Hydroponics Culture of Edible Opuntia ‘Maya’: Drought Stress Affects the Development of Spines on Daughter Cladodes

The stem of the cactus Opuntia (genus Opuntia, subfamily Opuntioideae, family Cactaceae) is widely consumed as a vegetable in Mexico and Mediterranean countries (Stintzing and Carle, 2005; Cruz-Hernández and Paredes-López, 2010). With respect to its growth behavior, daughter cladodes develop from the areole of the mother cladode and this process is repeated (Pimienta-Barrios et al., 2005). In Japan, edible Opuntia plants are also produced as vegetables, mainly in Kasugai city, Aichi Prefecture. However, cladodes have a characteristic that diminishes their acceptance by the consumer; the presence of spines on the areole. A number of beneficial functions have been ascribed to spines, including participation in zoochorous dispersal (Frego and Staniforth, 1985; Bobich and Nobel, 2001), mechanical protection from herbivores (Norman and Martin, 1986), shading of the stem (Nobel et al., 1986), reflection of light (Loik, 2008), and thus a reduction in water loss (Stintzing and Carle, 2005). In addition to the above, a further report shows that cactus spines also function as a fog collection system (Ju et al., 2012). Therefore, drought stress on cladodes might be related to the appearance and number of spines. Reducing the number of spines will lead to an improvement in the edible quality of Opuntia and thus increase consumer acceptance. Opuntia plants are commonly produced through soil or pot culture. Major problems in growing vegetables, including edible Opuntia, using soil are soil-borne disease, salt accumulation, and difficulty in fertilizer management (Lakkireddy et al., 2012). Hydroponics culture is a method of growing plants using nutrient solution (water and fertilizer) with or without the use of an artificial medium. No soil means absence of weeds or soil-borne disease, and precise fertilizer management is possible (Lakkireddy et al., 2012). Thus, hydroponics culture conveys many advantages for edible Opuntia production, although there is no report investigating the effects of hydroponics culture on edible cactus growth as far as we searched. In this study, we attempted to investigate the effects of hydroponics culture with a deep flow technique (DFT) on the growth of edible cacti and to assess the effect of drought stress on the spine frequency of daughter cladodes.