Relationship between the phytochemical diversity in creole avocado (Persea americana var. drymifolia) leaves and the incidence of foliar gall psyllid (Trioza anceps)

We studied the relationship between the leaf volatile biochemical diversity (relative abundance of secondary metabolites in tissue) in the Creole avocado (Persea americana var. drymifolia) growing in germplasm bank and herbivory of the foliar gall psyllid (Trioza anceps). The gall density per leaf was recorded and the volatile fraction of Creole avocado leaves was analysed and quantified by gas chromatography-mass spectrometry. The foliar biochemical diversity was correlated positively with the incidence of the gall insect. There were neither significant correlations between the incidence of the insect galls and the accessions per latitude or altitude of origin, nor between the foliar biochemical diversity of accessions. Few compounds were found associated with the incidence of psyllid: (i). Estragole was negatively correlated with the number of galls per leaf (Sperman r= -0.209 n= 93, p < 0.05) and its concentration was higher in the leaves of trees without galls (4.39 + 0.3 mg/g dry wt) than those with galls (3.34 + 0.06 mg/g dry wt). (ii). Caryophyllene oxide and (iii) sesterterpene 2,6,10,14,16-pentamethyl-2,6,10,14,18-eicosapentaene were more concentrated in the tree leaves with galls than without galls.