Assessment of gene flow from a herbicide-resistant indica rice (Oryza sativa L.) to the Costa Rican weedy rice (Oryza sativa) in Tropical America: factors affecting hybridization rates and characterization of F1 hybrids

Abstract

Herbicide-resistant rice cultivars allow selective weed control. A glufosinate indica rice has been developed locally. However, there is concern about weedy rice becoming herbicide resistant through gene flow. Therefore, assessment of gene flow from indica rice cultivars to weedy rice is crucial in Tropical America. A field trial mimicking crop-weed growing patterns was established to assess the rate of hybridization between a Costa Rican glufosinate-resistant rice line (PPT-R) and 58 weedy rice accessions belonging to six weedy rice morphotypes. The effects of overlapping anthesis, morphotype, weedy accession/PPT-R percentage, and the particular weedy accession on hybridization rates were evaluated. Weedy rice accessions with short overlapping anthesis (4-9 days) had lower average hybridization rates (0.1%) than long anthesis overlapping (10-14 days) accessions (0.3%). Hybridization also varied according to weedy rice morphotype and accession. Sativa-like morphotypes (WM-020, WM-120) hybridized more readily than intermediate (WM-023, WM-073, WM-121) and rufipogon-like (WM-329) morphotypes. No hybrids were identified in 11 of the 58 accessions analyzed, 21 accessions had hybridization rates from 0.01% to 0.09%, 21 had rates from 0.1% to 0.9%, and 5 had frequencies from 1% to 2.3%. Another field trial was established to compare the weedy rice-PPT-R F(1) hybrids with their parental lines under noncompetitive conditions. F(1) hybrids had a greater phenotypic variation. They had positive heterosis for vegetative trait and reproductive potential (number of spikelets and panicle length) traits, but negative heterosis for seed set. This study demonstrated the complexity of factors affecting hybridization rates in Tropical America and suggested that the phenotype of F(1) hybrids facilitate their identification in the rice fields.

Conspecific Crop-Weed Introgression Influences Evolution of Weedy Rice (Oryza sativa f. spontanea) across a Geographical Range

“…Biological factors may have played an essential role in determining outcrossing rates among weedy rice populations, although environmental conditions, such as air temperature, strength and direction of wind, and air humidity, could also considerably affect outcrossing rates. Previous studies indicated variable frequencies of gene flow from cultivated rice to diverse groups of weedy rice with different genetic backgrounds [20], [30], [31], [48], which is in a good accordance with data of outcrossing rates in this study. Our findings demonstrate that it is relatively easy for weedy rice to receive pollen from its sexually compatible rice cultivars (including GM rice) occurring at the close vicinity.…”

Gene flow from herbicide-tolerant GM rice and the heterosis of GM rice-weed F2 progeny

“…However, even in the absence of such an advantageous environment, heterosis might play an important role that enhances the phenotypic performance of those transgenic hybrids (Oard et al 1996). The success of heterotic hybrids may also vary widely depending on taxa and genotypes (Ellstrand 2003), environments and seasons , and phenotypic traits (Oard et al 2000;Zhang et al 2003Zhang et al , 2008Cao et al 2009;Sanchez Olguin et al 2009). Some traits may lead to better performance and vigor compared with parental lines, while others exhibit a mid-parent level or even decreased performance.…”

“…Previous studies found that GM rice may hybridize with traditional cultivars (Messeguer et al 2001(Messeguer et al , 2004Rong et al 2005Rong et al , 2007Jia et al 2007;Yuan et al 2007;Yao et al 2008), weedy rice (Zhang et al 2003(Zhang et al , 2006Chen et al 2004;Messeguer et al 2004;Sanchez Olguin et al 2009), and wild rice (Chen et al 2004;Yao et al 2008). A few GM rice lines have been developed in Korea, including those tolerant to herbicides (Lee et al 2007) and abiotic stresses (Jang et al 2003).…”

“…International concern is increasing about the ecological and environmental impacts of transgene escape into wild or weedy populations (Delouche et al 2007). However, few studies have been conducted on the fitness advantage of hybrids between transgenic rice and weedy rice (Zhang et al 2003(Zhang et al , 2008Cao et al 2009;Sanchez Olguin et al 2009). Those studies are important in assessing the long-term persistence and spread of transgenic rice populations.…”

Biotechnology: Herbicide-Resistant Crops

“…Glufosinateresistant rice was deregulated (approved for sale) but never commercialized, perhaps partly because of the potential problem of gene flow to weedy rice and nontransgenic rice (Oard et al, 2000;Olofsdotter et al, 2000;Sanchez-Olguin et al, 2009;Song et al, 2011). The adoption of glufosinateresistant crops has been only a small fraction of the HR crop market, primarily because glyphosate is a more effective herbicide than glufosinate on many weed species.…”