# How Biological and Environmental Factors Affect the Quality of Lavender Essential Oils
## 3 Biological and Environmental Factors Affecting EO Production
### Genetic Factors  
EO production is usually highly variable between populations and within the same plant population [14]. Genotype predominantly affects the amounts of lavender oil compounds (Table 2) [37; 38; 44; 45]. In twelve varieties grown in Canada, linalool was the primary compound, ranging from 17% to 43% [44]. On the other hand, linalyl acetate ranged from 0 to 14.5% [44]. Moreover, the amounts of camphor were reasonably abundant, ranging from 2% to 13%, among the investigated varieties [43]. Similarly, cultivated genotypes in Hungary affect linalool and linalyl acetate percentages [37].  
Factors Affecting Monoterpene Biosynthesis Gene Expression in Lavender Flowers  
The synthesis of volatile organic compounds (VOCs), including monoterenes, is a dynamic process that varies throughout plant development. This variation arises from patterns of differentially expressed genes from distinct cell types [60]. In lavender, monoterenes biosynthesis is highly controlled at the transcription level [61]. Table 3 presents the effect of several environmental and developmental factors on the gene expression of monoterenes biosynthesis in lavender.  
Most genes that encode enzymes involved in the accumulation of linalool, linalyl acetate and lavandulyl acetate are expressed in flowers and glandular trichomes [6]. The genotype affects the gene expression involved in lavender monoterenes biosynthesis, like GGPPS, GPPS, LPDS and (R)-linalool synthase. Furthermore, several reports suggest that monoterene biosynthetic gene expression is regulated by flower developmental stage [6; 34; 62; 63]. In early flower development, the content of limonene synthases and one transcript of alcohol acetyltransferase expression are high, and subsequently, their expression decreases in the later developmental stages [6; 34]. During inflorescence development, genes that encode enzymes involved in the accumulation of linalool, linalyl acetate and lavandulyl acetate displayed increased expression, with the flowers being picked at 50% of blossoming [6; 34; 62; 63]. Moreover, lavender EO production is regulated diurnally [13]. Likewise, linalool synthase, limonene synthase and terpene synthase expression are regulated during the day, with picking being carried out at mid-day until 15:00, suggesting that circadian rhythms affect the transcription of monoterenes synthases in lavender flowers [64].  
Linalool and linalyl acetate attract pollinators [17], a process mediated by jasmonates [65]. Methyl jasmonate (MeJa) affects the diurnal emission of lavender volatiles in a quantitative and chronologically dependent manner [66]. The expression of LaGPPS and LaCINS was considerably increased by MeJA [66]; moreover, TPS genes (La05G1453/La05G1454) are highly expressed in MeJa-treated flowers [6]. Interestingly, the expression levels of five BAHD acyltransferase genes (LaBAHD57; 63; 104; 105, and 119) also increased  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Environmental Factors**} & \multicolumn{2}{c}{**Plant Development**} \\ \cline{2-5}  & **Rain** & **Temperature** & **Diurnal** &
\begin{tabular}{c} **Ontogeny** \\ **Inflorescence** \\ **Development** \\ \end{tabular} & **Plant Age** & **Genotype** \\ \hline Ocimene & & & + Late & \\  & & & [26] & \\ \hline trans-\(\beta\)- & & Max at six h & + Late & \\ Ocimene & & [13] & [26; 41; 52] & \\ \hline Lavandulol & & & + Late & \\  & & & [26; 41; 52] & \\ \hline \hline \end{tabular}
\end{table}
Table 2: _Cont._significantly after MeJA treatment, especially in sepals [67]. These genes, which are thought to be involved in the biosynthesis of linalyl acetate and lavandulyl acetate, and their expression are also induced by abiotic stress, including drought and salt treatments [67].