ARS | Publication request: Impact of plant and environmental factors on ALS-resistant gene transfer rate from ClearfieldTM rice to red rice biotypes

Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Proceedings
Publication Acceptance Date: October 2, 2007
Publication Date: February 5, 2008
Citation: Shivrain, V.K., Burgos, N.R., Sales, M.A., Smith, K.L., Black, H.L., Gealy, D.R. 2008. Impact of plant and environmental factors on ALS-resistant gene transfer rate from ClearfieldTM rice to red rice biotypes. Weed Science Society of America Meeting Abstracts. Vol 48: No. 234.

Technical Abstract: Pollen-mediated transfer of ALS-resistant gene from ClearfieldTM (CL) rice to red rice can affect the population dynamics and long-term management of red rice. To mitigate gene flow, it is important to understand the plant and environmental factors which affect gene transfer rate. This experiment aimed to: 1) evaluate the flowering behavior of red rice biotypes and CL rice cultivars with respect to planting dates, 2) determine the compatibility between CL rice and red rice types, and 3) investigate the reproductive factors which may affect the outcrossing rate. Field experiments were conducted at Rohwer, Stuttgart, and Kibler, AR from 2005 to 2007. Experimental design was split-split plot with four replications. Planting time, CL cultivar, and red rice accessions were main, sub, and sub-subplot, respectively. In 2005 and 2006, rice and red rice were planted from the beginning of April to the end of May at two-week intervals to establish four planting dates (PD). Twelve red rice accessions (7 strawhull, 3 blackhull, 2 brownhull) originating from 10 counties in Arkansas were planted in the middle of 9-row, 5-m long plots flanked by four rows of CL161 or CL hybrid rice on both sides. Flowering times of red rice and rice were recorded. At maturity, red rice seeds were collected from individual plots. In the following year, a sub-sample of ~3000 red rice seeds from each plot collected in 2005 and 2006 was planted. Red rice seedlings were treated with three applications of imazethapyr at 0.14 kg ai/ha. DNA was extracted from leaf tissues of survivors to confirm hybridization using SSR primers RM 253 and 234. Outcrossing rate was calculated as the percentage of confirmed hybrids relative to the number of plants sprayed. In the summer of 2007, manual crosses were performed between the 12 red rice accessions and CL161, using three biological replicates of each accession. The flowering period of red rice accessions ranged from 80 to 128 days at different planting dates. In all plantings, there was synchronization in flowering (> 50%) between both cultivars and at least six red rice accessions. Interactions between planting date by CL cultivar and planting date by red rice accession were significant (p< 0.05) for outcrossing rate. However, no interaction was detected between CL cultivars and red rice accessions for outcrossing rate. The outcrossing rate in different red rice accessions varied from 0 to 0.7% in different planting dates. In general, highest outcrossing was observed with brownhull red rice followed by blackhull and strawhull. The highest and lowest outcrossing rates between CL161 and the red rice accessions were observed at PD1 and PD 4, respectively. In CL hybrid rice, the highest outcrossing rate also occurred at PD1, with the lowest at PD3. The outcrossing rate differed between red rice accessions at the same planting date due to differences in their flowering time. Averaged over planting dates, the outcrossing rate between CL hybrid and red rice accessions was 0.3% compared with 0.06% in CL161. Experiments related to compatibility between red rice accessions and CL161, pollen load, and pollen viability are in progress.