Spontaneous Sexual Triploids from Intraspecific Crosses of Cassava (Manihot esculenta Crantz): Molecular Evidence

A triploid cassava with somatic chromosome number 2n=54 had been identified from a hybridisation made in 1984 involving two diploid parents, �H-165� and �Sree Sahya�. It was a first report, in cassava, at that time, and as such the parentage of the triploid hybrid was questioned. In tuber characters, it showed more resemblance to the female parent, but it had the striking dark purple petiole colour inherited from the male parent. This hybrid has broad leaves typical of triploids. This paper gives the molecular evidence for the parentage of this �spontaneous sexual triploid� derived from intraspecfic cross. RAPD analysis of the parents and hybrids using 12 random primers was performed. It was interesting to find that all the DNA bands in the hybrid had come from either of the parents and not a single new band appeared. Analysis of the Similarity Index showed that the hybrid was more similar to Sree Sahya, the male parent (0.83) than the H-165 female parent (0.54). This hints at the role of 2n pollen in production of this �spontaneous sexual triploid�. The superiority of this triploid over the parents and the significance of sexual triploids in crop improvement are discussed.