Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2011
Publication Date: 6/13/2011
Citation: Lamprecht, S.C., Tewoldemedhin, Y.T., Calitz, F.J., Mazzola, M. 2011. Evaluation of strategies for the control of canola and lupin seedling diseases caused by Rhizoctonia anastomosis groups. European Journal of Plant Pathology. 130:427-439. Interpretive Summary: Canola and lupin are economically important crops in the Western Cape province of South Africa. The sustainable production of these crops is threatened by soilborne diseases that affecting seedlings of these crops resulting in significant stand reductions. Rhizoctonia spp. are a significant component of a pathogen complex that contributes to canola and lupin seedling death. Studies were conducted to evaluate the efficacy of a variety of treatments for the control of canola and lupin diseases incited by these fungal pathogens. Host resistance to Rhizoctonia spp. was identified among both canola and lupin cultivars/species, however the effectiveness of this resistance varied with the Rhizoctonia anastomosis group (AG). For instance, the canola cultivar Spectrum was resistant to Rhizoctonia solani AG-4, but all canola cultivars were highly susceptible to R. solani AG-2-1. The fungicide seed treatment designated SA-combination, which consisted of several fungicide chemistries including iprodione, metalaxyl, thiram, was highly effective in improving the survival of lupin and canola seedlings when planted into soils infested with Rhizoctonia spp. Binucleate Rhizoctonia spp. that are not pathogenic to either crop plant were examined for the ability to suppress disease caused by pathogenic isolates of Rhizoctonia solani. The binucleate Rhizoctonia spp. were capable of suppressing disease incited by R. solani, but typically this was only observed when the binucleate strain was applied at a ratio of 10:1 relative to the pathogen. Future studies will examine the integrated use of these methods for control of canola and lupin seedling diseases caused by R. solani.
Technical Abstract: Several methods with potential for the management of Rhizoctonia diseases of canola and lupin including several methods with potential for the management of Rhizoctonia plant resistance, fungicide seed treatment and biological control using binucleate Rhizoctonia anastomosis groups (AGs) were evaluated under glasshouse conditions. Screening included the examination of resistance of eight canola and eight lupin cultivars/selections to damping-off and hypocotyl/root rot caused by the multinucleate Rhizoctonia solani AG-2-1, 2-2, 4 and 11. All canola cultivars were highly susceptible to AG-2-1, although they differed in their reaction. Spectrum and 44C73 were more resistant to AG-4 than the other canola cultivars. On lupin, R. solani AG-2-2 and 4 were most virulent, and the cultivar Cedara 6150 and selection E16 were most resistant to AG-2-2, while Cedara 6150, E16, Mandelup and Quilinock were more resistant to AG-4 than the other cultivars/selections. The Lupinus luteus selections, E188.8.131.52 and E82.1.1 were most susceptible to AG-2-2, 4 and 11. Seed treatment with the fungicides, Cruiser OSR (a.i. difenconazole, fludioxonil, metalaxyl-M, thiamethoxam) and SA-combination (a.i. iprodione, metalaxyl, thiram) significantly increased survival of canola (cvs Muster, Rocket and Thunder) and lupin (cultivar/selection Cedara 6150, E82.1.1 and Mandelup) seedlings, decreased hypocotyl/root rot and improved the percentage healthy seedlings, with SA-combination being significantly more effective than Cruiser. Application of the binucleate Rhizoctonia AGs (A, Bo, K and I) significantly increased the survival of lupin seedlings inoculated with R. solani AG-2-2 and 4, and AG-I and K significantly improved survival of canola in the presence of AG-4. A low inoculum ratio of the binucleate AGs [1:1 (multinucleate AG :binucleate AG)] was less effective than a high inoculum ratio [1:10 (multinucleate AG :binucleate AG)]. It appeared that AGs-A, Bo and I were more effective than AG-K in protecting lupin from infection by R. solani. This is the first report of the potential of binucleate AGs to protect canola and lupin seedlings against infection by multinucleate AGs. Results obtained in this study will significantly contribute to management strategies that can be employed against Rhizoctonia diseases of canola and lupin in the Western Cape province of South Africa.