Plant Growth Regulators and Transplant Management Effects on Germination, Root Traits, Yield and Quality
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Onions (Allium cepa L.) are known for their slow germination and relative growth rate, due to their unique germination mechanism. In addition, onions lack root hairs and only develop a few lateral roots. A first study was conducted to evaluate onion seed germination and root growth traits of two cultivars Don Victor (yellow) and Lambada (red). Seeds were soaked in various hormonal solutions at low, medium, high and combination of concentrations of IAA, trans-zeatin, ethephon and ACC for ten hours; then dried under a laminar hood with lights on and continuous air flow for two days. Seeds treated with tZ had significantly increased root length (RL) as compared to control, while seeds with ethephon had reduced RL. Conversely, root surface area (RSA) increased with ethephon RL and significantly increased by the combination of ACC + tZ and ACC + tZ + Eth. The benefits of enhancing early seed germination and early root growth components in onion may improve stand establishment, water and nutrient uptake efficiency and ultimately increase in yield. A second study was conducted to evaluate the effect of seedling density (direct seeding, DS; one plant per cell, T1; and three plants per cells, T3), planting date (Nov 14, early; Dec 8, mid; and Jan 9, late) and transplants growing environments (Alamo, TX and Ruskin, FL) in Uvalde, TX during 2016 – 2017 on three onion cultivars (Caramelo, yellow; Don Victor, yellow; and Lambada) DS treatments and early plantings required more days to reach maturity than mid and late plantings. However plant height, leaf number and fresh weight were greater in late-transplanted onions. Early planted transplants and DS resulted in higher yields compared to mid and lateseason transplants. No significant differences in final yield were observed across the three plant density treatments. However, DS and T1 produced a higher numbers of more valuable jumbo and colossal bulb sizes compared to T3. Onion quality was only affected by cultivar, with cv. Lambada expressing the highest levels of total soluble solids, pyruvic acid and anthocyanins. The technique of establishing onions from transplants produced from 1 plant per cell (1 seed per cell) or multiple plants (2 or more seeds per cell) transplants provides a practical and economical alternative to produce earlier crops reducing the time of exposure to biotic and abiotic stresses during stand establishment in field conditions.
root surface area
Macias Leon, Maria Andrea (2017). Plant Growth Regulators and Transplant Management Effects on Germination, Root Traits, Yield and Quality. Master's thesis, Texas A & M University. Available electronically from