Date of Graduation

8-2016

Document Type

Thesis

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Nilda R. Burgos

Committee Member

Johnnie L. Gentry

Second Committee Member

Nathan Slaton

Third Committee Member

Tom Barber

Fourth Committee Member

Krishna N. Reddy

Keywords

Biological sciences, Barnyardgrass, Junglerice, Morphology, Phenology, Rough barnyardgrass, Seed dormancy

Abstract

Echinochloa species are the most problematic grass weeds in rice and soybean production throughout the southern United States. The species under this genus has high intra- and interspecific variability, with many ecotypes, observed within a species. This study was conducted to: i) characterize the morphology and phenology of Echinochloa accessions from Arkansas in a common garden; ii) verify the species identity of these accessions based on their morphological traits, and iii) evaluate the dormancy characteristics of Echinochloa accessions. Junglerice (E. colona) was identified as the most common species, comprising about 78% of the accessions collected, with barnyardgrass (E. crus-galli) and rough barnyardgrass (E. muricata) representing about 9% and 12% of the population, respectively. Thus, junglerice is the most problematic Echinochloa species affecting farmers in Arkansas. The height of junglerice ranged from 65-94 cm; barnyardgrass, 87-126 cm; and rough barnyardgrass, 79-118 cm. Rough barnyardgrass was the largest species with the longest (19.8-42 cm) and widest (1.2-2.1 cm) leaves, followed by barnyardgrass. Junglerice and barnyardgrass were the earliest to flower, at about 39-59 days after planting (DAP), followed by rough barnyardgrass (46-63 DAP). Junglerice produced the largest amount of seed (9,098-217,217 per plant) with an average of 539 seeds per panicle. Barnyardgrass produced 7,186-71,494 seed/plant with an average of 345 seeds per panicle. The dominance of junglerice over the other species could be due to its high seed production and high seed germination capacity. The growth habit of junglerice could be either prostrate, decumbent or open whereas that of barnyardgrass and rough barnyardgrass could be decumbent to open. Junglerice and barnyardgrass had similar panicle characteristics with an almost similar color range that could lead to misidentification. Junglerice had the highest germination capacity (41-99%), followed by barnyardgrass at 11-79%. Rough barnyardgrass exhibited deep dormancy, with germination capacity between 2 and 73%. Further investigations are needed to characterize the germination requirements of rough barnyardgrass and its relative abundance in North America. The differential tolerance of these species to various herbicides are being investigated in follow-up research. This information is useful in making weed management decisions and is informative in understanding speciation and adaptation of weedy Echinochloa species.

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