Ohanenye I C, Alamar M C, Thompson A J, Terry L A
Plant Science Laboratory, Cranfield University, Bedfordshire, MK43 0AL, UK.
Postharvest Biol Technol. 2019 Mar;149:221-234. doi: 10.1016/j.postharvbio.2018.12.002.
Continuous supply of high quality onion bulbs to meet year-round demand is dependent on maintaining dormancy and bulb quality during storage. Sprouting impacts negatively on the storage quality of onion bulbs. Ethylene supplementation has previously been revealed to inhibit sprout growth in stored onion bulbs. Fructans content, especially those at higher degree of polymerisation (DP), are reported to positively correlate with delayed sprouting. However, little is known about the impact of pre-harvest irrigation regimes on fructans accumulation and redistribution in relation to onion bulb dormancy and quality in store. Across two seasons, onion plants of cultivars 'Red Baron' and 'Sherpa' were subjected to full irrigation (FI) (100% replenishment of crop evapotranspiration) or deficit irrigation (DI) (50% of FI treatment) from bulb initiation to harvest. Bulbs were harvested at full maturity and stored at 1 °C for five months. Bulbs were treated with or without 1-MCP (1 μL L) for 24 h before storage under continuous ethylene supplementation (10 μL L) or air. DI had no effect on dormancy-break, sprout emergence, total fructans content and total sugar content. In contrast, ethylene delayed sprout emergence and suppressed sprout growth; added 1-MCP enhanced this effect. The concentration of DP3-8 fructans were higher in top and bottom sections compared to the baseplate. Before sprout emergence, fructans of DPs 7-8 were no longer present in the top and bottom wedges, while they accumulated in the baseplate; irrespective of pre- or postharvest treatments. This redistribution of fructans within the bulb suggested a transition in dormancy state and could be used as a predictive marker for sprouting in stored onion bulbs.
持续供应高质量洋葱鳞茎以满足全年需求取决于在储存期间维持休眠和鳞茎品质。发芽对洋葱鳞茎的储存品质有负面影响。先前已发现补充乙烯可抑制储存洋葱鳞茎的发芽生长。据报道，果聚糖含量，尤其是那些聚合度（DP）较高的果聚糖，与发芽延迟呈正相关。然而，关于收获前灌溉制度对与洋葱鳞茎休眠和储存品质相关的果聚糖积累和再分配的影响知之甚少。在两个季节中，‘红男爵’和‘夏尔巴’品种的洋葱植株从鳞茎开始形成到收获期间接受充分灌溉（FI）（作物蒸散量的100%补充）或亏缺灌溉（DI）（FI处理的50%）。鳞茎在完全成熟时收获，并在1℃下储存五个月。在连续补充乙烯（10μL/L）或空气的条件下储存前，鳞茎用或不用1-MCP（1μL/L）处理24小时。DI对休眠打破、发芽、总果聚糖含量和总糖含量没有影响。相比之下，乙烯延迟了发芽并抑制了芽的生长；添加1-MCP增强了这种效果。与鳞茎盘相比，顶部和底部切片中DP3-8果聚糖的浓度更高。在芽出现之前，顶部和底部楔片中DPs 7-8的果聚糖不再存在，而它们在鳞茎盘中积累；无论收获前还是收获后处理都是如此。鳞茎内果聚糖的这种重新分布表明休眠状态发生了转变，可作为储存洋葱鳞茎发芽的预测指标。
