The input costs of pesticides to control biotic constraints are often prohibitive to the subsistence farmers of Africa and seed based solutions to biotic stresses are more appropriate. Plant breeding has been highly successful in dealing with many pest problems in Africa, especially diseases, but is limited to the genes available within the crop genome. Years of breeding and studying cultural practices have not always been successful in alleviating many problems that biotechnology may be able to solve. We pinpoint the major intractable regional problems as: (1) weeds: parasitic weeds (Striga and Orobanche spp.) throughout Africa; grass weeds of wheat (Bromus and Lolium) intractable to herbicides in North Africa; (2) insect and diseases: stem borers and post-harvest grain weevils in sub-Saharan Africa; Bemesia tabaci (white fly) as the vector of the tomato leaf curl virus complex on vegetable crops in North Africa; and (3) the mycotoxins: fumonisins and aflatoxins in stored grains. Abiotic stresses may exacerbate many of these problems, and biotechnological alleviations of abiotic stress could partially allay some predicaments. Some of these constraints are already under study using biotechnological procedures, but others may require longer-term research and development to alleviate the problems. Despite the huge impacts of post-harvest weevils and of mycotoxins in grains, these issues had not been given high priority in national biotechnological programs, possibly due to a lack of knowledge of their immensity. The need for public sector involvement is accentuated for cases where immediate profits are not perceived (e.g. lowering mycotoxin levels in farmer utilized grain, which does not increase yield) but where the public weal will gain, and will be invaluable, especially where the private sector supplies genes already isolated.

Rhizobacteria strains were characterized for ability to synthesize hydrogen cyanide and for effects on seedling root growth of various plants. Approximately 32% of bacteria from a collection of over 2000 isolates were cyanogenic, evolving HCN from trace concentrations to > 30 nmoles/mg cellular protein. Cyanogenesis was predominantly associated with pseudomonads and was enhanced when glycine was provided in the culture medium. Concentrations of HCN produced by rhizobacteria were similar to exogenous concentrations inhibiting seedling growth in bioassays, suggesting that cyanogenesis by rhizobacteria in the rhizosphere can adversely affect plant growth. Growth inhibition of lettuce and barnyardgrass by volatile metabolites of the cyanogenic rhizobacteria confirmed that HCN was the major inhibitory compound produced. Our results suggest that HCN produced in the rhizospheres of seedlings by selected rhizobacteria is a potential and environmentally compatible mechanism for biological control of weeds.

Aim: To develop an appropriate formulation of the deleterious rhizobacterium Pseudomonas trivialis X33d and to evaluate its effectiveness to reduce brome growth. Methods and Results: Two formulations of Ps. trivialis X33d, a semolinakaolin granular formulation (Pesta) and talc-kaolin powder, were prepared and their effectiveness in reducing brome growth was evaluated. Both brome suppression and cell viability of X33d were higher in Pesta granular formulation than in talc-kaolin powder one. The impact of storage temperature and the addition of adjuvants (sucrose and oil) to the granular formulation of X33d were assessed in order to improve the shelf life of the formulation. The longest viability was found in formulated product supplemented with adjuvants and stored at 4°C. The effect of Pesta granules supplemented with adjuvants and stored for 6 months at 4°C on brome and wheat growth under controlled and greenhouse conditions was evaluated. The X33d formulation in Pesta increased the growth of wheat and reduced brome growth. Conclusion: Our results indicate that Ps. trivialis X33d formulated in Pesta has potential as a bioherbicide to control brome. Significance and Impact of the Study: Because of the impracticality of applying bacterial cell suspension on a large scale, the use of Pesta granules of X33d against brome could help in achieving a sustainable agriculture application of a bioherbicide.

No abstract

No abstract