Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Baldwin, Brian S.

Committee Member

Lemus, Rocky W.

Committee Member

Rushing, J. Brett

Committee Member

Tomaso-Peterson, Maria

Committee Member

Rude, Brian J.

Date of Degree

1-1-2018

Document Type

Dissertation - Open Access

Major

Agronomy

Degree Name

Doctor of Philosophy

Department

Department of Plant and Soil Sciences

Abstract

Abiotic stress tolerance and biotic stress resistance have long been targets for trait improvement in the field of plant breeding. To date, much of the target crop focus has been centered on commodity crops such as corn, soybean, wheat, and rice. However, little work has been conducted on improvement of these traits in forage grasses. This is due to a number of issues, particularly that most species are obligately outcrossing, the traits are governed by many genes at unknown loci, and are greatly affected by environmental variation. This creates major complications in successfully selecting and breeding populations of forage grasses tolerant to extreme high or low temperatures, as well as disease resistance. Recurrent phenotypic selection was used to select elite individuals of annual ryegrass (Lolium multiflorum Lam.) and orchardgrass (Dactylis glomerata L.) that expressed improved germination at high temperature. Selections were conducted within growth chambers at fixed temperature and light regimes (40/30 DEGREES C, 12/12 hr, light/darkness) to eliminate environmental variation. Following three cycles of selection, we observed gains (P LESSTHAN 0.001) in selection over the base population for both species. Annual ryegrass mean cumulative germination for cycle 3 peaked at 45.8%, and orchardgrass mean cumulative germination for cycle 3 peaked at 82.67%. Further selection of annual ryegrass for freezing tolerance was also conducted. Flats of unselected germplasm were grown to the three-leaf stage, then frozen for nine hours. Significant differences (P LESSTHAN 0.05) in freezing tolerance were observed between selected germplasm in both cycle 1 (0.076%) and cycle 2 (0.125%) over the unselected cycle 0 (0.025%). Finally, initial stages of resistance breeding work were conducted involving gray leaf spot (causal agent Pyricularia grisea Cke. [Sacc.]) on annual ryegrass. Isolates of the pathogen were obtained and stored for future use. It was determined that the actual pathogen species responsible was Pyricularia oryzae Cavara. Future work for annual ryegrass and orchardgrass germplasm that germinates at high temperatures will involve variety testing and cultivar release. Freezing tolerance and disease resistance work will require larger-scale screening methodology that was able to be conducted in this work to acquire sufficient population sizes for breeding.

URI

https://hdl.handle.net/11668/19728

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