2018 ASHS Annual Conference

In Chile, onion production is mostly based on long-day cultivars, which are harvested during summer, stored, and marketed from autumn to early spring. The open-pollinated (OP) cultivars that have been traditionally used have good resistance to bulb sprouting; hybrids with competitive yields and high quality bulbs but lower resistance to sprouting have been introduced in recent years. The objectives of these experiments were to determine the timing and outcome of maleic hydrazide (MH) treatments to inhibit bulb sprouting. Two experiments were conducted, in 2015 (Exp. 1) and 2016 (Exp. 2). In Exp. 1, MH was applied to cultivars Cobra (OP) and Pandero (hybrid) 2, 9, 16 and 23 days before harvest (DBH). Effects of MH treatments were compared with a non-treated control of each cultivar. In Exp. 2, the effect of HM applied 15 DBH was compared with non-treated bulbs of cultivars Cobra and Titan (hybrid). Storage of bulbs in both experiments was carried out in similar conditions to those traditionally used by local growers (ambient temperature, 12,5ºC average, and 77,5% average relative humidity). Results from Exp. 1 showed that HM treatments did not have any effect on bulb yield or size. Non-treated bulbs of ‘Cobra’ presented 11 and 53% sprouting after 204 and 245 days of storage, while non-treated bulbs of ‘Pandero’ had 39 and 94% sprouting after the same period of storage. In both cultivars, sprouting of bulbs treated with HM 2 DBH was similar with non-treated bulbs, while the use of HM 16 or 23 DBH reduced sprouting around 50% compared to non-treated bulbs; bulbs treated with HM 9 DBH had an intermediate response. In Exp. 2, after 199 and 245 days of storage, non-treated bulbs of ‘Cobra’ had 22 and 58% sprouting, and non-treated bulbs of ‘Titan’ had 63 and 86% sprouting. The HM treatment had a positive effect in ‘Cobra’, reducing sprouting in around 60% compared with non-treated bulbs; in ‘Titan’ the effect was even greater, reducing sprouting more than 90%. In conclusion, HM treatment of plants two weeks before bulb harvest had a positive effect in reducing the sprouting of bulbs during storage. For Chilean growers, the use of HM would be specially recommended when using new hybrid onion cultivars, which have shown to have higher susceptibility to bulb sprouting during storage than traditional OP cultivars.