Cytogenetics of saffron (Crocus sativus), a natural autotriploid species; an investigation on the reasons for its sterility

The red-orange-colored stigmas of saffron are one of the most expensive spices in the world. Meiosis processes in saffron showed that Crocus sativus L. is an autotriploid species with 2n=3x=8+8+8=24 chromosomes. The results obtained from the meiosis behavior indicated that the major role in the sterility of saffron is autotriploidy in this crop. Arrangement of chromosomes as trivalents in meiosis and formation of these trivalents in the forms of frying pan, chain type, Y type, V type, and triangle type at metaphase I, causes their imbalance junction at anaphase I. Unbalance disjunction of chromosomes at anaphase I and II with the occurrence of the lagging chromosomes in these phases, causes sterile gametes. Also, the formation of chromatid bridges at anaphase I and II with the occurrence of micronuclei at telophase II and tetrad stage are the other reasons for the sterility.