Cultural, Morphological, Molecular Characterization of Rhizoctonia solani, and its Pathogenicity on Zoysiagrass and Bentgrass.

Rhizoctonia solani Kuhn is complex fungal pathogen composed of different genetic or anastomosis groups (AGs) with genetic diversity within and between each group. Therefore, breeding for cultivars resistant to Rhizoctonia becomes a challenging task.  The objective of this study was to identify and characterize different isolates of Rhizoctonia into various AG’s through cultural, morphological, and molecular analysis along with determining the pathogencity of an individual isolate from within each AG’s, namely, AG2-1, AG2-2III-B, AG2-2IV, AG2-2-LP, AG1-IA, AG4, and AG5 on zoysiagrass and bentgrass.  Rhizoctonia characteristics studied were colony color, nuclear condition, aerial mycelium, sclerotia, zonation, and phylogenetic analysis of ITS region of ribosomal DNA.  The pathogenticity of an individual isolate from within each AG, was determined in growth chamber studies with 'Zenith' zoysiagrass (Zoysia japonica Steud.) and ‘SR1020’ bentgrass (Agrostis palustris) established from seed (42kg/ha^-1). Three replications of established seedlings were challenged with a 5mm PDA plug of each fungal isolate, in inoculation chambers maintained at 25^ºC with lighting at ca. 24µmol sec^-1-m^-2. Isolates from AG-1, AG2-2IIIB, AG-4 and AG-5 initiated colonization on both zoysiagrass and bentgrass within 24hours. An isolate from AG4 had a significantly greater radial colonization rate (14.75mm after 48hrs), than isolates from AG2-1 and AG2-2LP. Disease rating index (0=no disease;4=75-100%) of 3.2 was observed on  ‘Zenith’ and 4.0 on ‘SR1020’. Data showing colonization and disease index rate of various vegetative cultivars of zoysiagrass upon infection with different AG's of Rhizoctonia will also be presented.