| Popis: |
An experiment was conducted in the laboratory and field to study the interaction among three sheath diseases of rice namely sheath blight, sheath spot and aggregated sheath spot and their causal agents, Rhizoctonia solani, R. oryzae and R. oryzae-sativae. In addition to RFLP-PCR analysis and DNA sequencing of three sheath disease species, antagonism among the species was studied using dual culture technique. The results showed that antagonist, R. solani, inhibited radial growth against test fungi (R. oryzae and R. oryzae-sativae) from 37.08-46.49%. Disease incidence and severity of sheath blight was not reduced when R. solani was inoculated with either R. oryzae, R. oryzae-sativae, or a combination of the two. However, the incidence and severity of sheath spot and aggregated sheath spot were inhibited significantly when either R. oryzae or R. oryzae-sativae was inoculated with R. Solani. The highest percentage of relative lesion height and infected tiller was found at maturity followed by hard dough and flowering stage. Average yield losses ranged from 13.99-18.62 % when R. solani inoculated with both of R. oryzae-sativae and R. oryzae or any of them while R. solani alone caused 19.15% loss. DNA sequence analysis differentiated R. solani, R. oryzae and R. oryzae-sativae and phylogenetic tree revealed the close similarity of the species to the isolates of Philippines, Japan and Malaysia, respectively. In HhaI restriction enzyme, fragments 375 and 345 bp were specific for R. solani and 375, 235, and 120 bp was for R. oryzae-sativae which showed identical pattern across the isolates of two species. |
