Outcrossing potential between U.S. red rice (Oryza sativa) and Chinese indica rice (Oryza sativa) lines

Authors: Gealy, David; BURGOS, NILDA - University Of Arkansas

Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 1/29/2012
Publication Date: 1/29/2012
Citation: Gealy, D.R., Burgos, N.R. 2012. Outcrossing potential between U.S. red rice (Oryza sativa) and Chinese indica rice (Oryza sativa) lines. Weed Science Society of America Meeting Abstracts. Volume 52: Abstract #286.

Interpretive Summary:

Technical Abstract: Red rice in southern U.S. rice fields remains a widespread, economically challenging problem despite nearly a decade of rice production systems that include true-breeding rice cultivars and indica-derived hybrid rice with resistance to imazethapyr. Both of these herbicide-resistant rice systems have provided good control of red rice, but outcrossing between red rice and rice, which has been investigated previously, has reduced the effectiveness of these approaches in some instances. True-breeding indica rice lines and cultivars are being used increasingly as a source of high yield and pest tolerance in U.S. rice breeding programs as well as in low-input production systems, however their levels of outcrossing with red rice have not been investigated. Thus, the objectives of this study were to determine the rates of red rice outcrossing with four indica cultivars from China in comparison to a tropical japonica, southern US long grain, commercial standard. The red rice type and rice cultivars were selected based on previous field trials in which the red rice exhibited significant overlap in flowering dates with the rice cultivars. Indicas were Teqing, Rondo, 4484, and 4593 (PI 536047, PI 657830, PI 615022, PI 615031, respectively). Kaybonnet served as the tropical japonica standard. Outcrossing plots, consisting of drill strips of a single row of red rice (TX4, awned blackhull type; PI 653424) flanked by four rows of the rice cultivar on each side, were established at Stuttgart, AR in 2008 and 2009. Subsamples of seed collected from panicles of these rice and red rice plants were planted subsequently in observation field plots for screening purposes in 2009 and 2010, respectively. Putative F1 hybrid plants were identified based on expected phenotypic traits. Green leaves of these putative hybrids were sampled and extracted for DNA. True F1 hybrids were confirmed to be heterozygous at five selected loci using genetic markers (Rid12, RM5, RM232, RM234, and RM253). Outcrossing rates were calculated as: 100 x (number of true F1 hybrids in screening plot) / (number of seedlings in screening plot). With rice serving as the female, all indicas had similar outcrossing rates, which averaged 0.0088%. Among all cultivars, outcrossing was greatest for Kaybonnet (0.0326%). The greater outcrossing rate for Kaybonnet appeared to be due in part to its close synchronization in flowering with red rice. Outcrossing rates were positively correlated with flowering synchronization among all rice entries. With red rice as female, outcrossing with indicas was usually undetectable. This follows the trend typically observed for tropical japonica cultivars in similar tests, that outcrossing rates are substantially lower with red rice as female than with rice as female. These studies show that late maturing indica cultivars have outcrossing rates similar to or less than that of the tropical japonica cultivar Kaybonnet, and that flowering synchronization can play an important role in determining outcrossing rates between red rice and rice.