Phaseolus albicarminus (Leguminosae, Phaseoleae), a new wild bean species from the subhumid forests of southern central Costa Rica

During a search for populations of wild common bean, namely south of the Central Valley of Costa Rica, a new bean species, Phaseolus albicarminus, has been found on the slope of a mountainous range named Cerros Llano Bonito in the western part of Talamanca range, where it appears to be endemic. Its main morphological features are: short pseudoracemes with four small deltoid primary bracts, small early caducous deltoid bracteoles, calyx lobes reduced to two lips, white wings contrasting with carmine purple inner face of standard, and smoothly curved 3–4 seeded pods with prow-shaped beak. The differences with apparently closely related species, P. hygrophilus and P. angucianae, are: in primary bracts (orbicular versus oval acuminate), larger bracteoles (cordate versus rounded), inner face of standard (pale pink to white versus purple), lower calyx lobes (rounded versus triangular), and pod dorsal suture (straight versus sigmoid), respectively. The fact that to date only three populations of P. albicarminus are known from the same small area of Costa Rica, calls for monitoring its conservation status. This new species is tentatively assigned to the section Brevilegumeni which seems well represented in Costa Rica (with five out of six taxa).

Diversity and phenotypic analyses of salt- and heat-tolerant wild bean Phaseolus filiformis rhizobia native of a sand beach in Baja California and description of Ensifer aridi sp. nov.

In northern Mexico, aridity, salinity and high temperatures limit areas that can be cultivated. To investigate the nature of nitrogen-fixing symbionts of Phaseolus filiformis, an adapted wild bean species native to this region, their phylogenies were inferred by MLSA. Most rhizobia recovered belong to the proposed new species Ensifer aridi. Phylogenetic analyses of nodC and nifH show that Mexican isolates carry symbiotic genes acquired through horizontal gene transfer that are divergent from those previously characterized among bean symbionts. These strains are salt tolerant, able to grow in alkaline conditions, high temperatures, and capable of utilizing a wide range of carbohydrates and organic acids as carbon sources for growth. This study improves the knowledge on diversity, geographic distribution and evolution of bean-nodulating rhizobia in Mexico and further enlarges the spectrum of microsymbiont with which Phaseolus species can interact with, including cultivated bean varieties, notably under stressed environments. Here, the species Ensifer aridi sp. nov. is proposed as strain type of the Moroccan isolate LMR001T (= LMG 31426T; = HAMBI 3707T) recovered from desert sand dune.

Conservation status of eleven wild bean (Phaseolus spp. Fabaceae) species in northeastern Mexico

Rare and endemic plants, such as the wild species of Phaseolus (Fabaceae) in northeastern Mexico, deserve high priority in conservation efforts because of their uniqueness and usefulness as plant genetic resource. This is particularly important because during the last decades, some of these species have become endangered because of anthropogenic and natural factors. The study aimed to determine the current conservation status of 11 reported wild bean species in northeastern Mexico, using wild bean data from 77 expeditions to the states of Nuevo León and Tamaulipas during the period 1869-2013.The conservation status of the different species was determined according to the Official Mexican Standard NOM-059-SEMARNAT-2010. The categories of risk were based on four indicators: amplitude of distribution, habitat status, biological vulnerability and impact of human activity. The following eight wild Phaseolus species are not at risk of extinction: P. albiflorus, P. glabellus, P. leptostachyus, P. maculatifolius, P. neglectus, P. pedicellatus, P. vulgaris and P. zimapanensis. On the other hand, P. altimontanus Freytag & Debouck is categorized as threatened; P. novoleonensis Debouck, in danger of extinction; and P. plagiocylix Harms, possibly extinct. Current in situ and ex situ conservation programs need to be strengthened and expanded for the medium- and long-term protection of wild bean species in northeastern Mexico.

Signatures of Environmental Adaptation During Range Expansion of Wild Common Bean (Phaseolus vulgaris)

