Possibly Involving P. Costaricensis and P. Dumosus in Humid Montane Forest
Total Page：16
File Type：pdf, Size：1020Kb
Figure 1 - Natural hybrid (# 3314) possibly involving P. costaricensis and P. dumosus in humid montane forest. 2 Report on Bioprospecting for Phaseolus germplasm in Costa Rica, November 2016. D.G. Debouck R. Araya Villalobos, N. Chaves Barrantes Genetic Resources Program Agricultural Experimental Station ‘Fabio Baudrit Moreno’ Centro Internacional de Agricultura Tropical Universidad de Costa Rica Cali, COLOMBIA San José, COSTA RICA [email protected] [email protected] ; [email protected] Cooperative work between the Estación Experimental Agrícola ‘Fabio Baudrit Moreno’ of the Universidad de Costa Rica (UCR), and the International Center for Tropical Agriculture (CIAT), with the support of the Global Crop Diversity Trust (GCDT), in the framework of the Crop Wild Relatives Project. Introduction Wild relatives of crops have often been reported as sources of useful genetic variation in crop improvement when this variation is absent in the crops themselves (Hajjar & Hodgkin 2007; Harlan 1978). The reason for this situation might be two-fold: i) the fact that the major part of the original genetic variation has not been included in the cultivated genetic stock during the domestication process, and ii) the relative shorter duration in existence of the cultivated forms as compared to their wild relatives. Common bean, Phaseolus vulgaris L., provides a good example of this double situation. On the one hand, all cultivated varieties of common bean in Central America, even though they diversify into three races (Singh et al. 1991), originate from a single domestication area in western Mexico (Chacón-Sánchez et al. 2005; Kwak et al. 2009). All other populations have been left as part of the natural wild flora not being considered by people except when used as a famine food when local communities harvest the green pods (Araya-Villalobos et al. 2001; Gentry 1969). On the other hand, available archaeological evidence let to infer a relatively late domestication in Central America – some 2,000 years before present (bp) (Kaplan & Lynch 1999) – as compared to the central Andean region (twice as old: Kaplan & Lynch 1999). Dates of 6-8,000 years bp in Central America have been reported for maize (Piperno & Flannery 2001) and squash (Piperno et al. 2002). Genetic data however show the beginning of a bottleneck associated with domestication in Mesoamerica some 8,200 years bp (Mamidi et al. 2011). The species P. vulgaris itself as wild might have an age of 1-2 million years (Chacón-Sánchez et al. 2007; Delgado-Salinas et al. 2006), and therefore has accumulated much more genetic variation as wild as compared to the cultivated forms. The wider genetic variation found in wild forms of common bean results in a higher probability to find traits of interest, for example in the amount of storage proteins in the seed (Baldi & Salamini 1973). The long presence of wild beans in their original habitats has resulted in different adaptation of photosynthetic traits with significant differences between the Mesoamerican and the Andean wild forms (González-Mejía et al. 1995; Lynch et al. 1992). Resistance to bruchids – insects that destroy the bean seeds in storage – is not found in cultivated forms (Schoonhoven & Cardona 1982), but in wild forms (Cardona & Kornegay 1989). The explanation is that domestication taking place in western Jalisco, Mexico (Chacón-Sánchez et al. 2005; Kwak et al. 2009) did not include the resistant wild forms which have a small geographic range in eastern Jalisco and central Michoacán (Acosta- Gallegos et al. 1998). Resistance is due to the presence of a lectin-like protein in the seed cotyledons causing lack of development in bruchid larvae (Cardona et al. 1990). Noteworthy is the fact that individual plants with resistance seem to be present at low frequency between and within original populations thriving in situ (Osborn et al. 1986), thus inciting to sample a large number of populations and a large number of individuals within each population in order to find the resistance. The protein 3 responsible for the resistance and named arcelin is part of the natural variation existing in seed storage proteins; strangely enough it does not confer a definite evolutionary advantage since most populations distributed over 8,000 km (Toro-Chica et al. 1990) do not have it and host bruchids year after year. The presence of wild common bean in Costa Rica has been well established (Debouck et al. 1989; Araya-Villalobos et al. 2001; Zamora 2010), with clear indications about differences with weedy forms and escapes from cultivation. There is some evidence based on molecular markers that wild P. vulgaris populations of Costa Rica have some affinity with wild populations distributed in southwestern Ecuador and northwestern Peru (Chacón-Sánchez et al. 2007). They would thus be different from the other wild populations of Central America and represent the northernmost extension of the ancestral branch of the species (Kami et al. 1995; Kwak & Gepts 2009; Kwak