Pathogenicity of isolates of Beauveria bassiana to the banana weevil Cosmopolites sordidus

Bananas constitute a major staple food crop for millions of people in developing countries, providing energy as well as important vitamins and minerals. Itfs production in Kenya has been on the decline due to, among other factors, pests and disease of which the banana weevil, Cosmopolites sordidus, is the most important. The aim of this study was to screen ten isolates of the entomopathogenic fungus Beauveria bassiana for pathogencity against C.sordidus. Twenty weevils were inoculated with the fungus by dipping them into a fungal suspension containing 1x108 conidia ml-1 for 11 seconds. The suspension was then drained out and pieces of banana corm introduced as food for the weevils. All the ten isolates of B. bassiana tested were found to be pathogenic to adult banana weevil  causing mortalities of between 20]50% by 40 days post exposure. ICIPE 273 was the most pathogenic isolate killing 50% of adults, followed by M313 at 36% and M207 at 30%. Isolates KE300, M221, ICIPE 50, M573, M618, M470 and ICIPE 279 killed less than 30% of the weevils, ICIPE 279 was the least pathogenic isolate to the adult C. sordidus killing 6% of the inoculated weevils. The dead weevils were incubated in sterile moist filter papers in Petri dishes for two weeks and fungal mycelia was observed on the surface of the weevils starting from intersegmental junctions. Mortality caused by fungus was confirmed by microscopic examination. Since isolate ICIPE 273 has reasonable pathogenicity to C. sordidus and  field/screenhouse studies are recommended to validate the findings.Key words: biocontrol, entomopathogens, pest managemen

Table sugar as an alternative low cost medium component for in vitro micro-propagation of potato (Solanum tuberosum L.)

Most developing countries are limited in maximizing tissue culture technology due to the overhead costs involved. In view of this, the aim of this research was to evaluate alternative cheap sources ofcarbon and energy in potato culture media in order to reduce the overall cost of micro-propagation. A randomized complete block design was used to compare laboratory grade sucrose with two types oflocal commercial table sugar, specifically white and brown sugar. Three selected Kenyan potato cultivars, Tigoni, Asante and Kenya Sifa were cultured on full strength Murashige and Skoog (MS) medium at 3% (w/v) in combination with the 3 different sugars. The variation in growth performance of the cultivars was then observed. Plantlet survival of 100% was recorded after four subculture generations on all sugars for all the cultivars. The mean number of nodes per plantlet was significantly higher in brown sugar for cultivars Kenya Sifa and Asante. Brown sugar enhanced significantly higher mean number of roots per plantlet after four subculture generations for all cultivars. There was nosignificant difference in percentage of plantlet survival after transplanting for cultivars Asante and Kenya Sifa but significantly lower for cultivar Tigoni on grade sucrose medium. Results also showedthat table sugar not only enhanced micro-propagation but also significantly lowered the production input costs by 34 to 51% when compared with the analytical grade sucrose

Cassava starch as an alternative cheap gelling agent for the in vitro micro-propagation of potato (Solanum tuberosum L.)

The potential of cassava starch as an alternative and cheap gelling agent for potato in vitro culture micro-propagation media was investigated. A two-factor experiment in randomized complete blockdesign was conducted. Four levels of gelling agents; 10% (w/v) cassava starch, 8% cassava starch mixed with 0.25% agar, 0.8% agar and a liquid medium, were evaluated using three selected Kenyanpotato cultivars (Tigoni, Asante and Kenya Sifa). Cassava starch at 10% gave adequate support of explants, though it had low viscosity and softened at 42 days after explant inoculation. Cassava starchmixed with 0.25% agar provided the same firmness as 0.8% agar and maintained gel integrity throughout the culturing period of 84 days. Survival in- and ex vitro was lowest in liquid medium culture. Potato transplants from the liquid medium and cassava starch gelled medium had similar (p > 0.05) mean number of nodes and biomass. These mean values were significantly higher compared to the transplants from the agar gelled medium. The use of 10% cassava starch reduced cost by 42.5% in comparison with use of agar

The use of biotechnology in the search of hardy Sorghum bicolor (L) Moench cultivars

No Abstract.Journal of Agriculture, Science and Technology Vol. 10 (1) 2008: pp. 3-2

Production gradients in smallholder banana (cv. Giant Cavendish) farms in Central Kenya

Banana is an increasingly demanded food and cash crop in sub-Saharan Africa. Reported yields in smallholder farms vary substantially. The importance and spread of yield constraints have not been properly quantified. A study was carried out in Central Kenya to (i) quantify the yield levels, the primary yield constraints, and the spatial production gradients in such systems (ii) explore how soil fertility gradients relate to gradients in soil fertility management, and whether this is a function of farmer resource availability. Data was collected on crop management aspects, pests and diseases, and soil and plant tissue samples analyzed for nutrient contents. Bunch yields were higher near homesteads (29.8 t ha?1 yr?1) than at mid-distance (26.8 t ha?1 yr?1), or far away 20.2 t ha?1 yr?1. Yields were much higher than previously reported (11 14 t ha?1 yr?1) in Kenya. Both soil and tissue K levels were higher near and mid-distance, than far from the homestead. Gradients of soil pH, total N, available P and Organic carbon were found, being higher near the homestead, while Mg and Ca were lowest near the homesteads. K was the most deficient nutrient, with tissue K index (IK) decreasing when moving away from the homesteads. P and Ca deficiencies were also observed. Resource-poor farmers soils were higher in exchangeable K and Mg, pH, and total N, and supported higher mat densities compared to resource-endowed farmers farms. Soil quality problems were the biggest yield loss factors and not pests and diseases