Response of Local Cassava Varieties in Uganda to Cassava Mosaic Virus Disease

Abstract

Cassava mosaic disease (CMD) resistant varieties have been used to manage CMD inUganda. In spite the availability of a number of CMD resistant cultivars, several locallandraces are continually grown in Uganda because they possess certain desirable traits,which may not have been fully met by the resistant varieties. Field based trials weresetup to evaluate the response to CMD of some landraces that became prominent afterthe 1990s CMD pandemic. Experiments were located in areas where CMD is reported tohave subsided namely, Mukono (Central Uganda) and Bulindi (Western Uganda). Threelandraces were evaluated per site along with resistant (Nase 4) and susceptible (Bao)standards. Plots were planted with materials obtained from either diseased or healthyfields. The results showed differences in sensitivity to CMD among varieties tested, withlandraces consistently having higher CMD incidences than Nase 4. The landraces testedin Mukono were more susceptible to CMD than even the Bao, while at Bulindi on theother hand, only Sibampale proved to be more resistant than Bao. There weredifferences in the whitefly populations among the cassava varieties and locations. Highwhitefly populations characterized all landraces and Nase 4. In most tested varieties,there was a higher infestation of whiteflies on healthy than diseased plants. Low spreadof CMD among local landraces was observed in Bulindi as would be expected in areaswhere CMD has almost subsided (low pressure areas). However, in Mukono, diseasespread among landraces was very rapid and high CMD incidences reaching 100% wererecorded regardless of whether plots were planted with healthy or diseased cuttingssuggesting it to be a CMD hot-spot. Thus, the use of clean planting materials as aneffective phytosanitary method can only be employed under low disease pressure whilehigh disease pressure areas need use of resistant varieties.