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Effects of Puccinia sorghi Rust on Yield and Several Agronomic Traits of Maize in Hawaii¹

Ten paired doublecross hybrids of maize (Zea mays L.), genetically similar except for the gene Rp-d conferring resistance to Puccinia sorghi Schw., were studied under natural rust epiphytotics in an area with continuous corn production in Hawaii. Data on eight agronomic traits are summarized from April and November plantings, including grain yield, plant weight, ear length and diameter, 1,000-kernel wt, plant and ear height, and days to silk. Rust was severe in both seasons, and slightly more so in winter (6.0 vs. 5.2 on a seven-point scale). In this area, winter corn yields are characteristically about half those of summer, due to reduced light intensity and daylength.

The rust affected all traits significantly when data combined over the two seasons were considered. Average reductions caused by rust were 35% for grain yield, 27% for fresh plant weight, 11% for ear length, 10% for kernel wt and ear diameter, and less than 5% for plant and ear height and days to silk. Highly significant interactions of season with treatment (resistant vs. susceptible hybrids) were detected in grain yield and plant height, with the rust effect generally enhanced in the winter planting. Grain yield reductions by rust were best correlated with changes in kernel weight (r = 0.78), but clearly reflected major effects on ear lengths and diameters as well. In areas of continuous corn production, uncontrolled P. sorghi rust can be a serious disease affecting essentially all components of yield.

Key Words: Zea mays L. • Ear length

² Maize breeder, Office of Rural Dev., Suwon, Korea (former student, Univ. of Hawaii and Food Institute, East-West Center), and professor of horticulture and genetics, Univ. of Hawaii, Honolulu, HI 96822, respectively.

Received for publication November 8, 1975.