Tepary bean (Phaseolus acutifolius A. Gray) is a dry-land crop species that originated in the deserts of Mexico and the south-western United States and therefore is proposed as a source of drought and salt tolerance for related species and for production in marginal rainfall areas. Few genetic tools have been developed or tested for tepary bean but microsatellites from common bean are an obvious choice for diversity analysis in the crop. The first goal of this study was to validate a set of gene-derived and non-gene simple sequence repeat or microsatellite markers from common bean in tepary bean cultivars and wild relative accessions. The second and more extensive objective of this study was to evaluate the genetic diversity and population structure of the tepary bean accessions to determine if leaf-morphology variants are valid as separate sub-groups of wild tepary beans; if P. parvifolius exist as a separate variants or species; and if cultivated tepary beans originated from one domestication event or several events. Our analysis of 140 tepary bean genotypes showed that a single domestication was likely as the cultivars were most closely related to accessions from Sinaloa and northern Mexico and that diversity was much higher in the wild genotypes compared to the cultivated ones. Other results were that P. parvifolius was classified as a separate species by population structure analysis while the variants P. acutifolius var. acutifolius and var. tenuifolius were admixed and inter-crossed. P. latifolius is not a valid species or variant of P. acutifolius but represents a group of cultivars within tepary bean. This is the first analysis of microsatellite diversity in tepary beans and has implications for breeding and conservation of this crop and its wild relatives.

Tepary bean (Phaseolus acutifolius A. Gray), a low‐rainfall crop from the Sonoran desert, is thought to have low diversity; however, its relationship to its wild relatives is poorly understood. In this study, a total of 147 accessions were evaluated by means of AFLP markers to (i) establish the taxonomic relationships within and between the Acutifolii and other sections and (ii) to understand tepary bean domestication. The structure among the 10 species analyzed corresponded to currently recognized sections: Phaseolus glabelus and Phaseolus lunatus L. were equally distant from the phaseoli and coccinei sections and the rugosi section included Phaseolus angustissimus, Phaseolus carteri and Phaseolus filiformis We also compared the gene pool differences for common (Phaseolus vulgaris L.) and lima bean (P. lunatus) with differences observed within the Acutifolii section. The wild relative, Phaseolus parvifolius persistently separated from the bulk of both cultivated and wild tepary, validating its status as a separate species; while within the wild accessions, there was no obvious grouping along the foliar variants. On the basis of our results, one of two Mexican states, Sinaloa or Jalisco, could have been the domestication center, although the hypothesis of multiple domestication events cannot be discarded. Furthermore, domesticated tepary bean was most likely derived from wild genotypes of var. acutifolius rather than genotypes of var. tenuifolius

Some of the major impacts of climate change are expected in regions where drought stress is already an issue. Grain legumes are generally drought susceptible. However, tepary bean and its wild relatives within Phaseolus acutifolius or P. parvifolius are from arid areas between Mexico and the United States. Therefore, we hypothesize that these bean accessions have diversity signals indicative of adaptation to drought at key candidate genes such as: Asr2, Dreb2B, and ERECTA. By sequencing alleles of these genes and comparing to estimates of drought tolerance indices from climate data for the collection site of geo-referenced, tepary bean accessions, we determined the genotype x environmental association (GEA) of each gene. Diversity analysis found that cultivated and wild P. acutifolius were intermingled with var. tenuifolius and P. parvifolius, signifying that allele diversity was ample in the wild and cultivated clade over a broad sense (sensu lato) evaluation. Genes Dreb2B and ERECTA harbored signatures of directional selection, represented by six SNPs correlated with the environmental drought indices. This suggests that wild tepary bean is a reservoir of novel alleles at genes for drought tolerance, as expected for a species that originated in arid environments. Our study corroborated that candidate gene approach was effective for marker validation across a broad genetic base of wild tepary accessions.

Congruity and recurrent backcross interspecific hybrids between common bean (Phaseolus vulgaris L.) and tepary bean (P. acutifolius A. Gray) were compared for the amount of introgression occurring between genomes by amplified fragment length polymorphism (AFLP) markers. A total of 60 genotypes were analyzed of which 34 were obtained by congruity backcrossing, four by single backcrossing and 14 by recurrent backcrossing, with parental and representative tepary and common bean genotypes used as controls. The level of introgression of tepary bean marker bands into the common bean genome background was higher in the congruity backcross lines than in the recurrent backcross derived genotypes. Congruity backcross lines derived from five cycles of interspecific hybridization showed an average introgression of 8.8% of AFLP bands while lines derived from a single backcross with the same parents showed an average introgression of only 5.2% of the bands. For both types of backcrossing, these levels of introgression were significantly below those expected. A multiple correspondence analysis showed three major clusters consisting of the common bean accessions and interspecifics with low rates of introgression, an intermediate group of interspecific congruity backcross lines with higher rates of introgression and a more distant group that included all the tepary bean accessions. These results suggest that congruity backcrossing can be used to increase introgression rates between the species and to transfer favorable oligogenic traits from tepary bean to common bean but that levels of introgression between the species remains low.

