Effect of soil moisture on the survival of Rhizoctonia solani and Trichoderma harzianum
Paula, T.J. de, Jr; Hau, B.
Bulletin OILB/SROP 25(10): 295-298
The effect of soil moisture on the survival and dynamics of R. solani and its antagonist (Trichoderma harzianum) were studied under greenhouse conditions. Inoculum of R. solani was grown on rice grains, while that of T. harzianum was grown on wheat bran. Both fungi were inoculated at the same time, and the sowing of bean seeds to test the survival was carried out immediately after soil infestation at 20, 60, 180 and 360 days after soil infestation (DAI), and at 3, 6, 12 and 18 DAI in a complementary experiment. Soil moisture was periodically monitored and kept at four levels varying from 15 to 57% (v/v). The pathogen survived in the soil and caused disease at all tested dates. However, in the first survival tests (0, 20 and 60 DAI), severity of root rot initially increased, but decreased later (180 and 360 DAI). On the other hand, dry weight of R. solani-infected plants was reduced in the initial tests, but increased later so that, at 360 DAI, values similar to the control were reached. Soil moisture did not affect disease severity. The pathogen could easily be recovered even from drier soil, but this was hardly possible in the presence of T. harzianum. The antagonist improved the emergence of seedlings and led to higher weights of plants grown in R. solani-infested soil. However, when the pathogen was well established in the soil, antagonistic protection was lower. Consistent antagonistic effects were observed until 180 DAI, but they were hardly detectable at 360 DAI. The antagonist improved plant growth until 60 DAI even on plants not infected by R. solani. The antagonistic ability and the survival of T. harzianum were greater in soils held at intermediate soil moisture levels than in wet or dry soils, but were also influenced by the inoculum potential of both fungi in the soil.