Characterisation and management of Rhizoctonia associated with sunflower seedlings in South Africa
Sandra Lamprecht: Agricultural Research Council-Plant Health and Protection
<div>Poor establishment is a major yield limiting factor in sunflower production in South Africa. Surveys conducted during 2014 and 2015 showed that many potential fungal soilborne pathogens are associated with seedlings. <em>Rhizoctonia</em> species and anastomosis groups (AGs) were among these potential pathogens. Eighty-four <em>Rhizoctonia</em> isolates were obtained and identified by sequencing the internal transcribed spacer (ITS) regions. Of these, 37 isolates were multinucleate and 47 binucleate. The multinucleate AGs included 2-2LP (4.8%), 3TB (1.2%), 4-HGI (9.5%), 4-HGIII (2.4%), <em>R. zeae</em> (9.5%), and an unidentified multinucleate AG (SB-3, 16.7%). The binucleate AGs included A (19.0%), F (7.1%), K (7.1%), Q (3.6%) and four unidentified binucleate AGs (SB-1, 7.1%; SB-2, 3.6%; SB-4, 4.8% and UNR-1, 3.6%). Glasshouse trials showed that AGs 2-2LP, 4-HGI, 4-HGIII and SB-3 significantly reduced seedling survival to 53.4, 2.8, 88.3 and 7.9% respectively compared to 96.7% survival for the control. Seed treatment with a compound with active ingredients fludioxonil, mefenoxam and thiamethoxam significantly improved survival to 87.5, 39.7, 92.9 and 88.5% for AGs 2-2LP, 4-HGI, 4-HGIII and SB-3 respectively, compared to 95.8% for the control. The binucleate AGs did not cause a significant reduction in survival. Findings indicate that <em>Rhizoctonia</em> spp. may contribute to poor establishment of sunflower, and seed treatment can significantly reduce the impact of these pathogens.</div>
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