tepary bean has a number of favorable characteristics that makes it a potentially useful donor parent in crosses Congruity and recurrent backcross interspecific hybrids between with common bean. First, tepary bean has a number of common bean (Phaseolus vulgaris L.) and tepary bean (P. acutifolius A. Gray) were compared for the amount of introgression occurring resistances to diseases and pests that are not found in between genomes by amplified fragment length polymorphism common bean (Pratt and Nabhan, 1988;Honma, 1956; (AFLP) markers. A total of 60 genotypes were analyzed of which 34 Singh and Muñ oz, 1999;Urrea et al., 1999). Second, were obtained by congruity backcrossing, four by single backcrossing tepary bean has a higher regeneration capacity in tissue and 14 by recurrent backcrossing, with parental and representative culture than common bean (Dillen et al., 1996(Dillen et al., , 1997, tepary and common bean genotypes used as controls. The level of and third it has elevated levels of tolerance to high introgression of tepary bean marker bands into the common bean temperatures, drought, and salinity (Miklas et al., 1994; genome background was higher in the congruity backcross lines than Lin and Markhart, 1996). Of the positive traits found in the recurrent backcross derived genotypes. Congruity backcross in tepary bean, only resistance to the common bacterial lines derived from five cycles of interspecific hybridization showed blight pathogen [Xanthomonas axonopodis pv. phaseoli an average introgression of 8.8% of AFLP bands while lines derived from a single backcross with the same parents showed an average (Smith) Dye] has been transferred successfully from introgression of only 5.2% of the bands. For both types of backcross-tepary bean to cultivars and advanced breeding lines of ing, these levels of introgression were significantly below those excommon bean (Parker and Michaels, 1986, Singh and pected. A multiple correspondence analysis showed three major clus-Muñ oz, 1999). ters consisting of the common bean accessions and interspecifics withInterspecific hybrids between common and tepary low rates of introgression, an intermediate group of interspecific conbean were first obtained with a great deal of effort by gruity backcross lines with higher rates of introgression and a more Honma (1956) for a few genotypes, including a Great distant group that included all the tepary bean accessions. These Northern line and four tepary bean accessions. Haghighi results suggest that congruity backcrossing can be used to increase et al. (1984) later used three genotypes from each speintrogression rates between the species and to transfer favorable oligocies to obtain simple cross hybrids. Waines et al. (1988) genic traits from tepary bean to common bean but that levels of introgression between the species remains low.

The lack of good quality planting material of farmers' cassava varieties, produced locally and at low cost, is a major constraint limiting the expansion of cassava production in Colombia. This article describes the adaptation of conventional cassava propagation to a low-input scheme for rural tissue-culture multiplication, developed and run by small, resource-poor farmers (referred in this article as an informalfarmers' seed production system). Developed through a two-phase participatory process by a group of women farmers, a non-governmental organization and International Center for Tropical Agriculture scientists in a farmers' community in the hillsides of southern Colombia, the project resulted in alternative, economical and readily available sources of tissue-culture material and equipment. Rates of multiplication achieved with the system were as high as with conventional tissue-culture procedures.

Tepary bean (Phaseolus acutifolius A. Gray) is more heat and drought tolerant than common bean (P. vulgaris L.). Four hundred mutant lines of two tepary accessions (G40068 and G40159) were generated by ethyl methane sulfonate (EMS) treatment. In preliminary studies of the M5 mutant lines under abiotic stress, three mutant lines (CMT 38, CMT 109, CMT 187) were selected from six mutated lines based on morpho-physiological traits and superior yield and advanced to the M6 generation. The M6 mutant lines were uniform and genetically stable. These mutant lines and their original (M0) parents were evaluated for heat and drought tolerance under greenhouse conditions. Their performance was evaluated for morpho-physiological attributes, seed yield and yield components. Under high temperature and drought conditions, the CMT 38 mutant (M6 line) and its original tepary (M0) accession (G40068) showed greater values of pod biomass, pod number and 100-seed biomass than the other lines tested. The CMT 109 and CMT 187 mutant lines and their G40159 original accession (M0) also showed the highest value of seed number under high temperature and drought conditions. This suggests that the previous screening performed during the population advancement of these mutant lines, based on morphological traits like growth habit, was not detrimental to the yield variables evaluated here. Under combined heat and drought conditions, different parameters could be incorporated into tepary breeding programmes, as selection criteria to screen genotypes for tolerance to heat and drought stress. These parameters included: chlorophyll (SPAD) readings, seed biomass, 100-seed biomass and seed number because they explain the observed variance in the principal component analysis. Two additional traits (root biomass and stem diameter) were also identified as useful attributes, based on univariate analysis. The mutant lines evaluated here offer potential for further improvement of tepary bean to high temperature and drought

Heat stress is a major limitation to grain yield in common bean (Phaseolus vulgaris L.). Tepary bean (Phaseolus acutifolius A. Gray) is better adapted to heat stress than common bean. Ten tepary bean accessions, four common bean genotypes and four interspecific lines involving P. vulgaris and P. acutufolius, P. coccineus and P. dumosus were evaluated for tolerance to heat stress conditions induced under greenhouse conditions and these were compared to plants grown under ambient temperatures. The high temperature treatment was 29 ±5 °C during the day and was >24 °C (up to 27 °C) during the night, while the ambient temperature (AT) treatment was 25 ±5 °C during the day and 19± 2 °C at night. The genotypic differences were evaluated for morpho-physiological characteristics of shoot and root and also yield components. The Genotype and Genotype × Temperature interactions were significant for all shoot and root morpho-physiological characteristics evaluated. Higher temperature (HT) significantly affected leaf photosynthetic efficiency, total chlorophyll content, and stomatal conductance. The effect was positive or negative, depending on the genotypes. Tepary accessions showed reduced total chlorophyll content, while common bean genotypes and the interspecific lines were less affected. Tepary accessions also showed reduced stomatal conductance, but increased leaf photosynthetic efficiency under HT. Common bean genotypes increased stomatal conductance and decreased leaf photosynthetic efficiency. High temperature decreased total root length, specific root length and pod biomass compared to ambient conditions, but there was no marked effect on pollen viability of the tested genotypes. The superior adaptation of tepary germplasm accessions to high temperature is attributed to their ability to regulate stomatal opening and photosynthetic efficiency, together with a superior ability to remobilize photosynthates from older leaves to pods during physiological maturity