Submitted to: Arkansas Crop Protection Association Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/8/2005
Publication Date: 11/28/2005
Citation: Shivrain, V.K., Burgos, N.R., Gealy, D.R., Black, H.L., Estorninos, Jr., L.E., Meier, J.R. 2005. Flowering of red rice biotypes and CL cultivars as affected by planting dates. Arkansas Crop Protection Association Proceedings. 9:13-14. Interpretive Summary:
Technical Abstract: Clearfield (CL) rice is a promising new technology for red rice management. However, sustainability of this technology will depend on the extent of outcrossing between CL cultivars and red rice biotypes. Disparity in CL cultivars, planting time, and flowering time of red rice biotypes in fields may have significant impacts on gene transfer. Our objectives in this study were to 1) evaluate the flowering behavior of red rice biotypes and CL rice cultivars with respect to planting dates, 2) to determine yield losses in CL cultivars due to different biotypes of red rice, and 3) to determine outcrossing rate between CL cultivars and red rice biotypes. The experiments were conducted at the Southeast Research and Extension Center, Rohwer and at the Rice Research and Extension Center (RREC), Stuttgart, AR in summer of 2004. Only Stuttgart experiments are discussed in this paper. Experimental design was split-split plot with three replications. Planting time, CL cultivar, and red rice biotypes were main, sub, and sub-subplot, respectively. Planting times were April 16, April 27, May 13, and May 26. CL cultivars, CL161 and hybrid CL-XL8, were planted at 30 and 90 lb/A, respectively. Twelve red rice accessions representing red rice from 10 counties in Arkansas (strawhull – 7, blackhull – 3, and brownhull – 2) were used. The accessions represent an assortment of characteristics: short and tall, awned and awnless, and early and late to flower. Each red rice accession was planted in the middle of 9-row, 10-ft long plots with four rows of rice on both sides. Data on emergence, flowering, agronomic traits, and yield were recorded. At maturity, red rice plants were bagged and harvested to collect seeds for outcrossing rate determination. Strawhull red rice in general emerged faster than brownhull and blackhull red rice. Red rice emergence varied from 10 to 35 days after planting (DAP) among and between biotypes across planting dates. Earlier planted CL rice and red rice biotypes took longer to flower than later planted ones and vice-versa. Flowering period of red rice biotypes ranged from 88 to 128, 87 to 117, 79 to 118, and 71 to 116 DAP, in the first, second, third, and fourth planting, respectively. On average, CL-XL8 flowered 3 to 5 days earlier than CL161, although flowering was over within a week in all plantings in both CL cultivars. In all plantings, there was synchronization in flowering (50 %) between both CL cultivars and at least six red rice biotypes. Red rice produced 50% less tillers in CL-XL8 than in CL161 plots, causing higher yield losses in CL161. Red rice biotypes caused different degrees of yield reduction in CL rice cultivars. In general, yield loss of up to 54 and 66% in CL-XL8 and CL161, respectively was observed. The yield reduction was lower in earlier plantings, and it increased with later planting time in both CL-XL8 and CL161. To determine outcrossing rate, collected red rice seeds will be screened using imazethapyr. Survivors of screening will be confirmed as hybrids using simple sequence repeat (SSR) primers.