Botanical characteristics and genetic resources

As all dicotyledon, lulo has a pivot, or main root with a high percentage of shallow fibrous roots. The stem is cylindrical, semi-wooded and succulent, tender and green; this is transformed into a brown woody stem in the adult stage and can reach up to 3 m in height. Some genotypes have lots of thorns (i.e. S. quitoense var. septentrionale) while others are smooth or with soft hairs (i.e. S. quitoense var. quitoense). From these, the first ones are more common in Colombia, while the seconds (without thorns) are more common in Ecuador (^{Denis et al., 1985}; ^{Gómez et al., 1999}; ^{Heiser, 2000}; ^{Sahaza and Henao, 2001}; ^{Franco et al., 2002}; ^{Angulo, 2008}). The branches are succulent and green when they are young, and they become woody and brown over time; they can have diameters up to 5 cm and present or not thorns.

The leaves are usually large, at least 40 cm long and 34 cm wide; they are green on the beam and violet on the underside. The flowers are grouped in clusters, to a number that varies between 5 and 10 per each inflorescence; the petals are white and purple. There are flowers of long, medium and short pistils, but only the long ones are fertile. Lulo does not produce pollen fertile in temperate zones, which constitutes a great competitive advantage for its cultivation in the tropics and a disadvantage for breeding in mild zones (^{Angulo, 2008}). The fruit is a globose Berry with 4 to 8 cm in diameter and weighing between 40 and 80 g; in the improved hybrid "La Selva" the bark is smooth, deep yellow or deep reddish yellow at maturity; the pulp is green and with many seeds, and sweet-sour flavour.

The plant can bear fruit throughout the year, resulting in production of flower buds, flowers and fruits of different sizes. The seeds are smooth and round, can be up to 1 000 per fruit that can weigh between 4 and 40 mg. The original varieties produced, specially in Colombia and Ecuador, can be spread by seed, while hybrid materials such as lulo "La Selva" must be propagated through sticks, tillers, and plant tissue culture in-vitro (^{CORPOICA et al., 1999}; ^{Lobo-Arias et al., 2007}).

In general terms, lulo started its production between eight and 12 months of age, which mainly depends on the temperature, with yields that can range between seven and 30 t h^-1 (^{Lobo-Arias et al., 1983}: ^{Sahaza and Henao, 2001}; ^{Angulo, 2008}).

According to ^{Medina et al . (2009)}, Colombia has a germplasm bank of lulo in charge of the Colombian Corporation for agricultural research (CORPOICA), which conserves 77 accessions of S. quitoense, 17 S. pseudolulo, 8 S. hirtum, five of S. vestissimum, two of S. pectinatum, two S. sessiliflorum, two S. flexor and one of S. stramonifolium, all of them in the section Lasiocarpa (^{Lobo-Arias et al., 2002}).

Based on the development of some controlled experimental crossings, we have been able to know the phylogenetic relationship between lulos, tomatoes- tree and other related wild species. For example, lulo (S. quitoense) can form fertile hybrids with S. hirtum (^{Bernal et al., 1998}; ^{Lobo-Arias, 2000}; Lobo-Arias et al., 2007). These findings have been very useful for the generation of materials improved as lulo "La Selva", result from the cross between S. quitoense and S. hirtum (Bernal et al., 1998; Lobo-Arias, 2000). Deepening in phylogenetic studies, ^{Enciso-Rodríguez et al. (2010)} determined that Colombia is the main centre of diversity of lulo and the genetic diversity that exists enables for obtaining of new hybrids with superior characters in terms of yield, quality of fruit and resistance or tolerance to biotic and abiotic factors. Progress on initiatives such as SOL genomics network (http://solgenomics.net/) and the recent publication of ^{the Tomato Genome Consortium 2012}) will significantly advance the development of molecular markers and on the identification of functional genes that explain lulo responses to the agronomical management and the environment, as well as their use for genetic improvement.

Molecular studies have revealed significant polymorphisms and a larger genetic variability in inter-specific hybrids of S. hirtum * S. quitoense (^{Fory-Sánchez et al., 2010}; ^{Enciso-Rodríguez et al., 2010}), regarding the parental materials, which highlights the need to increase the base genetics for breeding programs.