Landscape genomics integrates population genetics with landscape ecology, allowing the identification of putative molecular determinants involved in environmental adaptation across the natural geographic and ecological range of populations. Wild Phaseolus vulgaris, the progenitor of common bean (P. vulgaris), has a remarkably extended distribution over 10,000 km from northern Mexico to northwestern Argentina. Earlier research has shown that this distribution represents a range expansion from Mesoamerica to the southern Andes through several discrete migration events and that the species colonized areas with different temperature and rainfall compared to its core area of origin. Thus, this species provides an opportunity to examine to what extent adaptation of a species can be broadened or, conversely, ecological or geographical distribution can be limited by inherent adaptedness. In the current study, we applied a landscape genomics approach to a collection of 246 wild common bean accessions representative of its broad geographical and climatic distribution and genotyped for ∼20K SNPs. We applied two different but complementary approaches for identifying loci putatively involved in environmental adaptation: i) an outlier-detection method that identifies loci showing strong differentiation between sub-populations; ii) an association method based on the identification of loci associated with bio-climatic variables. This integrated approach allowed the identification of several genes showing signature of selection across the different natural sub-populations of this species, as well as genes associated with specific bio-climatic variables related to temperature and precipitation. The current study demonstrates the feasibility of landscape genomics approach for a preliminary identification of specific populations and novel candidate genes involved in environmental adaptation in P. vulgaris. As a resource for broadening the genetic diversity of the domesticated gene pool of this species, the genes identified constitute potential molecular markers and introgression targets for the breeding improvement of domesticated common bean.Author SummaryThe ancestral form of common bean has an unusually large distribution in the Americas, extending over 10,000 km from ∼35° N. Lat. to ∼35° S. Lat. This wide distribution results from discrete long-range dissemination events to the Andes region from the original environments in Mesoamerica. It also suggests adaptation to new environments that are distinct from those encountered in Mesoamerica. In this research, we identified genes that may be involved in adaptation to climate variables in these new environments using two methods. A first method – outlier detection – was used to identify genome regions that differentiated the wild bean groups in the Andes resulting from discrete dissemination events among themselves and the different groups in Mesoamerica. The second method – genome-wide association – was used to identify candidate genome regions correlated with these same variables across the entire distribution from Mesoamerica to the southern Andes. The two methods identified two sets of candidate genes, several of which were related to the water status of plants, and illustrate how the genetic architecture of adaptation following long-range dissemination. This study provides sets of candidate genes as well as candidate wild bean populations that need to be corroborated for their use in increasing the water use efficiency of domesticated beans.

Phaseolus angucianae (Leguminosae: Phaseoleae), a new bean species from Fila Cruces of southeastern Costa Rica

A new wild bean found in the mountainous range “Fila Cruces” of southeastern Costa Rica is described. To date, only four populations are known from different sites on the slopes of Cerro Anguciana and “Fila Cruces” where it seems to be endemic. The differences (slender curved racemes, small oval acuminate primary and pedicelar bracts, lilac inner face of standard, white wings) are presented with closely related species such as P. hygrophilus and P. oligospermus of the section Brevilegumeni to which it may belong.

Evidence for genotypic differences among elite lines of common bean in the ability to remobilize photosynthate to increase yield under drought

SUMMARYCommon bean (Phaseolus vulgaris L.) is the most important food legume for human consumption. Drought stress is the major abiotic stress limitation of bean yields in smallholder farming systems worldwide. The current work aimed to determine the role of enhanced photosynthate mobilization to improve adaptation to intermittent and terminal drought stress and to identify a few key adaptive traits that can be used for developing drought-resistant genotypes. Field studies were conducted over three seasons at Centro Internacional de Agricultura Tropical, Palmira, Colombia to determine genotypic differences in adaptation to intermittent (two seasons) and terminal (one season) drought stress compared with irrigated conditions. A set of 36 genotypes, including 33 common bean, two wild bean and one cowpea were evaluated using a 6 × 6 lattice design under irrigated and rainfed field conditions. Three common bean elite lines (NCB 226, SEN 56, SER 125) were identified with superior levels of adaptation to both intermittent and terminal drought stress conditions. The greater performance of these lines under drought stress was associated with their ability to remobilize photosynthate to increase grain yield based on higher values of harvest index, pod harvest index, leaf area index and canopy biomass. Two wild bean germplasm accessions (G 19902, G 24390) showed very poor adaptation to both types of drought stress. One small-seeded black line (NCB 226) was superior in combining greater values of canopy biomass with greater ability to mobilize photosynthates to grain under both types of drought stress. Two small-seeded red lines (SER 78, SER 125) seem to combine the desirable traits of enhanced mobilization of photosynthates to seed with effective use of water through canopy cooling under terminal drought stress. Pod harvest index showed significant positive association with grain yield under both types of drought stress and this trait can be used by breeders as an additional selection method to grain yield in evaluation of breeding populations for both types of drought stress.

Complete Genome Sequence of Bradyrhizobium sp. Strain CCGE-LA001, Isolated from Field Nodules of the Enigmatic Wild Bean Phaseolus microcarpus

We present the complete genome sequence of Bradyrhizobium sp. strain CCGE-LA001, a nitrogen-fixing bacterium isolated from nodules of Phaseolus microcarpus. Strain CCGE-LA001 represents the first sequenced bradyrhizobial strain obtained from a wild Phaseolus sp. Its genome revealed a large and novel symbiotic island.