Genetic variation for seedling vigor traits in rice

Seedling vigor is important for stand establishment in direct-seeded rice (Oryza sativa L.) culture. Genetic variation for, heritability of, and relationships among seedling vigor traits in 27 diverse rice cultivars and two segregating populations from crosses between low- and high-vigor cultivars were studied. Growth chamber slantboard tests were conducted at 18 degrees and 25 degrees C. In a greenhouse test, entries were seeded directly in standing water. Field tests, conducted during 2 yr, used drill-seeding. Genotypic differences were highly significant for all growth chamber, greenhouse, and held seedling vigor traits. Groupwise, temperate japonicas and indicas were more vigorous than tropical japonica types. Italica Livorno and Black Gora were the most vigorous cultivars across traits. For shoot length in the slantboard test, temperate japonica cultivars showed lower response to higher temperature than tropical japonicas and indicas. Response of root length was pronounced in tropical japonicas. Based on correlation analyses, shoot weight, shoot length, and coleoptile length in slantboard tests best predicted greenhouse and field seedling vigor. Heritabilities of slantboard traits were estimated in two segregating populations. Heritability for shoot length, the most important trait, was high (0.80) in the cross Labelle/Black Gora and low (0.26) in the cross Labelle/Italica Livorno. The slantboard test was a reliable screening procedure for seedling vigor, and promising donors were identified for incorporation into breeding programs.