Leaf and Neck Blast Resistance in Tropical Lowland Rice Cultivars

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Abstract
Pyricularia oryzae, the rice blast pathogen, can infect both leaves and panicle neck nodes. The leaf blast and neck blast resistance of 27 tropical lowland rice cultivars and breeding lines was assessed and classified relative to as susceptible check, IR50, and a partially resistant check, IR36. Leaf blast resistance was scored in four upland miniplot trials. Neck blast resistance was scored in five inoculated, lowland field plantings. The classification of the relative leaf blast resistance of entries in the miniplots was generally consistent for resistant and susceptible lines, but varied between trials for lines with intermediate resistance. The classification of neck blast resistance of intermediate and susceptible lines also varied between trials, mostly due to differences in flowering data. The mean leaf blast values from the miniplot trials were positively correlated with the mean neck blast values (r = 0.81, P = 0.01) from the lowland trials. Some lines, however, were exceptions to this general relationship. The lines IR25604-99-1-3-2-2 nd IR37704-98-3-2-2 were leaf blast susceptible, but resistant to neck blast in most of the lowland plantings. Lines of particular interest to breeders should be screened for neck blast resistance; improved methods are required, particularly for neck blast testing.