Genetic analysis and molecular breeding tools for improvingsummer patch tolerance in hard fescue
Creators: name: Wu, Shidi
Publisher: name: No Publisher Supplied
Year: 2024

description: Hard fescue (Festuca brevipila Tracey) is a cool-season turfgrass species that is commonly categorized within the fine fescue group. This species is well-known for its excellent performance under low-maintenance conditions, such as landscapes with limited water, pesticides, and fertilizer inputs. However, the popularity of hard fescue is limited by its susceptibility to summer patch disease. Summer patch is a root disease caused by Magnaporthiopsis poae and Magnaporthiopsis meyeri-festucae. This highlights the necessity of breeding hard fescue cultivars with improved tolerance to this disease.The purpose of this thesis was to gain a better understanding of the inheritance of summer patch tolerance in hard fescue and to explore the application of QTL mapping for summer patch tolerance in hard fescue. The ultimate goal was to improve the efficiency and efficacy of selection for summer patch tolerance in hard fescue. The specific research objectives of this thesis were divided into three chapters, as follows: (1) to determine the heritabilities of summer patch disease tolerance in populations derived from a diallel crossing design between tolerant and susceptible hard fescue clones, (2) to construct a high-density, single nucleotide polymorphism-based (SNP-based) genetic linkage map for hard fescue, and (3) to identify quantitative trait loci (QTL) associated with summer patch tolerance in hard fescue. For the first objective, full-sib progeny populations were created by crossing three tolerant and three susceptible parents in a diallel cross. One hundred progeny from each of the 15 crosses and reciprocals were established in mowed spaced-plant trials in 2017 and 2019. The disease severity of hard fescue clones was assessed by visual rating during the summers of 2018, 2019, 2020, and 2021. The observed variation in disease responses among the progeny suggests that inheritance is controlled by a few major genes. The estimate of narrow-sense heritability was 0.20 (± 0.01), while the estimate of broad-sense heritability was 0.67 (± 0.08). These heritability estimates are modest but still suggest that selection and breeding schemes could be useful for improving summer patch tolerance in hard fescue.For the second objective, full-sib progeny populations were created through crosses of T10 (♀) X S5 (♂) and S5 (♀) X T10 (♂). A total of 178 progeny, with 91 from the T10 (♀) X S5 (♂) population and 87 from the S5 (♀) X T10 (♂) population, along with their parental genotypes, were sequenced to call SNP markers. After filtering out SNPs shared by less than 80% of the progeny in each case, 3876 SNPs for the T10 background dataset and 4432 SNPs for the S5 background dataset were obtained. Two linkage maps with 21 linkage groups (LGs) each, one for T10 and another for S5, were independently constructed. The T10 linkage map comprised 1020 SNPs, spanning a total of 1981.1 cM, while the S5 linkage map contained 897 SNPs, covering a total of 1644.8 cM.For the third objective, the T10 (♀) X S5 (♂) and S5 (♀) X T10 (♂) populations were visually evaluated for the percentage of green present in each individual in 2018, 2019, and 2020 at Rutgers University Horticultural Farm II located in New Brunswick, NJ. QTL analysis was then applied to identify the association between the markers in the linkage map and summer patch tolerance. Nine QTLs were identified with significant LOD scores exceeding the genome-wide LOD thresholds. These QTLs were distributed across three regions on three linkage groups and explained phenotypic variations ranging from 4.1% to 5.3% for summer patch stress. These are the first studies to report heritability estimates for summer patch tolerance in any turfgrass species, including hard fescue, and to report the first QTL mapping of summer patch tolerance in hard fescue. The findings of these studies will aid in determining the most effective and efficient selection procedures for summer patch tolerance in hard fescue. The successful application of the techniques used in this study on hard fescue will also be valuable for future studies investigating heritabilities and marker-assisted selection in closely related plant species. Last but not least, the development of the T10 X S5 populations and the high-density linkage map will serve as valuable resources for upcoming studies on hard fescue for other traits of interest.