Yield, growth components and processing quality of potatoes as influenced by crop maturity under short and long days.

Abstract

Five potato cultivars, belonging to early and medium maturing groups, grown under short (Min. 5-21°C, Max. 15-34°C, day length 11.5-9.75 hr) and long day (Min. 6-25°C, Max. 17-41°C, day length 11-13.5 hr) conditions in autumn and spring, respectively, were evaluated for important crop characteristics, contents of chemical compounds and indices of tuber quality at different stages of growth. Mean tuber yield, tuber specific gravity and dry matter content, tuber dry matter production and starch yield increased up to the last stage of harvest in both the crop seasons, but were significantly higher in autumn. Both long day conditions and high temperature favour high growth of the foliage apparently at the cost of the tubers, which initiated later and developed slowly in spring. Fresh weight of the foliage decreased up to the last harvest in both seasons and the average harvest index (fresh tuber yield/total fresh biomass) of the cultivars at 100 days after planting was 0.77 and 0.64 in autumn and spring, respectively, indicating higher translocation of photosynthates from the source to the sink during autumn. Mature tubers grown in autumn displayed a significantly higher content of reducing sugars and total phenols and produced darker chips, while those grown in spring showed higher levels of sucrose and free amino acids. 'Kufri Lauvkar' was most suitable for the preparation of chips during autumn, while all five cultivars produced chips of acceptable colour quality during spring. The yield of fried products from tubers grown during spring was expected to be much lower due to less tuber dry matter production, but these tubers can be used to prolong the period of processing. 'Kufri Jyoti' produced the highest starch yield per unit area in both seasons and was the most suitable for the production of starch and dehydrated products.