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Relationships among measures of wheat blast under field conditions

Karasi Mills: Ohio State University

<div>Wheat blast, caused by <em>Magnaporthe oryzae, </em>affects the leaves and spikes of wheat. However, little is known about the relationship between spike and leaf blast or whether development of the former is influenced by the latter. In 2015, six research plots were planted with a highly susceptible cultivar at each of three sites (OK1, OK2, and CC) in Santa Cruz de la Sierra, Bolivia. Spike blast incidence (INC) and severity (SEV) and leaf blast severity (LEAF) were rated twice a week on a grid of one hundred points in each plot. Ratings began in mid-June, when spikes emerged, and continued until the milky-ripe growth stage in early August. Regression models were fitted to the data to quantify relationships among transformed INC, SEV, and LEAF. There were significantly positive linear relationships (<em>P</em> < 0.05) between complementary-log-log transformed SEV (CLL_SEV) and square-root-transformed INC (SQRT_INC), between CLL_SEV and CLL_LEAF, and between CLL_INC and CLL_LEAF. An estimated 81 to 89% of the variation in CLL_SEV was explained by the variation in SQRT_INC; 57 to 71% of the variation in CLL_SEV was explained by variation in CLL_LEAF; and 48 to 81% of the variation in CLL_INC was explained by CLL_LEAF. These results suggest that INC may be a good predictor of SEV, and provide some empirical support for the idea that leaf and spike blast may be associated when the two occur simultaneously in the same field.</div>