Genotypic Characterization of Blast-Resistant Trinity Lines

Rice blast is a major disease that causes significant yield loss in many rice-growing areas worldwide. One of the most effective and economical approaches to controlling the disease is incorporating resistance genes into a rice cultivar. Rice cultivar Trinity has excellent grain quality and favorable agronomic traits adapted to Texas rice-growing conditions, but it lacks major blast-resistant genes. It was developed from a Saber/Cocodrie//Presidio cross by the Texas A&M AgriLife Research Center at Beaumont and was released in 2022. The Pi-b gene, which confers resistance to several races of the rice blast pathogen Magnaporthe oryzae, was introgressed into Trinity after 2-3 cycles of marker-assisted backcrossing, with Saber as the Pi-b donor parent. This study aims to genotypically characterize BC2 F 2 and BC3 F 1 plants, possessing the Pi-b gene and Trinity background, and their progenies. Twenty-seven BC2 F 1 plants, which possessed the Pi-b gene and with genetic similarities to Trinity ranging from 87.4% - 93.5% based on genotyping-by-sequencing data, were used in this study. These were backcrossed to Trinity in 2022 to produce BC3 F 1 seeds with higher genetic similarities to the recurrent parent. Seventy-seven BC3 F 1 plants were evaluated for the presence of the Pi-b gene using the 'Pibdom' marker in 2023, and 44 of these BC3 F 1 plants were positive for the Pi-b gene. These 44 BC3 F 1 plants were selfed, and the BC3 F 2 lines will be grown in the field in 2023 to select those with their Pi-b gene fixed. Selfed seeds from the 27 previously-selected BC2 F 1 plants were also grown and genotyped for the Pi-b gene. A total of 139 BC2 F 2 plants with the Pi-b gene were selected. To confirm the genetic similarities of the 44 BC3 F 1 and 139 BC2 F 2 plants to Trinity, they will be genotyped using an AgriPlex panel. The BC3 -derived lines will be further advanced to produce near-isogenic blast-resistant Trinity lines. In addition, BC2 F 3 lines are being seedincreased this year for yield trials that will evaluate their potential as a new blast-resistant cultivar.