Genotypic Distribution, Resistance Effects, and Breeding Implications of Rice Blast Resistance Genes in 120 Cultivars Released Over the Past Five Decades

Abstract Rice blast, caused by Magnaporthe oryzae , is a destructive disease worldwide. Deployment of broad-spectrum resistance ( R ) genes is an effective strategy for sustainable disease control, but the actual resistance effects of individual genes and their combinations in commercial rice cultivars remain largely unknown. In this study, we evaluated 120 main cultivated rice varieties grown over the past five decades in Chadi, a national rice blast resistance identification nursery, Fujian Province, Southeast China. Fifteen well-known R genes ( Pi5/i , Pib , Pid3/25 , Bsr-d1 , Pi9 , Pi2 , Piz‑t , Pigm , Pi1 , Pik‑p , Pik‑m , Pik , Pid2 , Pit , and Pi‑ta ) were screened using molecular markers. Seedling, leaf, and panicle blast resistance were evaluated under natural field conditions. The average number of detected R genes per variety was 1.00 in period A (≤ 1980, n = 24), 1.57 in period B (1981–1999, n = 42), and 1.48 in period C (≥ 2000, n = 54), with the highest value observed in period B. Genes including Pigm , Pi1 , Pid2 , Pid3/25 , and Bsr-d1 exhibited significant negative correlations with seedling blast, tillering blast, mature-stage blast, and the comprehensive resistance index ( P < 0.01), indicating that their presence is associated with enhanced resistance. These findings demonstrate that pyramiding effective broad-spectrum R genes has significantly enhanced blast resistance in modern rice cultivars and provide practical guidance for gene deployment and breeding programs targeting durable and broad-spectrum resistance.