Meiosis in Solanum phureja

Meiosis and pollen mitosis were studied in a clone of Solanum phureja in order to elucidate the generally high frequency (about 90 %) of tetraploid progeny in tetraploid X diploid crosses involving S. phureja. The first meiotic division was normal with 12 bivalents in metaphase and apparently normal chromosome disjunction. The second meiotic division showed normal metaphases with 12 chromosomes in each of the two spindles, along with cells showing a bi- or tripolar spindle (cell wall formation was simultaneous). At the end of the second division those disturbances resulted in unreduced cells either with two diploid nuclei or with one diploid and two haploid nuclei along with the normal tetrads with four haploid nuclei. The frequency of unreduced gametes was about 50 %. First and second pollen mitoses were also represented by normal haploid as well as unreduced diploid cells. Hence, the high frequency of tetraploid offspring in Solanum tuberosum X S. phureja crosses could be caused by selective fertilization with unreduced diploid pollen grains.