The volatile constituents of leaf samples were analysed to determine genetic relationships among 39 avocado (Persea americana Mill.) cultivars (25 from Taiwan and 14 from El Salvador) representing all three horticultural races (Mexican, Gutemalan, and West-Indian). A stable isotope, internal standard-based, solid-phase micro-extraction (SPME) GC-MS method was used to provide calibrated, quantitative measures of the concentrations and compositions of volatile organic compounds (VOCs) in avocado leaves in heated headspace vials. The calibrated intensity of VOCs in the leaves of Mexican race avocados was higher than in the Guatemalan and West-Indian races. Twelve race-specific VOCs, and ten VOCs of variable abundance were selected as indicators for further analysis. A similarity matrix of VOCs was calculated using Euclidean distances of the log(10) values of the calibrated abundances of the indicator compounds. A dendrogram was produced based on the unweighted pair group method using arithmetic averages (UPGMA). The 39 avocado cultivars clustered into three major groups based on their VOCs. Thirteen Taiwanese cultivars and three West-Indian cultivars were clustered in the same group in the dendrogram. The results showed that most Taiwanese cultivars were closely related to cultivars of the West-Indian race.
