Outcrossing Potential between U.S. Blackhull Red Rice and Indica Rice Cultivars

Abstract

Weedy red rice is a major weed pest of rice in the southern United States. Outcrossing between red rice and commercial tropical japonica rice cultivars has resulted in new weed biotypes that further hinder the effectiveness of weed management. In recent years, indica rice has been used increasingly as a germplasm source for breeding and for reduced-input systems in the United States, but little is known about its outcrossing potential with U.S. weedy red rice biotypes. In a 2-yr study, simple sequence repeat marker analysis was used to show that blackhull (BH) red rice (PI 653424) outcrossing to four, late-maturing indica cultivars averaged 0.0086% and ranged from 0.002% for ‘TeQing’ to 0.0173% for ‘4484’ (PI 615022). Rates of outcrossing to a tropical japonica cultivar standard, ‘Kaybonnet’ (0.032%), were substantially greater than for the indica cultivars. These differences in outcrossing were due largely to synchronization of flowering times between rice and red rice, with Kaybonnet and TeQing exhibiting the greatest and least synchronization, respectively. Outcrossing rates also may have been affected by rice–red rice flower density differences within the rice plots. Outcrossing from cultivated rice to the red rice (as pollen recipient), which was taller than all rice cultivars, was undetectable in these studies, and environmental conditions (e.g., temperature, humidity, solar radiation, and rainfall) were not strongly correlated with the outcrossing rates observed. Grain yields of the original BH red rice line were greatest in the Kaybonnet plots, demonstrating that the indica cultivars were superior competitors against this weed. Collectively, these results suggest that red rice biotypes that flower synchronously with rice cultivars are a potential source of pollen for outcrossing and gene flow in rice fields in the southern United States.

Benzobicyclon as a Post-Flood Option for Weedy Rice Control

“…Conversely, 96% of the black hull accessions had an awn. These findings are similar to those found by Burgos et al (2014) and Gealy et al (2015) when assessing the phenotypic characteristics of weedy rice accessions across the mid-South. The majority of weedy rice in the midsouthern United States is straw hull in color and does not bear awns, whereas those that are black hull in color will most likely have an awn.…”

“…Highly competitive and difficult to control in a cultivated rice system, weedy rice can in some cases lead to total crop failure and reduced milling quality (Burgos et al 2006). Gealy et al (2015) reported that US weedy rice populations can be divided phenotypically and evolutionarily into two distinct groups: straw hull (awnless) and black hull (awned).…”

The superwoman1‐cleistogamy2 mutant is a novel resource for gene containment in rice

“…Outcrossing rates in cultivated rice are estimated to be less than one per cent (Messeguer et al ., ); however, figures well above twenty per cent have been reported for crosses between cultivated and wild rice species when grown in specific conditions (Marathi and Jena, ; Phan et al ., ). Cross‐pollination between cultivated species and weedy wild relatives is problematic to rice producers as it may hinder the effectiveness of weed management and/or lead to the loss of favourable traits in a given line (Gealy et al ., ). For example, Clearfield ® rice is a commercial, nontransgenic variety of rice which is resistant to a herbicide called imazethapyr.…”

Pink‐awned weedy rice (Oryza sativa): a potential conduit for gene exchange in rice agro‐ecosystems

“…However, introgression from cultivated rice into weedy rice has been detected in both SH and BHA ecotype backgrounds (see InStruct mix group from Reagon et al ., ). There is also evidence of hybridisation between BHA rice and some late flowering indica cultivars based on field trials (Gealy et al ., ), indicating that crop–weed introgression is possible. Outcrossing rates between transgenic lines of cultivated rice and weedy rice in field trials have been measured between 0 and 6.66% (Zuo et al ., ).…”