ADAPTIVE TRAIT DIVERSITY, MECHANISMS AND MANAGEMENT OF ITALIAN RYEGRASS (LOLIUM MULTIFLORUM)

Italian ryegrass (Lolium multiflorum), an important forage crop, especially in temperate countries such as the United States, is a high-protein diet for animals, besides its use as a cover crop and turf species. However, it is predominantly a troublesome weed in major wheat producing regions worldwide including the Texas Blackland Prairies. High phenotypic diversity observed in this species for adaptive traits complicates cultivar improvement and maintenance breeding in forage types, and field identification management in weedy types. Moreover, evolution and spread of herbicide resistance in this species is occurring at a faster rate because of its self-incompatibility, which favors natural outcrossing with other Italian ryegrass populations as well as other compatible Lolium species. Understanding the adaptive trait diversity and their mechanisms both at the agronomic and molecular levels is valuable for ryegrass breeding as well as field management where it occurs as a weed. In order to achieve this, 70 wild ryegrass populations collected from the Texas Blackland Prairies wheat fields and 29 breeding lines were utilized. The populations were characterized for adaptive trait diversity, and the correct species was taxonomically identified by comparing with the reference samples obtained from the Germplasm Resources Information Network (GRIN) of USDA-ARS. The need for taxonomic revision to facilitate accurate species identification was established. Further, significant correlations were observed between herbicide resistance and plant adaptive traits such as seed dormancy. Exposure to altered environmental factors, such as atmospheric CO2, drought, and air temperature, showed significant influences on the plant adaptive traits and progeny fitness. Investigation on harvest-time weed seedbank management using harvest weed seed control (HWSC) in combination with herbicides proved to be a better alternative than herbicides alone for effective management. Additionally, molecular mechanisms governing the adaptive traits notably seed shattering, tiller count, and regrowth rate were investigated with a genome wide association study (GWAS) using the Genotyping by Sequencing (GBS) approach. Findings provide novel insights into the population genetic diversity as well as physiological and molecular control of selected adaptive traits. Knowledge generated in this study will be helpful for improving ryegrass breeding programs as well as developing suitable integrated management tactics where this species occurs as a problematic weed