Genetic variability for disease resistance in Brazilian upland rice native germplasm

Thirty nine rice genotypes were evaluated under dryland field conditions for resistance to leaf and neck blast, brown spot, leaf scald, narrow brown leaf spot and grain discoloration in 13 test sites during a three-year period. These include 17 land races, six traditional cultivars, 11 improved breeding lines and three exotic cultivars. There was a great diversity in the native germplasm in relation to resistance to different pathogens. The land races Iguape Redondo, Arroz de Guerra, Cateto and Chatao exhibited partial resistance to leaf blast comparable to IRAT 13 and IRAT 104 and superior to the traditional cultivar IAC 47. The leaf blast severities and neck blast incidences of medium maturing genotypes were positively correlated (r = 0.86, P < 0.01). A number of genotypes exhibited a high degree of resistance to grain discoloration relative to the susceptible controls, Vermelho miudo, Mimoso and Cajueiro Liso. The correlation between mean brown leaf spot and mean grain discoloration severities of different trials was positive both for early maturing (r = 0.93, P < 0.01) and medium maturing (r = 0.77, P < 0.01) genotypes. The early maturing improved line M 39 had shown a high level of multiple disease resistance. The localities Goiania (GO) and Jaciara (MT) were identified as hot spot screening sites for rice blast and grain discoloration, respectively.