Study of mechanisms of action involved in the Biocontrol of a strain of Aureobasidium pullulans (De Bary) Arnaud against Penicillium expansum Link on postharvest apples

L’agent de lutte biologique Aureobasidium pullulans souche Ach1-1 a présenté une grandepotentialité dans le contrôle de Penicillium expansum, l’agent causal de la pourriture bleue des pommes enconservation. Les mécanismes d’action qui sont les plus impliqués dans son activité antagoniste ont étéanalysés, au cours de ce travail. D’après des essais de protection réalisés sur pommes blessées, il apparaîtque l’efficacité de cette souche n’est pas liée essentiellement à la sécrétion des métabolites toxiques dans lemilieu ou à l’induction de la résistance de fruit. Par contre, le mécanisme de la compétition pour la nutritionsemble jouer un rôle important. Dans les essais in vitro, la souche antagoniste Ach1-1 a eu un importanteffet inhibiteur de la germination des conidies de P. expansum dans des milieux de jus de pomme à desfaibles concentrations. Mais cet effet était réversible et les conidies inhibées étaient capables de germer unefois remises dans des conditions favorables en éléments nutritifs. Sur pommes blessées, l’effet protecteurde la souche Ach1-1 vis-à-vis de P. expansum a été significativement affaibli par l’ajout dans les blessuresde concentrations élevées des principaux composants des pommes en sucres, en vitamines etparticulièrement en acides aminés. Il apparaît que l’antagoniste exerce une activité fongistatique plus quefongicide vis-à-vis de P. expansum et agit par une compétition efficace pour les éléments nutritifs desblessures des pommes sans affecter la viabilité des conidies du pathogène. Une application exogène desacides aminés des pommes avec des concentrations croissantes dans les blessures a progressivement réduitl’activité antagoniste de la souche Ach1-1 sans altérer son développement dans les blessures, montrant quela compétition pour les acides aminés joue un rôle important dans la suppression de P. expansum. Cerésultat a été appuyé par l’analyse biochimique de la cinétique de l’épuisement des acides aminés dans lesblessures des pommes qui a montré que ces composés et particulièrement la sérine, la glycine et l’acideglutamique sont mieux métabolisés par la souche antagoniste que par le pathogène. L’ajout en excès de cestrois acides aminés en groupe ou individuellement dans les blessures des pommes a fortement réduitl’efficacité de la souche Ach1-1 vis-à-vis de P. expansum. De plus, la présence de la sérine et la glycineavec des concentrations élevées dans des milieux synthétiques ne présentant aucune source azotée, a réduitl’effet inhibiteur de la germination des conidies de P. expansum par la souche Ach1-1. Ainsi, ces acidesaminés semble être parmi les éléments les plus limitants dans le mécanisme de la compétition./The biocontrol agent Aureobasidium pullulans strain Ach1-1 was very effective againstPenicillium expansum, the causal agent of blue mold on stored apple. Modes of action that could beinvolved in its biocontrol activity were analysed in this work. According to some biocontrol trials onwounded apples, it appears that neither the production of metabolites nor the induction of fruit resistancewere the principal modes of action of this strain. However the mechanism of nutrient competition appearsto play an important role. In in vitro assays, the strain Ach1-1 had an important inhibitory effect of conidialgermination of P. expansum in apple juice at low concentrations. However this inhibitory effect wassuppressed when inhibited conidia were placed in favourable nutrients conditions. On wounded apples theprotective activity of strain Ach1-1 against P. expansum was significantly reduced by adding, in thewounds, high concentrations of major apple compounds of sugar, vitamins and most particularly aminoacids. It appears that the antagonist exerts a fungistatic rather than fungicidal activi ty on P. expansum as itcan deplete limiting nutrient available at the infection site and inhibit conidia germination without affectingtheir viability. Moreover, an exogenous application of increasing apple amino acids concentrations inwounds had progressively reduced the antagonist activity of strain Ach1-1 without altering its developmentin wounds, suggesting that competition for apple amino acids by strain Ach1-1 plays an important role insuppressing P. expansum. This finding was strengthened by a time-course analysis of wounds amino acidsduring apple incubation in witch the strain Ach1-1 was able to assimilate apple amino acids better than P.expansum, most particularly Serine, Glycin and Glutamic acid. Exogenous additions of these three aminoacids at high concentrations on apple wounds as a mixture or individually, strongly lowered the Biocontrolactivity of strain Ach1-1. Moreover, the existence of amino acids serine and glycin at high concentration insynthetic media, without any nitrogen source, was able to reduce the inhibitory effect of conidialgermination of P. expansum by the strain Ach1-1.Therefore these amino acids could be among the mostlimited nutrients in the mechanism of competition

