Bacterial Sheath Brown Rot of Rice Caused By Pseudomonas-fuscovaginae in Malagasy

La pourriture brune de la gaine foliaire du riz, causée par la bactérie Pseudomonas fuscovaginae, est distribuée sur le riz irrigué entre 1300 et 2000 m d'altitude à Madagascar. La sévérité de l'inhibition de l'émergence paniculaire augmente avec l'altitude. Les variétés locales souffrent moins de l'attaque que les variétés semi-naines de l'Institut International de Recherches sur le Riz ou de la Pépinière Internationale de Riz pour la Tolérance au Froid. Dans des tests biochimiques et sérologiques de base, 22 souches de P. fuscovaginae de Madagascar ont réagi de manière similaire à des souches de référence du Burundi et du Japon. Dans des tests du pouvoir pathogène, plusieurs souches malgaches apparaissent comme plus agressive

Magnaporthe oryzae populations adapted to finger millet and rice exhibit distinctive patterns of genetic diversity, sexuality and host interaction

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 intensificatio