AUTHOR=She Xiaoman , Yu Lin , Lan Guobing , Tang Yafei , He Zifu 

TITLE=Identification and Genetic Characterization of Ralstonia solanacearum Species Complex Isolates from Cucurbita maxima in China

JOURNAL=Frontiers in Plant Science

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2017.01794

DOI=10.3389/fpls.2017.01794

ISSN=1664-462X

ABSTRACT=<p><italic>Ralstonia solanacearum</italic> species complex is a devastating phytopathogen with an unusually wide host range, and new host plants are continuously being discovered. In June 2016, a new bacterial wilt on <italic>Cucurbita maxima</italic> was observed in Guangdong province, China. Initially, in the adult plant stage, several leaves of each plant withered suddenly and drooped; the plant then wilted completely, and the color of their vasculature changed to dark brown, ultimately causing the entire plant to die. Creamy-whitish bacterial masses were observed to ooze from crosscut stems of these diseased plants. To develop control strategies for <italic>C. maxima</italic> bacterial wilt, the causative pathogenic isolates were identified and characterized. Twenty-four bacterial isolates were obtained from diseased <italic>C. maxima</italic> plants, and 16S rRNA gene sequencing and pathogenicity analysis results indicated that the pathogen of <italic>C. maxima</italic> bacterial wilt was <italic>Ralstonia solanacearum</italic>. The results from DNA-based analysis, host range determination and bacteriological identification confirmed that the 24 isolates belonged to <italic>R. solanacearum</italic> phylotype I, race 1, and eight of these isolates belonged to biovar 3, while 16 belonged to biovar 4. Based on the results of partial <italic>egl</italic> gene sequence analysis, the 24 isolates clustered into three <italic>egl-</italic> sequence type groups, sequevars 17, 45, and 56. Sequevar 56 is a new sequevar which is described for the first time in this paper. An assessment of the resistance of 21 pumpkin cultivars revealed that <italic>C. moschata</italic> cv. Xiangyu1 is resistant to strain RS378, <italic>C. moschata</italic> cv. Xiangmi is moderately resistant to strain RS378, and 19 other pumpkin cultivars, including four <italic>C. maxima</italic> cultivars and 15 <italic>C. moschata</italic> cultivars, are susceptible to strain RS378. To the best of our knowledge, this is the first report of <italic>C. maxima</italic> bacterial wilt caused by <italic>R. solanacearum</italic> race 1 in the world. Our results provide valuable information for the further development of control strategies for <italic>C. maxima</italic> wilt disease.</p>