The cytogenetics of Phaseolus vulgaris L., Phaseolus coccineus L, their interspecific hybrids, derived amphidiploid and backcross progeny in relation to their potential exploitation in breeding.

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Abstract
Chromosome number in P. vulgaris and P. coccineus is 2n = 22. In F1 hybrids pairing is predominantly bivalent, the formation of occasional multiple figures indicating some structural differentiation. Multivalent formation is observed in the derived amphidiploid; frequency declines from C1-C5 with corresponding improvement in seed fertility and pollen stainability. Factors favoring homologous pairing are evidently selected. Meiosis and seed fertility in F2 and most F1 backcrosses are more or less normal except for the BC1 F1 (P. vulgaris .times. P. coccineus) .times. P. coccineus which had very low fertility. Introgression is possible reciprocally between the 2 spp. because the F1 interspecific hybrid, initially made on P. vulgaris can be backcrossed as pollen parent to both original parents used as seed parent. It is very difficult to transfer 2 characters cotyledon and stigma positions between species which may be related to chromosome structural differences. The fertility of the amphidiploid may be raised to the diploid level by recurrent selection.

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