Abstract

False smut of rice (Oryza sativa L.) caused by Ustilaginoidea virens (Cooke) Takahashi (teleomorph Villosiclava virens) is one of the most common fungal diseases of rice in China. The objectives of the research were: 1) to study the biology of Ustilaginoidea virens, 2) to develop suitable media for inoculum production of U. virens, and 3) to develop an artificial inoculation technique for the study of false smut resistance in rice. Seventy diseased rice samples were collected from seven districts of Guizhou province, China during 2007-2008 and 138 single-spore isolates of U. virens were isolated. Among two inoculation methods applied at 3 rice growth stages of rice variety Gangxiang 707 using spore suspension of U. virens isolate 2008-33-1, conidia injection at late booting stage produced the highest false smut incidence of 50.43%, while conidia spraying during the same stage gave only 34.75% disease incidence. Pathogenicity test of selected eight U. virens isolates on rice variety Zhongyou 177 using the conidia injection at late booting stage, showed that the isolates were different in their aggressiveness in which isolate 2008-11-1 gave the highest virulence score of 9 with the disease incidence of 81.66%, while isolate 2007-48-1 gave the lowest score of 5 with only 15.57% disease incidence. These eight U. virens isolates were further tested on six rice varieties using the same inoculation technique. Most of the rice varieties were either susceptible or moderately susceptible except Fengyouxiangzhan that was highly susceptible to U. virens isolate 2007 -79-1 and Nongfengyou 256 was moderately resistant. When the evaluation was done across all the U. virens isolates, Gangyou 827, Jixiangyou 830 and Fengyouxiangzhan were among the most susceptible varieties with disease incidence of 55.06, 54.79 and 53.50%, respectively, while Nongfengyou 256 varieties showed the lowest disease severity as 23.85%. For the pathogen strain, 2008-33-1 was the most aggressive giving 58.09% disease incidence while the fungal pathogen strain 2008-2-2 gave the lowest of 28.17%.

Key words: False smut, rice, colony morphology, fungal characterization, Ustilaginoidea virens.