The rationale for the following research was to analyse the response of sunflower hybrids to different sowing dates and to evaluate hybrid response to critical environmental conditions. The data used are from an experiment conducted in a location-year combination over a period of two years (2007–09) in southern Italy. Eleven hybrids were tested following a randomized complete block design with three replications at each location-year combination. Eight agronomic characters including seed oil content were recorded. Classification and ordination procedures were used to investigate hybrid performance in relation to three different sowing dates. Combined analysis of variance showed that hybrids, location-year combination, sowing date and their interactions were highly significant for all characters. Hybrid performances were classified by cluster analysis into groups that were differentiable in terms of means and stability. The first three components accounted for 74%, 82%, and 87% of the total variation for the first, second and third sowing date respectively. Plotting component one against component two along Euclidean axes should therefore provide a reasonable representation of the spatial arrangements of hybrid performances in the original multi-dimensional space. The applied statistical method gives full information on hybrid performances similarity. 1. Introduction Sunflower (Helianthus annuus L.) is one of the most cultivated and widespread oilseed crops. In recent years sunflower seed production has decreased, compared to the four major oilseeds (soybean, rapeseed, cottonseed, and groundnut). This is because sunflower continues to be allocated to marginal environments and soils with low fertility where drought and high temperatures may continually impair the yield per unit area (see review [1]). Conventionally, sunflower is sown around mid March; grain filling and oil accumulation are reached in June and July, when high evaporative demand and rare rainfall events take place. Although the sunflower crop may rely on stored soil moisture, it remains subject to water deficits and rainfall during the growing season, which then results in low yields, ranging from 500 to 2500？kg？ha？1 across location and time [2]. In Southern Italy environmental factors such as water deficit and summer drought, typical of the Mediterranean climate, may represent a limit for all spring-planted crops as well as for sunflower. Rainfall, which ranges from 200 to 600？mm？year？1 and is generally concentrated in autumn-spring, does not satisfy the demands of the crop. To take as an
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