The impact of herbicide-resistant rice technology on phenotypic diversity and population structure of United States weedy rice.

Nilda Roma Burgos,Katie E Hyma,Zhongyun Huang,Howard Black,Ana L Caicedo,Vijay Singh,Te Ming Tseng,Nelson D Young,David R Gealy

doi:10.1104/pp.114.242719

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.

Highlights

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
Imidazolinones belong to group 2 herbicides, known as ACETOLACTATE SYNTHASE (ALS) inhibitors
The most notable of these are (1) implementation of herbicide programs that incorporate all possible modes of action available for rice production; (2) ensuring maximum efficacy of the herbicides used; (3) preventing seed production from escaped weedy rice, remnant weedy rice after crop harvest, or volunteer rice and weedy rice in the crop cycle; (4) rotating Clearfield rice with other crops to break the weedy rice cycle; and (5) practicing zero tillage to avoid burying HR weedy rice seed (Burgos et al, 2008)

Summary

Introduction

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. After the adoption of Clearfield technology, resistant weedy outcrosses were soon detected in commercial fields (Fig. 1), generally after two cropping seasons of Clearfield rice, where escaped weedy rice was able to produce seed (Zhang et al, 2006; Burgos et al, 2007, 2008). Similar observations have been reported outside the United States, in other regions adopting the technology (Gressel and Valverde, 2009; Busconi et al, 2012) Despite this complication, the adoption of Clearfield rice technology is increasing, albeit at a slower pace than that of glyphosate-resistant crops. The most notable of these are (1) implementation of herbicide programs that incorporate all possible modes of action available for rice production; (2) ensuring maximum efficacy of the herbicides used; (3) preventing seed production from escaped weedy rice, remnant weedy rice after crop harvest, or volunteer rice and weedy rice in the crop cycle; (4) rotating Clearfield rice with other crops to break the weedy rice cycle; and (5) practicing zero tillage to avoid burying HR weedy rice seed (Burgos et al, 2008)

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