefront to corroborate phytosanitary certification ( Barba M. 1992; Bertolini E., et al., 1998; Clara M.I.H., et al., 1997; Felix, M.R., et al., 2001, 2005; Gallitelli, D., Savino, V., 1985; Henriques M.I.C., et al., 1992; Lavee S., and Tanne E., 1984; Saponari, M. Savino,V. 2003; Saponari, M., et al., 2002; Triolo E., et al., 1996) . The olive too has been found to be an unsuspected host to numerous viruses (12) and phytoplasmas (5), most of which have been isolated in asymptomatic plants and identified as the source of damage in only some cases. A list follows of those reported in the literature: SRLV( Strawberry latent ringspot ); ArMV ( Arabis mosaic ); CLRV ( Cherry leafroll ); CMV (Cucumber mosaic ); OLRSV ( Olive latent ringspot ); OLV 1 OLV 1 ( Olive latent 1 ); OLV 2 ( Olive latent 2 ); OVYaV ( Olive vein yellowing associated ); OYMDaV ( Olive yellow mottling and decline associated ); TMV ( Tobacco mosaic ); OSLV (Olive semilatent ); OLYaV ( Olive leaf yellowing associated ); Spherosis ( Olive micro spheroblasts ).
Viruses are carried passively through small wounds or by insects and the symptoms are often non-specific. Consequently, nursery producers should be vigilant and should contact technical experts at the first suspicion of viral symptoms.
Animal pests
Insects. This group includes a large number of species capable of damaging olive plants: Eriophyes oleae - Hylesinus oleiperda - Otiorrhynchus cribricollis -Liothrips oleae - Metcalfa pruinosa - Palpita unionalis - Resseliella oleisuga - Saissetia oleae .
Photo 61 illustrates some of the most common damage observed during the stages of olive nursery production listed in Table 4 .
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Saissetia oleae
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Pseudomonas Savastanoi pv. Savastanoi
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Spilocaea oleagina
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Photo 61 . Most common damage observed during nursery olive production.
I. Symptoms, plant damage and preventive action during the certification process
I.I. Conservation of plant stock (cultivars and clones) in the motherstock collection ( Photo 62 )
Olive plants of differing ages grown in the field can be attacked by different insects. Besides damaging the plants, these can transmit infections to the shoots collected for grafting or for rooting cuttings ( Table 5).
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Alternaria - Spilocaea oleagina
Eriophyes oleae – Gloesporium olivarum - Liothrips oleae –
Metcalfa pruinosa – Mycocentrospora cladosporioides - Palpita unionalis –
Pseudomonas Savastanoi pv. Savastanoi - Resseliella oleisuga –
Saissetia oleae - Stictis panizzei –
Verticillium dahliae
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Photo 62 . Conservation of plant stock (cultivars and clones) in the motherstock collection.
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Table 5 . List of the most noxious insect pests for motherstock trees
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I.II. Propagation
Phytosanitary problems are linked to infections already present in the motherstock trees as well as to pathogens in the ground of the seed and graft facilities or in the soil of the mist propagation rooting benches .
During grafting, the biggest possibility of infection is when the scions have been taken from infected motherstock trees. The risk is greater if the plant material has been lifted arbitrarily from olive trees on private orchards. In mist propagation, the sudden development of fungi can alter the rooting performance of cuttings. Environmental conditions of high temperatures, near-saturation relative humidity, excessive watering of the rooting medium (perlite) and leaves and poor hygiene in the rooting benches and mist propagation greenhouses can all facilitate the development of fungi that can cause leaf drop and so harm root formation. Table 6 lists the insect pests most likely to infest olive plants during propagation .
Seed germination
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Leivellula taurica – Palpita unionalis - Pythium
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Graft development in greenhouse
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Pythium
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Mist propagation benches in greenhouse
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Armillaria mellea - Botrytis cinerea - Cylindrocarpon destructans – Resseliella oleisuga
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Table 6. Chief noxious insect pests during seed germination, seedling growth and mist propagation.
I.III. Hardening of rooted cuttings or growing of plantlets
Rooted cuttings and grafted olive plants are placed in containers ( Photo 63 ) and transferred to greenhouses or tunnels for about six months in the wintertime. The development of some fungal diseases is limited in these environments, but some plant-eating pests pose more of a hazard ( Table 7 ).
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Armillaria mellea - Cylindrocarpon destructans - Otiorrhynchus cribricollis - Hylesinus oleiperda - Resseliella oleisuga
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Photo 63. Hardening in the greenhouse of rooted cuttings (cv.Frantoio ).
