Aims Common bean is a major source of protein for many people worldwide. However, the crop is often subjected to drought conditions and its advantage in undertaking symbiotic nitrogen fixation can be ...severely decreased. The primary objective of this study was to compare the resistance of nitrogen fixation of 12 selected genotypes to soil drying. Methods Twelve common bean genotypes of diverse genetic background were compared. Plants were grown in pots and subjected to soil drying over about 2 weeks. Nitrogen fixation was measured daily using a flow-through acetylene reduction technique. The plants were exposed to acetylene for only a short time period allowing repeated measures. The acetylene reduction rate of plants on drying soil was normalized against the rates measured for well-watered plants. Results Substantial variability was identified among genotypes in the threshold soil water content at which nitrogen fixation was observed to decrease. Genotypes SER 16, SXB 412, NCB 226, and Calima were found to have the greatest delay in their decrease in nitrogen fixation rates based on soil water content. These four genotypes expressed substantial tolerance of nitrogen fixation to soil drying. These experiments also resulted in data on the threshold soil water contents at which transpiration rates decreased. A decrease in transpiration rates at high soil water contents is potentially advantageous since it allows soil water conservation for use as the severity of the drought increases. There was a general trend of those genotypes with sustained nitrogen fixation rates to low soil water contents also expressing decreased transpiration rates at high soil water contents. Conclusions This study identified genetic variation among common bean genotypes in their response of nitrogen fixation and transpiration to soil drying. Five genotypes (SER 16, SXB 412, NCB 226, Calima, and SEA 5) expressed the desired traits for water-limited conditions, which might be exploited in breeding efforts.
BACKGROUND AND AIMS: Aluminium (Al) resistance in common bean is known to be due to exudation of citrate from the root after a lag phase, indicating the induction of gene transcription and protein ...synthesis. The aims of this study were to identify Al-induced differentially expressed genes and to analyse the expression of candidate genes conferring Al resistance in bean. METHODS: The suppression subtractive hybridization (SSH) method was used to identify differentially expressed genes in an Al-resistant bean genotype ('Quimbaya') during the induction period. Using quantitative real-time PCR the expression patterns of selected genes were compared between an Al-resistant and an Al-sensitive genotype ('VAX 1') treated with Al for up to 24 h. KEY RESULTS: Short-term Al treatment resulted in up-regulation of stress-induced genes and down-regulation of genes involved in metabolism. However, the expressions of genes encoding enzymes involved in citrate metabolism were not significantly affected by Al. Al treatment dramatically increased the expression of common bean expressed sequence tags belonging to the citrate transporter gene family MATE (multidrug and toxin extrusion family protein) in both the Al-resistant and -sensitive genotype in close agreement with Al-induced citrate exudation. CONCLUSIONS: The expression of a citrate transporter MATE gene is crucial for citrate exudation in common bean. However, although the expression of the citrate transporter is a prerequisite for citrate exudation, genotypic Al resistance in common bean particularly depends on the capacity to sustain the synthesis of citrate for maintaining the cytosolic citrate pool that enables exudation.
A decline in pasture productivity is often associated with a reduction in vegetative cover. We hypothesize that nitrogen (N) in urine deposited by grazing cattle on degraded pastures, with low ...vegetative cover, is highly susceptible to losses. Here, we quantified the magnitude of urine-based nitrous oxide (N
O) lost from soil under paired degraded (low vegetative cover) and non-degraded (adequate vegetative cover) pastures across five countries of the Latin America and the Caribbean (LAC) region and estimated urine-N emission factors. Soil N
O emissions from simulated cattle urine patches were quantified with closed static chambers and gas chromatography. At the regional level, rainy season cumulative N
O emissions (3.31 versus 1.91 kg N
O-N ha
) and emission factors (0.42 versus 0.18%) were higher for low vegetative cover compared to adequate vegetative cover pastures. Findings indicate that under rainy season conditions, adequate vegetative cover through proper pasture management could help reduce urine-induced N
O emissions from grazed pastures.
