# Comparative Analysis of Volatile Compounds in Flowers of Different _Actinidia_ Species
## 1 Introduction  
Actinidia genus (_Actinidia_ spp.) includes 54 species [1]. However, only few species and varieties are commercially cultivated, including _Actinidia chinensis_, _Actinidia arguta_ and _Actinidia kolomikta_. All actinidia species are dioecious woody vines [2] and come mostly from Asia. The most popular species, cultivated worldwide, are _A. chinensis_ var. _chinensis_ and _A. chinensis_ var. _delicosa_ (amounting to 31% and 37%, respectively, of the total actinidia production), but other species are gaining in importance. In particular, _A. arguta_, also known as hardy kiwifruit, kiwiberry or minikiwi, and _A. kolomikta_, known as super-hardy kiwi, amounting already to 17% and 8% of the total output, respectively [3]. _Actinidia arguta_, a smooth-skinned, grape-sized fruit, contains a high amount of vitamin C, phenolic compounds and minerals, representing a high antioxidant activity, and hence a wide range of health benefits [4; 5; 6; 7; 8]. _Actinidia kolomikta_ is the most tolerant to low temperatures (up to \(-40\)\({}^{\circ}\)C). The fruit is smaller than kiwiberry and matures early in the season [2; 4]. Generally, _A. arguta_ and _A. kolomikta_ fruits both present higher levels of antioxidants, vitamin C and concentration of minerals than _A. chinensis_[3]. The fruit of _Actinidia polygamma_, which has a nice orange colour and a bitter taste, was used mainly in ancient Chinese and Korean folk medicine [9]. As actinidia are dioecious plants, a lot of attention is given to effective pollination. At first, _A. arguta_ was thought to be a wind-pollinated plant. However, previous studies showed that insects like to visit these flowers, and this has a high impact on the fruit set [10; 11; 12; 13]. Moreover, as was found in _A. polygamma_, the seemingly perfect (meaning bisexual) flowers (with stamens producing sterile pollen)are more attractive to insects than those with artificially removed stamens [14]. There are also reports that insects are sensitive to specific volatiles and that they visit certain species more on purpose rather than accidentally. Furthermore, many insect species are able to distinguish between enantiomers of different substances, but react only to one. Such behaviour was also found in the case of pollinating insects [15]. Among flower volatile compounds, lilac aldehyde is highly attractive to pollinators (e.g., Lepidoptera) and is emitted in high amounts in nocturnal plant species [16]. [PERSON] et al. [17; 18] found that certain volatiles of both _A. chinensis_ varieties are recognized by honey bees and bumble bees. Then, apart from the flowers' appearance and the number of stamens, the composition of volatile compounds in flowers is also an interesting subject. To date, more attention is paid to female rather male cultivars, and hence the offer of male selections in nurseries is very low. For various reasons, artificial pollination (often applied in the cultivation of _A. chinensis_) is not practised in kiwiberry production (due to the difficult access to _A. chinensis_ and _A. arguta_ pollen in most kiwiberry-growing countries and the potential risk of Pas transmission by imported _A. chinensis_ pollen). Therefore, the selection of effective pollinizers, both in terms of the pollen quantity and quality as well as the attractiveness of flowers to pollinators, is needed to produce good-quality fruit. Recent research also shows that the source of pollen may have an impact on some biochemical features of kiwiberries and that a proper selection of pollinizers appears to be important in commercial fruit production [19]. Therefore, it would be worthwhile to compare the composition of volatile compounds in flowers of different species of actinidia and to ascertain the diversity within one species. Volatile compounds in flowers of _A. chinensis_ var. _chinensis_ and _A. chinensis_ var. _delicious_ have been well analysed, as this species is of great economic importance.