Date of Graduation

7-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Crop, Soil & Environmental Sciences (PhD)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Burgos, Nilda R.

Committee Member

Pereira, Andy

Second Committee Member

Gbur, Edward E. Jr.

Third Committee Member

Gealy, David R.

Fourth Committee Member

Scott, Robert C.

Keywords

Education; Hybrid rice; Volunteer rice; Weedy rice

Abstract

Weedy rice (Oryza sativa L.) competes aggressively with rice, reducing yields and grain quality. ClearfieldTM rice, is nontransgenic herbicide-resistant (HR) rice introduced in 2002 to control weedy rice, has resulted in ALS-resistant weedy rice due to gene flow. Volunteers of ClearfieldTM rice (F2) accelerate the HR weedy rice evolution by acting as agents of gene flow. Weedy rice (89) collected from 11 counties in Arkansas were screened for resistance in a field experiment in Stuttgart (2011). Seventy-nine percent of accessions were resistant to imazethapyr and harbored S653N mutation. These HR weedy accessions were outcrosses of ClearfieldTM rice and weedy rice. Out of 727 characterized plants, nearly 70% of the HR weedy rice flowered at the same time as that of ClearfieldTM rice with greatly reduced seed shattering in progenies of some accessions (15 to 87%). Kernels of 20% of the parent accessions had segregating white and red bran color. Two of these parent accessions (goldhull) were homozygous for white bran, with 100% white-bran progenies. Winter-flood reduced the germination of rice seed by 40-50% after 130-160 d of burial. Hybrid rice seed had higher capability to survive the winter (13-53% viability) than inbred rice seed (8-27%). Therefore, hybrid rice is expected to leave more volunteer rice in the field than inbred rice. Fields with cropping history of hybrid rice had higher volunteer rice infestation (20%) than fields planted only with inbred rice (5.6%). The total grain yield of rice was reduced by 0.4% for every 1% increase in volunteer rice density, averaged over cultivars. The 1000-kernel weight, kernel length-width ratio, %protein, %amylose, and head rice yield were affected by volunteer rice density. Various herbicides were tested for efficacy on volunteer rice at SEREC, Rohwer and RREC, Stuttgart, Arkansas. Application of pyroxasulfone (0.12 kg ha-1) in the fall fb 2,4-D (1.12 kg ha-1) 35 d pre-plant caused minimal (6%) crop injury and did not reduce yield. This treatment resulted in better control of volunteer rice (73%) than pyroxasulfone alone at 0.12 kg ha-1 applied in fall (64%). Pyroxasulfone is not currently labeled for fall application prior to rice planting in the spring.

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