Introduction and Adaptation of the Andean Solanum Muricatum As a New Crop for the Mediterranean Region

Bulletin UASVM Horticulture, 67(1)/2010 Print ISSN 1843-5254; Electronic ISSN 1843-5394 Introduction and Adaptation of the Andean Solanum muricatum as a New Crop for the Mediterranean Region Jaime PROHENS, Ana FITA, Mariola PLAZAS, Adrián RODRÍGUEZ-BURRUEZO Instituto de Conservación y Mejora de la Agrodiversidad Valenciana, Universidad Politécnica de Valencia, 46022 Valencia, Spain; [email protected] Abstract. Introduction of new crops can make an effective contribution to the development of horticulture. The Andean region is home of several Solanaceae crops that could be introduced as new crops in Mediterranean climates. One of them is the pepino ( Solanum muricatum ). This is a herbaceous crop vegetatively propagated which produces juicy fruits. We have developed a programme for the introduction and adaptation of this neglected Andean crop in the Mediterranean region. Main adaptation problems have been the low yield, susceptibility to Tomato mosaic virus (ToMV), and low sugar content under these new conditions. By using the ample diversity available in the species and wild relatives S. caripense and S. tabanoense we have been able to deal with these adaptation problems and develop adapted and improved materials. Discovery of parthenocarpy P gene, as well as the use of genetic distances to select parents for obtaining segregating generations in which heterotic clones can be selected, have allowed improvement of yield. Screening of germplasm has also resulted in the discovery of sources of resistance to ToMV that have been used in breeding programmes. Finally, the use of intraspecific and interspecific diversity for sugar content has contributed to improving the flavor of pepino. As a result, we have developed several cultivars with improved characteristics. The use of molecular markers and genomic information will improve the efficiency of the pepino breeding programs. Keywords : breeding, fruit quality, parthenocarpy, Solanum muricatum , ToMV, wild relatives INTRODUCTION Introduction and adaptation of new crops has historically been one of the greatest technological challenges in agriculture, as it involves transferring cultivated species from their places of origin to new environmental conditions. New crops have always attracted the interest of societies that practice agriculture, as they allow the improvement of crop production and food supply (Janick, 1999; Murphy 2007). The success in the introduction of new crops has contributed to the spread and success of agriculture and to the production of an ample and wide diversity of plant products. In fact, nowadays, most of the crops grown in a given region of the World were not domesticated there and once were new crops (Prohens et al ., 2003a). Unlike in former centuries, in which exploration of new areas of the world allowed the discovery and exchange of potential new crops, nowadays attempts of introducing new crops to exotic regions is mainly based on already existing, mostly neglected, crops. In this respect, there are many “lost” crops, which in some cases have local importance, that could be of interest for introduction in other areas of the world (Janick, 1996; National Research Council, 1989). The Solanaceae family is one of the families with a greatest number of species, and the Andean region of South America holds a great diversity of cultivated crops and wild relatives of this family, in particular of the genus Solanum (Hunziker, 1979). In this respect, apart from 264 potato ( Solanum tuberosum L.) and of wild relatives of tomato ( Solanum lycopersicum L.), there are several native Solanum species that could be of interest as new crops for Mediterranean climates (Heiser and Anderson, 1999; Prohens et al ., 2004). One of these crops is the pepino ( Solanum muricatum Aiton), which is a neglected crop that was very important in the Andean region during pre-Columbian times (Anderson et al ., 1996; Prohens et al ., 2006). The pepino is a herbaceous crop which yields fleshy berries which weigh between 100 and 400 g, and are round, ovate or elongated, with a normally golden yellow skin. The flesh is yellow, juicy and has a subacid, mild flavor (Nuez and Ruiz, 1996). Although it is sexually fertile, in the agricultural practice it is vegetatively propagated, normally by cuttings, and clones are highly heterozygous (Prohens et al ., 1999). During the last years we have been developing a breeding program to introduce pepino into Mediterranean regions. Here, we present the results of this program. First attempts to introduce pepino in the Mediterranean region revealed three main adaptation problems, namely, the low an irregular fruit set, susceptibility to Tomato mosaic virus (ToMV), and low sugar content for the European consumers (Pérez-Benlloch et al ., 2001; Prohens et al ., 2004). The low and irregular fruit set is mostly caused by the dropping of flower buds, pollen sterility, and increased stigma exsertion at temperatures above 30 ºC (Ercan and Akilli, 1996; Nuez and Ruiz, 1996). Regarding susceptibility