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Table 7. List of most noxious pests during the first stages of olive growth
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I.IV. Growing the olive plants in the shade house
Growing conditions inside the shade house ( Photo 64 ) should be optimal to ensure a balanced ratio between the root system and aerial portion of the trees and so obtain marketable trees; the plants should also be checked for pests and diseases that could limit canopy development ( Table 8 ).
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Armillaria mellea - Cylindrocarpon destructans - Otiorrhynchus cribricollis - Hylesinus oleiperda - Resseliella oleisuga
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Photo 64. Growing olive plants in the shade house (cv. Leccino ).
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Table 8. List of most noxious pests in the last stages of plant growth
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Generally, the pests and diseases that occur in nurseries are handled by chemical treatments, which are capable of combating most harmful agents. Nevertheless, preventive agricultural techniques are fundamental to reduce the risk of contamination in the new plants.
In practice, this means paying special attention to working choices. During the different stages of production nurseries must implement a series of measures, now listed, which are essential for containing the development of pests and diseases.
If viral disorders, dieback or death occur as a result of fungal infections it is absolutely essential to remove and destroy the infected plants to stop the infection from spreading. Work tools should be ‘sterilised' with disinfectant solutions to avoid fungal and bacterial contamination; grafting wounds should likewise be disinfected and covered with grafting wax or mastic.
Shoots should be taken solely from healthy plants and the rooting medium in the rooting benches should be used for one growing cycle only; it should be kept as clear as possible of plant debris which, during rooting, could contaminate it and encourage the development of rot.
Water management is also very important. Drip irrigation is preferable, applying short, frequent watering. The motherstock collections should have optimal drainage and effective drainage channels to remove excess water. Overhead irrigation should also be avoided because it is conducive to the development of fungal diseases.
Because plants are kept in the nursery greenhouses for lengthy periods of time, it is advisable to cover the roof and side openings with extremely fine-meshed nets to stop insects from entering.
I.V. Chief pests and diseases
A list follows of the pests and diseases of various origins that can damage nursery olive production. For ease of reading, each is described in the same order: symptoms, damage and any preventive action.
Alternaria
Symptoms: Irregular crust on plants, which is black, sooty and almost oily.
Damage : By damaging the leaves, it heavily restricts plant photosynthesis and alters gas exchange.
Prevention: Control scale insects and let air into the canopy.
Armillaria mellea
Symptoms and damage : Responsible for root rot, this pathogen resides in dead wood lying in very damp soil. It develops on debilitated trees and can cause considerable economic damage.
Botrytis cinerea
Symptoms and damage: Heavy growth of mould on the leaf blades leading to extensive necrotic lesions, or on petioles and shoots leading to the appearance of dry lesions. As a result, the vegetative parts dry out.
Prevention : This disease develops at a temperature of around 25 °C and in conditions of high relative humidity. The greenhouses should therefore be heated or opened for brief periods at night and the plants should be watered regularly.
Spilocaea oleagina
Symptoms : Round blotches of varying diameter appear on the green organs of the plant, especially the leaves; they range in colour from brown to yellow and green on the upper surface of the leaves.
Damage : This disease does the most damage to the leaves. The lesions cause defoliation and debilitate the plant. Premature leaf drop may occur even before the symptoms become fully apparent. Persistent rain (two or three days) and a temperature of between 5 and 25 °C are conducive to its development. Most infections occur in spring and autumn.
Prevention: Prune in December and January to open up the canopy and prevent excess internal humidity.
Cylindrocarpon destructans
Symptoms and damage : Leaves turn yellow and rapidly wilt and become desiccated.
This pathogen is rarely observed in young nursery plants. Promoted by transplant shock, it appears suddenly after the trees are planted out in the field. It can be considered an ‘opportunistic' disease that is active mainly in cold, heavy soils with a low acidity.
Prevention: Pay close attention to re-potting lesions.
Eriophyes oleae
Symptoms and damage : These mites make feeding bites in the shoots, which cause deformations similar to those caused by thrips and typical, yellowish-green hollows on the lower surface of the leaves and matching chlorotic bumps on the upper surface. When they attack the inflorescences, the flowers or whole inflorescences drop off.
Gloesporium olivarum
Symptoms : Initially, isolated ochre spots appear; they then grow and may join up. Attacks normally begin at the apex of the fruit, where rainwater accumulates. As the disease progresses, the attacked fruits display a round, dark depression; they later turn grey, become mummified and fall off.
Damage : The negative effects of olive anthracnose primarily affect the colour, acidity and organoleptic characteristics of the oil obtained from the olives.
Otiorrhynchus cribricollis
Symptoms and damage : These are usually mild in mature olives. In young olive plants, however, they lead to heavy debilitation and very poor growth (short internodes) of the trees affected; sometimes they may even kill the tree.
