| Corn Curvularia leaf spot disease is a new potentially serious foliar disease that is distributed in many corn-growing zones in recent years in China, and the spread and development have been still increasing rapidly to other areas. The disease can damage crops significantly and is becoming an increasingly major threat even more than corn northern leaf blight and southern leaf blight in some regions. 148 Curvularia spp. isolates were obtained from disease samples covering 11 provinces. The study was undertaken to evaluate the composition of pathogens causing corn Curvularia leaf spot and to determine genetic diversity in the pathogen population, and to evaluate the resistance of Sichuan corn germplasms to Curvularia lunata.Based on morphologic characters, 148 isolates from corn were identified as C.lunata, C.pallescens, C.lunata var.aeria, C.clavata, C.ovoidea, C.inaequalis, C.senegalensis, C.cymbopogonis, Curvularia spi and Curvularia sp2 at 63.2%, 31.6%, 18.4%, 10.5%, 10.5%, 3.9%, 1.3%, 2.6%, 1.3%, and 1.3% frequency in these samples, respectively. Of 148 isolates, frequencies of the morphologic species at 42.6%, 24.3%, 10.0%, 10.8%, 6.8%, 2.0%, 0.7%, 1.4%, 0.7%, and 0.7%, respectively. These results showed that main populations were C.lunata, C.pallescens, C.lunata var. aeria, C.clavata and C.ovoidea. Of them C.lunata was prevalent population. The remaining 5 species, C.inaequalis, C.senegalensis, C.cymbopogonis, Curvularia sp1 and Curvularia sp2, could be isolated occasionally in a few of samples.Pathogenicity of 83 Curvularia isolates including 76 isolates from corn and 7 isolates from other hosts were tested in seedling and adult stage of corns. Among these species based on morphology, C. lunata, C.pallescens, C. lunata var. aeria, C. clavata and C. ovoidea could cause the typical Curvularia leaf spot symptom that lesions are grayish spots up to 1mm in diameter appear in the centers and straw-colored or chlorotic halos may surround the lesions. So they were demonstrated as pathogens whereas C. lunata was by far the most prevalent species. On the basis of pargogenicity test, the pathogens were divided into four pathotypes, strong pathotype, middle pathotype, weak pathotype and non-pargogenic pathotype. Most isolates were placed to either strong pathotype or middle pathotype. The remaining 5 species could not cause the typical lesions and were not considered as pathogens in this study.Eighty Curvularia isolates (of them 2 from other host), including C. lunata, C. lunata var. aeria, C.pallescens, C.ovoidea, C.clavata and Curvularia sp1 were selected to characterize genetic diversity by random amplified polymorphic DNA (RAPD) with 8 arbitrarily primers. There was extensive genetic diversity within these isolates. At similar level of 0.61, all isolates clustered into four distinct groups, 86.3% isolates assigned to the dominant group, RAPD I ,and 13.7% isolates to the 3 remaining groups. Theisolates assigned to the dominant group, RAPD I ,and 13.7% isolates to the 3 remaining groups. The dominant group (RAPD I) included most of C. lunata, all of C.lunata var. aeria, C.pallescens, C.clavata and C.ovoidea, and exhibited low genetic diversity. However, two prevalent subgroups were distinguished within RAPD I that encompassed 68 isolates (only one isolate not to any of two subgroups). The first subgroup included most of C. lunata and all of C. lunata var. aeria and exhibited high genetic similarity. The other one included all isolates of C.pallescens, C.clavata, C.ovoidea and exhibited also high genetic similarity. These results suggested RAPD data reveal a genetic difference between C.lunata and its similar species, C.pallescens, C.clavata, C. ovoidea.Analysis of internal transcribed spacer (ITS) sequences of 40 Curvularia spp. isolates including 35 from corn and 5 from other hosts were employed to determine the molecular and phylogenetic relationships within these morphologic species. Nearly all isolates of C.lunata except for 2 isolates and all of C.lunata var. aeria, C.pallescens, C.clavata, C.ovoidea ex...
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