Physiological and growth response to moderate water deficit of off-season potatoes in a Mediterranean environment

Since the Mediterranean climate allows for off-season production, potatoes are commonly planted in the autumn-early winter and harvested in the spring. During this growing period, the crop experiences low temperature and short day length, and periodic soil water deficit, all of which may modify the physiological responses, and consequently the growth characteristics of the plant. A field physiological analysis was conducted to clarify the effect of moderate water deficit on the rate of photosynthesis, the diffusive leaf resistance, the above-ground biomass, and the tuber growth and yield of potato. A number of relationships among physiological parameters, tuber yield and plant dry weight was also analyzed. Field experiments using two cultivars were conducted in Sicily (South Italy) over two planting dates and two irrigation regimes. Plants at moderate water deficit showed increased diffusive leaf resistance, and decreased photosynthetic rate, above-ground plant dry weight, tuber growth and consequently tuber yield in comparison to well watered controls. A linear, negative and significant relationship between photosynthetic rate and diffusive leaf resistance was established. The decrease in photosynthetic rate associated with increasing diffusive leaf resistance was more marked in the variety Spunta than in Sieglinde, reflected in a greater yield sensitivity of the former cultivar to moderate water deficit. On the basis of our results, and considering its good tuber quality characteristics, the cultivar Sieglinde is recommended in areas with limited water supply, while Spunta should be more favoured in areas with a better water supply. The mean photosynthetic rate was significantly and positively associated with the above-ground biomass (stems + leaves), but not with tuber yield.