Irrigation method and harvest time affect storage quality of two early-season, tablestock potato (Solanum tuberosum L.) cultivars

Storage quality was evaluated for two tablestock potato (Solanum tuberosum L.) cultivars grown in a sub-tropical climate under three irrigation methods and harvested over a three-week period. Early-maturing ‘Fabula’ and ‘Red LaSoda’ potatoes were irrigated with either seepage (SE), surface drip (SD), or sub-surface drip (Sub-SD; tape buried 15cm) irrigation, during two spring seasons. Inherent potato seed dormancy in ‘Fabula’ resulted in delayed and non-uniform plant establishment. At horticultural maturity, vines were killed using a chemical desiccant to promote tuber periderm maturation. Tubers were harvested 1–3 weeks after vine kill (H1, H2, H3), and tuber quality was evaluated weekly during 14 days storage at 10°C and 80–85% relative humidity (RH). In ‘Fabula’, H1 tubers, with more immature periderms, had the highest weight loss (5.3%) and were significantly less firm after 14 days of storage. Average cumulative weight loss for later harvests was 1.4% and tubers remained firm throughout storage. Pulp (cortex, xylem, perimedullary and pith tissue) ascorbic acid content of H1 ‘Fabula’ tubers decreased during storage; however, it was higher in SD and Sub-SD (17.1mg 100g−1) than in SE tubers (11.8mg 100g−1) after 14 days. There were no significant differences in whole tuber or peel ascorbic acid content during storage; average was 20.1mg 100g−1 and 7.2mg 100g−1, respectively. Although dry matter content in the peel decreased with increased delay to harvest time for all irrigation methods, it remained constant throughout storage. Average dry matter content, for all harvest times, during storage was 16.7%, 8.8% and 14.8% for whole tuber, peel and pulp tissue, respectively. ‘Red LaSoda’ plants tend to grow faster than ‘Fabula’ and, therefore were compositionally more mature at harvest; no significant differences in dry matter or ascorbic acid content were observed before or during storage. However, similar to ‘Fabula’ tubers at H1, firmness decreased by 7 days in storage for all irrigation methods, possibly due to excessive fresh weight loss. Harvest and storage quality of ‘Fabula’ and ‘Red LaSoda’ grown under either SD or Sub-SD was comparable to SE at H2 and H3, with the potential to significantly reduce irrigation water usage during production.