Low Temperature Tolerance of Curcurbit Scion and Rootstock Seedlings toward Development of Low Temperature Storage Techniques in Vegetable Grafting

Understanding the low temperature tolerance of seedlings of horticultural species provides a base knowledge of seedling storage potential and application. One application of seedling storage is its use with vegetable grafting, a technique that confers disease resistance, abiotic stress resistance, and increased yield. Low temperature storage of grafted vegetable seedlings enables propagators to meet the seasonal demand associated with the narrow window of transplanting in the field. However, information on storage of cucurbit seedlings in low temperature is limited. To evaluate the effect of low temperature storage on selected scion and rootstock cultivars, seedlings of watermelon (Citrullus lanatus ’Sweet Harmony’ & ‘Tri-X-313’), cucumber (Cucumis sativus ‘Cumlaude’ & ‘Rembrandt’), muskmelon (Cucumis melo ’Olympic Gold’, ‘Honey Brew’ & rootstock ‘DRO5018’), and two interspecific hybrid rootstocks (Cucurbita maxima x Cucurbita moschata ‘Tetsukabuto’ & ‘Strong Tosa’) were stored for a period of 4 weeks at 5 °C or 12 °C under 2 μmol·m^-2·s^-1 and 12 μmol·m^-2·s^-1 PPF, respectively. After 1 week in storage, all seedlings showed no major decrease in quality. By week 2, ‘Sweet Harmony’ and ‘Tri-X-313’ watermelon and ‘Olympic Gold’ and ‘Honey Brew’ scion muskmelon demonstrated the greatest degree of decline among genotypes examined and the decline was severer at 5 °C than at 12 °C. By week 3, plant quality declined further in those cultivars that had demonstrated a previous gradual decline in quality. At this point ‘Cumlaude’ and ‘Rembrandt’ cucumber demonstrated a high rate of mortality at 5 °C, but maintained storability at 12 °C. By week 4, most seedlings in the 5 °C treatment had died except for the interspecific rootstocks ‘Tetsukabuto’ and ‘Strong Tosa’ whose quality was maintained better at 5 °C than at 12 °C. Our results showed that: 1) ‘Tetsukabuto’ and ‘Strong Tosa’ interspecific squash hybrid rootstocks were storable at both temperatures examined; 2) ‘Sweet Harmony’ and ‘Tri-X-313’ watermelon and ‘Olympic Gold’ and ‘Honey Brew’ muskmelon performed well in the 12 °C treatment up to 2 weeks and poorly at 5 °C overall; and 3) ‘Cumlaude’ and ‘Rembrandt’ cucumbers, and ‘DRO5018’ muskmelon rootstock performed well at 12 °C throughout the 4 weeks but poorly at 5 °C. Further study is needed to see the effects of storage on growth and development of cucurbit seedlings and if rootstocks, with high storability, confer this trait to scions in grafted vegetable seedlings.