Characterization and pathogenicity of Rhizoctonia isolates collected from Brassica oleracea var. acephala in Ordu, Turkey

Abstract

A total of 30 Rhizoctonia isolates were collected from plants with Rhizoctonia-like symptoms in kale growing areas in Ordu province during the 2014-2015 growing seasons. All the isolates were identified using nuclear staining tecnique and the nucleotide sequence analysis of the nuclear rDNA internal transcribed spacer (ITS)1-5.8S-ITS2 region. The most prevalent anastomosis group (AG) was AG 2-1 (36.67% of isolates), followed by AG-A (30%), AG 4 HG-I (10%), AG 5 (6.67%), AG-Fb (6.67%), AG-E (6.67%) and AG-K (3.33%). Cultural characteristics showed that randomly selected RsCB-13 (AG 2-1), RsCB-20 (AG 4 HG-I), RsCB-21 (AG 5), RCB-16 (AG-A), RCB-7 (AG-E), RCB-22 (AG-Fb) and RCB-26 (AG-K) isolates representing each AG had greyed-yellow, brown, white-orange and greyed-orange colony colors, and optimum growth temperatures of the isolates ranged from 25.21 to 27.67 degrees C. Pathogenicity tests on the seedlings of kale cv. Arzuman revealed generally significant virulence differences between AG 2-1 and AG 4 HG-I isolates, and other Rhizoctonia isolates (P < 0.05). In addition, with the exception of several AG 2-1 isolates, the isolates of both groups caused severe root and stem rot and seedling deaths, unlike the relatively low and moderate virulent AG 5, AG-E, AG-Fb and AG-K isolates. However, AG-A had very low virulence and did not affect plant growth parameters such as plant height, shoot and root dry weights and root length while the isolates of all other groups generally reduced these parameters compared to control plants (P < 0.05). To our knowledge, this is the first study reporting AGs of Rhizoctonia isolates causing root and stem rot on kale plants in Turkey and in the world.