Effector Biology of Magnaporthe oryzae Isolates from Nigerian Rice and Wheat: Functional Characterisation and Implications for Durable Resistance Deployment

Magnaporthe oryzae, the causal agent of blast diseases on both rice and wheat, is among the most adaptive plant pathogens known, rapidly overcoming deployed resistance genes through effector evolution. Understanding the functional diversity of M. oryzae effectors in Nigerian field populations is critical for designing durable resistance strategies that will protect rice and wheat crops across the country's major production zones. This doctoral research functionally characterises the effector repertoire of 80 M. oryzae isolates collected from rice (Oryza sativa) and wheat (Triticum aestivum) across Nigeria's North West, North Central, and North East zones, representing the first effector-focused study of Nigerian M. oryzae populations. Whole-genome sequencing and comparative effector gene cataloguing are performed, followed by functional analysis of candidate effectors through Agrobacterium-mediated transient expression in Nicotiana benthamiana and targeted gene deletion in selected isolates. Effector-resistance gene interaction mapping using a curated differential host set identifies virulence-resistance compatibility patterns across Nigerian isolate populations. The research tests the original hypothesis that cross-pathotype effector sharing between rice-infecting and wheat-infecting populations occurs in zones of geographic overlap, constituting a novel risk pathway for resistance breakdown. Phylogenetic analysis of AvrPiz-t, AvrPi9, and PWT4 effector homologues across the isolate panel provides the molecular evidence base for this hypothesis. Findings will directly inform the design of resistance gene pyramiding strategies for both rice and wheat breeding programmes active in Nigeria. Keywords: Magnaporthe oryzae, effector biology, blast disease, durable resistance, Nigeria.