The Potential of Meiotic Polyploidization in Breeding Allogamous Crops
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1984-05
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Meiotic and mitotic polyploidization are compared as to frequency of occurrence in nature and potential for breeding allogamous crops. Meiotic polyploidization via diploid first-division-restitution-gametes is the more powerful approach and can be applied either unilaterally or bilaterally. It is explained how 2n-gametes can be traced by (1) seeking for polyploid plants in diploid populations followed by 4x-2x matings; (2) using colchicine-doubled genotypes in 4x-2x matings; (3) visual discrimination of stained 2n- and n-pollen in diploid plants; (4) establishing the frequency of dyad formation in diploid plants; and (5) large-scale reciprocal crosses between diploids and tetraploids. Basically all mechanisms leading to FDR gametes can be utilized for breeding through sexual polyploidization, because of the largely intact transfer of the parental genotype to the progeny via such gametes. FDR-genotypes mostly produce both 2n- and n-gametes in various proportions. The common occurrence of lethality of triploid zygotes ("triploid block") is explained and its significance discussed. Sexual polyploidization is a desirable breeding technique in those crops which at the polyploid level have a better potential performance than at the diploid level. Examples are given. Such better performance of polyploids is based on the larger potential of non-additive gene effects owing to multi-allelism. The highest degree of multi-allelism is obtained with unrelated highly heterozygous parents, the diploid parents producing FDR gametes. Experimental results are discussed which illustrate the great potential of sexual polyploidization, but at the same time reveal the need of divergent FDR-genotypes with high economic value including resistance to the most important diseases and with a stable mechanism for high-frequency production of 2n (FDR) gametes. An adequate breeding program at the diploid level aimed at breeding such FDR-genotypes is advocated. Index Descriptors: sexual polyploidization, breeding, 2n-gametes, autopolyploids, ornamentals, maize, and combining ability.
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Iowa State Journal of Research, May 1984, Vol.58 No.4, p.435-448