Genetic and morphological variants of subsp. cause red stripe of sugarcane in China.

Sugarcane ( spp.) is an important cash crop for production of sugar and bioethanol. Red stripe caused by subsp. () is a disease that occurs in numerous sugarcane-growing regions worldwide. In this study, 17 strains of were isolated from 13 symptomatic leaf samples in China. Nine of these strains produced white-cream colonies on nutrient agar medium while the other eight produced yellow colonies. In pairwise sequence comparisons of the 16S-23S rRNA internally transcribed spacer (ITS), the 17 strains had 98.4-100% nucleotide identity among each other and 98.2-99.5% identity with the reference strain of (ATCC 19860). Three RFLP patterns based on this ITS sequence were also found among the strains of obtained in this study. Multilocus sequence typing (MLST) based on five housekeeping genes (B, T, A, B, and A) revealed that the strains of from sugarcane in China and a strain of (30179) isolated from sorghum in Brazil formed a unique evolutionary subclade. Twenty-four additional strains of from sugarcane in Argentina and from other crops worldwide were distributed in two other and separate subclades, suggesting that strains of from sugarcane are clonal populations with local specificities. Two strains of from China (CNGX08 forming white-cream colored colonies and CNGD05 forming yellow colonies) induced severe symptoms of red stripe in sugarcane varieties LC07-150 and ZZ8 but differed based on disease incidence in two separate inoculation experiments. Infected plants also exhibited increased salicylic acid (SA) content and transcript expression of gene , indicating that the SA-mediated signal pathway is involved in the response to infection by . Consequently, red stripe of sugarcane in China is caused by genetically different strains of and at least two morphological variants. The impact of these independent variations on epidemics of red stripe remains to be investigated.