Epidemiology of cassava mosaic disease in Mozambique
Date
2011-07-07
Authors
Cossa, Nurbibi Saifodine
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Abstract
Cassava (Manihot esculenta Crantz) belongs to the family Euphorbiaceae. The crop was introduced to África, including Mozambique, in the 17th century by Portuguese traders. Cassava is one of the most important crops in Africa. It is widely grown in many countries of sub-Saharan Africa and Madagascar, and plays a major role in food security and poverty alleviation.
In Mozambique, cassava is the second most important root crop and used exclusively as human consumption: it is estimated that 70% of the total cassava production is utilized as human food. Cassava is chiefly vegetatively propagated from stem cuttings. The roots and leaves provide a major source of carbohydrate and vitamins. In areas prone to draught and floods, cassava is the main crop.
Cassava mosaic disease (CMD) was reported for the first time in Tanzania in 1894. CMD has since been observed throughout all cassava growing areas of sub-Saharan Africa and its adjacent islands, and occurs throughout Mozambique. The disease is caused by a single-stranded circular bipartite DNA geminivirus belonging to the Family Geminiviridae and Genus: Begomovirus. It is transmitted by the whitefly vector Bemisia tabaci Gennadius. Cassava begomoviruses are highly diverse and currently nine species have been identified. Limited surveys of CMD have been performed in Mozambique, and the widespread loss of crop yield threatens farmers in the region.
This study therefore performed epidemiological studies on CMD in six major cassava-growing provinces to evaluate the incidence and severity of disease. Transmission of CMD by either cuttings or whitefly was estimated, and the genetic identities of the B. tabaci vector and begomoviruses were established.
Two surveys were conducted in the 2005/2006 and 2006/2007 growing seasons in six provinces namely, Maputo, Gaza, Inhambane, Nampula, Zambézia and Cabo Delgado. The study showed that CMD incidence recorded was highly variable within districts and between provinces, in both surveys, witth mean incidence of 6% in Nampula and 75% in the Gaza Province.
The whitefly infection was very low (0 to 3%) compared to cutting infection (22 to 60%). Mean whitefly numbers per plant were variable but also low (0-15.8) in all the provinces in tZambézia and Cabo Delgado. The study showed that CMD incidence recorded was highly variable within districts and between provinces, in both surveys, witth mean incidence of 6% in Nampula and 75% in the Gaza Province.
The whitefly infection was very low (0 to 3%) compared to cutting infection (22 to 60%). Mean whitefly numbers per plant were variable but also low (0-15.8) in all the provinces in thvirus - [South Africa]; while the Zambezia Province virus was most closely aligned (94%) with EACMMV (East African cassava mosaic Malawi virus- [Malawi: MH]), and the isolate from the Cabo Delgado Province aligned most closely (96%) with East African cassava mosaic Cameroon virus- Cameroon and less closely (87%) to EACMMV.This study reports diversity for cassava begomovirus species in Mozambique for the first time. It is similar to previous studies in RFLP analysis that indicated that the cassava geminiviruses in Mozambique are mainly genetic variants of ACMV and EACMV, although full length DNA A sequences indicated that EACMMV and EACMCV are present in Mozambique. These results, as in South Africa, demonstrate the mixture of geminivirus species from east and west Africa. This is the first report of SACMV in Mozambique.