## 3 Discussion  
In their research based on in vivo material of _Hylocreus megalanthus_ fruit, the team of [PERSON] et al., (2012) [46] identified the same compounds as those found in the present study, namely hexanal, 2-hexanal, 1-hexanol, 1-octen-3-ol, octanal, hexanoic acid, limoneene, 1-octanol, nonanal, octanoic acid, decanal, 2-decenal, nonanoic acid, tetradecane, geranyl acetone, 1-dodecanol. However, our research revealed occurrence of 2-decenal, tetradecane and geranyl acetone only in plant tissues cultivated on a medium enriched with IAA and not containing BA. Compounds such as linear alcohols and aldehydes (LAs, e.g., 1-hexanol, 2-hexanal) that occurs in plant are synthesized mainly from \(\omega\)-3 and \(\omega\)-6 carboxylic acids via hyper-peroxidation reaction (LOX). It was found, that they could play an important role in plant defense against herbivores and pathogens. Although the biosynthetic pathway of Las is not directly triggered with auxins or BA mode of action [PERSON] found the relation between emission of 3-hexenyl acetate with changes in auxin concentration in maize. Also [47] (2013) proven that BA and IAA could directly effect on LOX activity, and in LAs emission as a response to stress. In grapes [48]. proven that cytokines effect on hexenals and hexenols biosynthesis, although it's pathway is unclear. Due to their activity, the most interesting volatile compounds, applicable in industry, including pharmaceuticals production or plant protection, which were detected in the tissues of _Hylocreus undatus_ were hexanal, 2-hexanal, 1-hexenol, \(o\)-cymene, limonene, eucalypt, \(\beta\)-linalool and thymol. Recent years, more and more volatile compounds from plants have been identified as protective compounds against pests [49; 50; 51]. Hexanal induces early apoptosis of saprophytic fungus (_Aspergillus flavus_) conidia and have actively inhibits the growth of _Aspergillus_ and _Penicillium_ species. In addition, it is one of the attracting compounds for _Holotrichia parallela_[52; 53; 54; 55]. Another component of the fresh green fragrance is 2-hexanal found in green plants. It is a typical defense compound of many insects, but it is also a component of the pheromone in several insects of the genus _Podisus_ and in the species _C. lectularis_[56; 57; 58]. 1-hexanol was identified during the analysis of volatile compounds of fruits, among others, of species from the genus _Pyrus spp_. And _Prunus spp_. Moreover, this compound has an antagonistic effect on the sex pheromones of _Adelphocoris lineolatus_, while it attracts the insect _Lobesia botrana_[59; 60; 61; 62]. Regarding the activities of hexanal and 2-hexanal, the abundance of those compounds in in vitro cultivations of pitaya supported with growth regulators may be a valuable feature for biotechnological production of agents dedicated for pest and fungi management. Moreover, the interesting result was the observation that samples cultivated on the medium with IAA were able to synthesis other compounds, like \(o\)-cymene than cultures with BA. \(o\)-Cymene is one of the major the main components (65.2%) of the essential oils from _Bursera simaruba_ (L.) Sarg., _Thymus vulgaris_ ((56.2%) and _Nigella sativa_ L. seeds (37.82%). The latter essential oil exhibits anti-oxidative properties, anti-microbial effect against clinically significant strains of bacteria and fungi whereas the thyme oil possesses potential activity against fungi causing the brown rot disease, what again brings the perspective of use of in vitro pitaya cultures industrial importance, however it has to be highlighted that for this purpose further optimization of the process would be required