Mechanism of seedling protection induced by a hypovirulent isolate of Rhizoctonia solani

Abstract

Among several hypovirulent isolates of Rhizoctonia spp. tested, one isolate (No. 521) provided significantly higher protection (76–94%) to radish and cotton seedlings against infection by virulent isoltes of Rhizoctonia spp. and also induced a higher increased plant growth response than the others. The hypovirulent strain did not compete for root exudates. The protected plants were not induced to produce new polyphenols, melanins, more lignins, or phytoalexins. Also they did not produce inhibitors of pectinases or cellulases released by the pathogen, nor did they produce cell wall lytic-type enzymes, such as chitinase and β-(1,3) glucanase. Ca2+ content was significantly higher in seedlings colonized by the hypovirulent isolate. The hypovirulent isolate densely colonized the surface of roots and hypocotyls, and removal of its hyphae nullified the protection provided by this isolate. Key words: Rhizoctonia solani, damping-off, hypovirulent isolate, biological control.