The Vrnl, Vrn2 and Vrn3 genes have different values of effects on heading date and related yield components . The genetic background and environment do not affect the ranking of Vrn genotypes according to earliness within near-isogenic line sets ; however, they do influence the level of differences between heading dates of particular genotypes and between effect values, respectively . The frequencies of defined Vrn genotypes in the global set of spring bread wheat cultivars are associated with grain weight per plant predicted on the basis of Vrn gene effects averaged over backgrounds and over environments . Peculiarities of backgrounds and environments alter the grain yield ranges of Vrn genotypes . For early photoperiodinsensitive wheats, planted in stress conditions at grain filling, the highest yield was predicted for double dominant Vrn genotypes with Vrn3 . This gene is rarely used by the breeders in middle latitudes and its wider adoption is encouraged .

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Alien dominant genes of spring habit were introgressed into bread wheat. The introgression was undertaken by simple crossing of winter bread wheat to related spring species or genera, followed by backcrossing to winter bread wheat, and did not involve the use of the ph mutants or embryo culture. The introgressed genes were located mostly on chromosomes of homoeologous group 5, and were allelic to the known Vrn genes in bread wheat. Nevertheless three groups of lines were discovered with the genes possibly located on other chromosomes. These genes were non-allelic to each other and to known Vrn genes and were designated Vrn6 so, Vrn7 sc (introgressed from Secale c ereale ) and Vrn8 T s (from Triticum sphaerococcum ).

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