GENETIC-VARIATION FOR SEEDLING VIGOR TRAITS IN RICE

Seedling vigor is important for stand establishment in direct-seeded r ice (Oryza sativa L.) culture. Genetic variation for, heritability of, and relationships among seedling vigor traits in 27 diverse rice cult ivars and two segregating populations from crosses between low- and hi gh-vigor cultivars were studied. Growth chamber slantboard tests were conducted at 18 degrees and 25 degrees C. In a greenhouse test, entrie s were seeded directly in standing water. Field tests, conducted durin g 2 yr, used drill-seeding. Genotypic differences were highly signific ant for all growth chamber, greenhouse, and held seedling vigor traits . Groupwise, temperate japonicas and indicas were more vigorous than t ropical japonica types. Italica Livorno and Black Gora were the most v igorous cultivars across traits. For shoot length in the slantboard te st, temperate japonica cultivars showed lower response to higher tempe rature than tropical japonicas and indicas. Response of root length wa s pronounced in tropical japonicas. Based on correlation analyses, sho ot weight, shoot length, and coleoptile length in slantboard tests bes t predicted greenhouse and field seedling vigor. Heritabilities of sla ntboard traits were estimated in two segregating populations. Heritabi lity for shoot length, the most important trait, was high (0.80) in th e cross Labelle/Black Gora and low (0.26) in the cross Labelle/Italica Livorno. The slantboard test was a reliable screening procedure for s eedling vigor, and promising donors were identified for incorporation into breeding programs.