SUMMARYFlowering time is a trait that has been extensively altered during wheat domestication, enabling it to be highly productive in diverse environments and providing a rich source of variation for studying adaptation mechanisms. Hexaploid wheat is ancestrally a long-day plant, but many environments require varieties with photoperiod insensitivity (PI) that can flower in short days. PI results from mutations in the Ppd-1 gene on the A, B or D genomes, with individual mutations conferring different degrees of earliness. The basis of this is poorly understood. Using a common genetic background, the effects of A, B and D genome PI mutations on genes of the circadian clock and photoperiod pathway were studied using genome-specific expression assays. Ppd-1 PI mutations did not affect the clock or immediate clock outputs, but affected TaCO1 and TaFT1, with a reduction in TaCO1 expression as TaFT1 expression increased. Therefore, although Ppd-1 is related to PRR genes of the Arabidopsis circadian clock, Ppd-1 affects flowering by an alternative route, most likely by upregulating TaFT1 with a feedback effect that reduces TaCO1 expression. Individual genes in the circadian clock and photoperiod pathway were predominantly expressed from one genome, and there was no genome specificity in Ppd-1 action. Lines combining PI mutations on two or three genomes had enhanced earliness with higher levels, but not earlier induction, of TaFT1, showing that there is a direct quantitative relationship between Ppd-1 mutations, TaFT1 expression and flowering.

Flowering time in wheat and barley is known to be modified by mutations in the Photoperiod-1 (Ppd-1) gene. Semi-dominant Ppd-1a mutations conferring an early flowering phenotype are well documented in wheat but gene sequencing has also identified candidate loss of function mutations for Ppd-A1 and Ppd-D1. By analogy to the recessive ppd-H1 mutation in barley, loss of function mutations in wheat are predicted to delay flowering under long day conditions. To test this experimentally, introgression lines were developed in the spring wheat variety ‘Paragon’. Plants lacking a Ppd-B1 gene were identified from a gamma irradiated ‘Paragon’ population. These were crossed with the other introgression lines to generate plants with candidate loss of function mutations on one, two or three genomes.Lines lacking Ppd-B1 flowered 10 to 15 days later than controls under long days. Candidate loss of function Ppd-A1 alleles delayed flowering by 1 to 5 days while candidate loss of function Ppd-D1 alleles did not affect flowering time. Loss of Ppd-A1 gave an enhanced effect, and loss of Ppd-D1 became detectable in lines where Ppd-B1 was absent, indicating effects may be buffered by functional Ppd-1 alleles on other genomes. Expression analysis revealed that delayed flowering was associated with reduced expression of the TaFT1 gene and increased expression of TaCO1.A survey of the GEDIFLUX wheat collection grown in the UK and North Western Europe between the 1940s and 1980s and the A.E. Watkins global collection of landraces from the 1920s and 1930s showed that the identified candidate loss of function mutations for Ppd-D1 were common and widespread, while the identified candidate Ppd-A1 loss of function mutation was rare in countries around the Mediterranean and in the Far East but was common in North Western Europe. This may reflect a possible benefit of the latter in northern locations.

BackgroundMeasuring grain characteristics is an integral component of cereal breeding and research into genetic control of seed development. Measures such as thousand grain weight are fast, but do not give an indication of variation within a sample. Other methods exist for detailed analysis of grain size, but are generally costly and very low throughput. Grain colour analysis is generally difficult to perform with accuracy, and existing methods are expensive and involved.ResultsWe have developed a software method to measure grain size and colour from images captured with consumer level flatbed scanners, in a robust, standardised way. The accuracy and precision of the method have been demonstrated through screening wheat and Brachypodium distachyon populations for variation in size and colour.ConclusionBy using GrainScan, cheap and fast measurement of grain colour and size will enable plant research programs to gain deeper understanding of material, where limited or no information is currently available.

FLOWERING LOCUS T2 (FT2) is expressed in the distal part of the developing wheat spike and contributes to the regulation of the number of spikelets per spike.