Host specificity controlled by PWL1 and PWL2 effector genes in the finger millet blast pathogen Magnaporthe oryzae in eastern Africa

Abstract

Magnaporthe oryzae, a devastating pathogen of finger millet (Eleusine coracana), secretes effector molecules during infec tion to manipulate host immunity. This study determined the presence of avirulence effector genes PWL1 and PWL2 in 221 Eleusine blast isolates from eastern Africa. Most Ethiopian iso lates carried both PWL1 and PWL2. Kenyan and Ugandan iso lates largely lacked both genes, and Tanzanian isolates carried either PWL1 or lacked both. The roles of PWL1 and PWL2 towards pathogenicity on alternative chloridoid hosts, includ ing weeping lovegrass (Eragrostis curvula), were also investi gated. PWL1 and PWL2 were cloned from Ethiopian isolate E22andweretransformedseparatelyintoUgandanisolateU34, whichlackedbothgenes.Resultingtransformantsharboringei ther gene gained varying degrees of avirulence on Eragrostis curvula but remained virulent on finger millet. Strains car rying one or both PWL1 and PWL2 infected the chloridoid species Sporobolus phyllotrichus and Eleusine tristachya, indi cating the absence of cognate resistance (R) genes for PWL1 and PWL2 in these species. Other chloridoid grasses, however, were fully resistant, regardless of the presence of one or both PWL1 and PWL2, suggesting the presence of effective R genes against PWLandothereffectors.PartialresistanceinsomeEra grostis curvula accessions to some blast isolates lacking PWL1 and PWL2also indicated the presence of other interactions be tween fungal avirulence (AVR) genes and host resistance (R) genes. Related chloridoid species thus harbor resistance genes that could be useful to improve fingermillet for blast resistance. Conversely, loss of AVR genes in the fungus could expand its host range, as demonstrated by the susceptibility of Eragrostis curvula to finger millet blast isolates that had lost PWL1 and PWL2.