et al. 2009). This information might have some practical consequence as crosses between the Mesoamerican genepool and the Andean one are often difficult (Singh & Gutiérrez 1984; Gepts & Bliss 1985). According to the last available data (González-Torres et al. 2004; Debouck et al. 2016a), there would be thirty populations of wild P. vulgaris in Costa Rica, distributed mainly around the Central Valley in four watersheds (W Reventazón, E Pirrís, E Virilla, E Candelaria). Apart from P. vulgaris, our knowledge about the other Phaseolus species growing in Costa Rica (Table 1) has progressed dramatically over the last twenty years mainly thanks to field explorations. One should note the presence of P. acutifolius Asa Gray and P. coccineus L. as cultivated forms in the northwestern and central part of the country, respectively (Zamora 2010), giving up a total of fifteen species to date. Table 1 – Progress in the number of Phaseolus species known for Costa Rica. Wild species mentioned (and checked for synonymy) Total Sources dumosus (weedy), leptostachyus, lunatus (wild), oligospermus, xanthotrichus 5 Standley 1937 vulgaris (wild) 6 Debouck et al. 1989 costaricensis Freytag & Debouck 7 1996 costaricensis, dumosus, lunatus, oligospermus, tuerckheimii, vulgaris, xanthotrichus Araya-Villalobos et 7 al. 2001 talamancensis Torres-González et 8 al. 2001 costaricensis, dumosus, leptostachyus, lunatus, oligospermus, talamancensis, Freytag & Debouck 9 tuerckheimii, vulgaris, xanthotrichus 2002 costaricensis, dumosus (weedy), leptostachyus, lunatus, oligospermus, 10 Zamora 2010 talamancensis, tuerckheimii, vulgaris, xanthotrichus hygrophilus Salcedo-Castaño et 11 al. 2011 albicarminus, angucianae, costaricensis, dumosus (escapado), hygrophilus, Araya-Villalobos et leptostachyus, lunatus, microcarpus, oligospermus, talamancensis, tuerckheimii, 13 al. 2015 vulgaris, xanthotrichus The priority species According to available evidence (Porch et al. 2013), in the case of Costa Rica the species of interest to common and Lima bean breeding – and therefore of interest to the Global Crop Diversity Trust – are: wild P. vulgaris, wild P. lunatus L. and P. costaricensis Freytag & Debouck. As a matter of fact, the latter being part of the secondary gene pool of common bean (Schmit et al. 1993) has been found resistant to white mold Sclerotinia sclerotiorum (Singh et al. 2013), and this resistance has been 4 transferred into commercial stocks (Singh et al. 2013). An important consideration is that levels of resistance depends on the accession (Schwartz et al. 2014); collectors have thus to sample as many populations as possible. A recent work (Mina-Vargas et al. 2016) has shown that P. costaricensis could have contributed genes to P. dumosus Macfady., a species that is currently grown in Costa Rica and reported as cubaz. Wild Lima beans have recently caught attention given the possibility of a second domestication event of the small seeded Lima beans (Serrano-Serrano et al. 2012; Andueza- Noh et al. 2015). Further, some populations of wild Lima bean have shown tolerance to salinity (Bayuelo-Jiménez et al. 2002). For the authorities in charge of wildlife conservation in Costa Rica, it is important to continue to document the species with low numbers of populations fully recorded so far (Table 2), namely P. albicarminus Debouck, P. angucianae Debouck & Araya-Villalobos, P. hygrophilus Debouck and P. microcarpus Mart.. One should mention however the possibilities opened up recently by gene editing (Li et al. 2013), and therefore genes currently non/ poorly expressed in the target species could be derepressed or genes could be duplicated in order to gain new functions (Vlasova et al. 2016). The implications for genebanks now mean a minimum representation of the species for which gene transfer cannot be done now under currently available technologies. Table 2 – Status of ex situ conservation of the different wild species for the collection kept at CIAT. Species No. populations as shown in No. conserved ex situ Ratio (%) Herbaria albicarminus 1 1 100 angucianae 2 1 50 costaricensis 46 20 43 dumosus 17 28 165 hygrophilus 2 1 50 leptostachyus 18 6 33 lunatus 100 36 36 microcarpus 2 1 50 oligospermus 5 2 40 talamancensis 7 2 28 tuerckheimii 20 6 30 vulgaris 30 27 90 xanthotrichus 14 9 64 natural hybrids --- 23 --- source: CIAT, PRG, 2016 (taking into account the transfer of accessions collected by this Project in 2015-2016. As it can be seen from Table 2, there is a relatively good matching between herbarium records (see Annex 1 for list of Herbaria studied to date) and accessions in genebank for wild common bean. For P. costaricensis about half of the populations existing in Herbaria (and identified as P. coccineus or P. formosus H.B.K. in the past) have representation in genebanks; data from Herbaria can thus help locate populations for seed collection. The situation of wild Lima bean is that of a deficit, that could be bigger given the important survey done for the Central Valley (Baudoin et al. 2004); the records of such survey are however not all available in accessible Herbaria.