The aim of the work was to study the relationships between different pathological characters and some yield components reduction in sunflower hybrids artificially inoculated at the base of the stem with the fungus Sclerotinia sclerotiorum. Eight commercial hybrids were inoculated at the closed flower-bud stage at three planting dates. They were evaluated for their suscept- ability by recording: the lesion lenght (LL), the percentage of dead plants (PD) and a disease severity index (DSI) based on the wilting degree at three different moments. At physiological maturity both non-inoculated and inoculated plants from all the hybrids were harvested to determine the number of fertile capitula. number of seeds per capitulum and 1000-cypselae weight. The percentages of yield reduction in the diseased plants were calculated with respect to each hybrid check.

Correlation studies showed highly significant and positive coefficients between all the pathological characters and yield reduction at two evaluation moments (10 and 13 days after inoculation) at first planting date. At second planting date the same type of correlation was observed for LL (7 and 13 days). and for DSI (13 days). At third planting date (most severe environment), yield reduction was not correlated with the pathological characters.

Positive and significant correlation coefficients were found between the lesion lenght measured 7 days after the inoculation with all planting dates. It was concluded that lesion lenght measured few days after the inoculation seems to be a simple and direct evaluation method that also related with yield reduction in moderate-attack conditions.