Effects of Temperature Stresses on the Resistance of Chickpea Genotypes and Aggressiveness of Didymella rabiei Isolates

Chickpea (Cicer arietinum L.) is an important food and rotation crop in many parts of the world. Cold (freezing and chilling temperatures) and Ascochyta blight (Didymella rabiei) are the major constraints in chickpea production. The effects of temperature stresses on chickpea susceptibility and pathogen aggressiveness are not well documented in the Cicer-Didymella pathosystem. Two experiments were conducted under controlled conditions using chickpea genotypes and pathogen isolates in 2011 and 2012. In Experiment 1, four isolates of D. rabiei (AR-01, AR-02, AR-03 and AR-04), six chickpea genotypes (Ghab-1, Ghab-2, Ghab-3, Ghab-4, Ghab-5 and ICC-12004) and four temperature regimes (10, 15, 20, and 25°C) were studied using 10 day-old seedlings. In Experiment 2, three chickpea genotypes (Ghab-1, Ghab-2, and ICC-12004) were exposed to 5 and 10 days of chilling temperature exposure at 5°C and non-exposed seedlings were used as controls. Seedlings of the three chickpea genotypes were inoculated with the four pathogen isolates used in Experiment 1. Three disease parameters (incubation period, latent period and disease severity) were measured to evaluate treatment effects. In Experiment 1, highly significant interactions between genotypes and isolates; genotypes and temperature; and isolate and temperature were observed for incubation and latent periods. Genotype x isolate and temperature x isolate interactions also significantly affected disease severity. The resistant genotype ICC-12004 showed long incubation and latent periods and low disease severity at all temperatures. The highly aggressive isolate AR-04 caused symptoms, produced pycnidia in short duration as well as high disease severity across temperature regimes, which indicated it is adapted to a wide range of temperatures. Short incubation and latent periods and high disease severity were observed on genotypes exposed to chilling temperature. Our findings showed that the significant interactions of genotypes and isolates with temperature did not cause changes in the rank orders of the resistance of chickpea genotypes and aggressiveness of pathogen isolates. Moreover, chilling temperature predisposed chickpea genotypes to D. rabiei infection; developing multiple stress resistance is thus a pre-requisite for the expansion of winter-sown chickpea in West Asia and North Africa

Optimising Subsidiary Crop Applications in Rotations (OSCAR): A Perspective for the North Africa Region

