Variability of overhead volatile organic compounds in clonal tea ( Camellia sinensis ) and their influence on red crevice mite ( Brevipalpus phoenicis Geijskes) infestations

Tea production in Kenya is under threat due to red crevice mites (Brevipalpus phoenicis) infestations during droughts. Cultural pests control practices, e.g. use of resistant/tolerant cultivars are used in their control since pesticide use is prohibited. Plants release volatile organic compounds (OVOCs) that may influence susceptibility/resistance to pest infestations. OVOCs profiles released by 11 tea cultivars were evaluated to assess relationship between OVOCs and cultivar tolerance/susceptibility to B. phoenicis. Five clones were susceptible, with high B. phoenicis infestations while four clones were resistant, exhibiting low infestation levels. The infestations were linearly correlated to (E)-2-hexenal, (Z)-3-hexenal (p≤0.001), (Z)-3-hexenol, (Z)-3-hexenyl acetate, linalool, germacrene D, sum of green leaf volatiles (GLVs) (p≤0.01), 1-pentene-3-ol, hexanal, indole and (E)-β-ocimene (p≤0.05) levels. Most of aromatic compounds, some terpenoids compounds and sum of aromatic compounds were inversely (p≤0.05) correlated with B. phoenicis infestations. Susceptible varieties to B. phoenicis emitted high amounts of GLVs, especially (E)-2-hexenal, (Z)-3-hexenal, (Z)-3-hexen-1-ol and (Z)-3-hexenyl acetate. Results demonstrate that OVOCs profile may provide selection criteria for cultivars resistant to B. phoenicis infestations. Resistant cultivars are recommended for commercial exploitation in red crevice mites prone areas while breeding/selection programmes should incorporate OVOCs profiles to develop tea cultivars that resist red crevice mites attack.