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Adaptation of populations to new environments is frequently costly due to trade-offs between life history traits, and consequently, parasites are expected to be locally adapted to sympatric hosts. Also, during adaptation to the host, an increase in parasite fitness could have direct consequences on its aggressiveness (i.e. the quantity of damages caused to the host by the virus). These two phenomena have been observed in the context of pathogen adaptation to host's qualitative and monogenic resistances. However, the ability of pathogens to adapt to quantitative polygenic plant resistances and the consequences of these potential adaptations on other pathogen life history traits remain to be evaluated. Potato virus Y and two pepper genotypes (one susceptible and one with quantitative resistance) were used, and experimental evolutions showed that adaptation to a quantitative resistance was possible and resulted in resistance breakdown. This adaptation was associated to a fitness cost on the susceptible cultivar, but had no consequence either in terms of aggressiveness, which could be explained by a high tolerance level, or in terms of aphid transmission efficiency. We concluded that quantitative resistances are not necessarily durable but management strategies mixing susceptible and resistant cultivars in space and/or in time should be useful to preserve their efficiency. [ABSTRACT FROM AUTHOR]

The cowpea weevil, Callosobruchus maculatus (F.), cowpea, Vigna unguiculata (L.) Walpers, and wild Vigna species (progenitors of cowpea) have interacted for thousands of generations in Africa. Consequently,cowpea weevil virulence to Vigna species and the resistance within Vigna species to cowpea weevil populations may vary significantly. Given the current interest in using wild Vigna species as sources of cowpea weevil resistance, it is essential to determine the importance ofthe variation in cowpea weevil and Vigna interactions. To examine cowpea weevil and Vigna interactions, 3 experiments were conducted using 6 cowpea weevil populations and multiple accessions of 4 cowpea weevil-resistant Vigna species. In general, we found significant variation among cowpea weevil populations for virulence to resistant cowpea landrace TVu 2027. Unexpectedly, we found that TVu 2027 was susceptible to a cowpea weevil population from an unknown location in Nigeria.In addition, we found significant variation among accessions within each of the 3 wild Vigna species for resistance to cowpea weevil populations. Considering the potential for low durability of resistance (when using Vigna species as sources of cowpea weevil resistance), coupled with the difficulty of moving cowpea weevil resistance genes from wild Vigna species to domesticated cowpea, it may be more productive to focus on developing a transformation system for cowpea, and search for cowpea weevil resistance genes outside the genus Vigna and outside other genera having species that serve as host plants for the cowpea weevil. [ABSTRACT FROM AUTHOR]