Background: For sustainable improvement of wheat-based farming systems in the North Africa, there is a need to improve plant health, soil health and fertility. One approach to achieve this is by integrating subsidiary crops (SC) as living or dead mulches or cover crops with the main crops in rotations, which will increase plant species and microbial diversity and reducing water demand in dry climates. Methods: A collaborative research project funded by EU FP 7 (Project No. 289277) was initiated in April 2012, in partnership with European Union (public research organizations and private sector small and medium enterprises of Germany, Norway, Sweden, Denmark, the Netherland, UK, Poland, Switzerland and Italy), Brazil and Morocco (INRA-Morocco and ICARDA), in order to enhance understanding and use of SC systems, develop suitable farm technologies, increase the range of SC species, and enhance understanding of impact of SC on soil ecology, biology and microbial diversity and crop pests and diseases. Results: Based on two field experiments in Morocco (Sidi AI-Aidi and Sidi Allal-Tazi), the project will assess the economic and ecological impact including legume root health and soil health, fertility and microbial diversity and compare the results with other sites in Europe. Screening of new species and genotypes will result in identification of range of potentially useful plant species for SC for the North Africa and Europe. The identified SC species will be tested for their potential as forage and for extraction of useful biochemicals. Conclusion: The results of the project as a whole will be of use for and improve sustainability in low-input, organic, and conventional farming systems in the North Africa, Latin America and Europe

Towards identification of novel legume species of potential interest as cover crops and living mulches for the North Africa region.

Subsidiary crops (SC) grown either as cover crops (CC) preceding or following the main crops, or as living mulches (LM) together with the main crops can deliver multiple ecological services within farming systems. These include increasing the duration of soil cover in the rotation, increasing plant and microbial diversity, improving plant health, soil health and fertility, minimizing the use of tillage and agrochemicals, enhancing biological N fixation and soil C content, and reducing water demand in dry climates. However, species available for growing as SC for dry areas are limited. To identify species of potential interest to CC and LM, we screened 197 accessions from the ICARDA genebank, belonging to 142 species/sub-species at Rabat, Morocco in one square meter plots. The preliminary assessments based on visual observations enabled us to identify: (1) 21 accessions belonging to Medicago and Trifolium species with prostrate growth habit, early maturity and senescence, determinate growth cycle and good potential for seed production, as potentially suitable for LM; and (2) 28 accessions belonging to Vicia, Lathyrus, Medicago and Trifolium species with high biomass and competitive ability, and also good potential for seed production, as potentially suitable for CC or green manure crops. Further evaluations in replicated trials are in progress. The selected accessions have been planted in the field during autumn 2013 at Sidi El Aidi

Development of SCAR markers and a semi-selective medium for the quantification of strains Ach 1-1 and 1113-5, two Aureobasidium pullulans potential biocontrol agents.

peer reviewe

Rôle des acides aminés dans l'activité antagoniste d'Aureobasidium Pullulans vis-à-vis de la pourriture bleue des pommes en post-récolte

Aureobasidium pullulans (souche Ach1-1) a montré une grande efficacité vis-à-vis de Penicillium expansum agent de la pourriture bleue des pommes en conservation. Le présent travail a été réalisé dans le cadre de l’analyse des mécanismes d’action qui sont les plus impliqués dans son activité antagoniste. Dans des essais in vivo sur pommes blessées, l’effet protecteur de la souche Ach1-1 vis-à-vis de P. expansum a été significativement affaibli par l’ajout dans les blessures de concentrations élevées en acides aminés. L’importance de la réduction étant dépendante de la concentration appliquée, a montré que la compétition pour les acides aminés joue un rôle important dans la suppression de P. expansum. Ce résultat a été appuyé par l’analyse biochimique de la cinétique de l’épuisement des acides aminés dans les blessures des pommes qui a dévoilé que ces composés et particulièrement la sérine, la glycine et l’acide glutamique sont mieux métabolisés par la souche antagoniste que par le pathogène. L’ajout en excès de ces trois acides aminés individuellement dans les blessures des pommes a fortement réduit l’efficacité de la souche Ach1-1 vis-à-vis de P. expansum. Ainsi, ces acides aminés semble être parmi les éléments les plus limitants dans le mécanisme de la compétition. Ces résultats indiquent que l’antagoniste A. pullulans souche Ach 1-1 exerce une activité fongistatique plus que fongicide vis-à-vis de P. expansum et agit par une compétition efficace pour les éléments nutritifs limitants des blessures des pommes et particulièrement les acides aminés sans affecter la viabilité du pathogène