Linkage between Morphology and Viability in Plant Species

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Abstract
Genes determining morphological characters which are 1st expressed in late stages of development in higher plants, particularly in the flowers and fruits, are frequently linked with genes affecting growth and vigor in early developmental stages. Related plant species commonly differ allelically with respect to the linked morphological and viability genes, as indicated by the evidence of artificial interspecific hybridizations in many plant groups. The so-called M-V linkage system is found on presumably homologous chromosome segments in related species of Mimulus, Gossypium, Lycopersicon, Triticum, Tragopogon, Phaseolus, and perhaps Rubus; and in related subspecies of Potentilla glandulosa. The M-V linkage evidently occurs on rearranged segments differentiating related species of Clarkia, Gossypium, Zea, Triticum, and Gilia. There does not appear to be any basic difference in the M-V linkage as found between chromosomally homologous species and between structurally differentiated ones. A special case is that of linkage between morphological genes affecting the sporophyte generation and viability genes affecting the gametophyte. This interesting type of M-V linkage is known from intraspecific crosses in Lycopersicon and Triticum, and is suspected within species of Matthiola and Hordeum. It may exist also at the interspecific level in Nicotiana, Phaseolus, and Chrysanthemum, though other interpretations of the available evidence are possible. The M-V linkage thus appears to be a general feature in the genetic architecture of plant species. This condition leads to end results in natural interspecific hybridization which are indistinguishable from the effects of introgression.