A. P. Rodiño

Allozyme evidence supporting southwestern Europe as a secondary center of genetic diversity for the common bean.

Abstract.Genetic diversity within a common bean (Phaseolus vulgaris L.) collection, comprising 343 accessions from the Iberian Peninsula, was examined using six allozyme markers. Two major clusters corresponding to the Andean and Mesoamerican gene pools were identified. Both gene pools were characterized by specific alleles, with the former exhibiting Skdh100, Me100, Rbcs100 or 98 and Diap-1100, and the latter exhibiting Skdh103, Me100, Rbcs100 and Diap-195. Some accessions from both clusters, deviating from these allozyme patterns, exhibited Skdh100, Me100, Rbcs100 and Diap-195 or Skdh103, Me100, Rbcs100 and Diap-1100 allozyme profiles and were considered as putative hybrids.The levels of genetic variation has not been eroded since the introduction of the common bean from the American centers of domestication to the Iberian Peninsula. Instead, obvious signs of introgression between the two gene pools were observed, mainly among white-seeded genotypes. The intermediate forms adapted to the Iberian Peninsula could have emerged from initial recombination between Mesoamerican and Andean gene pools. The Iberian common bean germplasm is therefore more complex than previously thought, and contains additional diversity that remains to be explored for genetic and breeding purposes. The Iberian Peninsula could be considered as a secondary center of genetic diversity of the common bean, especially the large white-seeded genotypes.

A core collection of common bean from the Iberian peninsula

Characterization of crop germplasm from specific regions helps understand the patterns of genetic variation that facilitates further germplasm collection, characterization, management and their more efficient utilization in genetics, breeding and other studies. Common bean (Phaseolus vulgaris L.) is a traditional crop in the Iberian Peninsula (Spain and Portugal) where subsistence farmers have been growing and maintaining their own cultivars since their introductions from the Americas in the sixteenth century. Our objectives were to: (i) characterize diversity in the landraces collected from the Iberian Peninsula and (ii) form a core collection. Of 388 landraces from the major production regions characterized for 34quantitative and 13 qualitative characters, including morphological, agronomic and biochemical traits, 74.7% had an Andean origin, 16.8% a Mesoamerican origin and 8.4% had seed mixtures or were recombinants between the two gene pools. Landraces of indeterminate climbing growth habit Type IV(47.2%) and bush determinate Type I(26.4%) with large (52.9%) and medium(27.4%) seeds of white (38.8%) and cream(25.9%) colour were predominant. Similarly, the ‘T’ phaseolin pattern and common bean race Nueva Granada were the most frequent(51%). Some exceptionally large-seeded landraces of Andean (e.g., PHA-0917 with119 g 100-seed weight-1) and Mesoamerican (e.g., PHA-0399 with 66 g100-seed weight-1) were found. These and other possible recombinants between the two gene pools merit further investigation. Fifty two landraces (13%) were chosen to form a core collection representing the genetic diversity in the Iberian Peninsula.

Interactions of bush bean intercropped with field and sweet maize

Abstract Common bean, Phaseolus vulgaris L., is traditionally intercropped with maize by small-scale farmers in northwest Spain. Interactions of genotypes of beans with cropping systems and seasons were studied to determine if selection of bean in sole cropping would be a valid approach to genetic improvement for intercropping. In this experiment, 10 dry bush bean varieties were evaluated in sole cropping and intercropping with two types of maize (field and sweet maize) at two locations for 2 years. The performance of bean genotypes in each cropping system was compared with respect to developmental plant characteristics, seed yield and yield components and food quality traits. A significant bean genotype×cropping system interaction was found for period of flowering and seed yield, and there were significant differences between cropping systems for pods per plant, seed length and seed coat proportion. Intercropping with field maize reduced bean yield by 55% and intercropping with sweet maize reduced bean yield by 44%. Significant and high correlations of bean yields were obtained between sole cropping and intercropping with maize. Mean yields were used to calculate the land equivalent ratios (LERs), which averaged 1.12 for intercropping with field maize and 0.93 for intercropping with sweet maize. Specific variety combinations reached LER values greater than one. Net income was higher for some intercrop patterns than for bush bean sole crop. The most competitive bean varieties yielded the most when intercropped with maize but those varieties were not necessarily the highest yielding in sole cropping. The most competitive bean varieties were the latest to flower. The evaluation of bush bean genotypes for agronomic and food quality traits under sole cropping provides sufficient information to select varieties efficiently for the field maize-bean and sweet maize-bean intercropping systems. Greatest net income was realized when bush beans intercropped with sweet maize, provided a system with higher added value compared to intercropping with field maize.