to ToMV, this is a mechanically transmitted virus that spreads very efficiently and that cause important loses in terms of yield and quality (Pérez-Benlloch et al ., 2001). Finally, fruits that ripen under temperatures above 30ºC have a reduced sugar content and on occasion develop unpleasant off-flavour (Pluda et al ., 1993; Prohens et al ., 2000a). Because of this, we have proposed that the most adequate growing cycle for pepino in Mediterranean climates is the so-called autumn-winter cycle, in which the plant avoids the summer heat both during the fruit set and ripening (Prohens et al ., 2000a). MATHERIALS AND METODS Our approach to breeding pepino for adaptation has consisted in making use of the ample diversity of the available genetic resources of pepino and wild relatives. In this respect, the pepino presents an ample phenotypic and genetic diversity (Anderson et al ., 1996; Prohens et al ., 1996; Rodríguez-Burruezo et al ., 2002; Blanca et al ., 2007). Also, the pepino gives fertile hybrids with related species of Solanum section Basarthrum , like S. caripense and S. tabanoense (Rodríguez-Burruezo et al ., 2003a). The screening of these materials has allowed us to use materials with interesting traits for the breeding programmes. The discovery of parthenocarpic clones, which circumvented the fertility problems associated to high temperatures, allowed a regular and high yield (Prohens et al ., 1998). By means of genetic analysis in segregating generations, we found that parthenocarpy in pepino was controlled by a single dominant gene, which we called P. Carriers of gene P have increased yield under a wide range of conditions, and furthermore this gene does not have a negative effect on fruit quality (Tab. 1). The discovery of an AFLP marker associated to gene P facilitates its use in breeding programs by means of marker assisted selection (Prohens et al ., 2000b). Another strategy for the improvement of pepino yield, apart from making use of the P gene, has been the use of genetically distant parents to obtain hybrid segregating generations in which highly heterotic clones can be selected (Prohens and Nuez, 1999; Rodríguez-Burruezo et al ., 2003b). Therefore, by using crosses of genetically distant parents, as assessed by AFLP markers, in which at least one of the parents is parthenocarpic we have been able to select highly productive clones. 265 Tab. 1 Effects of parthenocarpy gene P on pepino yield and fruit quality data in segregating generations. Data are expressed on the percentage value (±SE) of parthenocarpic plants over the non-parthenocarpic plants, which are given a value of 100% Trait Mean value compared to non-parthenocarpic (%) Yield 152.8 ± 4.9 Soluble solids content 96.0 ± 2.9 Fruit weight 95.8 ± 8.1 Fruit shape (length/width) 103.0 ± 5.4 Fruit core shape (length/width) 100.0 ± 8.0 Screening of germoplasm also resulted in the detection of several clones of the cultivated species that displayed hypersensitive resistance to ToMV (Pérez-Benlloch et al ., 2001). Although it has not been determined if the genes conferring these resistances are allelic or not, some of these sources show a different performance (Leiva-Brondo et al ., 2006), which suggests that there may be diversity in the gene/s responsible for the resistance. The use of these sources of variation in the breeding programs has allowed developing commercially interesting materials resistant to this viral disease. Regarding sugar content, the content within the cultivated species is low and under the Mediterranean conditions normally is below 9% (Rodríguez-Burruezo et al ., 2002). However, some variation exists within the cultivated species, which can be used for developing improved materials with a higher soluble solids content when grown under Mediterranean conditions. Given the lack of enough variation in the cultivated species, the wild species S. caripense Humb. & Bonpl. ex Dunal and S. tabanoense Correll, which may have soluble solids content of up to 14% (Prohens et al ., 2003b), represent sources of variation of great interest for the improvement of pepino sugar content. The crossings of pepino with these wild species have shown that soluble solids content is under the control of several genes and that the genetic control of this trait is mostly additive (Rodríguez-Burruezo et al ., 2003a). Interspecific hybrids with these species have been used to develop pepino materials with improved soluble solids (Tab. 2). Tab. 2 Range of fruit weight (g) and soluble solids content (%) in pepino ( S. muricatum ), wild related species S. caripense and S. tabanoense , interspecific hybrids, and selected backcrosses of interspecific hybrids to S. muricatum . Data were obtained from several experiments. Type of material Fruit weight (g) Soluble solids content (%) Solanum muricatum (cultivated) 113.0 – 161.4 7.7 – 9.1 Solanum caripense (wild) 1.9 – 9.7 10.3 – 13.6 Solanum tabanoense (wild) 18.2 – 21.4 10.5 – 12.1 S. muricatum x S. caripense hybrids 11.7 – 37.9 8.7 – 12.2 S. muricatum x S. tabanoense hybrids 11.0 – 57.6 8.7 – 9.3 S.

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