Use of dihaploids in the breeding of Solanum tuberosum L. I. Cytological considerations

Abstract

Chiasma frequency in 21 clones derived from crosses between Solanum tuberosum L. dihaploids or hybrid dihaploids and diploid species was estimated at diakinesis. The most common configurations at this stage were cross-, rod- and ring-shaped bivalents. The first two were considered to have one chiasma, the third one two chiasmata. Bivalents with three chiasmata were observed only at early diakinesis. The statistical analysis for chiasma frequency, carried out as a three level hierarchic analysis of variance with unequal sample sizes, showed that neither the variation among mothers nor that among fathers within mothers were statistically significant. The variation among clones within fathers was significant at the 0.001 level. Discussion on genomic relationships between S. tuberosum dihaploids and Solanum diploid and hexaploid species was based on the analysis of variance as well as on the occurrence of univalents, multivalents and laggards. Crossability and meiotic behaviour of the material studied may depend on genes controlling self- and cross-incompatibility, pairing and chiasma formation rather than on differences in the chromosomal structure of the genomes. The production of unreduced gametes was related to asynapsis and to nuclear restitution at AII. Endomitosis in tapetal cells was also recorded and mention was made of the similarity between chromosomes from asynaptic PMC's and those from endomitotic tapetum cells, especially when both have reached their maximal contraction. Chromosomes at endoprophase showed a quite sharp differential staining density pattern which may be useful for the identification of individual chromosomes. The origin of the common potato as well as the use of S. tuberosum dihaploids in the utilization of desirable genes present in some Solanum diploid and hexaploid species were discussed.