Phytophthora disease of rubber (Hevea brasiliensis Muell.-Arg.): Identification, clonal reaction and some chemical control
1995
Phayao Srisa-arn
Fifteen rubber clones were examined for isozyme pattern variability and peroxidase activity in the correlation to disease resistance. There is a non-significant correlation between two isozyme patterns namely peroxidase and esterase, with disease resistance levels. However, the level of peroxidase activity correlated to the level of the disease resistance. The higher peroxidase activity level observed, the higher degree of resistance was found. The efficacy of seven fungicides were tested against mycelium growth and sporangium formation of P. nicotianae var. parasitica isolate C-2 and P. botryosa isolate S-1, metalaxyl 25 percent WP showed the best inhibition. The fungicidal activity against zoospore release and germination of P. botryosa isolate S-1 were detemined. Dimethomorph 50 percent WP, metalaxyl 25 percent WP and fosetyl-Al 80 percent WP were ineffected on zoospore release while mancozeb 80 percent WP and metalaxyl 25 percent WP ineffected on zoospore germination. For chemical control under greenhouse conditions, rubber seedlings were inoculated with zoospore suspension of P. nicotianae var. parasitica isolate C-2 before sprayed fungicides for 3 days. The comparison of disease development in 4 weeks showed that spraying with dimethomorph 74.2 percent WP 2.5 g/l gave the best control, whereas dimethomorph 50 percent WP gave better control when applied before zoospore inoculation for 1 day.
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