Prevalence of blast and quality genes and traits in the Uniform Regional Rice Nursery (URRN)

Authors: Jia, Melissa; ANGIRA, BRIJESH - Louisiana State University; Edwards, Jeremy; HUANG, YIXIAO - Orise Fellow; Jia, Yulin

Submitted to: Rice Technical Working Group Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/14/2024
Publication Date: 1/5/2026
Citation: Jia, M.H., Angira, B., Edwards, J., Huang, Y., Jia, Y. 2026. Prevalence of blast and quality genes and traits in the Uniform Regional Rice Nursery (URRN). Rice Technical Working Group Meeting Proceedings. New Orleans, Louisiana. February 14-17, 2025.

Interpretive Summary:

Technical Abstract: Breeding for rice blast resistance and improved quality are high priority objectives in many US rice breeding programs. Rice blast disease is one of the most lethal diseases of rice globally. Quality traits determine cooking quality and harvestability. Major blast resistance (R) genes are effective in preventing infections by the fungus Magnaporthe oryzae when corresponding avirulence genes are present. The major blast resistance gene Pi-ta is effective in preventing infections from the two predominant races, IB49 and IC17, both of which contain AVR-Pita. Molecular markers have been developed for numerous blast genes. Similarly, markers for quality were developed for marker assisted breeding. The Uniform Regional Rice Nursery (URRN) prior to 2022 consisted of 200-250 elite lines per year submitted by the southern US rice breeding programs that are in the final stages of selection prior to potential registration and release as new varieties. In 2022 the number of annual entries was decreased to 50. Starting in 1982 the URRN was screened for phenotypic traits related to yield, quality and disease resistance and in later years molecular markers for rice blast disease resistance and quality traits were added. Here we present data on the prevalence of blast genes and quality genes in the URRN between 2009-2023 to determine what genes are most utilized in southern US breeding programs and whether there have been potential shifts in the prevalence of blast resistance or quality genes being incorporated in varieties. From 2009-2023 the URRN was screened with molecular markers for the major blast genes Pikm, Piks, Pita, Pib, and Piz. Pikm is the most prevalent blast gene in the URRN followed by Pita. Piz and prior to 2020 Pib were rarely incorporated into the URRN. Since 2020 the number of lines containing Pib has been steadily increasing. Stacking of R genes can result in more durable and enhanced resistance. The stacking of two R genes is fairly common, however; three R genes are rarely stacked together. The R gene most commonly stacked is Pita. Since 2012 the URRN has been screened with markers for amylose content, gel temp, aroma and pubescence. In 2015 markers for Clearfield herbicide resistance and Rapid Visco Analyser (RVA) were added. Intermediate amylose content is most common and high amylose is least common. Intermediate gel temp is highly prevalent. The marker for weak RVA is most common, but its frequency has been steadily decreasing. Pubescence and aroma are rarely found in the URRN. Presence of the Clearfield marker is fairly common but has been decreasing since 2018