Abstract:
In situ flower volatiles from six green-fleshed kiwifruit cultivars (Actinidia chinensis var. deliciosa); ‘Hayward’, ‘Chieftain’, ‘M56’, ‘Zes007’ (Green11), ‘M36’, and ‘M43’ and three yellow-fleshed cultivars (Actinidia chinensis var. chinensis); ‘M33’, ‘M91’ and ‘Zesy002’ (Gold3) were collected by dynamic headspace sampling. Forty-five compounds were detected in the headspace of the green-fleshed kiwifruit flowers, with straight chain hydrocarbons and terpenes accounting for > 98% of the volatiles emitted quantitatively across the six cultivars. Analysis of the flower headspace of the three yellow-fleshed cultivars yielded 48 compounds in total, which were also dominated by straight chain hydrocarbons and terpenes. The yellowfleshed cultivars showed more variation both qualitatively and quantitatively between cultivars than green-fleshed kiwifruit and also had lower levels of hydrocarbons in the headspace. Of these hydrocarbons, (3Z,6Z,9Z)-heptadecatriene is reported for the first time from a floral source while (8Z)-hexadecene and (9Z)-nonadecene are reported for the first time from kiwifruit flowers. All three hydrocarbons were verified by synthesis. Quantitative comparison of the honey bee (Apis mellifera) perceived compounds from the headspace of flowers of the green-fleshed cultivars showed that the males ‘M36’ and ‘M43’ closely matched the female cultivar Green11 that they are used to pollinate. Males ‘M56’ and ‘Chieftain’ were not as closely matched to the female cultivar ‘Hayward’ that they are used to pollinate. The male ‘M56’ in particular differed significantly from the female ‘Hayward’ in four of the six honey bee perceived compounds. Electrophysiological responses of honey bees and bumble bees (Bombus terrestris) were recorded to the headspace of yellow-fleshed kiwifruit flowers. The headspace of the Gold3 pistillate flowers consistently produced 11 antennal depolarisations in the honey bee and five antennal depolarisations in the bumble bee. Nonanal, 2-phenylethanol, 4-oxoisophorone and (3E,6E)-α-farnesene from pistillate flowers elicited responses from both bee species. Honey bees were more sensitive towards the straight chain alkenes than bumble bees, which represented one of the main differences between the responses of the two bee species. The male pollenisers of Gold3; ‘M33’ and ‘M91’ varied greatly from the pistillate flower in floral emissions, with most of the bee active compounds significantly different from the Gold3 flower headspace.