GxE Interaction in the U.S. Cynodon Germplasm Collection for Bermudagrass Stem Maggot.

Bermudagrass (Cynodon spp. L.) is an important warm-season perennial grass grown for forage and turf in Southeastern U.S. The bermudagrass stem maggot (Atherigona reversura; BSM) is a new invasive fly species, native to southeastern Asia, which has caused a significant economic impact due to the reduction in forage yield and quality. The objective of this study was to calculate genetic parameters in a set of 287 bermudagrass genotypes for BSM resistance across the southeastern U.S. (Citra and Ona, FL; Tifton, GA) across multiple years. The population was composed of: i) 146 PI’s from the bermudagrass core collection maintained at Tifton, GA; ii) 137 PI’s from the NPGS maintained at Griffin, GA; and iii) commercial cultivars (“Tifton 85”, “Coastal”, “Jiggs”, and “Florida 44”). The experiment, established in 2014, was designed as a row-column with two replicates and augmented representation of the cultivars. The population was evaluated in Florida for BSM damage on a scale of 0 to 9 (scale: 0 = no visible damage; 9 = more than 90% damage) and in Georgia from a scale of 0 to 5 (scale: 0 = no visible damage; 5 = more than 90% damage). Linear mixed models with repeated measures were implemented in ASReml. Broad sense heritability (H²) for BSM resistance ranged from 0.14 to 0.53 for analyses performed by location, while H²=0.20 for the multi-location model. Genotype by measurement correlation (r_B) was 0.74 for analyses by location in Tifton and Citra, indicating stable genotypic performance for BSM resistance across measurements. Likewise, the high correlation (r_B =0.87) for the multi-location model shows that genotypes performed similarly across locations. Hence, there is genetic variability for BSM susceptibility in the population. Selections can be made for more tolerant lines at any time of the year and in any location, given the high GxE correlations (r_B).