Statistical evidence linking the zigzag stem habit with tolerance to cassava brown streak disease

Cassava (Manihot esculenta Crantz) provides the cheapest source of food calories in Africa and forms the major staple for roughly 40% of Africans. More than 200 million people in sub-Saharan Africa derive over 50% of their carbohydrate intake from cassava. It has been recognised as a powerful poverty fighter with the potential to help alleviate poverty both through food security and commercialization..

DISTRIBUTION AND SPECIES COMPOSITION OF CEREAL STEMBORERS IN THE EASTERN ZONE OF TANZANIA

A survey was conducted in the four regions of Tanga, Morogoro, Coast and Dar es Salaam in eastern Tanzania to determine the distribution and species composition of cereal stemborers and their natural enemies. A total of 22 fields were sampled in Tanga, 28 in Morogoro, 17 in Coast and one in Dar es Salaam. Chilo partellus was found to be the predominant species, accounting for 80 % of all stemborers collected. Busseola fusca, Sesamia calamistis and Chilo orichalcociliellus made up 15, 4 and less than 1 % of the stemborers collected respectively. Infestation levels varied with the age of the plants, whereby younger plants were more severely infested (infestation ranging from 20 - 40 %) than mature plants (infestation ranging from 5 - 15 %). Two larval parasitoids, Cotesia sesamiae and Cotesia flavipes, were the main natural enemies collected. However, the levels of parasitism of the stemborers were very low. The exotic natural enemy Co. flavipes may have spread from the Kenya coast (where it is established) into eastern Tanzania. RÉSUMÉ Une enquête a été menée dans les quatre régions de Tanga, Morogoro, Coast et Dar es Salaam dans l'est de la Tanzanie afin de déterminer la distribution et la composition en espèces des foreurs de tige de céréales et de leurs ennemis naturels. Au total, 22 champs ont été échantillonnés dans Tanga, 28 dans Morogoro, 17 dans Coast et un dans Dar es Salaam. Chilo partellus est l'espèce dominante, il représente 80% de tous les foreurs des tiges récoltés. Busseola fusca, Sesamia calamistis et Chilo orichalcociliellus représentent respectivement 15, 4 et moins de 1 % des foreurs de tige récoltés. Les niveaux d'infestation varient avec l'âge des plantes; ainsi les plantes les plus jeunes sont plus sévèrement infestées (l'infestation est comprise entre 20 - 40%) que les plantes mûres (l'infestation est comprise entre 5 et 15%). Deux parasitoïdes larvaires, Cotesia sesamiae et Cotesia flavipes, sont les principaux ennemis naturels récoltés. Cependant, les niveaux de parasitisme des foreurs des tiges sont très bas. L'ennemi naturel exotique Co. flavipes a dû s'étendre de la côte kenyanne (où il est établi) vers la côte tanzanienne

Biological control of cassava green mite in Tanzania

The cassava green mite Mononychellus tanajoa (Bondar) (Acari: Tetranychidae) is one of the most important pests of cassava, a main staple food crop in Tanzania. The International Institute of Tropical Agriculture (ETA) in collaboration with the Tanzania National Biological Control P r o m (NBCP) launched in 1998 the biological control campaign against cassava green mite in Tanzania with the release of the neotropicd phytoseiid predator Z)phlodromallus aripo DeLeon (Acari: Phytoseiidae), which had proven to be an efficient biological control agent of the cassava green mite in West Mca. The campaign consisted of new introductions and redistributions of I: aripo from infested cassava shoot tips, follow-up surveys to determine establishment, spread, and impact, as well as extension and farmer training on pest and natural enemy recognition and means of enhancing predator efficacy. ~phlodromallusa ripo was h t fo und in March 1998 in the Tanga region, most likely invading h m the southern Kenya coast where it was released in 1996. Subsequently, the Tanzania NBCP in close collaboration with IITA has carried out numerous introductions and redistributions of the predator. Surveys conducted in the following 6 years revealed success M establishment, persistence and spread in five agro-ecological zones including the Lalce (Mars and Kagera regions, except parts of Mwanza region), Western (Kigorna region except Shinyanga region), Southern Highlands (Mbeya and Iringa region), Eastem (Tanga and Coast regions) and Southern (Lindi and Mtwara regions) zones. Up to 2005, there was still no T. arip in parts of 3 regions: Mwanza, Shinyanga and Ruvuma. Cassava green mite mean densities have declined to low levels (less than 20 actives per leaf) in all regions where 'I: a r b has been present. In on-fm impact assessment trial, 'I: aripo was capable of reducing population density of cassava green mite by 64.3% and increasing total and marketable cassava root weights by 61.2% and 71.7%, respectively. There was also a significant increase in total number of roots (25.4%), number of marketable roots (45.78%), stem weights (47.39%), and leaf weight (40.7%) where T, aripo was not eliminated. This report present evidence of the impact of biological control on cassava green mite populations and cassava yield in Tam&, and recommends the use of exotic isolates of the fungal pathogen Neozygites tanajoae, which has been established in West Africa, as a complementary alternative approach in controlling further the cassava green mite in the remaining spots of high infestations