Comparison of inhibition of N2 fixation and ureide accumulation under water deficit in four common bean genotypes of contrasting drought tolerance

BACKGROUND AND AIMS Drought is the principal constraint on world production of legume crops. There is considerable variability among genotypes in sensitivity of nitrogen fixation to drought, which has been related to accumulation of ureides in soybean. The aim of this study was to search for genotypic differences in drought sensitivity and ureide accumulation in common bean (Phaseolus vulgaris) germplasm that may be useful in the improvement of tolerance to water deficit in common bean. METHODS Changes in response to water deficit of nitrogen fixation rates, ureide content and the expression and activity of key enzymes for ureide metabolism were measured in four P. vulgaris genotypes differing in drought tolerance. KEY RESULTS A variable degree of drought-induced nitrogen fixation inhibition was found among the bean genotypes. In addition to inhibition of nitrogen fixation, there was accumulation of ureides in stems and leaves of sensitive and tolerant genotypes, although this was higher in the leaves of the most sensitive ones. In contrast, there was no accumulation of ureides in the nodules or roots of stressed plants. In addition, the level of ureides in the most sensitive genotype increased after inhibition of nitrogen fixation, suggesting that ureides originate in vegetative tissues as a response to water stress, probably mediated by the induction of allantoinase. CONCLUSIONS Variability of drought-induced inhibition of nitrogen fixation among the P. vulgaris genotypes was accompanied by subsequent accumulation of ureides in stems and leaves, but not in nodules. The results indicate that shoot ureide accumulation after prolonged exposure to drought could not be the cause of inhibition of nitrogen fixation, as has been suggested in soybean. Instead, ureides seem to be produced as part of a general response to stress, and therefore higher accumulation might correspond to higher sensitivity to the stressful conditions.

Variation for nodulation and plant yield of common bean genotypes and environmental effects on the genotype expression

Common bean symbiotic nitrogen fixation provides an ecological and economical alternative to increase bean production but it depends on soil fertility and climate conditions. The objectives of this work were to characterize common bean genotypes for their ability to establish symbiosis under controlled conditions and to study the effect of the environment on the expression of those genotypes. The experiment under controlled conditions was conducted in a greenhouse with 158 genotypes that represented the major dry bean market classes. The field experiment was carried out in six environments with 64 genotypes that were previously selected for their contrasting nodulation ability and/or root development under the controlled conditions experiment. Nodulation, plant, and grain yield data of the bean genotypes were measured in both experiments. There was a significant high variability in plant development responses among the studied genotypes associated with the rhizobial strain inoculated under controlled conditions. Two nodulation phenotypes were observed among the genotypes tested: the big-nodules phenotype (BNO) associated with almost 63% fewer nodules and 58% higher proportion of nodule biomass in the below-ground compartment than the small-nodules phenotype (SNO) with less developed aerial parts. Genotype plus genotype × environment (GGE) biplot model analysis enabled identification of the highest-yielding genotypes for the different environments. The soil chemical factors of these environments were associated with the nodule number or the biomass of the common bean genotypes. Genotypes with a BNO phenotype showed a good plant response, indicating that this phenotype may be more beneficial for plant growth and seed yield in environmental conditions that may limit nodule development. The amplitude of the genotypic variability found in this work confirms the potential for rhizobial symbiosis of adapted bean genotypes, which could constitute a preferential material for initial breeding of symbiotically active lines. The data also indicate the potential of bean breeding to identify environments containing effective strains of rhizobia essential for sustainable agriculture, improving productivity, and maintaining environmental quality.

Variation in traits affecting nodulation of common bean under intercropping with maize and sole cropping

Common bean (Phaseolus vulgaris L.), an important food crop in Europe, America, Africa and Asia, is thought to fix only small amounts of atmospheric nitrogen. It contributes significantly to the sustainability of traditional cropping systems because of the predominance of small-scale farmers who cultivate beans in those areas. The objectives of this work were to evaluate bush bean varieties under common agronomic cropping systems and to evaluate breeding lines under low N-fertility sole cropping and intercropping systems. The purpose of the study was to characterize the genotype and cropping systems variability in symbiotic and plant characters and to identify the most suitable genotypes to establish an effective symbiosis with indigenous strains of Rhizobium. No significant differences among the bush bean varieties evaluated under typical fertilization practices were observed for N2-fixation and plant traits except for seed nitrogen. Significant differences among the bean lines studied under low N-fertilization conditions were detected for plant growth,plant component and N2-fixation traits. A significant interaction of bean genotype x cropping system was found for number of nodules per plant and nodule moisture on the bush bean varieties studied, and for days to emergence, days to flowering, end of flowering, shoot length, root dry weight and shoot nitrogen on the bean lines evaluated. Nodulation parameters were correlated positively with the yield components, shoot and root parts and duration of flowering, and correlated negatively with seed crude protein, pod and seed dimensions and seed dry weight. These observations indicate that it may be possible to increase both the symbiotic N2-fixation and seed yield through plant breeding.

