Date of Graduation

12-2018

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Burgos, Nilda R.

Committee Member

Richardson, Michael D.

Second Committee Member

Hardke, Jarrod T.

Third Committee Member

Roberts, Trenton L.

Keywords

Echinochloa Colona; Fitness; Multiple Herbicide Resistance; Weed Science

Abstract

Echinochloa spp. are major weed problems for rice (Oryza sativa L.) on a global scale. In the southern rice belt of the U.S.A., Echinochloa colona (L.) Link (junglerice) and E. crus-galli (L.) P. Beauv (barnyardgrass) are the most troublesome weeds. These species are morphologically diverse, and its high ploidy level augurs high genetic diversity, which favors high adaptability to stress, including herbicide selection pressure. The objectives of these studies were to 1) isolate resistant (R) and sensitive (S) biotypes from eight accessions of E. colona with different resistance profiles; 2) determine the resistance levels of selected R and S biotypes of each accession; and 3) characterize the vegetative and reproductive traits of these plants. Populations with different levels of resistance to propanil and quinclorac were characterized. Quinclorac was the least effective on most accessions, with all plants in Eco-45 and Eco-76 surviving at 36,164 g ai ha-1 (64x rate). The LD50 values ranged from 565-24,408 g ai ha-1 (1-32x rate). Propanil was slightly more effective than quinclorac with LD50 values ranging from 3,991-80,730 g ai ha-1 (approximately 1-16x rates). All accessions were susceptible to cyhalofop. Since segregation of biotypes into R and S biotypes was not successful, biotypes with high resistance levels (R1) and biotypes that had lesser resistance (R2) were used. The R1 and R2 biotypes did not differ in the number of seeds per panicle, except for Eco-35. The Eco-35R1 biotype produced 23% more seed than its R2 counterpart. The number of days to seed shattering did not differ between biotypes, except for Eco-208 where seeds of R1 plants shattered 2 wk later than those of R2 plants. Therefore, except for delayed maturation, the R1 biotypes did not exhibit fitness penalty in terms of fecundity under optimum growing conditions, with the exception of Eco-35R1.

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