RESUMO
Scab, caused by the plant-pathogenic fungus Venturia effusa, is a major disease of pecan in South America, resulting in loss of quantity and quality of nut yield. Characteristics of the populations of V. effusa in South America are unknown. We used microsatellites to describe the genetic diversity and population structure of V. effusa in South America, and determined the mating type status of the pathogen. The four hierarchically sampled orchard populations from Argentina (AR), Brazil (BRC and BRS), and Uruguay (UR) had moderate to high genotypic and gene diversity. There was evidence of population differentiation (Fst = 0.196) but the correlation between geographic distance and genetic distance was not statistically significant. Genetic differentiation was minimal between the UR, BRC, and BRS populations, and these populations were more clearly differentiated from the AR population. The MAT1-1 and MAT1-2 mating types occurred in all four orchards and their frequencies did not deviate from the 1:1 ratio expected under random mating; however, multilocus linkage equilibrium was rejected in three of the four populations. The population genetics of South American populations of V. effusa has many similarities to the population genetics of V. effusa previously described in the United States. Characterizing the populations genetics and reproductive systems of V. effusa are important to establish the evolutionary potential of the pathogen and, thus, its adaptability-and can provide a basis for informed approaches to utilizing available host resistance and determining phytosanitary needs.
Assuntos
Ascomicetos , Carya , Ascomicetos/genética , Brasil , Carya/genética , Carya/microbiologia , Fungos do Gênero Venturia , Genes Fúngicos Tipo Acasalamento/genética , Variação Genética , Genética Populacional , Doenças das Plantas/microbiologiaRESUMO
Current declines in biodiversity put at risk ecosystem services that are fundamental for human welfare. Increasing evidence indicates that one such service is the ability to reduce virus emergence. It has been proposed that the reduction of virus emergence occurs at two levels: through a reduction of virus prevalence/transmission and, as a result of these epidemiological changes, through a limitation of virus genetic diversity. Although the former mechanism has been studied in a few host-virus interactions, very little is known about the association between ecosystem biodiversity and virus genetic diversity. To address this subject, we estimated genetic diversity, synonymous and non-synonymous nucleotide substitution rates, selection pressures, and frequency of recombinants and re-assortants in populations of Pepper golden mosaic virus (PepGMV) and Pepper huasteco yellow vein virus (PHYVV) that infect chiltepin plants in Mexico. We then analyzed how these parameters varied according to the level of habitat anthropization, which is the major cause of biodiversity loss. Our results indicated that genetic diversity of PepGMV (but not of PHYVV) populations increased with the loss of biodiversity at higher levels of habitat anthropization. This was mostly the consequence of higher rates of synonymous nucleotide substitutions, rather than of adaptive selection. The frequency of recombinants and re-assortants was higher in PepGMV populations infecting wild chiltepin than in those infecting cultivated ones, suggesting that genetic exchange is not the main mechanism for generating genetic diversity in PepGMV populations. These findings provide evidence that biodiversity may modulate the genetic diversity of plant viruses, but it may differentially affect even two closely related viruses. Our analyses may contribute to understanding the factors involved in virus emergence.
RESUMO
Background Genetic diversity and genetic variation of 10 populations and subpopulations of Magnolia wufengensis, a new and endangered endemic species, were examined by inter simple sequence repeat (ISSR) and sequence-related amplified polymorphism (SRAP) molecular markers. Compared with other endangered endemic Magnolia taxa, M. wufengensis holds a relatively high level of genetic variation. Result Total genetic diversity was found to be 87.7% for ISSR and 88.0% for SRAP markers. For polymorphic loci (P), the effective mean number of alleles (Ae) was 1.414 for ISSR markers and 1.458 for SRAP markers, while the mean expected heterozygosity (H) was 0.256 using ISSR and 0.291 for SRAP markers. Within-population variation was estimated for P as 74.9% using ISSR and 74.6% with SRAP markers; the number of alleles Ae was 1.379 with ISSR and 1.397 for SRAP and H 0.235 with ISSR and 0.247 for SRAP markers. Conclusion The analysis of molecular variation of both ISSR and SRAP marker systems indicated that most genetic variation is within populations, with values of 90.64% and 82.92% respectively. Mantel tests indicated a moderate association between the two marker systems and a low correlation between genetic and geographic distances. High levels of genetic diversity and low levels of population divergence suggest that genetic drift is not currently of great concern for this species. Severe habitat loss and fragmentation, predominantly ascribed to anthropogenic pressures, caused in-situ developing restriction of this species. Action for conserving this rare species for its long-term survival should be taken immediately.