Biological nitrogen fixation associated with rice production

Research on biological nitrogen fixation began in Western Europe during the nineteenth century, under conditions where a mere increase in nitrogen fertilization inevitably increased yields : it was the beginning of the triumphal era of fertilizers. In the thirties began the era of legume inoculation : and this again was due to a very simplistic situation in western countries : the absence of bacterial symbionts adapted to crops such as soybeans. Biological nitrogen fixation (BNF) appeared as an extension of nitrogen fertilization, with the same effects on farmers' incomes. The amount of nitrogen available was the limiting factor of the farmer's income, whatever its origin ; mineral nitrogen from soil or fertilizers as well as nitrogen derived from biological fixation. In a way, this very clear-cut situation allowed for the rapid development of our knowledge about BNF, and its use by farmers. Nevertheless, when the time came to extrapolate to tropical countries, some difficulties arose. Some were due to a lack of knowledge about BNF systems in warm countries. Other difficulties were due to the interference of many yield-limiting factors other than nitrogen. But the main difficulty resulted from a misunderstanding about the objectives : the goal of developing BNF is not to achieve the maximum nitrogen input, it is really to achieve the maximum income (money and/or food) for farmers. In many tropical countries, the farmer's income is not directly proportional to nitrogen availability. We, as scientists, are confined to scientific objectives (maximum nitrogenase activity) whereas countries, such as Bangladesh, must aim at a maximum farming efficiency, biological science being largely secondary to other disciplines such as sociology or economics. (Résumé d'auteur

Prospect and potential of Burkholderia sp. against Phytophthora capsici Leonian: a causative agent for foot rot disease of black pepper

Foot rot disease is a very destructive disease in black pepper in Malaysia. It is caused by Phytophthora capsici Leonian, which is a soilborne pathogenic protist (phylum, Oomycota) that infects aerial and subterranean structures of many host plants. This pathogen is a polycyclic, such that multiple cycles of infection and inoculum production occur in a single growing season. It is more prevalent in the tropics because of the favourable environmental conditions. The utilization of plant growth-promoting rhizobacteria (PGPR) as a biological control agent has been successfully implemented in controlling many plant pathogens. Many studies on the exploration of beneficial organisms have been carried out such as Pseudomonas fluorescens, which is one of the best examples used for the control of Fusarium wilt in tomato. Similarly, P. fluorescens is found to be an effective biocontrol agent against the foot rot disease in black pepper. Nowadays there is tremendous novel increase in the species of Burkholderia with either mutualistic or antagonistic interactions in the environment. Burkholderia sp. is an indigenous PGPR capable of producing a large number of commercially important hydrolytic enzymes and bioactive substances that promote plant growth and health; are eco-friendly, biodegradable and specific in their actions; and have a broad spectrum of antimicrobial activity in keeping down the population of phytopathogens, thus playing a great role in promoting sustainable agriculture today. Hence, in this book chapter, the potential applications of Burkholderia sp. to control foot rot disease of black pepper in Malaysia, their control mechanisms, plant growth promotion, commercial potentials and the future prospects as indigenous PGPR were discussed in relation to sustainable agriculture