Nectar secretion in winter oilseed rape, Brassica napus -: quantitative and qualitative variability among 71 genotypes

The genotypic variability in nectar secretion among 71 genotypes of winter oilseed rapes was tested for floral nectar volume, sugar composition and concentration. Differences were found between seed quality genotypes: double low [00] oilseed rape varieties tended to secrete much more nectar than single low [0 + ] and double high [+ +] varieties. Male-sterile lines (Ogura CMS) secreted one-half to one-third the amount of their isogenic male-fertile counterparts. Restored lines behaved as conventional rape varieties. On average, amounts of nectar were 2 mu l/flower and ranged from 0.7 to 6 mu l/flower. Among the genotypes under test, the male-sterile lines were not the least productive. The analysis of 'Samourai' winter oilseed rape showed that total sugar concentrations in nectar were highest at the beginning of the flowering period (30 g/100 ml) and lowest towards the end (10 g/100 ml). At a given date, total sugar contents in nectar of [0 +] varieties were significantly higher than those of[+ +] varieties and were due to higher fructose contents. Differences between genotypes within the same type also occurred, depending on the day of sampling. Oilseed rape nectar was confirmed to be predominantly composed of hexose (glucose and fructose). From the results of these investigations, it is concluded that the opportunity exists to select oilseed rape genotypes, including male-sterile lines, that secrete sufficient amounts of nectar to attract honeybees to ensure pollination of male-sterile lines for hybrid seed production.