The Impact of Herbicide-Resistant Rice Technology on Phenotypic Diversity and Population Structure of United States Weedy Rice    

Abstract

The use of herbicide-resistant (HR) Clearfield rice (Oryza sativa) to control weedy rice has increased in the past 12 years to constitute about 60% of rice acreage in Arkansas, where most U.S. rice is grown. To assess the impact of HR cultivated rice on the herbicide resistance and population structure of weedy rice, weedy samples were collected from commercial fields with a history of Clearfield rice. Panicles from each weedy type were harvested and tested for resistance to imazethapyr. The majority of plants sampled had at least 20% resistant offspring. These resistant weeds were 97 to 199 cm tall and initiated flowering from 78 to 128 d, generally later than recorded for accessions collected prior to the widespread use of Clearfield rice (i.e. historical accessions). Whereas the majority (70%) of historical accessions had straw-colored hulls, only 30% of contemporary HR weedy rice had straw-colored hulls. Analysis of genotyping-by-sequencing data showed that HR weeds were not genetically structured according to hull color, whereas historical weedy rice was separated into straw-hull and black-hull populations. A significant portion of the local rice crop genome was introgressed into HR weedy rice, which was rare in historical weedy accessions. Admixture analyses showed that HR weeds tend to possess crop haplotypes in the portion of chromosome 2 containing the ACETOLACTATE SYNTHASE gene, which confers herbicide resistance to Clearfield rice. Thus, U.S. HR weedy rice is a distinct population relative to historical weedy rice and shows modifications in morphology and phenology that are relevant to weed management.

A future scenario of the global regulatory landscape regarding genome-edited crops

“…technique, has led to the emergence of herbicide-resistant weeds through hybridization with wild species in Italy and the USA (Busconi et al, 2012;Burgos et al, 2014). This accident underscores the significance of carefully considering the potential environmental impacts of a phenotype or multiple phenotypes which can be readily introduced in a crop by robust genome editing tools, in addition to the ecological characteristics of the field surrounding the cultivated land.…”

Weedy rice in sustainable rice production. A review

“…Crop-to-weed gene flow is of special concern when transgenes are involved as it leads to the movement of genetically modified (GM) genes to weeds that might confer survival advantages that enable them to outcompete local strains (Oard et al 2000;Lu and Snow 2005;Cao et al 2006;Zhang et al 2006;Yang et al 2012). Crop-weed hybrids have been found to show variable levels of adaptability and survival capabilities (Burgos et al 2008(Burgos et al , 2014Reagon et al 2011;Song et al 2011;Yang et al 2012). Morphological (Sato 2000).…”

“…b Three-dimensional phylogenetic tree showing the relationships among wild, weedy, and cultivated strains of O. sativa (Sato 2000) variations, such as short height and earlier flowering, are traits that have been suggested to be of adaptive significance to the weeds and allow them to escape eradication (Reagon et al 2011). In contrast, reduced weediness in terms of reduced shattering can decrease the likelihood of weedy rice persistence (Burgos et al 2014). Herbicide resistance genes could become common in weedy rice populations through continuous gene flow within 3 to 8 years of the initiation of herbicide-resistant rice production (Madsen et al 2002).…”

Consumer acceptance of food crops developed by genome editing

“…Notably, the cultivation of Clearfield rice with an ALS variant, which is a herbicide-resistant crop developed by a non-GM technique (Tan, et al 2005), has led to the emergence of herbicide-resistant weeds by hybridization with wild species in Italy and the USA (Burgos, et al 2014;Busconi, et al 2012). This example underscores the importance of considering the potential environmental risks of a trait induced in genome edited crops, in addition to the ecological characteristics of the field surrounding the cultivated land.…”