Secondary Metabolites and Lignin in 'Hass' Avocado Fruit Skin during Fruit Development in Three Producing Regions

In plants, secondary metabolites (SMs) have functions of both defense and adaptation to the environment in which they develop. In Mexico, 'Hass' avocado is cultivated in different climate types, so during its development, the fruit is exposed to extreme climatic factors, especially temperature and solar radiation. A recent study showed that the thickness and roughness of 'Hass' skin increased in the hottest climate. It is unknown how these factors affect the presence of SMs and lignin in the skin. The aim of this research was to quantify the concentration of total phenolic compounds (TPCs), chlorophylls, total carotenoids (TCARs), and lignin in the skin of 'Hass' avocado fruit over five developmental stages (S), based on fruit diameter [Olive (20-30 mm empty set), S-I (35-45 mm empty set), S-II (50-60 mm empty set), S-III (60-70 mm empty set) and Harvest (mesocarp dry matter >= 21.5%)], in three producing regions of Mexico: Nayarit (warm subhumid climate, elevation 1151 m), Jalisco (semiwarm, subhumid climate, elevation 2180 m), and Michoacan (temperate climate, elevation 1579 m). Both fruit developmental stage and producing region had a significant influence on the concentrations of SMs and lignin in the skin. During fruit development, the skin showed a decrease in the concentration of phenolic compounds (PCs) and an increase in the presence of chlorophylls, carotenoids, and lignin. The skin of fruit produced in regions with a semiwarm and temperate climate had higher production of lignin and PCs, as well as a lower concentration of chlorophylls.