Date of Award:

8-2022

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Plant, Soils, and Climate

Committee Chair(s)

Earl Creech

Committee

Earl Creech

Committee

Kevin Jensen

Committee

Shaun Bushman

Committee

Grant Cardon

Committee

Paul Johnson

Abstract

Dactylis glomerata L., orchardgrass, is commonly grown with perennial forages such as alfalfa (Medicago sativa L.). However, commercial orchardgrass cultivars currently grown in the Intermountain West generally flower earlier than alfalfa. This results in a reduction in grass nutritional value if harvested to maximize the alfalfa yield, because the two species mature at different rates. Thus, there is a need to better understand the genetic basis of flowering time in orchardgrass and develop late-flowering populations. The objectives of this research were to evaluate the ability to identify and use molecular markers to identify and select late-heading orchardgrass; and to select superior orchardgrass plants from a promising late-heading orchardgrass breeding population to for further cultivar development. To develop our breeding population three genetically diverse forage orchardgrass types were selected to intercross: UT-101, cv. ‘Toyomidori’, and PI538922. Each of those parents exhibited late-flowering and other desirable characteristics such as high forage yield or drought tolerance. One hundred and eight orchardgrass plants from the second-year intercross (named the OP2 population) were grown for tissue, data collection, and seed. Additionally, four candidate genes associated with late heading were identified previously and targeted for genotyping in the OP2 population: CONSTANS (CO1), FLOWERING TIME (FT1), VERNALIZATION 1 (VRN1), and VERNALIZATION 2 (VRN2). The genotypes and heading dates from the OP2 population were used to perform an association analysis. Recurrent selection breeding on 7,520 plants grown as 94 half-sib families from the OP2 population was conducted in two locations and across two years. Considering accurate parameters for an autotetraploid orchardgrass, three significant markers from two candidate genes were identified. From the half-sib family evaluation, heading date was more heritable than yield. The half-sib family population varied significantly for both traits, but also was characterized by significant variation across years and locations. Nevertheless, late heading and high forage yielding families were identified through a selection index. Finally, association analysis of OP2 heading dates and the half-sib progeny trait means onto OP2 population genotypes supported the significant markers found when measuring the OP2 traits and further selected ideal plants of the OP2 population to continue for further breeding.

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