Despite numerous efforts to generate and systematize scientific knowledge on this crop, the offer of improved material is still limited, and currently there is only cultivar developed in Colombia, "La Selva" lulo. The process of creation of a broad-based genetic to support improvement efforts, will allow generating lulos for agro-industrial processing, besides its fresh consumption. In breeding programs, it is important to emphasize the attributes of a plant of lulo according to ^{Lobo-Arias (2000)}: absence of thorns, erect growth habit, high rate of mooring of fruits and low activity of the enzyme polygalacturonase and polyphenoloxidase in berries. In addition, the plant requires major studies on physiological, biochemical, genetic and adaptability (interaction genotype).

Environmental requirements and agronomic management

Solanum quitoense grows between 1 000 and 2 500 m of elevation, mostly interspersed with coffee, although it develops best between 1 200 and 1 600 m in Colombia (^{Muñoz-Belalcázar, 2011}). ^{Medina et al. (2009)} pointed out that lulo is a plant adapted to humid mountain forest and thrives well in coffee-growing areas under the shadow. In Mexico, the mountain cloud forest occupies about 8 800 km², which is equivalent to about 0.5% of the national territory (^{González-Espinosa et al., 2012}), which means a large area with potential for cultivation interspersed with coffee plantations that are developed in these mountain ecosystems.

Lulo is a short-day species that exhibits its best development in shaded places, near running water, at temperatures from 15 °C to 24 °C, with an optimum 20 °C. For its better development it requires slightly acidic soils (pH between 5.5 and 6.0), moist, deep and well drained, as well as sites with rainfall between 2 000 and 3 000 mm per year (^{Foundation Codesarrollo, 2006}). In general, native materials as "Castilla" are more demanding in terms of soil and climate conditions than the hybrid "La Selva", which is better suited to restrictive environments.

Once the site for the establishment of commercial scale for lulo is selected, it will be necessary to identify the genotype which best fits the environmental conditions of the region. In the case of the "La Selva" hybrid, in Colombia there are at least two companies, laboratories AM of C. In Medellín, and the “Fundación Universitaria Santa Rosa de Cabal” (UNISARC), which provide quality seedlings cultivated through the technique of plant tissue culture.

Native materials that have not been systematically improved grow normally under some level of shade in natural conditions of Colombia and Ecuador. The hybrid "La Selva" can be grown to free exposure and lower height than native lulo named "Castilla" and the first yields are higher than those obtained with the latter, being resistant to nematodes. In commercial crops is recommended only the planting of clones of hybrid "La Selva" (Solanum quitoense x S. hirtum) (^{Muñoz-Belalcázar, 2011}), for which plants propagated in vitro are required.

Since the hybrid require partial shade, planting with coffee recommended, taking advantage of the streets, once the renovation of the coffee plantation is made. In this case, to the interlayer of both species (coffee and lulo) a system can be used in real frame (3 * 3 m), with a density of 1 111 plants by ha; When set as a monoculture, using 2.5 x 3 m planting distances for a density of 1 333 plants per has (^{Muñoz-Belalcázar, 2011}).

One of the more complete reports on the description of pests and diseases of this crop and its control was published by ^{Tamayo (2001)}, for the case of Colombia. Later, ^{García-Lozano et al. (2008)} reviewed the phytosanitary conditions of cultivation for the Department of Huila and stood out as the most common pests: piercing worms of the fruit, flower weevils, mites and nematodes.

According to ^{Carreño et al. (2007)}, the most affecting phytosanitary problems are the fruit anthracnose, caused by Colletotrichum gloeosporioides, radical knot nematodes (Meloidogyne javanica and M. incognita) and rot, caused by Sclerotinia sclerotiorum. Associated diseases have also been reported to Phytophthora infestans, Fusarium oxysporum and Ralstonia solanacearum. ^{Tamayo et al. (2001)} described in detail the main agents causing diseases in this crop and noted that its control is carried out through the application of chemicals, biological control agents transmitting and appropriate agronomic practices.

However, where growing conditions are conducive to the development of certain pathogens, it is necessary the work of selection of resistant varieties. For example, "La Selva" hybrid shows resistance to root nematodes and it continues to work to develop clones with resistance to Phytophthora infestans, Fusarium oxysporum and nematodes (^{Montes-Rojas et al., 2010}).

A way to produce plants free of pathogens and genetic purity is through in vitro cultivation. In this regard, several recent studies have shown the feasibility of lulo spread using this technique (^{Medina-Rivas et al., 2008}; ^{Andrade-Díaz et al., 2013}; ^{Martín et al., 2013}).

