Chromosome pairing set and the presence of unreduced gametes explain the possible origin of polyploid progenies from the diploids 'Tosa-Buntan' X 'Suisho-Buntan' pummelo

Abstract

To clarify why polyploids were generated from the cross of the diploids 'Tosa-Buntan' and 'Suisho-Buntan' pummelo (Citrus grandis [L.]Osb.), the chromosome compositions of their di-, tri-, and tetraploid progenies, based on CMA staining, and their chromosome parings were observed. 1. Thirteen kinds of chromosome composition were manifested by 38 diploid seedlings indicating that the chromosome compositions of seedlings are highly variable. 2. Among the 13 kinds of diploid chromosome composition, the number of chromosome varied 1 to 3 in chromosome type-A, 0 to 1 in type-B, 3 to 5 in type-C, 2 to 4 in type-D, and 8 to 10 in type-E. The number of chromosome type-A varied 1 to 2 among the chromosome compositions with chromosome type-B. From these results, the paring set of the chromosome type in 'Tosa-Buntan' was estimated as AB+CC+CC+CD+DE+EE+EE+EE+EE or AB+CC+CC+DD+ CE+EE+EE+EE+EE. 3. Among six triploid seedlings, three kinds of chromosome composition exist which suggested that they resulted from unreduced female gamete at the first or second meiotic division, or unreduced male gamete at the second meiotic division. 4. Among three tetraploid seedlings, two kinds of chromosome composition exist. Because the chromosome compositions had two type-B chromosomes and an even number of chromosome of any other type, they probably resulted from the combination of an unreduced female with unreduced male gametes at the second meiotic division. These results showed that the triploid seedlings from diploid 'Tosa-Buntan' X 'Suisho-Buntan' crossing also originated from an unreduced male gamete as well as from an unreduced female gamete.