Fungal diversity associated to the olive moth, prays oleae Bernard : a survey for potential entomopathogenic fungi

Olive production is one of the main agricultural activities in Portugal. In the region of Trás-os-Montes this crop has been considerably affected by Prays oleae. In order to evaluate the diversity of fungi on P. oleae population of Trás-os-Montes olive orchards, larvae and pupae of the three annual generations (phyllophagous, antophagous and carpophagous) were collected and evaluated for fungal growth on their surface. From the 3828 larvae and pupae, a high percentage of individuals exhibited growth of a fungal agent (40.6%), particularly those from the phyllophagous generation. From all the moth generations, a total of 43 species from 24 genera were identified, but the diversity and abundance of fungal species differed between the three generations. Higher diversity was found in the carpophagous generation, followed by the antophagous and phyllophagous generations. The presence of fungi displaying entomopathogenic features was highest in the phyllophagous larvae and pupae, being B. bassiana the most abundant taxa. The first report of B. bassiana presence on P. oleae could open new strategies for the biocontrol of this major pest in olive groves, since the use of an already adapted species increases the guarantee of success of a biocontrol approach. The identification of antagonistic fungi able to control agents that cause major olive diseases, such as Verticillium dahliae, will benefit future biological control approaches for limiting this increasingly spreading pathogen.This work was supported by Science and Technology Foundation (Fundação para a Ciência e Tecnologia – FCT) project PTDC/AGR-AAM/102600/2008 “Entomopathogenic fungi associated to olive pests: isolation, characterization and selection for biological control”. The first author is grateful to the Science and Technology Foundation for the PhD grant SFRH/BD/44265/2008

Biological control of Phytophthora cambivora (Petri) Buisman in chesnut tree (Castanea sativa Mill.)

“Ink disease” of chestnut tree, caused by Phytophthora cambivora, produces serious damages in chestnut orchards in Crete during the last years. Natural environment has been affected and agricultural income has been significantly decreased. The biological control of this pathogen has been studied in this work by the use of the two antagonist fungi Trichoderma harzianum Rifai and T. koningii Oudem. The commercial biological product “Promot”, which contains the above antagonists in concentrations 2xl07 and 3xl07 respectively, was used. Two strains of the pathogen were tested for the artificial soil infections, which was carried out one week before the chestnut sow. The first strain (P. cambivora 1) was isolated by infected chestnut trees from the area of Chania in Crete, while the Benaky Phytopathological Institute in Athens provided the second one (P. cambivora 2). Seedlings of “Rodgiano” variety chestnut seeds of Castanea sativa were used. Chestnut seeds were soaked into a suspension-dilution of the biological product in the dose of 100 g/hl just before their transplantation. The same dose of suspension-dilution of the biological product was used for root watering of young trees of 10 cm stem height, as well as two months later. The treatment's effect was estimated by the number of the trees with leaf wilting, at the plant tip infection of the root system, and base of the trunk, as well as apoplexia symptoms. Chestnut trees treated with the biological product were protected by the pathogen with efficiency ranged from 98.9 to 100% depending on the evaluation criteria for the strain P. cambivora 1 and P. cambivora 2 respectively. This efficiency was statistically significantly different from the control.La maladie de l’encre du châtaignier, causée par Phytophthora cambivora, a engendré de sérieux dommages aux châtaigneraies de Crète au cours ces dernières années. L’environnement naturel a été affecté et les revenus agricoles ont diminué de façon significative. Ce travail vise à étudier le contrôle biologique de ce pathogène en utilisant deux espèces de champignons antagonistes Trichoderma harzianum Rifai et T. koningii Oudem. Le produit commercial biologique “Promot”, qui contient les deux espèces antagonistes, aux concentrations respectives de 2x1 07 et 3x1 07, a été utilisé. Deux souches de ce pathogène ont été testées en infectant des sols artificiels, une semaine avant l’ensemencement en plantules de châtaignier. La première souche (P. cambivora 1) a été isolée à partir de châtaigniers contaminés de la région de Chania (Crète), tandis que l’Institut Phytopathologique d’Athènes a fourni la seconde (P. cambivora 2). Des plantules de la variété “Rodgiano” de Castanea sativa ont été utilisées ; les graines ont été trempées dans une supsension-dilution du produit biologique “Promot” dosée à 100 g/hl, juste avant leur transplantation. La même dose de suspension-dilution de “Promot” a été utilisée pour humecter les racines de jeunes arbres de 10 cm de haut, et ce traitement a été renouvelé deux mois plus tard. L’effet du traitement a été estimé en considérant le nombre d’arbres ayant des feuilles desséchées, une zone infectée au niveau du système racinaire et à la base du tronc. Les châtaigniers traités avec le produit biologique ont été protégés de l’agent pathogène avec une efficacité de 98,9 à 100% respectivement, selon les souches de P. cambivora 1 et P. cambivora 2. Cette efficacité est statistiquement significative par rapport au traitement témoin.Bourbos V. A., Metzidakis Ioannis. Biological control of Phytophthora cambivora (Petri) Buisman in chesnut tree (Castanea sativa Mill.). In: Ecologia mediterranea, tome 26,2000. pp. 123-127

