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The rate of organ emergence and the duration of developmental phases are key components of plant fitness to its environment. Here, we describe a hybrid genetic algorithm for the estimation of the parameters of complex non-linear simulation models that we used to estimate the varietal parameters of a well-evaluated ecophysiological model (Sirius) of wheat phenology. The aim of this study was to analyze the correlations between the varietal parameters of Sirius and to determine the minimum number of parameters that need to be estimated in order to accurately simulate the effect of the genotype and environment on wheat anthesis date. A panel of 16 bread wheat cultivars was grown under controlled conditions with different vernalization and daylength treatments and in a field nursery with different sowing dates in order to characterize their vernalization and photoperiodic requirements and earliness per se. These cultivars were also grown in the field in two consecutive growing seasons in France and in the UK along a 800 km latitude transect, where the dynamics of leaf appearance and anthesis date were determined. Variation in both final leaf number and anthesis date in response to the environment and the genotype was predicted with a mean error of 0.55 leaves and 3.94 d, respectively, after estimation of only three of the seven varietal parameters of Sirius: the phyllochron, the response of vernalization rate to temperature, and the daylength response of leaf production. Among them, the phyllochron was reasonably well estimated and showed a positive association with earliness per se (Spearman's coefficient of rank correlation = 0.59). This study showed that the number of varietal parameters in Sirius was overestimated and that considering only three varietal parameters reduced the correlations between the parameters and the root mean square error of prediction for final leaf number and anthesis date. We conclude that a phenomenogical model of wheat development can be used to estimate key phenological parameters that are difficult to determine in the field; offering the possibility to conduct large-scale quantitative genetic studies to understand better the genetic control of flowering time in cereals.

Of the 2 million ha of wheat grown annually in the UK, about 700,000 ha are grown on drought-prone soils. With predicted climate change, the frequency of summer droughts is likely to increase. By mapping genes controlling improved end-use quality under stress, the objective is to provide UK plant breeders with information on genes, and selection methods for traits conferring more stable end-use quality under drought-stress conditions. A mapping population of 48 doubled haploid lines and their parents (Beaver & Soissons), has been investigated over two seasons (2002 and 2003 harvest years), on a drought-prone, loamy sand at ADAS Gleadthorpe. The different lines were grown both with, and without irrigation, in fully replicated field experiments, to examine the differential response of the lines to drought. Physiological assessments were made throughout the season, and yield determined at grain maturity. Hand harvested grain was assessed for mealiness (=100-vitreosity), hardness, grain size, grain weight, grain protein content and measurements made of gel protein quality. The initial observations suggest that the effect of drought was to reduce grain size, increase grain crude protein concentration, and to increase vitreosity of the grain. At the same time, grain protein quality was improved, and grain hardness increased under drought conditions. New QTL have been identified and further work is ongoing to understand the interactions between genotype and environment on grain quality in these lines.

Crop species can show differential responses to successful, widely used, herbicides where some varieties are unaffected by application, whilst others show symptoms of damage ranging from a slight reduction in vigour to complete plant death. The elucidation of the genetical control of such responses is important for developing strategies for breeding for herbicide resistance within crop species and also in understanding the modes of action of the herbicides and the evolution of resistance in weed species. To investigate this phenomenon in cereals detailed studies of the control of responses of wheat to difenzoquat and to three phenylureas, chlorotoluron, metoxuron and isoproturon, have been carried out. These have revealed that the primary differences in response between resistant and susceptible varieties are due to single major genes, although the influence of other “modifier” genes has also been detected. It has also been shown that the responses to chlorotoluron and metoxuron are determined by the same gene. Studies of related wild grass species have indicated that polymorphisms for response also exist in such species. This suggests that the genes for differential responses have evolved prior to the domestication of the cultivated cereals and not in response to the development and use of the chemicals. The importance of these results for developing strategies for the incorporation of herbicide resistance in new varieties of crop species by conventional and non-conventional methods of plant breeding is discussed.