Although commonplace in human disease genetics, genome-wide association (GWA) studies have only relatively recently been applied to plants. Using 32 phenotypes in the inbreeding crop barley, we report GWA mapping of 15 morphological traits across ∼500 cultivars genotyped with 1,536 SNPs. In contrast to the majority of human GWA studies, we observe high levels of linkage disequilibrium within and between chromosomes. Despite this, GWA analysis readily detected common alleles of high penetrance. To investigate the potential of combining GWA mapping with comparative analysis to resolve traits to candidate polymorphism level in unsequenced genomes, we fine-mapped a selected phenotype (anthocyanin pigmentation) within a 140-kb interval containing three genes. Of these, resequencing the putative anthocyanin pathway gene HvbHLH1 identified a deletion resulting in a premature stop codon upstream of the basic helix-loop-helix domain, which was diagnostic for lack of anthocyanin in our association and biparental mapping populations. The methodology described here is transferable to species with limited genomic resources, providing a paradigm for reducing the threshold of map-based cloning in unsequenced crops.genetic variation | small grain cereals | colinearity

The ability of roots to extract soil moisture is critical for maintaining yields during drought. However, the extent of genotypic variation for rooting depth and drought tolerance in Northern European wheat (Triticum aestivum L.) germplasm is not known. The objectives of this study were to measure genotypic differences in root activity, test relationships between water use and yield, examine trade-offs between yield potential and investment of biomass in deep roots, and identify genotypes that contrast in deep root activity. A diverse set of 21 wheat genotypes was evaluated under irrigated and managed drought conditions in the field. Root activity was inferred from patterns of water extraction from the soil profile. Genotypes were equally capable of exploiting soil moisture in the upper layers, but there were significant genotypic differences in rates of water uptake after anthesis in deeper soil layers. For example, across the three years of the study, the variety Xi19 showed consistently deeper root activity than the variety Spark; Xi19 also showed greater drought tolerance than Spark. There were positive correlations between water extraction from depth and droughted yields and drought tolerance, but correlations between deep water use and yield potential were not significant or only weakly negative. With appropriate screening tools, selection for genotypes that can better mine deep soil water should improve yield stability in variable rainfall environments.

The suitability of an electrical conductivity assay of leaf material for determining frost hardiness in winter cauliflower was established. The assay was used to monitor the changes in hardiness of field-grown plants during two seasons at two sites.Levels of frost hardiness were related to mean air temperature over the 7-day period prior to sampling (r = 0.6008, P < 0.001). There was no clear disjunction of any temperature to indicate a threshold temperature of hardening. Dehardening occurred in spring and during mild spells in winter. In the mild regions where this crop is grown commercially it is likely that plants are not fully hardened for much of the winter. This may facilitate curd growth but may put the crop at risk from frost damage. Frost hardening in winter cauliflowerRumleigh 1986/87

SUMMARYThe role of leaves as insulation for mature curds during exposure to frost has been investigated for winter‐harvested cauliflower. The inner, wrapper‐leaves and their enclosed air spaces provided significant protection for the curd tissues in mild frost, but under more severe conditions (below – 2.5°C) were ineffective. A relationship between higher wrapper‐leaf number and increased insulation was described. The increase in insulation however, was small even with much higher wrapper‐leaf numbers. Exposure of the curd surface at maturity was found to prevent the insulating effect of wrapper‐leaves, particularly if the diameter of the exposed area was greater than 6 cm. The data also suggested a possible role for the exposed stem of the cauliflower as a site of heat loss that may adversely affect curd temperature.It is postulated that breeding for improved frost resistance by greatly increasing wrapper‐leaf number would not be effective, although any reduction in wrapper‐leaf number and the presence of tightly wrapped curds should be avoided. Furthermore, exposure of the curd surface at maturity should be kept to a minimum.

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