ARS | Publication request: MULTI-YEAR EVALUATION OF RECIPROCAL OUTCROSSING RATES BETWEEN SELECTED RICE CULTIVARS AND RED RICE TYPES AT STUTTGART, ARKANSAS

Submitted to: Proceedings of Southern Weed Science Society
Publication Type: Abstract Only
Publication Acceptance Date: January 24, 2006
Publication Date: July 1, 2006
Citation: Gealy, D.R., Estorninos, L.E., Burgos, N.R. 2006. Multi-year evaluation of reciprocal outcrossing rates between selected rice cultivars and red rice types at Stuttgart, Srkansas. Proceedings of Southern Weed Science Society. 59:186

Technical Abstract: In Arkansas various reports and observations have long indicated that hybridization between rice and red rice in farm fields can occur with either of these rice types serving as the pollen donor (male) or pollen acceptor (female). Reliable measurements of the outcrossing rates between rice and red rice have been problematic because these rates are often near the lower limits of detection, depending on the particular local environmental conditions in a given year. Experiments were conducted in isolated field plots (typically 2 or 4 m wide by 5 m long) from 2000 to 2004 to determine reciprocal outcrossing rates between pairs of diverse rice cultivars and red rice biotypes growing in adjacent drill rows. Seed from individual plots containing the rice cultivars and red rice biotypes was harvested and stored separately. In 2005, this seed was planted in long (~13 m) drill strips and the resulting seedlings were observed for the presence of phenotypic traits expected in F1 hybrids (e.g. from preliminary observations, hybrids growing in rice plots were easily distinguished by their pubescent leaves and tall heights; hybrids derived from awned blackhull red rice and growing in red rice plots were easily distinguished by their purple colored stems and pink colored awns). Plants exhibiting an expected hybrid phenotype were sampled for subsequent DNA SSR marker analysis. Preliminary results based only on phenotypic traits indicate that outcrossing rates varied greatly with Kaybonnet rice and #8 awned blackhull red rice ranged from 0.03% to 0.79% and averaged 0l.36% when red rice served as the pollen donor. However, when rice served as the pollen donor, outcrossing rates ranged from 0.03% to 0.l13% and averaged only 0.07%. By contrast outcrossing rates in plots seeded with CI-121 imidazolinone-resistant rice and StgS strawhull rice were 0.06% each year when red rice served as the p9ollen donor. Thus, outcrossing rates among year varied by more than an order of magnitude and generally were much greater when red rice served as the pollen donor. The highest outcrossing rate observed for any imidazolinone-resistant rice was 0.54% with awned #8 blackhull red rice serving as the pollen donor to CI-161 rice in 2004. DNA SSR marker analyses of all putative hybrid phenotypes are underway to confirm the presence of the expected parental alleles.