By: Thind TarlochanS, Aggarwal Rohit
Potato is planted after rice in several parts of Punjab in India and both
crops are attacked by Rhizoctonia solani Kühn. Potato tubers showing black scurf
and rice plants affected by sheath blight were collected from different regions
of the state and the isolates of R. solani so obtained were studied to determine
their variability and to ascertain their cross-infectivity and response to
fungicides. Potato isolates of R. solani did not infect rice plants but some
rice isolates were weakly pathogenic on potato, the sclerotia being less firmly
attached on tuber surface, indicating a possible unsuccessful attempt of rice
isolates to infect potato. Rice isolates (66.6%) grew faster (>20 mm colony
growth per 24 h) than those of the potato isolates (15-20 mm growth rate per 24
h). Hyphal width of isolates from both hosts varied from 7.2 to 12.1 μm. Colony
growth of most potato isolates (61.2%) was appressed, whereas that of most rice
isolates (53.3%) was fluffy. Rice isolates (73.3%) formed larger sclerotia
(1.5-2.0 mm in diameter) than those of the potato isolates (0.5-1.0 mm in
diameter). Anastomosis studies indicated that potato isolates belonged to AG-3
and AG-5 groups while rice isolates belonged to the AG-1-1-A group.
Representative R. solani isolates from the two hosts showed significant
variation in response to fungicides (i.e. carbendazim, carboxin,
pencycuron, propiconazole and validamycin) based on their values.Yangzhou pioneer chemical CO.,LTD
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