Tuber quality of early potato in Sicily as affected by genotype, sowing time and irrigation rate

The effects of two sowing times and two rates of irrigation (50% and 100 % recovery of crop ET) were evaluated on dry matter and carbohydrates accumulation in tubers of two potato varieties (Solanum tuberosum L. cv. 'Spunta' and 'Sieglinde') in early cultivation in Sicily. 'Sieglinde' showed a slightly higher dry matter content, and more variations of this parameter due to the sowing time and to the rate of irrigation than 'Spunta'. Non structural carbohydrates (glucose, fructose, sucrose and starch) accounted for more than 60% of the dry matter in tubers at harvest, with little effect of the experimental treatments even during the season. Total soluble sugars (glucose fructose and sucrose) showed large variations during the season between the cultivars and the sowing times. At harvest total soluble sugars were more abundant in the cv. 'Spunta' (more than 2% of the fresh weight) than in 'Sieglinde'. Starch content started to increase at about 45 days after sowing and its accumulation had almost stopped at harvest. The sowing time and the irrigation rate had little effect in starch content of 'Spunta' tubers while in 'Sieglinde' it was affected by the sowing time particularly early in the season. At harvest the starch content of 'Sieglinde' was higher than that of 'Spunta'. Our data show that quality attributes of early potato in Sicily can be affected mainly by the cultivar while the sowing time and the rate of irrigation, at least in the season studied, had limited if any effect on tuber quality.