Management of Aphid vectors of virus diseases on commercial potato (Solanum tuberosum L.) cultivars in Kenya
Aphid resistance in the potato (Solanum tuberosum L.) crop is one of the methods of managing aphid pests in potato production, which are also known vectors of virus diseases. Results from field experiments using 18 commercially available potato varieties to evaluate varietal differences to aphid infestation indicated that Aphis gossypii, Macrosiphum euphorbiae and Myzus persicae species infested the potato crop. A. gossypii and M persicae were the most and least abundant species respectively. A. gossypii and M euphorbiae differed significantly (P=O.05) in times of sampling and among treatment means. Kerr's Pink and Anett had the highest infestation of A. gossypii and M euphorbiae. Desiree supported the highest population of M persicae while Roslin Tana was the least infested variety. Kerr's Pink, Desiree and Anett can be considered as susceptible varieties and Roslin Tana as relatively aphid resistant. All other varieties were moderately infested and can be considered as moderately susceptible. Mavuno and Desiree varieties had high incidence of Potato leaf roll disease while Tigoni and D.Robyjn varieties had low disease incidence. There was no correlation of time of aphid infestation and the incidence of Potato leaf roll disease, hence the aphids present on the potatoes may not have been responsible as vectors in the transmission of the virus observed on the potatoes. Potato leaf roll disease may have been introduced to the potatoes from alate viruliferous vectors and not from apterae aphids present in the potato crop. Total yields were highest in Nyayo, Asante and Tigoni varieties, which supported low aphid populations. Mavuno and Desiree recorded relatively low yields. Aphid resistant and moderately susceptible varieties are therefore recommended to farmers, as these are more likelyto support low aphid populations and low viral incidence. Several years of seed multiplication may be lost if attention is not paid to aphid dissemination of viruses during storage. M euphorbiae populations on the sprouted Tigoni and Asante potatoes in the store were observed to increase from the onset of the study. With ideal temperatures and relative humidity, the aphid populations multiplied rapidly with new generations being formed within a period of two weeks. Since aphid population increased throughout the storage phase, stringent aphid and viruses control measures need to be put in place to reduce seed degeneration. It is recommended that specific control measures be implemented and adopted for specific aphid species on specific potato cultivars. This would target the reduction of aphid infestation over the growingperiod of the crop when the aphid species is known to infest over and this would in turn lower the virus load present in the seed potato over time.