Analysis of physiological and molecular changes in melon (Cucumis melo L.) varieties with different rates of ripening

Seven melon varieties (Alpha, Delada, Marygold, Sirio, Topper, Tornado, and Viva) known to exhibit differences in their ripening behaviour were used in this study. The expression of mRNAs for ACC oxidase (MEL1) and phytoene synthase (MEL5), required for synthesis of ethylene and carotenoids, respectively, and two ripening-related cDNAs (MEL2 and MEL7), of unknown function, was examined and correlated with the development of colour and softening of fruits. The MEL2 and MEL7 mRNAs were present and accumulated in all varieties, indicating their importance in melon fruit ripening. The fruits of Delada and Marygold did not show any change in the colour of the flesh even at 50 daa (days after anthesis). All other varieties changed colour from green to orange between 25-30 daa. The phytoene synthase mRNA levels in most varieties seemed to be unrelated to change in fruit flesh colour. The firmness of all the fruits was reduced significantly between 25 and 40 daa. The expression of ACC oxidase mRNA showed the most variation among the different varities and was delayed in Sirio and undetectable in Marygold fruits even at 40 daa. Varieties with delayed expression of ACC oxidase mRNAs after anthesis also showed delayed softening during ripening. The prospects of genetic engineering and breeding for melon fruits with improved quality characteristics and extended storage life are discussed.