Date of Graduation

7-2020

Document Type

Thesis

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor

Leandro Mozzoni

Committee Member

Kristofor Brye

Second Committee Member

Ryan Dickson

Third Committee Member

Larry Purcell

Keywords

Hydroponics, Hypoxia, Soybean

Abstract

Soybean [Glycine max (Merr.)], the second most planted crop in the United States, is sensitive to field flooding due to depletion of oxygen and accumulation of CO2 in the rhizosphere. There is a need to breed cultivars that are adapted to areas prone to flooding, but field evaluations in the U.S. are limited because of time (one generation per year) and availability of resources (impermeable soils, irrigation, equipment to build levees). The purpose of this study was to develop and execute a protocol of germplasm screening for hypoxia tolerance using hydroponics in a controlled greenhouse environment. Germination rates and vigor of soybean seeds directly sown onto four substrates were reported using rockwool pellets, perlite, expanded clay pebbles, and a rockwool pellets placed into clay pebbles. Also, a screening protocol was developed consisting of an uninterrupted CO2 gas treatment at a rate of 200 mL min-1 initiated at V2 stage and applied for five consecutive days under hydroponic conditions to produce symptoms akin to those present in flooded soybean fields. Plant responses (normalized difference vegetation index (NDVI), soil-plant analysis development (SPAD), and visual rating) were assessed at termination of treatment and three, six, and nine days thereafter. Such protocol was utilized to screen 34 soybean genotypes of known field reaction, on an experiment that was repeated four times between May and December 2019. Mean NDVI responses differed among genotypes (p=0.0002), which were ranked using a Tukey honest significant difference test following application of the predetermined rates and duration of gas treatment. Mean NDVI values ranged from 0.199 to 0.363, with the seven highest ranked genotypes being significantly different than the six lowest ranked genotypes (p=0.05). The methodology developed had a high level of repeatability and will help breeding programs screen a larger volume of materials prior to submission for field testing for flood tolerance.

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