Aphid resistance status of tobacco genotypes in Zimbabwe.
Host plant resistance to insects (PRI) is an underutilized pest management strategy in tobacco production. Deploying resistant varieties is a more environmental friendly and sustainable solution to managing tobacco aphids. Breeding for insect pest resistance is the foremost method in any integrated pest management approach. Although it is impossible to obtain a completely aphid-resistant plant, a certain degree of resistance (through antibiosis, antixenosis or othercombinations of mechanisms) can help to reduce the number of insecticide applications. Thisstudy aimed to evaluate selected flue-cured and burley varieties and breeding lines in Zimbabwefor resistance to the tobacco aphid, Myzuspersicctenicotianae. Resistance of tobacco genotypes(Nicotianaetahacum L.), KRK 26 R, BRK 2, BRK 4, T66, BU 21, Landrace 4, Landrace 12,Landrace 17, Landrace 18, Landrace 19, Habana 92, Kva 1, TN 86, VAM and DSD were studiedin field experiments conducted at the Kutsaga Research Station, Harare. Significant differences(P < 0.05) in aphid populations amongst genotypes evaluated at all assessment were noted. Aphid populations started building up at 6 weeks after transplanting (WAT) with Landrace 4, Landrace17, T 66 and VAM having the lowest mean aphid scores than the other varieties. Similarly at 7, 8and 9 WAT, Landrace 4 and VAM had the least number of aphids making them resistant to aphid infestations than the other susceptible varieties. The low aphid scores observed in Landrace 4 and VAM can be explained by the presence of hairy leaf characteristics of the two lines which makes it difficult for aphids to probe and insert their style into the leaf so as to extract sap. Results are consistent with the past two seasons which showed that Landrace 4 and VAM were resistant to aphid infestations. However, since they only achieved some degree of resistance to the M. nicotianae, their use is recommended in breeding programmes as well as in crop protection programmes where combinations with a low insecticide dose can be practiced.