The Interrelationship between Source and Sink of the Grafts of Wild Type and Improved Variety of Ipomoea

Abstract

This investigation was conducted to make clear the interrelationship between thc source (photosynthate donor, top part of sweet potato plant) and the sink (main photosynthate acceptor, tuberous root) from the side of tuberous root growth. The plants used for grafting were the cultivar (Okinawa No.100) (Ipomoea batatas Poiret), the wild type (IB63005) [1.trifida (H.B.K.)Don.], and the interspecific hybrid between wild type and cultivar (IB66403, IB66502). The wild type plants and interspecific hybrid plants were inferior in thickening growth of tuberous roots to the cultivar. For the purpose of study of interrelationship between source and sink of photosynthates, twelve kinds of sample grafts were cultured. The study results are as follows: (1) The dry weights of whole plants and tuberous roots of the plants grafted on 0kinawa No.1OO stock were far superior to those grafted on the wild type and interspecific hybrid stocks. In general, the dry matter production ranked higher in order of quantities: The grafts of Okinawa No.10O stock>the grafts of IB66502 stock>the grafts of IB66403 stock>the grafts of IB63005 stock. (2) The growth of tuberous roots was promoted in case of grafts of Okinawa No.100 stock. The growth of tuberous roots was small in case of grafts of wild type and interspecific hybrid stocks. In addition, the starch content in the tuberous roots was high in case of grafts of Okinawa No.100 stock notwithstanding their large tuberous roots. (3) In case of grafts of wild type and interspecific hybrid stocks, it was observed that the dry weights of tuberous roots were Small. The growth of pencile type roots and the fibrous roots was promoted. In case of top part of grafts, a decided increas was found in the dry weight of the stems. The starch contents in their leaf blades, leaf petioles, stems, and fibrous roots were higher than those the grafts of cultivar stock. (4) Total ¹⁴C-radioactivities of the plants ranked higher in order: the grafts of Okinawa No.100 stock > the grafts of IB66502 stock. In case of grafts of Okinawa No.100 stock, high ¹⁴C translocation rates to tuberous roots were found after twenty-four hours and seven days after the exposure to ¹⁴CO₂gas, and high ¹⁴C translocation rates to stems were found on the seventh day after the exposure to ¹⁴CO₂gas. (5) From the above-mentioned facts, it may be considered that the interrelationship between source and sink is close in case of grafts of Ipomoea, and that the sink function is active. It can also be considered that the sink action has effects on the parts of the source