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

Andy Pereira

Committee Member

Nilda R. Burgos

Second Committee Member

Penying Chen

Third Committee Member

Andrew Sharpley

Fourth Committee Member

Ainong Shi

Keywords

Biological sciences; Drought resistance; Gene expression; Phenotypic; Rice

Abstract

Drought is one of the most limiting factors for rice (Oryza sativa L.) growth and development with vegetative and reproductive stages the most sensitive and distinct phases. During the vegetative stage, drought can cause reduction in growth and biomass accumulation. Moreover, water stress at reproductive stage can reduce yield significantly. Plants are protected against drought by three different mechanisms: drought avoidance, drought tolerance, and drought escape. An integrated approach combining physiology, breeding, and genomics could be an effective way to characterize and mitigate this problem. The objectives of this research were to (1) screen a diverse set of rice genotypes at both vegetative and reproductive stages for drought response; (2) characterize the genetic differences in mechanisms of drought response conferring drought stress resistance; and (3) study the expression patterns of genes that contribute to yield under water stress conditions. At the vegetative stage, drought was applied by withholding water at 50% of the field capacity for ten days, while in the reproductive stage drought was given at pre-anthesis for three to four days. Results from the first study showed that the diverse genotypes exhibit different drought resistance mechanisms. Padi Tarab Arab and N22 exhibit drought avoidance and tolerance mechanisms while GPNO 25912 exhibits a tolerance mechanism. Gene expression analysis using RNA from plants early after drought stress identified clear differences between resistant and sensitive genotypes. The resistant genotypes showed a high induction in the relative expression of drought stress genes under drought compared to control, while the three sensitive genotypes showed low, no, late, or inconsistent induction in expression. Results from the second study demonstrated that between the two types of samples for gene expression analysis in four different genotypes, the inflorescence gives a higher correlation with phenotypic measurements than the flag leaf during reproductive stage. Meanwhile, both invertase genes and transcription factors confer positive effects to drought resistance particularly in relation to number of grain per panicle and panicle length.

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