Screening Techniques for Stem Rot Resistance in Rice in California. J. J. Oster, California Cooperative Rice Research Foundation, Inc., Biggs, CA 95917. . Plant Dis. 74:545-548. Accepted for publication 14 December 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0545.

Inoculum production and inoculation techniques are reported. Rating plants 35–42 days after 50% flowering in the field produced the highest stem rot disease severity scores and differentiation among cultivars previously known to vary in susceptibility and growth duration. A fertilizer rate of 0.21 g of nitrogen per pot (15.8 kg of N/ha) as 16-20-0 applied 21 days after seeding differentiated among cultivars nearly as well as higher nitrogen rates and minimized pest proliferation in the greenhouse. Correlations between field and greenhouse disease ratings ranged from r² = 0.89 to 0.94 (significant at P = 0.03 to 0.06) within years and from r² = 0.36 (P = 0.40) to 0.94 (P = 0.03) between years. Correlations of between-year greenhouse disease ratings ranged from r² = 0.47 (P = 0.31) to 1.00 and from r² = 0.67 (P = 0.18) to 0.97 (P = 0.02) for field disease ratings. Correlations of stem rot rating with number of sclerotia formed per tiller for all cultivars ranged from r² = 0.51 to 0.60 (P <0.001).