Chromosome number and chromosome behaviour of F1 and F2 plants of the crossSolanum phureja x Solanum tuberosum

Cytogenetical Studies in Relation to the Origin and Differentiation of Species in the GenusSolanumL.

“…BucK concludes from this that Downloaded by [North West University] at 12:18 20 December 2014 the diploid species studied by him carry a nuclear factor which reacts with the .cytoplasm of some clones of verrucosum to produce male sterility in the hybrids. KooPMANS (1952KooPMANS ( , 1954KooPMANS ( , 1955KooPMANS ( and 1959 found in the F 2 of the cross S. phureja (S. rybinii) x S. chacoense, a larger number of floral abnormalities. Analysis of later backcross generations in which the backcross with chacoense had a greater number of progeny with floral abnormalities, suggested the possibility that these were brought about by the interaction of the cytoplasm of phU1·eja and the genes of chacoense (for alternative explanation see section VI).…”

“…Tetraploid hybrids from S. tuberosum x diploid species and reciprocal crosses are fairly common (OPPEl 'lHEIMER 1933, PROPACH 1938a and b, IVANOVSKAJA 1941, STELZNER 1943, PRAKKEN and SWAMINA-THA.J. "l 1952, KoOPMANS and VAN DER BERG 1952, GoPPART and Ross 1954, WANGE-NHEIM 1957. They are generally more fertile than the triploids and exhibit associations approaching 24n at meiosis, a few univalents and quadrivalents being also observed.…”

“…Similarly RYBIN (1933) emphasized that unreduced gametes do not function in crosses with S. tuberosum, inspite of the fact that dyad formation is very common in this speCies. According to KooPMANs and VAN DER BERG (1952) doubling of a reduced gamete may occur even after the pollen has entered the micropyle and the male gamete has entered the egg cell, perhaps due to plasmatic influence.…”

“…A probable example of hybrid breakdown at a somewhat later stage is the case recorded by KooPMANS (1952KooPMANS ( , 1954KooPMANS ( , 1955KooPMANS ( and 1959 who found many floral abnormalities among the F 2 individuals of the cross, S. rybinii x S chacoense. Though KooPMANS herself attributes these to plasmatic effects, such breakdown of the hybrid progeny can perhaps be also due to disharmonius interactions between the combinations of parental genes resulting from their random assortment during meiosis in the hybrid.…”

Meiosis in Solanum phureja

“…As already mentioned, KOOPMANS and VAN DER BURG (1952) suggested that doubling after the sperm nucleus had entered the egg cell accounted for the presence of tetraploid embryos in this type of crosses. Judging from my results one would rather assume that due to some plasmatic influence from the tetraploid pistil tissue or from the diploid egg cell, there might be a selective preference to already doubled pollen grains to affect fertilization and to give rise to the high frequency of tetraploid progeny in tetraploid X diploid crosses.…”