Date of Graduation

12-2015

Document Type

Thesis

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor

Pengyin Chen

Committee Member

Edward E. Gbur

Second Committee Member

John R. Clark

Third Committee Member

Kristofor R. Brye

Abstract

Flooding can significantly reduce soybean growth, development, and yield. Therefore, screening and identification of flood-tolerant soybeans will enhance development of cultivars that are well suited for flood-prone areas. Sets of screening tests were conducted in Stuttgart, Arkansas using three separate but related experiments, with the purpose of establishing effective flood tolerance screening protocol that can identify tolerant and sensitive cultivars. Each experiment was completely randomized with three replications. The first experiment involved screening of 256 maturity group (IV and V) cultivars. Flooding was imposed at the fifth-node (V5) or first-bloom (R1) stage for ten days. Post-flood visual ratings and stand counts were done three times every 3-5 days interval. Flood responses differed significantly among cultivars, within MG, and between growth stages (GS). Soybeans were more sensitive to flooding at V5 than R1. Maturity group had no main effect on flood damage; however, the severity of flood damage at a particular GS was dependent on the MG. In the second experiment, 30 cultivars were subjected to 5, 10, and 15-day floods at R1 and post-flood visual ratings and stand counts done on the 1st, 3rd, and 6th day. In the final experiment, 40 cultivars were subjected to 3, 6, 9, 12, and 15-day floods at V5 and R1 followed by flood damage ratings on the 2nd, 4th, 6th, and 8th day. Flood duration, scoring time, and GS had a significant effect on genotypic response to flooding. Damage caused by flood increased linearly with flood duration and scoring time after flood removal. Plants were more sensitive to flooding at R1 than V5. Significant reduction of chlorophyll content was observed in plants subjected to longer flooding durations. Significant correlation between visual scores and percent dead plants can support decisions in identifying flood-tolerant cultivars. Cultivars with extreme responses to flood stress were identified and will have utility in future genetic studies for tolerance mechanisms and breeding for flood-tolerant cultivars. Five effective and relatively inexpensive screening methodologies for flood tolerance in the field at the V5 and R1 were established. However, the established methodologies need to be assessed under different soil types and environmental conditions.

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