Biochemical aspects of lettuce plant resistance to leafminers and aphids

Nasir Masood,Beiquan Mou,Michael Diaz, Jianlong Bi Host plant resistance is an important component of integrated pest management while understanding the biochemical mechanisms. To study the biochemical mechanisms of lettuce plant resistance to its major insect pests, leafminer (Liriomyza langei) and aphids, sixteen lettuce genotypes with various degree of resistance were planted in growth chambers and a field with four replications. Protein, sugars, phenolics, carotenoids, and chlorophylls were extracted from plant leaves, and damage by leafminers and numbers of aphids in different species were recorded. Leafminer stings per cm2 leaf area of young plants were highly correlated with sting/cm2 of mature plants. Sucrose concentration of young plants was correlated with leafminer stings per cm2 leaf (r=0.730, p=0.01) and mines per plant (r=0.790, p=0.01), suggesting that low sucrose content could be used as a marker for early screening or selection for leafminer resistance. Leafminer stings/cm2 were negatively associated with contents of flavonoids (r=-0.560, p=0.05) and chlorogenic acid (r=-0.598, p=0.05), while mines per plant were negatively associated with concentrations of flavonoid (r=-0.700, p=0.01), chlorogenic acid (r=-0.594, p=0.05) and rutin (r=-0.603, p=0.05), implying a role of phenolics in the leafminer resistance. Total number of apterous aphids including Myzus persicae, Macrosiphum euphorbiae and Aulacorthum solani per 100 g plant weight was correlated with contents of protein (r=0.890, p=0.01), -carotene (r=0.828, p=0.01), lutein (r=0.819, p=0.01), chlorophyll (r=0.739, p=0.01), and glucose (r=-0.771, p=0.01) of young lettuce plants, which could serve as early indicators of aphid resistance. Aphids per 100 g plant weight were also associated with chicoric acid