Postharvest storage studies of the short day onion "Texas Grano 1015Y"

Abstract

Postharvest losses and physiological changes were investigated in bulbs of a short day onion, Texas Grano 1015Y, stored at different temperatures. Sprouting rate was highest at 13° and 20°C, but water loss and decay rate were increased with storage temperatures. The optimum storage temperature was obtained to be below 13°C and above freezing, and the expected storage time was estimated to be 6 to 8 weeks at these temperatures. Shoot growth was initiated at 4 weeks and fastest at 13°C but no growth was observed in bulbs stored at 1° and 34°C. On the contrary, shoot growth in bulbs stored at 13° and 20°C was suppressed but that in bulbs stored at 1°, 7°, and 34°C was promoted after bulbs were transferred to 27°C. Respiration rates were changed similarly like shoot growth. CO2 level in bulb was increased with storage temperatures but was not directly related with respiration rates and gas volume in bulbs. A hypothesis that shoot growth was suppressed by high CO2 level in bulbs at high temperature was rejected. It was postulated that pH changes by storage temperatures controlled shoot growth by modifying distribution of hormones between cytoplasm and vacuoles. A decrease of fructose and glucose, and an increase of sucrose at high temperature was noticed and this change was reversible after transfer to 27°C. But increase of fructose at lower temperature was not shown, differently from long day onions. Osmolality was decreased rapidly in inner scales at higher temperatures. As a result, the osmolality difference between the inner and outer scales became greater at lower temperature and this was assumed to affect early sprouting at lower temperatures. Shoot growth could be promoted by in vitro culture of inner scales. Light promoted shoot growth but pH in media had no effect. Shoot growth was highest at 24°C. Kinetin highly promoted shoot growth but IAA or GA were less effective. On the other hand, ABA suppressed shoot growth.