Many common bean (Phaseolus vulgaris L.) plants cultivated in areas of the world with acidic soils exhibit difficulties adapting to low phosphorus (P) availability, along with aluminum (Al) toxicity, ...causing yield loss. The objective of this study was to evaluate the influence of an increase in P supply level on the agronomic, phenological, and physiological performance of two common bean breeding lines grown in acidic soil, with low fertility and under high temperature conditions, in a screenhouse. A randomized complete block (RCB) design was used under a factorial arrangement (five levels of P × 2 genotypes) for a total of 10 treatments with four replications. The factors considered in the experiment were: (i) five P supply levels (kg ha−1): four levels of P0, P15, P30, and P45 through the application of rock phosphate (RP), and one P level supplied through the application of organic matter (PSOM) corresponding to 25 kg P ha−1 (P25); and (ii) two advanced bean lines (BFS 10 and SEF10). Both bean lines were grown under the combined stress conditions of high temperatures (day and night maximum temperatures of 42.5 °C/31.1 °C, respectively) and acidic soil. By increasing the supply of P, a significant effect was found, indicating an increase in the growth and development of different vegetative organs, as well as physiological efficiency in photosynthesis and photosynthate remobilization, which resulted in higher grain yield in both bean lines evaluated (BFS 10 and SEF10). The adaptive responses of the two bean lines were found to be related to phenological adjustments (days to flowering and physiological maturity; stomatal development), as well as to heat dissipation strategies in the form of heat (NPQ) or unregulated energy (qN) that contributed to greater agronomic performance. We found that, to some extent, increased P supply alleviated the negative effects of high temperature on the growth and development of the reproductive organs of bean lines. Both bean lines (BFS 10 and SEF 10) showed adaptive attributes suited to the combined stress conditions of high temperature and acidic soil, and these two lines can serve as useful parents in a bean breeding program to develop multiple stress tolerant cultivars.
Plant root development can be largely affected through the association of roots with plant growth-promoting rhizobacteria (PGPR). However, little is known about the identity of plant genes enabling ...such PGPR-plant root associations. Differences in the responsiveness to PGPR among cultivars suggest genetic variation for this trait within germplasm. In this study, two genotypes of common bean (Phaseolus vulgaris L.), BAT477 and DOR364, were identified showing contrasting responsiveness in root development to inoculation with the PGPR Azospirillum brasilense Sp245. Inoculation with an A. brasilense Sp245 mutant strain strongly reduced in auxin biosynthesis or addition of increasing concentrations of exogenous auxin to the plant growth medium, indicated that the differential response to A. brasilense Sp245 among the bean genotypes is related to a differential response to the bacterial produced auxin. To further assess the role of the plant host in root responsiveness, a population of Recombinant Inbred Lines (RILs) of the DOR364xBAT477 cross was used to evaluate the efficacy of exogenous auxin on root development. We detected significant phenotypic variation among the RILs for basal root formation during germination upon addition of auxin to the growth medium. Genetic analysis revealed two quantitative trait loci (QTLs) associated with basal root responsiveness to auxin of which one explained 36% of the phenotypic variation among the RILs. This latter QTL mapped to the same location as a QTL for root tip formation at low P, suggesting that the host effect on root responsiveness to IAA interacts with specific root development. Also, significant correlations between basal root responsiveness to auxin and growth, root tips and root dry weight at low P were identified. To our knowledge, this is the first report on QTL detection for root responsiveness to auxin.
This study was planned to analyse the basis that make Brachiaria species with greater feeding value than Napier grass (Pennisetum purpureum) for lactating dairy cows. Forty lactating crossbred cows ...were stall-fed on Brachiariabrizantha cv. Piatá or Napier grass cv. French Cameroon supplemented (mixed on fresh matter basis) or unsupplemented with Desmodium distortum, a forage legume. All cows were fed on fresh matter basis under small-holder farming conditions. Results showed that B. brizantha cv. Piatá had higher contents of dry matter (DM), crude protein (CP) and organic matter (OM), but lower contents of neutral detergent fibre (NDF) and acid detergent fibre (ADF) than Napier grass (P < 0.001). The legume supplementation increased intakes of CP and metabolizable energy (ME; P < 0.001), with higher effect on cows fed B. brizantha cv. Piatá than on cows fed Napier grass. Average daily milk yield was lower on diets based on Napier grass than those based on B. brizantha cv. Piatá (P < 0.001). The retention time of the particle phase of digesta in the digestive tract was longer on Napier grass (83.1 h) than on B. brizantha cv. Piatá (62.8 h) (P < 0.05). It was concluded that in dairy cows, legume supplementation of B. brizantha cv. Piatá increases nutrient intake, hence resulting in higher milk yields than supplementation of Napier grass.