Hylesinus oleiperda
Symptoms : External symptoms on the wood are reddish–brown notches with roundish edges with the female entry hole at the centre. The symptoms only become noticeable after the trees are planted out.
Damage : The maternal and larval feeding galleries damage the woody structures of the plant.
Leivellula taurica
Symptoms and damage : This endoparasitic pathogen penetrates through the stomata. Chlorotic blotches covered with a floury mould appear on the upper surface and subsequently become necrotic.
Liothrips oleae
Symptoms and damage : The adults and greenish larvae puncture and suck the sap of the buds, leaves, flowers and young fruitlets, causing shoot, leaf and fruit deformation and flower drop.
Metcalfa pruinosa
Damage : The damage this insect causes to olive plants – honeydew on the leaves, with layers of mould and abundant, very visible wax – is very evident, but often well tolerated.
Direct damage in the form of sap sucking and fruit deformation is only reported sporadically.
Mycocentrospora cladosporioides
Symptoms : Irregularly shaped blotches appear on the lower surface of the leaves, with a very thin layer of lead–grey conidiophores. The matching areas on the upper surface of the leaves are marked with blotches, which are initially yellowish and then turn necrotic. Irregular, greyish blotches can appear on herbaceous shoots, leaf stalks and fruit stems.
Damage : Damage is primarily to one-year-old leaves, shoots and fruits.
Prevention : Motherstock trees whose canopy has been continually renewed owing to the collection of plant material are less affected by this pathogen. When the motherstock trees are container-raised and sheltered in the greenhouse in the colder months of the year, there is very little risk of exposure to the weather conditions necessary for its development.
Palpita unionalis
Symptoms and damage : The larvae are a particular hazard in young olive orchards because they can strip the leaf apparatus completely; they feed on leaves and fruit. The damage to mature olive orchards is not generally of economic importance. Conversely, in the nursery and in young orchards, the larvae can affect up to 90% of plant shoots and leaf surface.
In September, when the larvae attack the fruit, the damage can cut crop production by up to 30%.
Pythium
Symptoms and damage : This basically causes damping off in seedlings, as well as other diseases. The seeds may be affected pre- and post-emergence. In the first case, the seeds are attacked when they have just started to swell or they have germinated; in the second, infections develop in the crown area and make the plantlets bend and wither. Infection of the seedbeds causes patches where seeding has failed.
Prevention: Attacks are promoted by high soil moisture and relatively high temperatures. Waterlogging does not aggravate infections but does encourage the dispersal of the zoospores. The soil in the seedbeds should be partially or fully disinfected and the seeds and soil should be applied mixes of specific fungicides. Damage is often observed in conjunction with damage by other fungal species such as Rhizoctonia and Phytophtora .
Pseudomonas Savastanoi pv. Savastanoi
Symptoms: Rough galls develop on all the plant organs. The disease is very likely to spread because infection is heightened by the presence of wounds (hail, temperature drops, pruning cuts, harvesting wounds, early leaf drop) as well as by high humidity conditions and mild temperatures.
Damage: Damage severity is linked to the extent of organ necrosis and poor product characteristics, especially when the olive fruits are also affected.
Prevention: Disinfect pruning cuts and work tools.
Resseliella oleisuga
Symptoms and damage : Olive stems and shoots under 5 cm in diameter which have wounds come under attack the most. Localised cortical necrosis develops around the oviposition site and varies in size. In spring and summertime damage takes the form of hollows, cracking and changes in the colour of the bark, which turns yellow or reddish. The attacked areas may be desiccated partially or fully, so compromising plant growth. In nurseries, plants propagated by grafting are primarily sensitive to attacks by this dipteran because if the graft wound is not properly protected it can be an optimal site for it to lay its eggs.
Saissetia oleae
Damage : Damage is caused by sap extraction but is only serious when the population is very high. Indirect damage is due to the production of the sugary honeydew and subsequent development of sooty mould which reduces photosynthetic activity.
Prevention : Pest activity is contained at high temperatures (35 °C).
Stictis panizzei
Symptoms and damage: Reddish–brown blotches appear on the leaves; the edges stand out clearly and corpuscles are evident in the middle. Leaf drop occurs when attack is heavy .
Verticillium dahliae
Symptoms : These are seen on woody and fruiting shoots, on suckers and on the tips of branches with all their lateral branching. The first symptoms can be seen on the leaves of apical shoots, which turn a bronze colour; they start to curl and wither suddenly if the temperature conditions are favourable. They remain for a long time on shoots attacked by this pathogen. During this stage of rapid decline, the woody tissues of the attacked organs start to darken; this darkening intensifies until necrosis occurs. In the summertime the plants often send out new shoots below the attacked areas.
Damage : This may be limited to a few shoots on a single small branch or it may affect whole branches.
Prevention: Use certified plant stock.
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