Submitted to: European Journal of Plant Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/11/2011
Publication Date: 5/27/2011
Citation: Lamprecht, S.C., Tewoldemedhin, Y.T., Hardy, M., Calitz, F.J., Mazzola, M. 2011. Effect of cropping system on composition of the Rhizoctonia populations recovered from canola and lupin in a winter rainfall region of South Africa. European Journal of Plant Pathology. 131:305-316. Interpretive Summary: Rhizoctonia spp. are a biologically and genetically diverse group of fungi, many of which incite devastating diseases on a variety of economically important crops. However, there is little information concerning the specific identity of the population contributing to plant diseases in agriculturally important regions on the African continent. As crop rotation is a primary means of controlling Rhizoctonia incited diseases in these production systems, it is important to have information concerning these populations so that effective rotation sequences can be generated. The species and anastomosis groups of Rhizoctonia recovered from canola and lupin when used in rotations with various crops in the western and southern regions of the Western Cape province of South Africa were identified. Rhizoctonia solani was recovered more frequently from lupin and canola when grown after wheat than when grown after barley. Tillage practices had little effect on the incidence of Rhizoctonia spp., with the only significant effect being a higher incidence of binucleate Rhizoctonia spp. when the crops were grown using conventional tillage relative to that observed in no-till or minimum tillage treatments. As binucleate Rhizoctonia spp. recovered from these systems were typically non-pathogenic, it does not appear that tillage practices will significantly affect diseases of lupin and canola incited by Rhizoctonia.
Technical Abstract: Rhizoctonia spp. are important pathogens of a broad range of crop plants that are economically important to the farm economy of the Western Cape region of South Africa. However, there is little information concerning the identity and relative importance of these fungal pathogens, and the effect of cropping system on their incidence. The identity of Rhizoctonia spp. recovered from lupin and canola and the effect of cropping sequence and tillage practice on the incidence of these fungal pathogens was examined in the southern and western region of the Western Cape Province. In the 2006 study, 93.5% of the Rhizoctonia isolates recovered were binucleate and 6.5% multinucleate; in 2007, 72.8% were binucleate and 27.2% were multinucleate. The most abundant AGs within the population recovered included A, Bo, I, and K, among binucleate isolates and 2-1, 2-2 and 11 among multinucleate isolates. Crop rotation sequence, tillage and plant growth stage at sampling all affected the incidence of recovery of Rhizoctonia, but certain effects were site specific. The binucleate group was more frequently isolated from lupin and the multinucleate group from canola. AG-2-1 was only isolated from canola and AG-11 only from lupin. This study showed that important Rhizoctonia AGs such as AG-2-1, 2-2 and 11 occur in both the southern and the western production areas of the Western Cape province and that crop rotation consistently influences the incidence and composition of the Rhizoctonia community recovered from the cropping system.