SCREENING FOR SOURCE-SINK POTENTIALS IN SOME SWEET POTATO (Ipomoea batatas(L.)Lam.) LINES IN JOS – PLATEAU, NIGERIA.

Fourteen (14) sweet potato (Ipomoea batatas(L.)Lam.) clones, TIS.8441, Ex Igbariam, TIS.86/0356, TIS.86/0306, TIS.2271, TIS.2532.OP.1.13, CIP 4400168, TIS.2544 Rusanya 1.5, TIS.82/0270.OP.1.85, TIS.82/0070.OP.120, TIS.8/637, NRCRI/UN/13, TIS.87/0087 and a farmer’s variety(Dan-Mangu), were screened during the cropping seasons of 2000 and 2001, to evaluate their yield potentials under the Jos-Plateau environment. The randomized complete block design was used with four replications. On the basis of differences in vine length, number of branches per plant, total tuber yield, dry matter content, leaf size, leaf orientation and harvest index, six out of the fourteen clones, Ex-Igbariam, TIS.87/0087, TIS.2532.OP.1.13, CIP 4400168, TIS.86/0356 and TIS.2544 Rusanya 1.5, were selected for grafting study during the 2003 cropping season. Results of the studies revealed that tuberous root yield of the sweet potato clones varied with genotype and environment. Petiole length, number of branches per plant, number of tubers/m 2 and per plant and mean tuber weight were shown to have greatly influenced total tuber yield. Total dry matter accumulated increased with crop age and varied with genotype. The proportion of dry matter in the above-ground portion decreased while that of the tubers increased with crop age. In low-yielding clones, more dry matter was left in the leaves and stems than in the tubers. Results of the grafting study showed a high degree of graft-compatibility amongst the clones used. Both total and dry tuberous root yields were influenced by the size and activity of the source and the sink as well as the rate of translocation of assimilates from the former to the latter. Clones Ex Igbariam and TIS.2544 Rusanya 1.5 had the highest source potential and the largest sink capacity, respectively. While clone CIP 4400168 showed the greatest response of source to sink, clone TIS.2532.OP.1.13 demonstrated the greatest response of sink to source. Clones Ex-Igbariam and TIS.2544 Rusanya 1.5 ranked amongst the highest yielders. Clone CIP 4400168 appeared to have been limited in its yield potential by a poor sink capacity and slow rate of translocation of assimilates from the source to the sink. Selection of clones with large sink capacities and ideal degree of response of sink to source will, to some extent, lead to higher yield in the sweet potato.