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Avocados are a popular subtropical fruit of high economic importance and the European Union is the biggest importer of the bulk of the fruit coming from countries like South Africa, Chile and Israel. The fruit is highly nutritious being rich in vitamins A, B, C, minerals, potassium, phosphorus, magnesium, iron and antioxidants10%. The Guatemalan is native to the Guatemalan highland and has medium round fruit with an oil content of 8 to 15% and a leathery, pliable and non-granular ski n. The tree is less cold tolerant than the Mexican. The Mexican race thrives best in the subtropics and has the smallest fruit of the three races, with a thin skin and the highest oil of up to 30%. (2) The tree is most tolerant of cold growing conditions. Chen et al. (3) confirmed that the substantial genetic differentiation among the three ecological races corresponded to the defined horticultural races, but they also reported that the previously undetected genetic differentiation has two subpopulations from Central Mexico. Many cultivars are hybrids between the races. "Hass" (a Guatemalan x Mexican hybrid) is considered to be the most dominantly grown cultivar in the subtropics (4) and is recognised as the best overall quality avocado available. The fruit weighs between 140 to 400 g with medium to thick skin, leathery, coarse corky in texture and it turns purplish black when ripe. Other popular cultivars include "Fuerte" (a Mexican x Guatemalan hybrid), "Bacon" (a Mexican x Guatemalan hybrid), Pinkerton (a Guatemala hybrid), "Edranol"(a Guatemala hybrid), "Ryan" (a Mexican x Guatemalan hybrid", "Ettinger" (predominantly Mexican) and "Fuchs" (West Indian). (4) The fruit characteristics of the above mentioned cultivars are shown in Table 1. Physical properties of avocadoThe fruit (berry) is pear-shaped, oval or round with a short neck. Fruit length can vary from 7.7 cm to 33 cm and its width can be up to 15 cm. The skin color of the fruit can vary from yellowish green, dark green or reddish-purple, to dark purple (almost black). The edible portion of the fruit, that is, its flesh or pulp can be pale to bright yellow in color and the fruit flavor is described as a buttery or nut-like flavor. Its single seed is situated at the center of the fruit and 3 Table 1 Fruit characteristics of different avocado cultivars a a Source: Whiley et al. (4) the shape of the seed can be oval, round or oblong and generally the length of the seed is around 5 to 6.5 cm long, but may be smaller. The seed is covered by a thin brown seed coat that adheres to the seed cavity. (4) Avocado production and trade European markets. In the EU, the Netherlands and France as well as the UK are the major avocado importing countries. Although the "Fuerte" cultivar displays a green skin color after ripening and is well known in the European markets, the "Hass" cultivar currently dominates the international trade market due to its longer shelf life, large fruit size and its higher consumer acceptance due to its rich nut-like flavor. (11,12) "Hass" is the dominant and m...

Highlights• Thyme oil fumigation effectively controlled the anthracnose in avocados.• Defence enzymes (chitinase and β-1,3-glucanase) were induced by thyme oil fumigation.• Thyme oil fumigation initiated the expression and activities of defense enzymes. AbstractThyme oil (TO) fumigation (96 μL L -1 ) to cv. Hass and Ryan avocados significantly reduced anthracnose incidence compared to prochloraz and to untreated control. Also enhanced activities of β-1,3-glucanase, chitinase were noted in both cultivars. TO fumigation induced the expression of both β-1,3-glucanase and chitinase genes in naturally infected fruit of both cultivars, during storage at 7 or 7.5 °C for up to 21 d and during subsequent simulated market shelf conditions at 20 °C for 5 d. However, the impact of TO fumigation on the β-1,3-glucanase gene expression was higher in both cultivars. Higher gene regulation and β-1,3-glucanase, chitinase activities were observed in cv. Ryan compared to Hass. Although TO 2 fumigation significantly reduced anthracnose incidence in both naturally infected cultivars, the inhibitory effect was slightly higher in cv. Ryan than Hass. Thus postharvest TO fumigation had positive effects on enhancing anthracnose disease resistance during storage and also gave a residual effect during the simulated shelf life.

Highlights • Thyme oil exposure led to up-regulation of PAL gene expression in Hass and Ryan fruit. • Thyme oil exposure led to down-regulation of LOX gene expression in both cultivars.

MeJA and MeSA have the potential for being used with 'Hass' avocado fruit shipped at low temperature to reduce its susceptibility to chilling injury. © 2017 Society of Chemical Industry.

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Trilayer low-density polyethylene (LDPE) films were prepared by incorporating varying concentrations of thyme oil, as the antifungal active additive for avocado packaging. A comprehensive thermal, structural, mechanical, and functional characterization of the prepared films was carried out. Thermal stability of the film reduced with the addition of thyme oil in higher concentration, whereas the degree of crystallinity increased upto 2.5 wt % thyme oil loading. The elastic modulus and elongation at break of the films decreased in presence of thyme oil. However, the incorporation of thyme oil did not change the water vapor transmission characteristics of the original film. The antifungal activity of the films was tested against Colletotrichum gloeosporioides causal organism of "anthracnose" postharvest disease in avocados. The results indicated that the films have great potential as antifungal packaging materials for avocado fruits.

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