Abstract
Rice blast fungus is notorious for changeability in pathogenicity, but it lacks sexual life cycle. It can be postulated that such an imperfect fungus has another mechanism for generating genetic variations. Recent studies concerning comparative genomics reveal that parasexual recombination may play important role in the evolution of rice blast fungus. To observe the parasexualism of rice blast (Pyricularia oryzae) and crabgrass blast (Pyricularia grisea) fungus double inoculation and punch method were applied in this experiment. A total of 520 isolates collected from the double inoculated lesions was subjected to PCR-RFLP analysis of the ITS region to identify subcultures of the inoculated rice blast isolates. As a result, four isolates from the three double inoculated lesions with SA13-1ME and TP106 were identified as subcultures of TP106. To access the recombination genotypes, a total of 17 isolates from the three lesions was subjected to MAGGY-DNA fingerprint analysis. However, recombinant DNA fingerprint patterns between TP106 and SA13-1ME were not detected among the 17 isolates. Although TP022 was not recovered from the double inoculated lesions, the fact that TP106 was recovered from the double inoculated lesion indicates that rice blast fungus can invade and colonized in blast lesion on crabgrass. The opportunistic infection on the double inoculated lesions observed in this study potentially provides new insight into the life cycle of rice blast pathogen.
Highlights
This study investigated whether parasexual recombination occurs between the blast fungi sourced from different host plants
These findings suggest the capacity of rice blast fungus to cause opportunistic infection in crabgrass leaf following wound inoculation
Rice blast fungus lacks sexual lifecycle in nature, and sexual recombination should be excluded from the mechanisms to regain and deleted Avr genes
Summary
It is the causal agent of rice blast, one of most devastating diseases of rice (Oryzae sativa L.) observed in most of the rice growing-countries across the world [3]. The perfect stage of the fungus was observed in cross experiments in which highly fertile laboratory strains were used as tester isolates [4]. Crosses between field isolates of this pathogen usually result in infertility [5]. Because of the infertility of the field isolates, this pathogen is considered to be limited to asexual reproduction in nature. Sexual recombination, if any, contributes little to the genetic variations in the pathogen
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