Relationship between epistasis and aggressiveness in resistance of pepper (Capsicum annuum L.) to Phytophthora nicotianae

This study evaluated the types of gene action governing the inheritance of resistance to Phytophthora nicotianae necrosis in populations derived from two crosses involving two susceptible (Beldi and Nabeul II) and one resistant (CM334) cultivars of pepper (Capsicum annuum L.). Populations, composed of Pr, Ps, F1 , F 2 , BC 1 Pr, and BC 1 Ps generations, were inoculated with six P. nicotianae isolates. Generation means analysis indicated that an additive-dominance model was appropriate for P. nicotianae isolates Pn Ko1 , Pn Ko2 and Pn Kr1 , which showed low aggressiveness in the two crosses. For the more aggressive isolates Pn Bz1 , Pn Bz2 and Pn Kr2 , epistasis was an integral component of resistance in the two crosses. The presence of epistasis in the resistance of pepper to P. nicotianae was dependent on the level of aggressiveness of the isolates. Selection in pepper with less aggressive isolates was efficient, but not with more aggressive isolates; on the other hand, selection with more aggressive isolates was more stable. The minimum number of genes controlling resistance was estimated at up to 2.71. In the majority of cases, the additive variance was significant and greater than the environmental and dominance variance

Comparaison de différentes techniques d'inoculation du piment par Phytophthora nicotianae var parasitica

Différentes techniques d'inoculation du piment, Capsicum annuum L, ont été évaluées pour leur aptitude à reproduire correctement la spécificité parasitaire de P nicotianae var nicotianae, espèce inféodée au tabac et non pathogène sur piment, P capsici, espèce habituellement décrite et reconnue parasitaire sur piment et P nicotianae var parasitica, la nouvelle forme décrite sur piment en Tunisie. Les différentes modalités d'inoculation incluant celles des racines, des tiges décapitées maintenues sur plante ou en survie, et des feuilles en survie ont été apliquées à six variétés de piment, dont PI 201232, PI 201234 et CM 334 connues pour leur résistance à P capsici. L'inoculation du système racinaire par dépôt d'un inoculum de 280 000 zoospores suivi d'une incubation de 20 jours et de l'évaluation de l'intensité des nécroses racinaires, permet de reproduire la spécificité parasitaire des trois espèces de Phytophthora et le classement des variétés établi sur la base de leur sensibilité à P capsici. Elle paraît bien adaptée aux objectifs recherchés. Les variétés résistantes à P capsici (PI 201232 et PI 201234) se sont avérées sensibles à P nicotianae var parasitica alors que la variété CM 334 est apparue résistante à ces deux pathogènes, confirmant le caractère spécifique de ce parasite du piment.Comparison of various inoculation methods of pepper with Phytophthora nicotianae var parasitica. Various inoculation methods for pepper were evaluated in order to reproduce the parasitic specificity of Phytophthora nicotianae var nicotianae, a specific tobacco pathogen, P capsici, the species usually found in pepper, and P nicotianae var parasitica, a new form recently isolated from pepper in Tunisia. The inoculation methods, including root inoculation, decapitated stem maintained on the plant or in vitro, and leaves kept alive in vitro, were compared on six pepper varieties including PI 201232, PI 201234 and CM 334, which are known for their resistance to P capsici. Root inoculation, performed by depositing 280 000 zoospores followed by 20 days incubation and evaluation of the necrosis intensity, made it possible to mimic the rating of pepper varieties on the basis of their susceptibility to P capsici. Two of the varieties resistant to P capsici (PI 201232 and PI 201234) appeared to be susceptible to P nicotianae var parasitica while CM 334 was resistant to both pathogens, thus confirming the species status of that new pathogenic form in pepper

Comparaison de différentes techniques d'inoculation du piment par Phytophthora nicotianae var parasitica

International audienc

Phytophthora nicotianae var parasitica pathogène du piment en Tunisie

International audienc

Phytophthora nicotianae var parasitica pathogène du piment en Tunisie

Une espèce de Phytophthora différente de Phytophthora capsici, extrêmement dommageable et fréquente sur piment en Tunisie est identifiée. Les symptômes se caractérisent par un brunissement des racines, du collet et un flétrissement rapide des plantes ou plantules atteintes. Ce pathogène sévit aussi bien sous abri-serre en hiver qu'en plein champ l'été. L'identification des souches du parasite fondée sur leurs caractéristiques morphologiques, biologiques, et l'inoculation artificielle de plants sains de piment, montrent que l'agent pathogène est Phytophthora nicotianae var parasitica sensu Stamps et al (1990), synonyme de Phytophthora parasitica sensu Tucker (1931). Une étude sur l'homothallisme, l'hétérothallisme et les 2 types sexuels de compatibilité génétique A1 et A2 chez les souches testées a été entreprise. Les variations morphologiques constatées au niveau des souches ainsi que la dénomination de cette espèce de Phytophthora sont discutées.Phytophthora nicotianae var parasitica pathogen of the pepper in Tunisia. A Phytophthora species infecting pepper plants in Tunisia was identified. The symptom characteristics are collar and root rot leading to diseased plants or plantlets and rapid wilting. The pathogen attacks the plants in the greenhouse during winter as well as in the field during the summer. The identification of the parasite strain using morphological and biological behavior and artificial inoculation of healthy pepper plants showed that the species causing the disease is Phytophthora nicotianae var parasitica sensu Stamps et al (1990), which is synonymous with Phytophthora parasitica sensu Tucker (1931). The study of the homothallism, heterothallism and sexual genetic compatibility of the A 1 and A2 types was undertaken. The morphological variations observed in the strains and the Phytophthora sp taxonomy are discussed

Basic Substances and Potential Basic Substances: Key Compounds for a Sustainable Management of Seedborne Pathogens

Seedborne pathogens represent a critical issue for successful agricultural production worldwide. Seed treatment with plant protection products constitutes one of the first options useful for reducing seed infection or contamination and preventing disease spread. Basic substances are active, non-toxic substances already approved and sold in the EU for other purposes, e.g., as foodstuff or cosmetics, but they can also have a significant role in plant protection as ecofriendly, safe, and ecological alternatives to synthetic pesticides. Basic substances are regulated in the EU according to criteria presented in Article 23 of Regulation (EC) No 1107/2009. Twenty-four basic substances are currently approved in the EU and some of them such as chitosan, chitosan hydrochloride, vinegar, mustard seed powder, and hydrogen peroxide have been investigated as seed treatment products due to their proven activity against fungal, bacterial, and viral seedborne pathogens. Another basic substance, sodium hypochlorite, is under evaluation and may be approved soon for seed decontamination. Potential basic substances such as essential oils, plant extracts, and ozone were currently found effective as a seed treatment for disease management, although they are not yet approved as basic substances. The aim of this review, run within the Euphresco BasicS project, is to collect the recent information on the applications of basic substances and potential basic substances for seed treatment and describe the latest advanced research to find the best application methods for seed coating and make this large amount of published research results more manageable for consultation and use