Soil solarization and sustainable agriculture

Pesticide treatments provide an effective control of soilborne pests in vegetable and fruit crops, but their toxicity to animals and people and residual toxicity in plants and soil, and high cost make their use hazardous and economically expensive. Moreover, actual environmental legislation is imposing severe restrictions on the use or the total withdrawal of most soil-applied pesticides. Therefore, an increasing emphasis has been placed on the use of nonchemical or pesticide-reduced control methods. Soil solarization is a nonpesticidal technique which kills a wide range of soil pathogens, nematodes, and weed seeds and seedlings through the high soil temperatures raised by placing plastic sheets on moist soil during periods of high ambient temperature. Direct thermal inactivation of target organisms was found to be the most important mechanism of solarization biocidal effect, contributed also by a heat-induced release of toxic volatile compounds and a shift of soil microflora to microorganisms antagonist of plant pathogens. Soil temperature and moisture are critical variables in solarization thermal effect, though the role of plastic film is also fundamental for the solarizing process, as it should increase soil temperature by allowing the passage of solar radiation while reducing energetic radiative and convective losses. Best solarizing properties were shown by low-density or vynilacetate- coextruded polyethylene formulations, but a wide range of plastic materials were documented as also suitable to soil solarization. Solar heating was normally reported to improve soil structure and increase soil content of soluble nutrients, particularly dissolved organic matter, inorganic nitrogen forms, and available cations, and shift composition and richness of soil microbial communities, with a marked increase of plant growth beneficial, plant pathogen antagonistic or root quick recolonizer microorganisms. As a consequence of these effects, soil solarization was largely documented to increase plant growth and crop yield and quality along more than two crop cycles. Most important fungal plant pathogenic species were found strongly suppressed by the solarizing treatment, as several studies documented an almost complete eradication of economically relevant pathogens, such as Fusarium spp., Phytophthora spp., Pythium spp., Sclerotium spp., Verticillium spp., and their related diseases in many vegetable and fruit crops and in different experimental conditions. Beneficial effects on fungal pathogens were stated to commonly last for about two growing seasons and also longer. Soil solarization demonstrated to be effective for the control of bacterial diseases caused by Agrobacterium spp., Clavibacter michiganensis and Erwinia amylovora, but failed to reduce incidence of tomato diseases caused by Pseudomonas solanacearum. Solarization was generally found less effective on phytoparasitic nematodes than on other organisms, due to their quicker soil recolonization compared to fungal pathogens and weeds, but field and greenhouse studies documented consistant reductions of root-knot severity and population densities of root-knot nematodes, Meloidogyne spp., as well as a satisfactory control of cyst-nematode species, such as Globodera rostochiensis and Heterodera carotae, and bulb nematode Ditylenchus dipsaci. Weeds were variously affected by solar heating, as annual species were generally found almost completely suppressed and perennial species more difficult to control, due to the occurrence deep propagules not exposed to lethal temperature. Residual effect of solarization on weeds was found much more pronounced than on nematodes and most fungal pathogens. Soil solarization may be perfect fit for all situations in which use of pesticides is restricted or completely banned, such as in organic production, or in farms located next to urban areas, or specialty crops with few labeled pesticides. Advantages of solarization also include economic convenience, as demonstrated by many comparative benefit/cost analyses, ease of use by growers, adaptability to many cropping systems, and a full integration with other control tools, which makes this technique perfectly compatible with principles of integrated pest management required by sustainable agriculture