Search

Hydrogen peroxide is an important signal molecule in plant defense against biotic and abiotic stress. Pepper golden mosaic virus (PepGMV) is a whitefly-transmitted geminivirus causing significant yield and quality losses in pepper and other horticultural crops in Mexico. Several pesticides have been used trying to control whiteflies and thus, PepGMV disease in host crops. The present work examined the effect of exogenous application of hydrogen peroxide (H2O2) on inducing resistance to PepGMV infection in pepper plants. Experiments were carried out under greenhouse conditions aiming to evaluate phenotypical, biochemical and molecular features in these pepper plants. Hydrogen peroxide at 6, 14 and 18 mM induced tolerance to PepGMV either by absence of symptoms as well as by attenuating and/or delaying them. The protection observed was directly dependent on the concentration of H2O2 sprayed on plants. Moreover, PepGMV DNA levels were inversely proportional to the protection level. Enzymatic and gene expression profiles related with plant defense were induced in protected, in comparison to susceptible control plants. Interestingly, the levels of some phenolic compounds were also associated with plant protection. Taking together, these results suggested that exogenous foliar applications of H2O2 protect pepper plants against PepGMV infection inducing the plant host defense arsenal.

Macrophomina phaseolina infects a wide range of plant species. In the case of Phaseolus vulgaris (the common bean), the fungus causes charcoal rot which can lead to severe losses especially under arid conditions. In order to combat the disease, it is necessary to have information on the population structure of the pathogen in terms of pathogenesis on different species which may be grown simultaneously or successively within a region. Previous reports have demonstrated the heterogeneity of the pathogen both in terms of morphological characteristics and molecular genotype; however no systematic attempt has been made to compare pathogenesis of different isolates in relation to genotype, species of origin or geographical location. With this aim 84 isolates of M. phaseolina from different plant species in different geographical regions of Mexico were analysed by inoculation on a set of P. vulgaris cultivars differing in reaction to the fungus and by determination of their amplified fragment length polymorphism (AFLP) genotype. Forty three distinct pathotypes were identified, only two of which were found in more than one species. All 84 isolates had distinct AFLP genotypes and cluster analysis showed a tendency of the isolates to form groups related to geographical origin or species of origin.