Despite many actions to mitigate the effects of climate change and enhance food production, the increasing size of human populations and demand for food continue to result in the conversion of natural vegetation to agricultural land (FAO 2017; Mora et al. 2018; IPCC 2021). Currently, commercial agriculture accounts for two-thirds of the total deforested land area in Latin America, and projections estimate that it will reach around 80% of deforested land worldwide (FAO 2017). In this context, many wild species, especially those that are crop relatives, are threatened, and the opportunities to use their germplasm for development of new crops or plant varieties decrease as their populations are destroyed. Ideally, the genes in wild plants could lead to development of crop varieties with tolerance to pests, diseases, drought, waterlogging, and salinity, and thus they would require fewer management requirements and land-intervention practices (Khoury et al. 2015; FAO 2017). Other goals for the improvement of crops are increased nutritional values and genetic diversity (FAO 2017).
Vasconcellea species (Caricaceae), often known as ‘highland papayas’ or ‘mountain papayas’, are wild relatives of common papaya (Coppens d’Eeckenbrugge et al. 2014). They are distributed from Mexico to Argentina and from sea level to highlands at 4300 m a.s.l.. These species grow mainly in Colombia, Ecuador and Peru, and only a few of them reach Argentina (Scheldeman et al. 2007). Vasconcellea spp. have good potential for domestication in tropical and subtropical regions, and their edible fruits have appealing organoleptic properties (taste, aroma, color) and are locally consumed fresh in juices and salads, or cooked in stews, jellies, syrups and jams. Only two of the 21 species of Vasconcellea have been developed as a crop. Vasconcellea × heilbornii (Badillo) Badillo (Babaco) is cultivated in Ecuador and southern Colombia, and it has been introduced in New Zealand, Australia, South Africa, Italy, Spain, Switzerland, the Netherlands, and Canada. Vasconcellea pubescens is cultivated in all Andean countries but particularly in Colombia and Chile (Carrasco et al. 2009; Coppens d’Eeckenbrugge et al. 2014). The remaining species are commercially and socially important in their local setting; thus, they could supply specific niches in national and international markets. Additionally, Vasconcellea spp. have many applications in folk medicine (the leaves, roots and seeds are used to remedy illness such as parasites), in the food industry (the plants secrete latex with high proteolytic activity useful in coagulating milk or making cheese), and in papaya breeding programs (Scheldeman et al. 2002, 2007, 2011; Coppens d’Eeckenbrugge et al. 2014). These wild relatives have been widely used in hybridization programs for their resistance to papaya ringspot virus, cold tolerance, and for some fertility (monoecious) and quality traits (soluble sugar) of C. papaya (Kyndt et al. 2005; Drew et al. 2006; Siar et al. 2011). However, crossability with C. papaya is highly variable and success depends on particular germplasm and eco-climatic conditions of the breeding site (Coppens d’Eeckenbrugge et al. 2014).
Nevertheless, the variability of wild populations is constantly threatened by changes in land-use and climate (Giamminola et al., 2020; Urtasun et al., in press.). In fact, six of the 21 Vasconcellea species are on the Red List of Threaten Species: V. omnilingua and V. horovitziana are endangered, V. palandensis and V. sphaerocarpa are vulnerable, V. sprucei and V. pulchra are near threaten (IUCN 2022). In this context, the design and implementation of in situ and ex situ conservation strategies for species of Vasconcellea are needed.
Only two Vasconcellea species (V. quercifolia and V. glandulosa) occur in Argentina (Zuloaga et al. 2008). Vasconcellea quercifolia grows in northern Argentina and in Brazil, Bolivia, Peru, and Paraguay (Siar et al. 2011; GBIF 2022). It is adapted to a wide range of climatic conditions and grows in the humid high and lowland forests and the drier Chaco and Monte ecoregion. It is a pioneer, heliophytic, dioecious, and xenogamy tree that can reach 12 m in height and 1 m in diameter. It produces an orange, juicy and sweet berry with numerous seeds (Fig. 1). The species has dietary potential, since its edible structures (fruits and medullar parenchyma) have high ash, protein, carbohydrate, fiber and carotenoid content (Folharini et al. 2019). The species has industry potential, since its fruits secrete latex with a higher specific activity than that of C. papaya. Also, it is one of the few species that has been successfully used in papaya breeding programs (Drew et al. 2007; Siar et al. 2011).
On the other hand, V. glandulosa is found in only two provinces of northwest Argentina and in Peru and Bolivia (GBIF 2022). In Argentina, the species grows exclusively in humid forests of the Yungas ecoregion, which is the lower slopes of the eastern side of the Andes Mountains (Zuloaga et al. 2008). The species is an umbrophilic, dioecious, little-branched shrub, with leaves clustered at the apex of the stem. It produces a green and elongated berry, with numerous seeds (Fig. 2).
Recent studies have demonstrated that both species are of high conservation priority due to wild populations being threatened by land-use and climate changes, and they are underrepresented in international and national genebanks (Urtasun et al., in press). Fortunately, the seeds of both species are orthodox; thus, they can be stored in genebanks (Urtasun et al., 2020; unpublished data). However, no specific studies have been conducted on germplasm variation of these species, which represents a key aspect to designing a conservation strategy. In this context, our overall purpose is to contribute to germplasm conservation of wild populations of V. quercifolia and V. glandulosa from northwestern Argentina. In particular, we assess morphological, physiological, and biochemical variability at the species and population levels and propose a conservation strategy. We expected higher variability among provenances of V. quercifolia than V. glandulosa, since the former has a wider and more heterogeneous distribution than the latter.