Specific Gravity and Tuber Dry Matter Characteristics of Taewa and Modern Potatoes in Response to Irrigation and Nitrogen

Abstract

Taewa has never been assessed tuber quality at varied N and irrigation. This study compared specific gravity (SG), tuber dry matter (tDM) and total sugar of Taewa and modern potato cultivars grown at different water and N regimes under glasshouse and field conditions at Massey University, Palmerston North. The glasshouse was 2*2*4 factorial design with two irrigation: 100% ET and 60% ET; two applied nitrogen: 50 kg N/ha and 200 kg N/ha as urea, two Taewa (Moe Moe, Tutaekuri) and two modern potato cultivars (Moonlight, Agria). The 2009/2010 field experiment was a split-plot, with irrigation and rain-fed regimes as the main treatments: four potato cultivars above were sub-treatments. The 2010/2011 field experiment was a split-split-plot, with three water regimes as the main treatments: three cultivars except moonlight were subplots; two N rates were sub-sub-treatments. Specific gravity was determined on ten thoroughly washed potato samples from each treatment by weighing the tuber in air and in water, using Mettler PJ3600 Delta Range scale. Specific gravity was calculated by dividing weight of tuber in Air by the difference between weight of tuber in air and weight tuber in water. The tDM was determined, by oven drying chopped potato at 70 ^oC, until the change in tuber dry matter was constant. The tDM was calculated, by dividing the final dry weight by the initial fresh weight and then multiplying it by 100%. Total sugars were determined from ground potato samples of 0.5g, taken from the outer equatorial portion of each tuber, excluding the skin at Massey Nutrition laboratory. The results revealed significant variations in tuber quality between Taewa and modern potato cultivars regardless of water and N regimes. Taewa had high SG (p<0.05, p<0.01, p<0.0001), tDM (p<0.05, p<0.0001, p<0.0001) and low total sugar content (p<0.0001, p<0.05), proving an exceptional processing quality, compared to modern potato cultivars. It was concluded that Taewa produces more suitable quality for high processing cost recovery and processing colour quality in crisps than modern potato. Therefore, Taewa can provide potential genetic resources for improvement in the processing quality of modern potato within the Asia and Pacific region