Performance of Rice Composites Dimorphic for Plant Height and for Pubescence 1

The effects on yield of two contrasting rice ( Oryza sativa L.) plant characteristics (tall vs. short, pubescent vs. glabrous) were studied. These plant types were developed from a cross between a pubescent short cultivar and a glabrous tall one with related parentage. Four plant types, glabrous short, glabrous tall, pubescent short, and pubescent tall, were selected in the F 2 and increased in panicle rows in the F 3 . These panicle rows were composited and evaluated in broadcast plots in the F 4 . The two short types produced grain yields about 10% greater than the two tall types at optimum N fertility levels. Differences were attributed to a combination of factors including greatly reduced lodging of short types, production of significantly more panicles per unit area, more grains per panicle, and a higher percentage of fertile florets (filled grains). The 100‐grain weight was similar for short and tall types. The pubescent and glabrous leaf and hull characteristics did not affect grain yields significantly but number of grains per panicle and percent of sterile florets were significantly less in the pubescent than in the glabrous types. The four plant types were evaluated at six N fertility levels applied as urea. Rates of application were from 33.5 to 201 kg/ha with 33.5 kg increments. Optimum yields were obtained at 167.5 kg/ha. A progressive increase, in internode length occurred with N rate increments. The lower internodes (fourth and fifth from the top) elongated relatively more than upper ones with increased nitrogen fertilizer applications. Internodes of tall types elongated more than short types with increased N rates.