the role of rootstock in antioxidant activity of citrus fruit: comparison of antioxidant activity of the fruits of two commercial citrus varieties with the fruits of four different rootstocks

introduction: all fruits that called citrus are from rutaceae family and aurantioideae subfamily. this subfamily have more than 33 different genus that only three of its genus (citrus, poncirus and fortunella) have economic aspects and in citrus producing country are important. it's reported that orange skin has a phenolic compounds which play a role in natural defense mechanism. also various compounds of phenolic and antioxidant have a major role in fruit tolerance to stressful condition suh as cold and drought. metabolites found in citrus fruits have antioxidant properties and it's very useful in pharmaceutical, food and cosmetics industries. oranges, like other citrus fruits, are an excellent source of vitamin c; vitamin c is a powerful natural antioxidant. consumption of foods rich in vitamin c helps the body develop resistance against infectious agents and scavenge harmful, pro-inflammatory free radicals from the blood. various factors such as rootstock type can effect on quality and quantity of citrus fruits. also, the usage of rootstock causes the change in plant characteristics such as flowering time, ripening time, fruit quality and antioxidant characters of the fruits. other factors except the rootstock such as scion, geographical and climate factors are effective on producing secondary metabolites. also active substances or secondary metabolites are producing by the conduction of genetic processes, but their production are being effected by other factors obviously. the aim of this study is to investigating the biochemical changes grafted tree fruit that affected by rootstock with study the correlation between grafted tree and rootstock changes. materials and methods: this study was done to compare the amount of total phenol, total flavonoids and antioxidant features of fruit flesh and skin with investigating the effect of cultivar and rootstock on these parameters based on completely randomized factorial design with three replications. for this purpose total phenol, total flavonoid and antioxidant activity in two citrus cultivar (morro and mars) that grafted on four rootstock (yuzu, citrumelo, sour orange and shel mahalleh) with seedling rootstocks fruit were studied in fruit skin and flesh. fruits were harvested in the middle of december according to their total soluble solid materials (tss) which was 10 and then transferred to the researching laboratory in gorgan agricultural science and natural resources university. antioxidant properties using dpph method in 517 nm wavelength, total amount of phenol using folin siocalteu method in 765 nm wavelength and the total amount of flavonoid were done using the aluminum chloride method in 415 nm wavelength and they were measured using spectrophotometer. results and discussion: the result showed that the two factors consisting rootstock and scion have significant effect on the amount of total phenol, total flavonoid and antioxidant properties of extracts of citrus skin and flesh. the greatest amount of phenolic compounds was produced in the skin of morro cultivar that grafted on shel mahalleh rootstock and the lowest amount was observed in the flesh of yuzu seedling rootstock. total flavonoid was affected by fruit tissue, cultivar and rootstock. the maximum amount of that was seen in the skin of morro and mars cultivar that was grafted on yuzu rootstock and the minimum amount was recorded in the flesh of morro cultivar that grafted on sour orange rootstock. also the highest antioxidant activity was produced in skin of citrumelo seedling rootstock and the lowest amount was seen in flesh of yuzu seedling rootstock. the investigation on citrus rootstock showed that, antioxidant activity, total phenol and total flavonoid had significant effect in different rootstock and cultivar fruit. these compounds were affected by climatic condition. because the light is effective in biosynthesis of phenolic compounds, in fact, these substances have a protective role against the light, especially short wavelengths. therefore their more accumulation is in skin. the results of this experiment and also the results of the other researcher show that the rootstock effect is related to the quality of grafted species with the species, rootstock type and their interaction. conclusion: based on these experiments, there was significant difference between antioxidant compounds of grafted tree fruit with rootstock fruit but there wasn’t a clear relationship between them. it seems this difference was due to combination and physiological characteristic of each fruit. it seems that the accumulation of chemicals in citrus fruit superior than every factors depends on genetic characteristics and inherent abilities. so that some factors specially rootstock has an important and determinant role in accumulation of these substances.