[Sink-source relationship of potato plants and its role involved in the reduction of tuber yield in continuous cropping system].

The Yellow River irrigation area in middle Gansu Province is one of the main production bases for processing potato and potato tuber seeds in China. However, continuous potato cropping (CPC), resulting from intensive cultivation, has been affecting the sound development of the potato industry. A long-term field experiment was carried out in order to reveal the mechanisms of CPC obstacles. Five treatments, with different years of continuous potato cropping, were designed marking as 0-5 a, 0 a was maize-potato rotation, used as the control (CK). The present study focused on how to change in sink size and sink activity as well as source activity of potato plants under CPC conditions, especially their roles involved in the reduction of tuber yield. There were no significant differences in tuber yield under short-term CPC (1-2 a) compared with CK, however, significant decline by 28.6%-32.8% occurred under long-term CPC (3-5 a), which was mainly derived from the decline in fresh mass of each tuber. Compared with CK, long-term CPC significantly decreased sink size by 38.4%-53.0%. In addition, long-term CPC not only postponed the potato development progress, by postponing the formation and development of potato tubers, but reduced dry matter accumulation in tubers as well. Long-term CPC significantly decreased source activity, showing that plant height, branch numbers per main stem, chlorophyll content, and dry-matter content of leaf were significantly lower than those of CK, besides, morphological development of root system was also restrained. Compared with CK, root vigor, ribulose diphosphate carboxylase (RuBP Case) and sucrose phosphate synthase (SPS) activities of leaves under long-term CPC significantly decreased by 28.6%-63.1%, 52.6%-64.6% and 26.3%-53.4%, respectively. Long-term CPC caused signi-ficant decline in production capability of source, consequently, reduced the production of assimilation product by a large margin, and contributed to the deficiency in translocation amount of assimilates into tuber during post-anthesis, which finally led to the reduction in tuber yield. In conclusion, the unbalance of sink-source relationship of potato plants was the main cause for CPC obstacles in the Yellow River irrigation area in middle Gansu Province.