Common bean (
L.) is sensitive to different types of abiotic stresses (drought, high temperature, low soil fertility, and acid soil), and this may limit its adaptation and consequently to its yield ...under stress. Because of this, a sister species, tepary bean (
A. Gray), has recently gained attention in breeding for improved abiotic stress tolerance in common bean. In this study, we evaluated the adaptation of 302 accessions of tepary bean (
A. Gray) and its wild relatives (grouped in four types of tepary bean genetic resource: cultivated, acutifolius regressive, acutifolius wild, tenuifolius wild) when grown under high temperature and acid soil conditions with aluminum toxicity in the Amazon region of Colombia. Our objective was to determine differences among four types of tepary bean genetic resource in their morpho-phenological, agronomic, and physiological responses to combined high temperature and acid soil stress conditions. We found that cultivated
var acutifolius presented a greater number of pods per plant, as well as larger seeds and a greater number of seeds per pod. Some traits, such as root biomass, days to flowering and physiological maturity, specific leaf area, and stomatal density, showed significant differences between types of tepary bean genetic resource, probably contributing to difference in adaptation to combined stress conditions of high temperature and acid soil conditions. The photochemical quenching (qP) was higher in cultivated
var. acutifolius, while energy dissipation by non-photochemical quenching (NPQ) in the form of heat and the coefficient of non-photochemical dissipation (qN) were higher in acutifolius regressive and tenuifolius wild accessions. We have identified 6 accessions of cultivated and 19 accessions of tenuifolius wild that exhibited grain yields above 1800 kg ha
. These accessions could be suitable to use as parents to improve dry seed production of tepary bean under combined stress conditions of high temperature and acid soil.
•New method was used to estimate symbiotic nitrogen fixation ability in bean.•Phenotypic variation in nitrogen fixation was observed under drought stress.•Four lines were superior in their ability to ...fix nitrogen under drought stress.•Several lines were found to combine drought resistance with ability to fix nitrogen.
Common bean (Phaseolus vulgaris L.) is the most important food legume, cultivated by small farmers and is usually exposed to unfavorable conditions with minimum use of inputs. Drought and low soil fertility, especially phosphorus and nitrogen (N) deficiencies, are major limitations to bean yield in smallholder systems. Beans can derive part of their required N from the atmosphere through symbiotic nitrogen fixation (SNF). Drought stress severely limits SNF ability of plants. The main objectives of this study were to: (i) test and validate the use of 15N natural abundance in grain to quantify phenotypic differences in SNF ability for its implementation in breeding programs of common bean with bush growth habit aiming to improve SNF, and (ii) quantify phenotypic differences in SNF under drought to identify superior genotypes that could serve as parents. Field studies were conducted at CIAT-Palmira, Colombia using a set of 36 bean genotypes belonging to the Middle American gene pool for evaluation in two seasons with two levels of water supply (irrigated and drought stress). We used 15N natural abundance method to compare SNF ability estimated from shoot tissue sampled at mid-pod filling growth stage vs. grain tissue sampled at harvest. Our results showed positive and significant correlation between nitrogen derived from the atmosphere (%Ndfa) estimated using shoot tissue at mid-pod filling and %Ndfa estimated using grain tissue at harvest. Both methods showed phenotypic variability in SNF ability under both drought and irrigated conditions and a significant reduction in SNF ability was observed under drought stress. We suggest that the method of estimating Ndfa using grain tissue (Ndfa-G) could be applied in bean breeding programs to improve SNF ability. Using this method of Ndfa-G, we identified four bean lines (RCB 593, SEA 15, NCB 226 and BFS 29) that combine greater SNF ability with greater grain yield under drought stress and these could serve as potential parents to further improve SNF ability of common bean.
Drought is a major constraint to common bean (
Phaseolus vulgaris
L.) production, especially in developing countries where irrigation for the crop is infrequent. The Mesoamerican genepool is the most ...widely grown subdivision of common beans that include small red, small cream and black seeded varieties. The objective of this study was to develop a reliable genetic map for a Mesoamerican × Mesoamerican drought tolerant × susceptible cross and to use this map to analyze the inheritance of yield traits under drought and fully irrigated conditions over 3 years of experiments. The source of drought tolerance used in the cross was the cream-seeded advanced line BAT477 crossed with the small red variety DOR364 and the population was made up of recombinant inbred lines in the F5 generation. Quantitative trait loci were detected by composite interval mapping for the traits of overall seed yield, yield per day, 100 seed weight, days to flowering and days to maturity for each field environment consisting of two treatments (irrigated and rainfed) and lattice design experiments with three repetitions for a total of six environments. The genetic map based on amplified fragment length polymorphism and random amplified polymorphic DNA markers was anchored with 60 simple sequence repeat (SSR) markers and had a total map length of 1,087.5 cM across 11 linkage groups covering the whole common bean genome with saturation of one marker every 5.9 cM. Gaps for the genetic map existed on linkage groups b03, b09 and b11 but overall there were only nine gaps larger than 15 cM. All traits were inherited quantitatively, with the greatest number for seed weight followed by yield per day, yield per se, days to flowering and days to maturity. The relevance of these results for breeding common beans is discussed in particular in the light of crop improvement for drought tolerance in the Mesoamerican genepool.
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