A longitudinal study on morpho-genetic diversity of pathogenic Rhizoctonia solani from sugar beet and dry beans of western Nebraska
Abstract Root and stem rot caused by Rhizoctonia solani is a serious fungal disease of sugar beet and dry bean production in Nebraska. The objective of this study was to analyze morpho-genetic diversity of 38 Rhizoctonia solani isolates from sugar beet and dry bean fields in western Nebraska over 10 years. Morphological features and ISSR-based DNA markers were used to study the morphogenetic diversity. Fungal colonies were morphologically diverse in shapes, aerial hyphae formation, colony, and sclerotia color. Marker analysis using nineteen polymorphic ISSR markers showed polymorphic bands ranged from 15 - 28 with molecular weight of 100bp to 3kb. Polymorphic loci ranged from 43.26 – 92.88%. Nei genetic distance within the population ranged from 0.03 – 0.09 and Shannon diversity index varied from 0.24 – 0.28. AMOVA analysis based on ΦPT values showed 87% variation within and 13% among the population with statistical significance (p<0.05). Majority of the isolates from sugar beet showed nearby association within the population. A significant number of isolates showed similarity with isolates of both the crops suggesting their broad pathogenicity. Isolates were grouped into three different clusters in UPGMA based cluster analysis using marker information. Interestingly, there was no geographical correlation between the isolates. Principle component analysis showed randomized distribution of isolates from the same geographical origin. This information may help in molecular pathotyping of the pathogen for better disease management.