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 ripeningbehaviour were used in this study. The expression of mRNAs forACC oxidase (MEL1) and phytoene synthase (MEL5), required forsynthesis of ethylene and carotenoids, respectively, and tworipening-related cDNAs (MEL2 and MEL7), of unknown function,was examined and correlated with the development of colour andsoftening of fruits. The MEL2 and MEL7 mRNAs were present andaccumulated in all varieties, indicating their importance inmelon fruit ripening. The fruits of Delada and Marygold didnot show any change in the colour of the flesh even at 50 daa(days after anthesis). All other varieties changed colour fromgreen to orange between 25–30 daa. The phytoene synthasemRNA levels in most varieties seemed to be unrelated to changein fruit flesh colour. The firmness of all the fruits was reducedsignificantly between 25 and 40 daa. The expression of ACC oxidasemRNA showed the most variation among the different varitiesand was delayed in Sirio and undetectable in Marygold fruitseven at 40 daa. Varieties with delayed expression of ACC oxidasemRNAs after anthesis also showed delayed softening during ripening.The prospects of genetic engineering and breeding for melonfruits with improved quality characteristics and extended storagelife are discussed. Key words: Cucumis melo, colour development, melon varieties, ripening genes, softening