Nigeria is a country endowed with enormous food and agricultural resources such as yam, cassava, cocoa, rice, sugar cane, maize and millet. In the early years of Nigeria's independence, cash crops such as rubber, cashew, groundnut and oil palm were the major crops around which the economy revolved. Today, there is a shift to alternatives for biofuel, pharmaceutical starch and derivatives using root and tuber crops, which have continued to play a significant role in the agricultural revolution of the country. The current agricultural transformation agenda in Nigeria is intended to engineer the bulk of root and tuber crops in the country into value-added products to match the increasing new tastes and demands for products across the globe. It is also intended to provide job opportunities and to generate additional income for low-income earners, especially in the rural areas. There is, therefore, the need to intensify research efforts aimed at exploring the potentials of major and minor root and tuber crops to ensure food security. In this review, six (6) major root and tuber crops, namely cassava (Manihot esculenta Crantz), yam (Dioscorea spp.), sweet potato (Ipomoea batatas (L.) Lam), potato (Solanum tuberosum L.), cocoyam (Xanthosoma sagittifolium Schott) and ginger (Zingiber officinale L.) as well as three (3) minor ones, namely the Hausa potato (Solenostemon rotundifolius (Poir) J. K. Morton), Livingstone potato (Plectranthus esculentus N.E.Br.) and the Polynesian arrowroot (Tacca leontopetaloides (L.) Kuntze) were examined. In spite of the numerous benefits derivable from these crops in terms of nutrition and medicinal values, some have been neglected to the extent that they are classified as orphan crops. Therefore, much more attention should be accorded to these crops, which have the potentials to contribute to food security in Nigeria.

The Hausa potato is a minor tuber crop with nutritional and medicinal values. A lack of balance between the photosynthetic source potential and the sink capacity in terms of dry matter accumulation and distribution is believed to affect fresh tuber yield. This study was aimed to investigate the dry matter production, distribution and tuber yield of reciprocal grafts of some accessions of the Hausa potato. The grafts were made in all possible combinations and laid out using the completely randomized design in four replicates. Results showed that harvest index increased with time in most of the grafts. The proportion of dry matter partitioned to the tubers was generally lower than those of the leaves and stems in all the grafts. The highest rootstock-scion ratio of 0.97 was observed in the graft Bokkos 2 - Manchok 2 while the lowest (0.07) was observed in the self-graft of Bokkos 2. Fresh tuber yield was generally low, ranging from 0.03 t ha -1 to 0.09 t ha-1. Apart from dry matter accumulation and distribution, the relationship between the source potential and sink capacity as well as the rate of translocation of assimilates from the photosynthetic source to the sink need to be investigated.