Identification Of Non-Russet Sport Of’golden Delicious’ Apple And Its Russeting Control

’Golden Delicious’, which is also known as Yellow Banana, is a popular and old variety of apple among growers and consumers. It is adaptable, high yield and the cultivation technology is relatively simple with excellent quality of fruits. It is among the major cultivars both in the developed countries such as Europe and the United States, and developing contries such as China, therefore, known as "the cultivar of the world". However, the fruit peels of the cultivar often form a large number of fruit russet during fruit development, in most areas, especially in coastal or high-temperature and high-humidity areas, so that fruit surface is rough, coverd with russet. This seriously affects the appearance of fruit quality, reduces the commercial value of the fruit, become a major problem to the production of ’Golden Delicious’ apple.A non-russet sport on the fruit surface was selected by the Center of Fruit Trees Technology Promotion at Dashahe Orchard in Feng County, from planted’Golden Delicious’trees. It appeared that, the fruit surface was yellow and smooth with less and smaller fruit dots than that of ’Golden Delicious’. Thus, the fruit appearance was better than the wild type. Grafting and multi-point cultivation showed that the trait of rust-free could be stably inherited after many years of observation and thus, it may be a new non-russet sport (lately named as ’Feng Shuai’). In order to judge furtherly whether ’Feng Shuai’ apple was the non-russet sport of’Golden Delicious ’apple or not, the two varieties were taken as the main experiment materials, and ISSR molecular markers and sugar metabolic characteristics were analyzed. On other hand, the peel characteristics of ’Golden Delicious’ and ’Feng Shuai’ apples were observed during fruit development by stereomicroscope and scanning electron microscope to compare the peel structural differences of both the two varieties and the reason of rust formation of ’Golden Delicious’ apple. Finally, the authors proposed a new method to control or reduce the rust of ’Golden Delicious’ by spraying exogenous chlorogenic acid. The main results are as follows: 1.’Feng Shuai’, a non-resset sport, was found in ’Golden Delicious’ tree in Dashahe Orchard of Feng County in Jiangsu Province.’Su Shuai’ is an excellent hybrid of ’Golden Delicious’ and ’India’, obtained by Professor Sheng Bingcheng of Nanjing Agricultural University. In order to reveal the genetic differences of ’Feng Shuai’,’Su Shuai’ and ’Golden Delicious’ at the DNA level, the inter-simple sequence repeat (ISSR) marker and the polyacrylamide gel electrophoresis (PAGE) were used to distinguish the series of cultivars of ’Golden Delicious’ apples. The results show that, DNA of ’Golden Delicious’ apple and ’Feng Shuai’ apple have significant differential band, and they had a closer genetic relationship than ’Golden Delicious’ and ’Su Shuai’. This implied that they had different genetic basis, but their genetic relationship were relatively close.2. In order to judge furtherly whether ’Feng Shuai’ apple was the non-resset sport of ’Golden Delicious’ apple or not, fruits of two varieties were used as experiment materials to analyze sugar metabolism differences. The results showed that the change of sugar accumulation and the related enzyme activities in sugar metabolism were similar, but there existed some differences, suggesting that the physiological and biochemical characteristics of ’Feng Shuai’ apple fruit was different from its parental ’Golden Delicious’ apples.3. The peel characteristics of ’Golden Delicious’ apple and its non-russet sport variety-’Feng Shuai’ were compared by a stereo microscope and a scanning electron microscope in the work. Additionally, their pigment and secondary metabolite levels in the peels were also analyzed. The results showed that the wax layers of the epidemical cells of ’Golden Delicious’ apple began to crack and abort at4weeks after bloom although there was no macroscopic russet could be observed. At5weeks after bloom, the cuticles of the epidemical cells cracked in large areas, and the cell walls were suberificated because cork cambium was activated. And at6weeks after bloom, a lot of russet occurred in the surface of apple fruits. Therefore, the time from4to6weeks after bloom was crucial for russet formation of ’Golden Delicious’ apple. On the other hand, the chlorophylls and carotenoids in ’Feng Shuai’ peels were significantly lower than that of ’Golden Delicious’, but its total flavonoid and chlorgenic acid were much higher than the latter. The differences were especially dramatic from4to6weeks after bloom. Therefore, the authors deduced that the chlorogenic acid accumulation in the peels at4-6weeks might be related with russet formation. 4. Chlorogenic aicd (CA) solutions in concentrations of0.05-5mmol L-1were sprayed on ’Golden Delicious’ fruits at4weeks after blooming (WAB), and found the fruit rust formation was significantly inhibited, where the treatment with0.5mmol L-1CA was the most effective. Exogenous CA treatments also promoted the endogenous CA and total flavonoid content in the skins, but depressed the lignin content. Furthermore, CA treatments induced phenylalnine ammonialyase (PAL) and cinnamate-4-hydrolase (C4H) activity, but depressed polyphenol oxidase (PPO) and peroxidase (POD) activity. Meanwhile, CA treatments up-regulated the expression quantity of phenylalnine ammonialyase (PAL), cinnamate4-hydroxylase (C4H),4-coumarte:coenzyme A ligase (4CL), chalcone synthase (CHS) and chalcone-isomerase (CHI), which were related with the synthesis of chlorogenic acid and total flavonoid; but CA treatments down-regulated the expression quantity of cinnamyl alcohol dehydrogenase (CAD), peroxidase (POD) and polyphenol oxidase (PPO), which were related with the synthesis of lignin. It can be deduced that the promotion of PAL and C4H activity and the relative expression quantity up-regulation of PAL, C4H,4CL CHS and CHI, which may favor biosynthesis of total flavonoid, while the depression of PPO and POD activity and the relative expression quantity down-regulation of CAD, PPO and POD, which may block the rust formation in skins of’Golden Delicious’ apples.