Frost, hailstorms and drought (^{Muñoz-Balalcazar, 2011}) can be cited within the abiotic factors that affect this crop. Frequent humidity and low winter temperatures can cause cracks of fruits, while prolonged drought significantly affect photosynthesis and the mooring of fruits.

Once they have germinated and the seedlings are growing in beds or containers under controlled conditions, it is recommended to inoculate them with mycorrhizal fungi. Ysabel-Posada et al. (2013) reported that lulo plants inoculated with Glomus sp. or Scutellospora heterogama grew 55% more than those without inoculation and mycorrhizal fungi allowed plants to tolerate the stress, caused by direct sunlight, in a way more successful than non-inoculated plants.

In order to offer recommendations on chemical or organic fertilization for this crop, it is necessary to study the fertility of the soils where intended to establish lulo plantation, as well as the dynamics of need of nutrients through the different phenological stages of the crop, aspects that are not entirely known either in Mexico or in Colombia. However, it is known if lulo responds well to organic and chemical fertilizer application. For example, according to ^{Ramírez and Duque (2010)}, "La Selva" shows superior returns with the application of compost of chicken manure, while applications of worms of vegetable waste with coffee pulp showed effects similar to the application of chemical fertilizers (10-30-10) and higher than the control´s treatment without application of fertilizer or manure.

In this study the lulo "La Selva" grew in a soil derived from volcanic ash, well drained and high fertility, in the coffee-growing zone of Colombia. In a recent study, ^{Gómez-Merino et al. (2013)} showed that lulo seeds can germinate and produce healthy seedlings in relations of peat: compost between 1.50 and 0.66, which corresponds to 40-60% of compost in the substrate, without the application of chemical fertilizers.

Although there is no general fertilization protocols, as these should be based on studies of soil nutrient availability and the needs of the plant, the ^{Codesarrollo Foundation (2006)} proposed that for the Department of Risaralda, Colombia, soil fertilization must be made every month until the fifth month. From the latter and until 18 after sowing, fertilization is made every 45 days, based on the following plan: the first fertilization must be at the time of planting, with the application of 1 kg of chicken manure more 200 g of a fertilizer mix containing phosphate (P₂O₅) 5%; calcium carbonate (CaCO₃) 55%; and magnesium carbonate (MgCO₃) 26%, for previously mycorrhizal plants.

Once a month an application of phosphate diammonium (DAP) is made with more elements in proportion 25:1, at doses of 20 to 30 g per plant; in the second month the same mixture is applied in doses of 60 g per plant; the third month apply 80 g of the formula 10-30-10 per plant; the fourth month apply 100 g 17-6-18 per plant and after the fifth month apply 150 g of formula 17-6-0 in associated with coffee plantations.

From planting and during crop development is necessary to make cultural activities that include the control of undesirable vegetation, insects pest and disease causing agents in accordance with protocol described by ^{Quinchía and Cabrera, (2006)}, ^{Tamayo (2001)}, ^{García-Lozano et al. (2008)}.

For the harvest of Lulo "La Selva", the production starts eight months after sowing, and the flowering period is five to six months, considering the climate of the area. In this hybrid, must of the fruits weighs between 40 and 45 g. For agribusiness, the fruit must be harvested when it reaches 75% of its maturity, that is, when most of the epicarp is yellow and reach 9 °Brix.

The recollection of fruits must be made manually, releasing the fruit, cutting off the stalk, and leaving the calyx, this for keeping it hydrated and prevent the entry of infectious agents that can cause illness. The fruits must be placed gently in the tank and carefully take the collection site. In order to avoid contamination, the diseased fruit should be discarded and buried in a special pit outside the agricultural land. Once harvested the fruit, is cleaned with light and gentle manual movements in sacks, 20 to 30 fruits per sack. Since we´ve got the cleaned fruits, these are packaged in plastic baskets between 10 and 20 kg capacity and are transported to the place of delivery. It is evident that in these stages is necessary the development of technology to automate the processes of harvesting, cleaning and packaging.

Colombian quality standards number 1 265 and 5 094 describe the most relevant aspects regarding the product, the packaging and labelling, and establish the minimum requirements to be fulfilled for each of them.

These data indicate that the cultivation of lulo in Mexico is possible, given that much of the mountainous area where they cultivate coffee above the 1 000 metres above sea level, presents desirable characteristics in terms of elevation, soil and climate. However, it is still necessary to study the potential of each coffee and mountainous region to determine those who have better chance of success for the cultivation of lulo.

