Magnaporthe oryzae Populations Adapted to Finger Millet and Rice Exhibit Distinctive Patterns of Genetic Diversity, Sexuality and Host Interaction
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In this study, host-specific forms of the blast pathogen Magnaporthe oryzae in sub-Saharan Africa (SSA) were characterised from distinct cropping locations using a combination of molecular and biological assays. Finger millet blast populations in East Africa revealed a continuous genetic variation pattern and lack of clonal lineages, with a wide range of haplotypes. M. oryzae populations lacked the grasshopper (grh) element (96%) and appeared distinct to those in Asia. An overall near equal distribution (47–53%) of the mating types MAT1-1 and MAT1-2, high fertility status (84–89%) and the dominance of hermaphrodites (64%) suggest a strong sexual reproductive potential. Differences in pathogen aggressiveness and lack of cultivar incompatibility suggest the importance of quantitative resistance. Rice blast populations in West Africa showed a typical lineage-based structure. Among the nine lineages identified, three comprised ~90% of the isolates. Skewed distribution of the mating types MAT1-1 (29%) and MAT1-2 (71%) was accompanied by low fertility. Clear differences in cultivar compatibility within and between lineages suggest R gene-mediated interactions. Distinctive patterns of genetic diversity, sexual reproductive potential and pathogenicity suggest adaptive divergence of host-specific forms of M. oryzae populations linked to crop domestication and agricultural intensification.
KeywordsFinger millet Rice Blast disease Magnaporthe oryzae Pathogen populations Genetic diversity Mating type distribution Fertility status Pathogenicity Adaptive divergence
This publication is an output from research projects funded by the United Kingdom Department for International Development (DFID) for the benefit of developing countries. The views expressed are not necessarily those of DFID. Projects R7552, R6738, R8030 and R8445 co-ordinated by S. Sreenivasaprasad supported the PhD programmes of J.P. Takan and J. Chipili. The authors are grateful to M.A. Mgonja, N.M. Wanyera, A. Mead, and colleagues from the ARC-WARDA and ICRISAT national networks for their help with various components of the projects and to Dr. J. Hamer and Dr. S. Kang for providing the M. oryzae reference strain and mating type sequences, respectively. The authors would like to thank F.M. Kimmins, A. Ward, J.M. Lennè and T. Chancellor for their support in the implementation of the projects.
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