Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 2/7/2005
Publication Date: 2/7/2005
Citation: Burgos, N.R., Shivrain, V.K., Scott, R.S., Moldenhauer, K.A., Gealy, D.R. 2005. Genetic introgression: a factor in weedy rice diversity in the U.S.? [abstract]. Weed Science Society of America Meeting Abstracts. 45:50-51. Interpretive Summary:
Technical Abstract: Weedy rice is among the most problematic weeds in rice production in the U.S. wherever it occurs. Several weedy species of Oryza have been reported worldwide, but red rice (Oryza sativa L.) is the primary species occurring in the U.S. Natural crossing between cultivated and weedy rice has been reported and it is hypothesized that this contributes to phenotypic diversity of the weedy species. Reciprocal crosses were made between rice and red rice to determine the segregation of traits among the offspring and an extensive collection of red rice from producers' fields were characterized. More than 200 accessions of red rice were collected from about 30 counties in Arkansas in the summer of 2002 and 2003. The accessions were planted 1 to 2 m apart at the Rice Research and Extension Center and at Lodge Corner, AR in 2003 and 2004. Morphological and agronomic data were collected. Early reports on red rice in the U.S. indicated two major types of plant based on hull color. These include strawhull and blackhull red rice. This still holds true of late, but variants were also observed including brown- and orange-colored hulls of red rice grains. Generally, red rice has a medium grain as was reported earlier, but there is significant variation in actual grain size with some accessions approaching the long grain category. Majority of cultivated rice in the U.S. have long grains. Red rice grains shatter upon maturity and this ensures replenishment of the seed bank long before rice is harvested. There was a significant difference in degree of shattering among accessions, with a few showing almost complete loss of this trait. In terms of stature, blackhull red rice was taller (145 cm) than strawhull red rice (135 cm), and weedy rice was generally taller than cultivated rice. However, some red rice accessions (strawhull and blackhull) were of the same height as cultivated rice and maintained the same stature when grown individually in a nursery setting. Red rice height ranged from 76 to 196 cm. Among the weedy traits of red rice is its capability to produce a lot of tillers and having an open growth, which is effective in crowding out the cultivated rice. The open growth characteristic is more common among strawhull than blackhull types. There was significant diversity in growth habit, with plants having an open, intermediate, or compact canopy. A more vertical culm orientation is characteristic of cultivated rice. Generally red rice flowers earlier than cultivated rice, but a wide range of flowering dates were observed among the accessions, ranging from 74 to 137 d after planting. Reciprocal crosses between rice and red rice show the same F1 phenotype, but exhibit a wide range of F2 traits with respect to height, growth habit, flowering, seed shattering, and other characteristics. Any one of these outcross progenies, which are compatible with the rice culture in any given environment could become a stable population and contribute to the diversity of weedy plants. The variability in traits was exemplified, to some extent, by the red rice accessions. This indicates that introgression is one of the contributing factors to the phenotypic diversity of weedy rice in the southern U.S. Genetic analysis can be used to support this theory.