Early drought effect on canopy development and tuber growth of potato cultivars with different maturities

The morphological growth characteristics of shoots, stolons, and tubers were measured on potatoes (Solanum tuberosum L.) grown in irrigation and drought from plant emergence. Three cultivars with a wide range of seasonal maturing patterns, Chubaek (very early), Superior (medium-early), and Jayoung (late), were used. The drought was maintained up to the tuberization stage in the year 2015, and it was extended to early tuber bulking in the year 2016. The drought delayed the time to full canopy development by 2-6 days and decreased the growths of shoots in terms of stem length, stem thickness, number of stems, and fresh weight of the shoots. The harvest index was increased in all cultivars due to the decreased shoot growth. The early drought also increased the length of underground stolons. However, the decreases in stem thickness and stem number and the increases in harvest index and stolon length were only significant in the year 2016. Even though the drought did not affect tuberization in early and medium-early cultivars, it decreased early tuber growth by suppressing the longitudinal growth expressed by the ratio of length to width of the tubers. The decrease of tuber growth was observed until the end of the season with the exception of Superior in 2016. In late maturing cultivar, tuber initiation and tuber yield were dependent on the season or length (severity) of the drought. In 2016 when late cultivar, Jayoung, experienced a long drought starting from the emergence of the plants to early tuber bulking, the drought induced earlier tuberization than irrigation treatment, and showed a higher harvest index than in 2015. The early tuberization and tuber bulking due to the long drought induced increased tuber yields. The occurrence of second growth tubers was highly attributed to the maturity of cultivars in both years and the drought in 2016.