Masters Theses

Date of Award

5-2021

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant Sciences

Major Professor

Avat Shekoofa

Committee Members

Vince Pantalone, Liesel Schneider, Lori Duncan, Angela McClure

Abstract

Ninety-four percent of U.S. grown soybeans are produced under rainfed conditions with intermittent droughts occurring late in the season during reproductive growth stages. Due to the temporary nature of drought, the ability of a crop to survive and recover effectively from water deficit stress is important for ensuring yield stability. In 2019 and 2020, two greenhouse experiments and two field studies were conducted to screen eleven soybean genotypes for transpiration response and recovery from water deficit stress and high vapor pressure deficit (VPD). In the first greenhouse study, soybean plants were grown in pots sealed to prevent evaporation and plants gradually transpired the full amount of water in each pot (dry-down) before being re-watered. In the second controlled environmental study, plants were exposed to three levels of VPD. In both controlled environmental experiments transpiration rate was measured gravimetrically. In the field, portable rainout shelters were used to exclude precipitation from soybean plots while stomatal conductance (gs), and specific leaf area (SLA) were measured. In the dry-down and field experiments, recovery irrigation was applied after a period of Stage III water deficit stress and leaf wilting score (WS) was rated visually on a scale of zero to five. In the field, pre- and post-recovery canopy temperature (CT) was measured. Genotypic differences in soybean contributed to differentiated response to water deficit and high VPD in both greenhouse and field experiments. In the dry-down experiment, the genotypes TN09-029, TN16-520R1, and Ellis had superior recovery from water deficit stress based on WS while USG Allen and TN09-008 had the highest transpiration recovery; RIL #1360 and USG 7496XTS showed the least ability to recover from stress. In the field, Ellis, USG Allen, and TN09-029 exhibited a more robust recovery based on WS and Ellis exhibited the highest post-recovery gs. TN09-029 and Ellis had the largest reduction in CT after recovery. Ellis had the highest yield at 3516.56 kg/ha and consistently expressed a desired response of early decrease in transpiration rate with drying-down, delayed wilting in the field when soil water deficit developed, and had highest stomatal conductance post-recovery under extreme water deficit environments.

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