Abstract
Wheat adaptability to a wide range of environmental conditions is mostly determined by allelic diversity within genes controlling vernalization requirement (Vrn-1) and photoperiod sensitivity (Ppd-1). We characterized a panel of 151 durum wheat Mediterranean landraces and 20 representative locally adapted modern cultivars for their allelic composition at Vrn-1 and Ppd-1 gene using diagnostic molecular markers and studied their association with the time needed to reach six growth stages under field conditions over 6 years. Compared with the more diverse and representative landrace collection, the set of modern cultivars were characterized by a reduction of 50% in the number of allelic variants at the Vrn-A1 and Vrn-B1 genes, and the high frequency of mutant alleles conferring photoperiod insensitivity at Ppd-A1, which resulted on a shorter cycle length. Vrn-A1 played a greater role than Vrn-B1 in regulating crop development (Vrn-A1 > Vrn-B1). The results suggest that mutations in the Vrn-A1 gene may have been the most important in establishing the spring growth habit of Mediterranean landraces and modern durum cultivars. The allele Vrn-A1d, found in 10 landraces, delayed development. The relative effects of single Vrn-A1 alleles on delaying the development of the landraces were vrn-A1 = Vrn-A1d > Vrn-A1b > Vrn-A1c. Allele vrn-B1 was present in all except two landraces and in all modern cultivars. The null allele at Ppd-A1 (a deletion first observed in the French bread wheat cultivar ‘Capelle-Desprez’) was found for the first time in durum wheat in the present study that identified it in 30 landraces from 13 Mediterranean countries. Allele Ppd-A1a (GS105) was detected in both germplasm types, while the allele Ppd-A1a (GS100) was found only in modern North American and Spanish cultivars. The relative effect of single Ppd-A1 alleles on extending phenological development was Ppd-A1(DelCD) > Ppd-A1b > Ppd-A1a (GS105) > Ppd-A1a (GS100). Sixteen Vrn-1+Ppd-1 allelic combinations were found in landraces and six in modern cultivars, but only three were common to both panels. Differences in the number of days to reach anthesis were 10 days in landraces and 3 days in modern cultivars. Interactive effects between Vrn-1 and Ppd-1 genes were detected.
Highlights
Flowering time is a major adaptive trait of wheat that allows the crop to fill the grains under the most favorable environmental conditions, so it has a strong effect on reproductive success and final yield
The winter allele vrn-A1 was found to be present in only two landraces, but vrn-B1 was identified in 99% of the landraces and in all modern cultivars
The selection performed in most spring wheat breeding programs for low latitude environments since the Green Revolution have reduced the allelic diversity at vernalization requirement (Vrn)-1 and photoperiod sensitivity (Ppd)-1 genes from that present in ancient landraces, resulting in a narrower developmental scope in modern cultivars
Summary
Flowering time is a major adaptive trait of wheat that allows the crop to fill the grains under the most favorable environmental conditions, so it has a strong effect on reproductive success and final yield (reviewed by Cockram et al, 2007). In environments such as the Mediterranean, where temperatures rise and water becomes scarce during grain filling, early flowering is a very efficient mechanism for escaping terminal stress. The complex process of wheat development is determined to a great extent by the allelic diversity within genes regulating the vernalization requirement (Vrn) and photoperiod sensitivity (Ppd). The molecular basis of the complex genetic regulation of flowering time in wheat has been extensively studied, but there is still considerable uncertainty about the phenotypic response of the plants due to the interactive effect of the genes involved
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