Genetic Diversity in Pyricularia Isolates from Various Hosts Revealed by Polymorphisms of Nuclear Ribosomal DNA and the Distribution of the MAGGY Retrotransposon.

Abstract

Pyricularia isolates from various gramineous plants were subjected to RFLP and sequence analyses of rDNA to clarify their genetic relationships. Based on rDNA-RFLP patterns produced by digestion with two restriction enzymes, 71 isolates from 27 plant species were grouped into 13 rDNA types. To estimate their genetic relatedness, a UPGMA dendrogram was constructed based on the rDNA-RFLP profiles. The ITS2 regions of 13 representative isolates were also amplified by PCR and directly se-quenced to construct another dendrogram. In both dendrograms, isolates from agronomically important crops (rice, foxtail millet, common millet, finger millet, wheat and oats) and their relatives were classified into a single cluster. Isolates from weeds, such as crabgrass and buffelgrass, were located outside the crop isolate cluster, and Japanese bamboo or bamboo grass isolates were farthest from the crop isolate cluster. In surveying the distribution of a retrotransposon, MAGGY, in these isolates, MAGGY was present in multiple copies in isolates from rice, foxtail millet and six other hosts, which formed a single subcluster within the crop isolate cluster. Multiple copies of MAGGY were also detected in an isolate from buffelgrass, which was distant from the other MAGGY carriers in the rDNA dendrograms. These results suggest that the horizontal transfer of MAGGY occurred during the differentiation of Pyricularia.