Characterization of Populations of Rhizoctonia solani in Paddy Rice Fields in Côte d'Ivoire

Characterization, Genetic Structure, and Pathogenicity of Rhizoctonia spp. Associated with Rice Sheath Diseases in India

ABSTRACT Isolates of Rhizoctonia spp. were obtained from rice in India during 2000-2003. Characterization by conventional techniques and polymerase chain reaction showed that from 110 isolates, 99 were R. solani and 11 were R. oryzae-sativae. Of 99 isolates identified as R. solani, 96 were AG1-IA, 1 was AG1-IB, and 2 were AG1-IC. Amplified fragment length polymorphism (AFLP) analyzes were used to determine genetic relationships in Rhizoctonia pathogen populations collected from different geographic regions. Cluster analysis based on the AFLP data separated isolates belonging to the three different intraspecific groups of R. solani AG1 and differentiated R. solani from R. oryzae-sativae. Analysis of molecular variance (AMOVA) revealed that geographic region was the dominant factor determining population structure of R. solani AG1-1A; host cultivar had no significant effect. Pathogenicity tests on Oryza sativa cv. Zenith revealed that isolates of R. solani AG1-1A and AG1-1B were more virulent than R. solani AG1-IC and R. oryzae-sativae isolates.

Genetic diversity in potato field populations of Thanatephorus cucumeris AG-3, revealed by ITS polymorphism and RAPD markers

DNA sequence analysis of the internal transcribed spacer region 1 (ITS1) and random amplified polymorphic DNA (RAPD) markers were used to survey genetic variability in relation to agronomic and regional factors among 60 isolates of Thanatephorus cucumeris (anamorph Rhizoctonia solani) collected from lesions on potato stems or sclerotia of potato tubers. Based on comparative sequence analysis it was shown that all isolates belonged to anastomosis group 3 subgroup Potato Type (AG-3 PT). ITS1 sequence polymorphisms were found within 45 of the 60 isolates showing that different types of the ITS-region are present in individual isolates. Cloning and sequence analysis of the ITS1 region from three selected isolates with sequence polymorphism showed that two different ITS1-types were present in each isolate. RAPD analysis identified 51 RAPD-phenotypes among the 60 investigated isolates indicating a high level of diversity within the subgroup AG-3 PT. Putative clonal isolates with identical RAPD- and ITS1-types were identified within fields, and in one case the same phenotype was found in two different fields separated by several hundred kilometers. Population subdivision analysis based on phenotypic as well as genotypic diversities showed differentiation among populations from different fields when isolates were sampled from tubers, indicating restricted gene flow among soil populations. Low differentiation was seen among field populations sampled from stems, indicating that gene flow is taking place. The population structure was not influenced by the previous crop in the rotation nor by the two cultivars 'Sava' and 'Bintje'.