Examining the Research Gap in Molecular Marker-Assisted Selection for Blast Resistance in Nigerian Rice Breeding Programmes

Rice blast disease (Magnaporthe oryzae) is the most important fungal disease of rice in Nigeria, causing yield losses of 20 to 50 percent in susceptible varieties, yet the application of molecular marker-assisted selection for blast resistance genes in Nigerian rice breeding programmes has been insufficiently documented and evaluated. This study examined the research gap in molecular marker-assisted selection for blast resistance in Nigerian rice programmes through systematic review and original laboratory analysis. A scoping review of nine databases from 2018 to 2024 identified 38 publications on blast resistance in Nigerian rice, of which only 8 applied molecular markers for resistance gene characterisation in materials collected from Nigeria and only 3 documented MAS in active Nigerian breeding crosses. The review confirmed that pi-genes (pi2, pi9, pi54, and Piz-t) have been identified in some NCRI breeding materials but that marker validation for Nigerian blast pathotype diversity has not been conducted. Original laboratory work genotyped 20 NCRI elite lines with pi9 and Piz-t flanking markers and conducted pathogen diversity analysis on 15 blast isolates from six states. Results showed that 7 of 20 elite lines carry pi9, while only 3 carry Piz-t. Pathotype analysis identified three distinct virulence groups with differential responses across resistance genes. The study identifies critical gaps in marker validation and pathotype-specific screening and recommends investment in a National Rice Blast Pathotype Monitoring programme coordinated by NCRI.

Keywords: blast resistance, marker-assisted selection, rice breeding, Nigeria, Magnaporthe oryzae