Root exudation of sorghum and utilization of exudates by nitrogen-fixing bacteria

Qualitative differences in the soluble exudates of seedlings of different sorghum (Sorghum bicolor) genotypes were demonstrated by variation in growth of diazotrophic bacteria in exudate-containing media. Isolates varied in their ability to utilize the exudate from a given genotype. Variation in the amounts of soluble carbon exuded by axenically grown seedlings of the different genotypes was also observed. However, the variation in plant-associated acetylene reduction activity of one strain, Azospirillum lipoferum 4ABL, did not reflect the variation in exudation of soluble organic carbon, nor the variation in ability of the isolate to utilize the exudates in semi-solid media

A Gap Analysis Methodology for Collecting Crop Genepools: A Case Study with Phaseolus Beans

Background The wild relatives of crops represent a major source of valuable traits for crop improvement. These resources are threatened by habitat destruction, land use changes, and other factors, requiring their urgent collection and long-term availability for research and breeding from ex situ collections. We propose a method to identify gaps in ex situ collections (i.e. gap analysis) of crop wild relatives as a means to guide efficient and effective collecting activities. Methodology/Principal Findings The methodology prioritizes among taxa based on a combination of sampling, geographic, and environmental gaps. We apply the gap analysis methodology to wild taxa of the Phaseolus genepool. Of 85 taxa, 48 (56.5%) are assigned high priority for collecting due to lack of, or under-representation, in genebanks, 17 taxa are given medium priority for collecting, 15 low priority, and 5 species are assessed as adequately represented in ex situ collections. Gap “hotspots”, representing priority target areas for collecting, are concentrated in central Mexico, although the narrow endemic nature of a suite of priority species adds a number of specific additional regions to spatial collecting priorities. Conclusions/Significance Results of the gap analysis method mostly align very well with expert opinion of gaps in ex situ collections, with only a few exceptions. A more detailed prioritization of taxa and geographic areas for collection can be achieved by including in the analysis predictive threat factors, such as climate change or habitat destruction, or by adding additional prioritization filters, such as the degree of relatedness to cultivated species (i.e. ease of use in crop breeding). Furthermore, results for multiple crop genepools may be overlaid, which would allow a global analysis of gaps in ex situ collections of the world's plant genetic resource

Atelier sur la Fixation Biologique d`Azote du Haricot en Afrique = Workshop on Biological Nitrogen Fixation of Beans in Africa (1988, Rubona, Rwanda). Actes = Proceedings

The background and current status of research on bean N fixation in Rwanda, Burundi, Zimbabwe, Tanzania, Malawi, Uganda, and Ethiopia are summarized. The 4 stages of the methodological framework for bean N fixation research of CIAT are described: (I) (a) Rhizobium strain isolation and characterization and (b) effectiveness of the symbiosis with native strains; (II) improvement of the symbiosis through inoculation and plant breeding; (III) management of agronomic and environmental factors; and (IV) inoculant production/inoculation methods. The lab of Institut des Sciences Agronomiques du Rwanda. and the main results of on-farm trials are reported. The projects proposed for future research are included and the discussion topics of the meeting are summarized. (CIAT

Nitrogen Fixation Associated with Sorghum and Pearl Millet.AIAS occasional publication No. 12

Sorghum and pearl millet are often growth in poor fertility conditions where estimates of the N balance in crop production indicate a very efficient uptake of soil nitrate and/or an input from biological N 2-Fixation. This is being examined in long term, nitrogen –balance field experiment at ICRISAT In the second season as much as 72 kgB/ha was removed by one sorghum cultivar, grown with no N fertilizer addition in a low fertility soil(c 0.03% in the top 30 cm)...