Mid-term In Vitro Preservation in Minimun Growth Condition of Wild Chayote (Sechium compositum Donn.Sm.)

Mexico is the origin center of chayote, which has cultivated species (Sechium edule) and wild species (Sechium compositum). This crop has a recalcitrant seed which make impossible  preservation in conventional seed storage protocol in genebank, because of high wather content, doesn't resist desiccation or -20ºC storage temperatures, losing viability in short period of time. Because of this biological characteristics, the preservation is conducted by the National Genebank of Sechium edule (BANGESe) in Huatusco, Veracruz, Mexico through field genebanks. However, this preservation technic has some risks for the accesions, it can be affected by natural desasters, plages and other plant disseases. In vitro storage by slow growth method is an important alternative and commonly used to complement field genebank. Slow growth techniques allow clonal plant material to be stored under tissue culture conditions with extended subculture intervals under reduced growth conditions, resulting minimizing the manipulation, subculture and cost for the conservation. The purpose of this project is to establish the optimal minimum growth conditions for the mid-term in vitro preservation for Sechium compositum. The experiment had different variables evaluated: room temperature (12, 18, 24 ºC), and combination of sucrose and manitol concentrations (0 and 60, 10 and 30, 15 and 20, 20 and 15, 25 and 10, 30 and 5, 60 and 0 g/L, respectively) with a MS media culture during 180 days. The evaluations showed significative diferences in the growth range of the shoots as an effect for combination of all the variables, the most successful temperture observed was 18ºC and best treatment was the combination of sucrose 15g/L and manitol 15 g/L. With this condition, the shoots can be preserved without subculture or new media culture by 9 months in the storage room. Lower temperture or higher manitol concentration caused damage on the tissue and eventualy death in only 45 days. In conslusion, the storage room temperture at 18ºC and the modificated media culture above allows longer preservation periods in accesions of wild chayote Sechium compositum, this opens an oportunity for the mid-term preservation of chayote accesiones in the genebank. This research was partially supported by JST/JICA, SATREPS.