Relationship between growth rate, sclerotia production, and virulence of isolates of Rhizoctonia solani Kuhn [Philippines]
1987
Shahjahan, A.K.M. | Fabellar, N. | Mew, T.W. (International Rice Research Inst., Los Banos, Laguna (Philippines))
Cultures of Rhizoctonia solani causing sheath blight were isolated from diseased specimens of rice, grass, weeds, water hyacinth, maize, and millet from fields on the IRRI [International Rice Research Inst., Los Banos, Laguna, Philippines] farm and in Laguna Province, Philippines. Growth rate (regression coefficient), Sclerotia production (no./plate in 10 d), and cultural characteristics of 98 isolates were studied using potato dextrose agar (PDA) medium enriched with 0.1% urea. Virulence of 10 isolates representing different culture types, growth rate, and sclerotia production were tested on IR58 grown in pots in the greenhouse with 1.6 g N/30 cm pot. IR58 was inoculated at booting and lesion height and plant height were measured 20 d after inoculation. The 10 isolates differed in growth rate, Sclerotia production, and virulence. Growth rate varied from 1.3 to 3.2 mm/h and Sclerotia production from 9 to 134 Sclerotia/plate. No correlation between growth rate and Sclerotia production (r = 0.23 ns) or between Sclerotia production and virulence (r = 0.37 ns) was noted. The correlation was significant (r = 0.78** ) between growth rate and virulence measured as relative lesion height (RLH) in IR58 20 d after inoculation, but if the extreme values for RS72-1 were excluded, the correlation coefficient becomes nonsignificant (r = 0.66 ns). The mean growth rates of the 9 other isolates (excluding RS72-1) do not differ much (2.5 to 3.2 mm/h). Virulence varied from 52 to 75%. The most virulent isolate (RS27-1) with the highest growth rate was isolated from millet grown during the dry season in an upland field following rice.
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