Studies on the Relation between Location of the First Peduncle Base of the Main Stem and Yield of Potatoes

Forecast of tuber yield by haulm growth, if possible, may mean a lot for the potato breeding and cultivation. Since it has been said that there is no high correlation between haulm growth and tuber yield in potatoes, we have tried to classify ecological types according to the different processes of haulm growth, thus studying relations between ecological type and tuber yield. The stem length from the first peduncle of main stem to soil surface was named the stem length under peduncle, and that from the first peduncle to the growing point the stem length above peduncle. The stem length under peduncle was revealed to have a close connection with haulm growth from early to middle stage of growing season, and the stem length above peduncle with that from middle to late stage. In many cases high positive correlations were found between the stem length under peduncle and starch yield from tubers, while relatively high negative or low positive correlations were found between the stem length above peduncle and starch yield from tubers. Haulm growth, showing longer stem length above the peduncle, especially provided with shorter stem length under the peduncle, resulted delayed growth, excessive foliage growth and lodging. Consequently growing conditions were unfavolable for tuber bulking and accumulation of starch in tubers. By means of laies the stem length under the peduncle on the X axis and the stem length above the peduncle on the Y axis, dividing both by their mean values, were obtained four ecological types. From the table 5, it was known that type I and IV, accompanied by longer stem length under the peduncle produced more starch yield than type II and III that have shorter stem length under the peduncle. Comparing type II with IV, although each type had nearly equal stem length, features of the growth are different and accumulation of starch in tubers was greater in the type IV than in the type II. In conclusion, it was suggested that studies of cultivation method accelerate the stem length under the peduncle must be done and in breeding potatoes, elimination of such type as II would be desirable.