CBN-V Video Archives - S8-01
Implications for Sustainable Cassava Cultivation in Uganda of Recovery and Production of Symptomless Progeny from Cassava Plants Affected by Cassava Mosaic Disease

Alicai¹ T., R.W. Gibson², G.W. Otim-Nape¹, J.P. Legg²,  S.E. Seal², E. Ogwok and W.S. Sserubombwe¹

1. Namulonge Agricultural and Animal Production Research Institute, P.O Box, 7084, Kampala, Uganda talicai@hotmail.com
2. Natural Resources Institute, University of Greenwich, Central Avenue, Chatham Maritime, Kent ME4 4TB, UK JLEGG@INFOCOM.CO.UG

        As a response to the cassava mosaic disease (CMD) epidemic in Uganda the National Cassava Programme adopted the use of resistant varieties. The Programme has so far released 12 CMD-resistant varieties for production by farmers. It has been shown that these resistant varieties attain low CMD incidence and moderate levels of severity. Moreover, diseased plants of such varieties gradually lose symptoms, some new shoots being without symptoms (recovery), while a proportion of the progeny of such plants sprout without symptoms (revertion). In a field trial, stem cuttings from naturally diseased and symptomless plants of 5 resistant and 1 susceptible variety were planted at Namulonge Research Institute in Uganda. Degree of reversion in this initial experiment ranged from 0% in Bao (susceptible) to 29% in Nase 4 (resistant), while the highest level of recovery (94%) was observed in Nase 11. In the next cycle of the trial, (planted with stem cuttings from the previous experiment) substantial increases in reversion in the resistant varieties were recorded, ranging from 15% in Nase 9 to 54% in Nase 4. More reversion was recorded in cuttings taken from recovered plants than from non-recovered (diseased) plants and levels of reversion increased in the order: bottom, middle and top portions of stems providing cuttings. These results have improved the health status of the same clonally propagated planting material over only 2 cycles. It is apparent that this trend would continue until lower levels of equilibrium of CMD incidence that is characteristic of resistant cassava varieties and translate into fewer foci of disease, from which further spread can occur. In the absence of other limiting stresses and epidemics, these features would play a role in improving yields on farmers’ fields, thus availing opportunities of increased food and cash incomes.

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