Identification of the anastomosis groups of Rhizoctonia spp.causing diseases on watermelon seedling
Watermelon is an important economic crop and is widely cultivated all over the world.Seedling disease of watermelon caused by Rhizoctonia spp.can lead to seedling death.In this study,149 Rhizoctonia iso-lates were isolated from the diseased seedlings of watermelon,which were collected from Beijing municipality,Heilongjiang and Jilin provinces,and Ningxia Hui autonomous region of China from 2014 to 2019.Based on morphological characteristics and sequence analysis of internal transcribed spacer of ribosomal DNA(rDNA-ITS),the 149 isolates were assigned to ten anastomosis groups(AGs)or subgroups,namely AG-l-IB,AG-1-IC,AG-2-1,AG-4HGI,AG-4HGⅡ,AG-4HGⅢ,AG-5,AG-A,AG-B(o)and AG-Fa,with R.solani AG-4(HGI,HGⅡ,and HGⅢ)being predominate.All tested Rhizoctonia isolates were pathogenic to watermelon seedling.The virulence of multinucleate Rhizoctonia(MNR)was significantly higher than that of binucleate Rhizoctonia.Among the MNR,R.solani AG-4HGI,AG-4HGⅡ,and AG-4HGⅢ were the most aggressive on watermelon seedling,and the average disease incidence and disease index of watermelon seedling caused by the three subgroups were 97.92％,96.15％and 99.14％,and 76.16,63.43 and 72.01,respectively.To the best of our knowledge,it is the first report of AG-1-1B,AG-1-1C,AG-2-1,AG-5,and AG-B(o)causing disease on watermelon seedling in China and perhaps worldwide.
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