"Sweetpotato weevils" Cylas puncticollis (Boheman) and Cylas brunneus F. (Coleoptera: Brentidae) are the most important biological threat to sweetpotato, Ipomoea batatas L. (Lam), productivity in sub-Saharan Africa. Sweetpotato weevil control is difficult due to their cryptic feeding behavior. Expression of Cylas-active Bacillus thuringiensis (Bt) Cry proteins in sweetpotato could provide an effective control strategy. Unfortunately, Bt Cry proteins with relatively high toxicity against Cylas spp. have not been identified, partly because no published methodology for screening Bt Cry proteins against Cylas spp. in artificial diet exists. Therefore, the initial aim of this study was to develop an artificial diet for conducting bioassays with Cylas spp. and then to determine Bt Cry protein efficacy against C. puncticollis and C. brunneus by using this artificial diet. Five diets varying in their composition were evaluated. The highest survival rates for sweetpotato weevil larvae were observed for diet E that contained the highest amount of sweetpotato powder and supported weevil development from first instar to adulthood, similar to sweetpotato storage roots. Seven coleopteran-active Bt Cry proteins were incorporated into diet E and toxicity data were generated against neonate C. puncticollis and second-instar C. brunneus. All Bt Cry proteins tested had toxicity greater than the untreated control. Cry7Aa1, ET33/34, and Cry3Ca1 had LC50 values below 1 microg/g diet against both species. This study demonstrates the feasibility of using an artificial diet bioassay for screening Bt Cry proteins against sweetpotato weevil larvae and identifies candidate Bt Cry proteins for use in transforming sweetpotato varieties potentially conferring field resistance against these pests.
Rice is a new crop in Uganda, but has quickly grown in importance. Between 2000 and 2010, total area under rice cultivation in the country grew by 94% from 140,000 ha. Changes in the agro ecosystem due to expansion in rice area may have altered the pest status of rice insect pests. However, far too little attention has been paid to assessing the prevalence and importance of rice insect-pests in Uganda. In this study, we interviewed 240 lowland-rice farming households from eight districts within the north, east and central regions of Uganda about their perceived insect-pest problems and control measures employed, if any. A semi-structured questionnaire was used. The farmers ranked rice insect pests as the most important biotic constraint in rice production, with stem borers and the African rice gall midge (AfRGM) perceived to be the 1st and 2nd most detrimental insect pests, respectively. In spite of this, only 36% of the respondents could positively identify symptoms of AfRGM damage on rice plants, while 64% were familiar with stem borer damage. Over 60% of interviewed farmers expressed confidence in the effectiveness of insecticides for controlling rice insect pests. Cultural control measures were not popular among the farmers.
Rice in the recent past has picked up as a food security and income generating crop among farming households in Uganda. Even though, the crop is playing a significant role in reducing food insecurity and poverty within the country, its productivity has remained constant and low at about 1.5 metric tonnes per hectare. Using cross-sectional data collected from rice farmers in Northern (Lira, Dokolo, Otuke and Alebtong Districts); Eastern (Iganga, Bugiri and Kamuli Districts) and Central (Kayunga District) regions of the country, this paper establishes farmers’ knowledge and management of rice diseases from a total of 224 farmers, as a baseline for research initiatives focusing on improving rice productivity within the country. Farmers ranked diseases as the second most important constraint in rice production, after insect pests. Moreover, farmers ranked rice yellow mottle virus (RYMV) as the most important disease in rice production, followed by leaf blast (LB), brown spot (BS), sheath rot (ShR), panicle blast (PB) and bacterial leaf blight (BLB). However, 60% of farmers identified RYMV while less than 30% could clearly diagnose the symptoms of each of the other diseases. Surprisingly, only about 18% of farmers employed management options against RYMV, whereas less than 6% practiced some form of management for each of the other major diseases. The predominant disease control measure was uprooting diseased plants followed by insecticide application. About 10% of farmers reported sedges (Cyperus spp.), goat weed (Ageratum conyzoides), black jack (Bidens pilosa), and cut grass (Leersia spp.) as alternative host plants for rice diseases. An integrated disease management approach, whose development and implementation recognizes farmers as the key players in the rice production chain, is required to achieve improved and sustainable rice productivity.
This study examined whether cutting the roots of rice seedlings before transplanting affects growth and yield of lowland rice.
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