Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 16, 2000
Publication Date: N/A
Interpretive Summary: Increased seedling vigor and cold tolerance would provide several benefits to commercial producers of rice. Rice is generally considered a tropical crop, and its growth is slowed or stopped by exposure to cool temperatures. The development of cold tolerant varieties would allow rice fields to be planted earlier in the season without risk of stunting by potential cool temperatures. Rice can grow new shoots from stubble left after harvest. If the growing season is long enough, this regrowth will produce a second crop, known as the ratoon crop. Ratoon cropping provides significant economic benefit to those Texas farmers who can plant early in order to lengthen the growing season. Increasing the cold tolerance of US rice varieties could expand the acreage on which ratoon cropping can be practiced. First crop rice yields and net income could also increase with improved seedling vigor. Rapid emergence and seedling elongation reduces exposure to birds and diseases and reduces the number of wetting irrigations required prior to flooding. Reducing the number of irrigations conserves water, soil, and fertilizers; and helps suppress weeds. Unfortunately, the short stature varieties now grown in the southern US exhibit less seedling vigor than older, tall varieties with less yield potential. This study identified as many as 20 genes associated with physiological traits associated with seedling vigor under tropical drill- seeded conditions as experienced in the southern USA. These genes were identified through their chromosomal linkage to molecular markers. The linked molecular markers identified here can identify breeding lines containing genes for improved vigor more reliably than field observation. Thus, these results can speed the development of improved rice varieties.
Technical Abstract: Increased seedling vigor and cold tolerance would provide several benefits to commercial producers of rice. Varieties that are cold tolerant can be planted earlier in the season allowing some producers to plant before seasonal rains begin or harvest a ratoon crop. Rapid emergence and tillering allow for earlier flood irrigation which saves water and helps suppress weeds. Seed of vigorous rices can be planted deep to take advantage of soil moisture reserves, further saving water and suppressing weeds. Unfortunately, currently grown southern US semidwarf varieties exhibit less seedling vigor than do the older, taller varieties. The present study was conducted to identify quantitative trait loci (QTLs) associated with aspects of seedling vigor relevant to southern USA rice production. A population of 259 recombinant inbred lines was evaluated for seedling emergence under both field and laboratory conditions; seed germination; and elongation of shoots, roots, mesocotyls and coleoptiles i laboratory-grown seedlings. Interval analysis of this phenotypic data and 175 RFLP loci identified three QTLs for field-plot seedling emergence, two for percentage germination, four for emergence through deep soil, four for shoot elongation, four for root elongation, two for mesocotyl elongation, and eight for coleoptile elongation. Each of the three QTLs associated with plot emergence were only detected from a single year of plot data. However, the analyses of seedling vigor component traits detected these three loci and many others putatively associated with field emergence. Component analysis greatly enhances the ability to identify QTLs associated with complex traits, like seedling emergence and vigor, which are affected by several biochemical and physiological processes and genes.