Nutraceutical properties of the fruit

The fruit of lulo has high concentration of vitamin C and iron, which gives it diuretic and toning properties. It is a solvent of toxins from the body and facilitates the elimination of uric acid (Muñoz-Balcazar, 2011). The Table 1 describe some of the chemical and nutritional characteristics of lulo.

Leading producers of lulo

The main production of the lulo in Colombia is intended for fresh consumption, and its market in the United States shows great potential for growth. In addition, lulo looms within crops with greater potential to contribute to food security; In addition to representing an activity generating employment and income (^{FAO, 2001}). Colombia and Ecuador are the main producers, but it is also cultivated in Venezuela, Peru, Panama, Costa Rica and Guatemala. In Colombia, lulo is gaining importance in the industrial sector for the manufacture of juices, yogurt, flavourings, sodas and processed foods (^{Medina et al., 2009}; ^{Muñoz - Balacazar, 2011}).

For 2011, the National Administrative Department of Statistics (^{DANE, 2011}) of Colombia reported an area sown with lulo from 5 469 has in Colombia, mainly distributed in coffee-growing areas. The main producing departments are Huila, Valle del Cauca, Nariño, Tolima, and Boyacá, which altogether represent about 62% of the total area cultivated with Lulo, with a total production of 21 225 t of fruits and a yield average of 9.2 t ha^-1, below average potential output which is close to the 30 t ha^-1. It is estimated that a healthy plant can produce between 100 to 150 fruits per year; with an average annual yield of 135 fruits per plant, each plant would be producing 9 kg of fruits, which translates in 27.2 t ha^-1. In general, native lulos of "Castile" can reach 9 t ha^-1 per year, while the Colombian national average is 16 t ha^-1 a year for "La Selva" (^{Ríos-Gallego et al., 2004}).

Research and innovation needs

Currently, the cultivation of lulo in countries such as Colombia and Ecuador has multiple problems that limit their productivity and competitiveness, since an estimated potential of approximately 30 t ha^-1, only gets an average of between 7 and 9 t ha^-1; this condition has led to the progressive abandonment of the crop, with the consequent loss of sources of employment, reduction in income and deterioration of the standard of living of the producers. The constraints of a technical nature is related with the agronomical management in general, that is, the selection of improved materials, the control of pests and diseases, and the management of the nutrition of the plants, which are made without a support of systematic research processes and a poor physiological and eco-physiologic knowledge (^{Gómez et al., 2005}), essential for the integral management of the production. Contemplating the establishment of this crop in Mexico, demands that the first step is to delimit the areas with the greatest potential for cultivation. At first, we could considered the cloud forests and coffee-growing areas located at elevations of 1 000 m, as favourable areas for the cultivation of lulo. The geomatic tools and meteorological data which possess different institutions in the country could be useful in achieving this task.

In the field of seedlings production it is necessary to explore organic substrates available in the potential production of lulo to assess their impact and use (^{Gómez-Merino et al., 2013}). Consulted research also detected the need for generating patterns for grafts, protocols of propagation of grafting, methods for rooting of patterns, among others. Both in seedlings from seeds, and cultured explants in vitro and patterns grown in greenhouse, an important attention should be put on bio-fertilizers. Since this species is infected by different fungal symbionts and have significant responses to this type of inoculant, investigations for the identification of specific mycorrhizal for this crop are a pressing need.

Regarding pests, diseases and abiotic factors of the environment it is necessary that in genetic improvement programs contemplated phases for testing resistance to insect pest and disease causing agents. In the case of Mexico, whose total agricultural production could fall by more than 25 percent to 2080 as climate change effect (^{Moyer, 2010}), if appropriate measures are not taken the development of tolerant to drought, low temperatures and frost improved materials also should be viewed in the short and medium term.

Regarding aspects of genetic improvement, it will be necessary to develop major technologies and molecular protocols. The complete sequencing of the genome of tomato in 2012 already gives an excellent reference.

On the organizational issue, in the case of Mexico, it is necessary to focus efforts towards the formation of associative figures able to develop specific strategic plans in the short, medium and long term. To this end, several Secretaries of State provide technical, logistical and financial support.

The managerial aspect of any project looking to increase the production of lulo, should consider creativity, anticipation and surveillance, in a field of comprehensive innovation of value chain.