Improvement of large-seeded common bean cultivars under sustainable cropping systems in Spain

Approaches are needed to broaden the genetic base and improve earliness and yield potential of large-seeded beans under sustainable cropping systems. The objective of this research was to develop adapted dwarf bean populations having a commercial seed quality and yield suitable for the production in the South of Europe. The original base populations were produced from crosses between genotypes within each Mesoamerica, Nueva Granada and Peru races, and between Peru and Nueva Granada, and Mesoamerica and Nueva Granada races. Visual mass selection for plant performance was practised in the F2 and F3 generations. In the F4 and F5, single plants were harvested under two cropping systems (sole cropping and intercropping with maize). From F4, selection was based on precocity, combined with seed yield and seed commercial type. The F4:7 selected lines from each original population were compared with their parents and five checks at four environments and two cropping systems. Differences among environments, populations, parents and checks were observed for all traits. Under intercropping with maize, there was a 50% reduction in seed yield. Yield of parents and checks belonging to Andean South American races, intraracial (Nueva Granada × Nueva Granada) and interracial (Nueva Granada × Peru) populations, was higher than that of those of Middle American origin. Intraracial crosses within large-seeded Andean South American (Peru race) and Middle American gene pools (Mesoamerica race) did not produce lines yielding more than the highest yielding parent. Only two large-seeded lines selected from crosses between small- and large-seeded gene pools out-yielded the best parent and check cultivar.

Effects of planting season and plant cultivar on growth, development, and pod production in snap bean (Phaseolus vulgaris L.)

The effects of cultivar and planting season on growth development and pod yield of snap bean (Phaseolus vulgaris L.) were analysed in a 2-year, 2-location experiment in Spain. Phenology, pod production, and quality differed significantly among snap bean cultivars. Planting season had a significant effect on most pod traits except the number of seeds per pod, length, thickness, soluble solids content, tenderness, and string, and this effect varied markedly among environments. High and negative correlations for vegetative growth traits between early and late planting seasons confirmed the strong planting season influence on those traits. Fresh pod yields were highest in the early planting season, and the longer pod maturation phase could be considered to be one of the main factors. Planting of snap bean earlier in the season should thus contribute to a longer growing vegetative cycle and greater productivity than normal or summer and late autumn planting. The earliest maturing snap bean cultivars would have the highest fresh pod yields in late planting seasons, while the latest maturing snap bean cultivars would have the highest yields in early and normal planting seasons. These results will allow breeders to optimise the level of earliness for each planting season without reducing the yield. This is a key requirement for snap bean crops, and it is the first step towards selecting parental lines with stability of pod traits to be used in breeding programs for different growing areas and planting seasons.

Seedling Emergence and Phenotypic Response of Common Bean Germplasm to Different Temperatures under Controlled Conditions and in Open Field

Rapid and uniform seed germination and seedling emergence under diverse environmental conditions is a desirable characteristic for crops. Common bean genotypes (Phaseolus vulgaris L.) differ in their low temperature tolerance regarding growth and yield. Cultivars tolerant to low temperature during the germination and emergence stages and carriers of the grain quality standards demanded by consumers are needed for the success of the bean crop. The objectives of this study were (i) to screen the seedling emergence and the phenotypic response of bean germplasm under a range of temperatures in controlled chamber and field conditions to display stress-tolerant genotypes with good agronomic performances and yield potential, and (ii) to compare the emergence of bean seedlings under controlled environment and in open field conditions to assess the efficiency of genebanks standard germination tests for predicting the performance of the seeds in the field. Three trials were conducted with 28 dry bean genotypes in open field and in growth chamber under low, moderate, and warm temperature. Morpho-agronomic data were used to evaluate the phenotypic performance of the different genotypes. Cool temperatures resulted in a reduction of the rate of emergence in the bean genotypes, however, emergence and early growth of bean could be under different genetic control and these processes need further research to be suitably modeled. Nine groups arose from the Principal Component Analysis (PCA) representing variation in emergence time and proportion of emergence in the controlled chamber and in the open field indicating a trend to lower emergence in large and extra-large seeded genotypes. Screening of seedling emergence and phenotypic response of the bean germplasm under a range of temperatures in controlled growth chambers and under field conditions showed several genotypes, as landraces 272, 501, 593, and the cultivar Borlotto, with stress-tolerance at emergence, and high yield potential that could be valuable genetic material for breeding programs. Additionally, the potential genetic erosion in genebanks was assessed. Regarding bean commercial traits, under low temperature at sowing time seed reached larger size, and crop yield was higher compared to warmer temperatures at the sowing time. Therefore, early sowing of bean is strongly recommended.