Novel interspecific hybridization between sweetpotato (Ipomoea batatas (L.) Lam.) and its two diploid wild relatives

Interspecific hybridization is an important approach to broaden the genetic base and create novel plant forms in breeding programs. However, interspecific hybridization in Ipomoea is very difficult due to the cross incompatibility. Here we report two novel interspecific F-1 hybrids between I. batatas (L.) Lam. (2n = 6x = 90) and two wild species, I. grandifolia (2n = 2x = 30) and I. purpurea (2n = 2x = 30). Hybridization was stimulated by applying plant growth hormones. Morphological, molecular and cytological tests were conducted to confirm their hybridity. We found that the two hybrids were quite distinctive in leaf color and morphology, and yielded intermediate sizes of storage roots compared to their respective parents. Inter-simple sequence repeat analysis showed that the unique DNA bands from the wild parents could be detected in these two hybrids. The cluster analysis also showed that the two F-1 hybrids were closer to I. batatas in phylogeny relationship. The number of chromosomes of the two hybrids was both 60, indicating that the hybrids were tetraploid. The meiotic configuration analysis of the H-1 of I. batatas x I. grandifolia revealed the occurrence of 17.58I + 14.28II + 1.36III + 2.48IV at metaphase I in average chromosome association per pollen mother cells (PMCs), 4.26I + 18.32II + 2.56III + 3.12IV was average meiotic configuration in the H-2 of I. batatas x I. purpurea. Both hybrids appeared to be polyads and multi-microcytes at tetrad phase and differed in their pollen fertility.