## 4 Discussion
### Chemical Compounds Detected by GC-Ms
[31] detected 36 chemical compounds in the volatile emissions of _B. amyloliquefaciens_ NJN-6. They then used antagonism tests to show that 11 of the 36 compounds tested completely inhibited the growth of _F. oxysporum_ f. sp. _cubense_[31]. Among others, [PERSON] et al. [31] identified seven ketones forming a homologous series from nonan-2-one to pentadecan-2-one in _B. amyloliquefaciens_ NJN-6 cultures. They found that nonan-2-one and decan-2-one completely inhibited the growth of the fungal species _F. oxysporum_ f. sp. _cubense_. Undecan-2-one, dodecan-2-one and tridecan-2-one only partially inhibited the growth of the test fungus, with the degree of inhibition (%) decreasing as the length of the ketone carbon chain increased. In contrast, tetradecan-2-one and pentadecan-2-one did not inhibit the mycelial growth of _F. oxysporum_ f. sp. _cubense_[31]. In our study, the compounds nonan-2-one and undecan-2-one were identified both in the pure _B. amyloliquefaciens_ culture and in the _B. amyloliquefaciens_ _+ F. oxysporum_ interaction. In contrast, decan-2-one was only found in the _B. amyloliquefaciens_ _+ F. oxysporum_ interaction, while tridecan-2-one was only detected in the pure _B. amyloliquefaciens_ culture (Table 3). Based on the results of [PERSON] et al. [31] and the results of our study, it can be concluded that the bacterium produces a higher amount of decan-2-one in the interaction, which causes a significant inhibition of _F. oxysporum_ growth. In contrast, the production of tridecan-2-one, whose inhibitory effect on the fungus is low, is reduced. The very different effects of ketones on the mycelial growth of _F. oxysporum_were also confirmed by the results of a study published by [PERSON] et al. [45], which showed that undecan-2-one inhibited the growth of _F. oxysporum_ by 56.96 \(\pm\) 1.95%, while tridecan-2-one inhibited growth by only 4.37 \(\pm\) 1.26%. The literature also indicates that a number of other volatile ketones inhibit the growth of _F. oxysporum_. Acetone, butan-2-one [23], heptan-2-one, acetophenone [40] and 3-hydroxybutan-2-one [47] have been shown to possess fungistatic properties. Our results confirm the presence of 3-hydroxybutan-2-one, commonly referred to as acetoin, when present in a pure culture of _B. amyloliquefaciens_, as well as in the interaction of _B. amyloliquefaciens_ and _F. oxysporum_ (Table 3). It is also worth mentioning that the hydroxycetone discussed not only causes a reduction in _Fusarium_ infections but also those caused by other pathogenic fungi, e.g., _Colletotrichum cococodes_[55]. In addition, the volatiles produced by _Bacillus_ are also effective against other pathogenic organisms, e.g., nematodes [56]. The authors showed that the volatile compounds secreted by the bacterium _B. subtilis_, such as nonan-2 one and benzaldehyde, completely eliminated nematodes of the species _Panagrellus relativus_ and _Bursaphelenchus xylophilus_. Our analyses also found the two carbonyl compounds mentioned above in the volatile emission of _B. subtilis_ (Table 1). Small-molecule alcohols produced by bacteria of the genus _Bacillus_ represent another group of chemical compounds that inhibit the growth of _Fusarium_ fungi. [PERSON] et al. [31] showed that undecan-2-ol contained in the volatile emission of _B. amyloliquefaciens_ NJN-6 completely inhibited the growth of _F. oxysporum_ f. sp. _cubense_. Our results showed that this alcohol was present in the _B. amyloliquefaciens_ + _F. oxysporum_ interaction (0.51 \(\pm\) 0.04%) and was not present in the pure _B. amyloliquefaciens_ and _F. oxysporum_ bacterial cultures (Table 3). Based on the information presented above, it can be surmised that _B. amyloliquefaciens_ increases the production of undecan-2-ol to combat _F. oxysporum_. The results available in the literature show that the growth inhibition of _F. oxysporum_ is also influenced by other alcohols produced by _Bacillus_ bacteria, such as isopentanol [23], heptan-2-ol [47] or phenethyl alcohol [34].