عنوان مقاله [English]
Introduction: Storage potential is an important characteristic for onion. Annually, a large quantity of produced onions worldwide deteriorated during storage. The storability of onion could be affected by several factors including cultivar and temperature. The genetic variation for onion storage ability is considerable. Rivera Martínez et. al. (2005) evaluated the storage ability of 18 local and 4 commercial cultivars of onions in Spain. Their results showed that there is significant variation for storage ability among different onion cultivars, and interstingly the local cultivars were more storage potent than commercial ones. Onion storage ability could also be affected by environmental conditions such as temperature. Benkeblia et al. (2000) studied the effects of various temperatures on respiratory parameters of onion. They reported that by increasing in temperature the respiration will raise. The positive effect of higher temperature in enhancing the growth of sprouts and elevating transpiration has been reported (Miedema, 1998; Yoo et al., 1997). Afghanistan is considered to be one of the origins of onion (Brewster, 1994). There are no reports on estimating storage ability of Afghan local varieties under different temperature conditions.
Materials and Methods: In this research, we studied the storage ability of eight local varieties “Hanaaie Harat”, “Zard-e-Harat”, “Ghermrz-e-Harat”, “Mazar-e-Sharif”, “Kabul”, “Sar-e-Pul”, “Ghonduz” and “Balkhaab” originated from Afghanistan, an Iranian cultivar (“Ghermez-e-Azarshahr”), along with a commercial cultivar “Sweet Grano” at two different temperature regimes (5°C and ambient temperature), in six-time intervals of 20 days. The average temperature of ambient storage was 13°C (ranging from 8-18 °C). The experiment lasted from November 6th of 2010 to March 5th. This research was performed in a completely randomized design based split factorial design, with 3 replications. For each replication, 50 healthy non-sprouted bulbs were packaged in plastic nets. Storage potential related characteristics such as sprouting percentage, weight loss percentage, sprout length, and sprout weight/ bulb weight ratio in 20 days intervals were measured. All data were subjected to analysis of variance (ANOVA) using SAS statistical software. Mean comparisons were calculated at 5% probability level using LSD when the F-value was significant (Fisher’s protected LSD).
Results and Discussion: Our results showed that there were significant differences among cultivars storage characteristics (weight loss percent, sprouting percent, length of sprouts and sprout weight/ bulb weight ratio). “Ghonduz” and “Ghermrz-e-Harat” local cultivars had the most and least storage ability, 50% of bulb sprouting after 105 and 35 days, respectively. Rivera Martínez et al. (2005) and Ramin (1999) also reprted Spanish and Iraninan local cultivars have more storability in comparision to commercial cultivars. In ambient storage, weight loss of onion bulbs was higher at the beginning and the end of storage period. But in 5 °C, it decreased with a linear model during storage period. The interaction between cultivar and time was also significant. It shows onion weight loss differs in various intervals. It may be attributed to genetic variation and morphological difference such as number and thickness of dry scales of onion bulbs. In ambient storage condition, onion sprouting percentage showed a sharp increase in early storage intervals and become fixed in the late intervals. Under 5 °C treatment, it raised as a linear model with very slow slope. It seems that weight loss and sprouting of onion bulbs in ambient storage is dependent to temperature and relative humidity of environment. This finding is in agreement with previous reports (Baninasab and Rahemi, 2006; Forudi, 2005). The sprout length and the ratio of sprout weight to bulb weight was lower in 5°C than ambient temperature. Abdalla and Mann (1963) and Yoo et al. (1997) also reported that smaller sprouts in lower temperatures.
Conclusions: In this research we studied the effect of cultivar and temperature on some local cultivars of onion from Afghanistan in different intervals. We found that storage potential of onion bulbs could be influenced by genetic factors and environment conditions such as temperature. Effect of cultivar on all characteristics was significant. There was also a high variation in storability of onion cultivars. Our findings show that local cultivars are more storable than commercial cultivars. Among the cultivars, “Ghonduz” cultivar had higher storage potential than other cultivars including the commercial cultivar of “Sweet Grano”. Our results confirmed that local cultivars could be a good source of desirable genes such as storability and therefore, they could be employed in breeding programs to broaden the genetic base of breeding matreials. In addition, sprouting percentage, weight loss percentage and onion sprout growth were less under 5 °C treatment than ambient temperature. Therefore, we could conclude that storing onion bulbs in low temperature conditions could reduce the onion spoilage and improve shelf life time.