| Malus sieversii (Ledeb.) Roem. is a remnant of the tertiary species and is also believed to be progenitor of cultivated apple(M. domestica). In China, M. sieversii is mainly distributed in the Ily State, Xinjiang Autonomous Region. In this study, trees in 3 M. sieversii populations (i.e., Daxigou Huocheng, Mohe Gongliu and Jiaowutuohai Xinyuan populations) were used as materials and genetic diversity of M. sieversii were discussed by measuring several phenotypic traits including morphological traits, chemical components and physiological activities. The aim of this study was to provide basic information for protection, conservation and utilization of M. sieversii. The main results were as follows:(1) Population age structures and crown densities of the two Malus sieversii populations endemic to Gongliu and Xinyuan respectively, were studied. A decline trend was assigned to Gongliu population revealed by construction of age classes and a slight ascend trend was assigned to Xinyuan population. Crown density of Gongliu population was 0.47 and that of Xinyuan population was 0.80. The survival curves of the two populations were breakpoint projection form and arc projection form, respectively. So, a severe involution form was suggested to Gongliu population while a stabilization form was suggested to Xinyuan population. A serious destruction has taken place to Gongliu population, so effective action should be taken to protect it. However, Xinyuan population is intact.(2) The morphological diversity of fruits during 1986~1990 and 2004~2005 respectively, were compared. The reducing value of CV for Huocheng population in the two decades was 42.18% and the value for Xinyuan population was only 18.93%. Furthermore, there was an extremely significant difference for Huocheng population between the two periods and no significant difference was found for Xinyuan population. So, the results indicated that a serious destruction has taken place in Huocheng population and Xinyuan population is well protected.(3) Morphological variations in fruits, leaves and flowers of M. seiversii seedlings were measured, which include fruit shape, size, color and length of carpopodium of the 132 seedlings from the three populations, leaf length, wideth, leaf shape index, thickness, length of petiole of the seedlings from Daxigou and Mohe populations, and flower diameter, petal length, wideth, shape index, and length of pedicel of the seedlings from Mohe population. The results showed that coefficients of variation for above traits were all above 10%. These results indicated abundant genetic diversity in the three M. seiversii populations. There was an identical variation tendence among the three populations. It should been pointed out that Mohe population was reported for the first time, with single fruit weight 9.95~47.47g (cv29.71%). The shape of fruits were oblateness, close roundness, roundness and conoid and the color of fruits were green, yellow, orange, pink, red and thick red. Therefore, these fruits possess typical characters of M. domestica. The results above sustain the conclusion'M. sieversii was assumed progenitor of domesticated apple M. domestica'.(4) Significant differences were found between seedlings for flesh hardness and soluable solid content, the two quality traits. According to the two government standards(i.e., GB/T 19557-2004,GB/T10651-1989), M. sieversii fruits were divided to middle, hard and extreme hard grades for flesh hardness and low, middle, high and extreme high grades for soluable solid content. So, M. sieversii is of potential for selecting elite seedlings.(5) The aroma components of M. sieversii fruits was analyzed for the first using HS-SPME and GC-MS. There were 230 volatile compounds in total belonging to 11 classes identified in 47 M. sieversii seedlings, including 68 esters, 52 alcohols, 32 ketones, 18 aldehydes, 6 acids, 16 benzene ramifications, 13 terpenes, 12 heterocycles, 6 hydrocarbon derivates, 3 acetals, and 4 lactones. There were 48 compounds in mean in one seedling and no significant difference was found in numbers of compounds between seedlings. However, M. sieversii seedlings showed considerable genetic variations in these aspects: the total content of volatile components, the classes and contents of each compound classes, the segregation ratio, and content of main components.(6) To get similarity coefficient of volatile compounds, the number of common volatile compounds between M. sieversii and domesticated apple cultivar (form) was used as numerator and the sum of volatile compounds in M. sieversii and those in domesticated apple cultivar was used as denominator. The result that the similarity coefficients were in accordance with the evolution of apple cultivars (forms) indicated that the strategy with the volatile composition to study the relationship and evolution of apple species was methodically feasible. In addition, the similarity coefficients between M. sieversii and domesticated apple cultivars were much larger than those between M. sieversii and 4 Malus wild species (M. robusta, M. prunifolia, M. toringoides, M. micromalus), which suggested a nearer relationship between M. sieversii and M. domestica than those between M. sieversii and the four Malus wild species respectively.(7) Comparison of volatile compounds between M. sieversii and M. domestica cultivars 'Ralls','Fuji','Golden Delicious'showed that the common compounds whose number were larger than 5 with the contents over 0.04 mg/L simultaneously between M. sieversii and M. domestica belonged to esters, alcohols, aldehydes or ketones. This suggests that fundamental identity in main compounds of M. sieversii and M. domestica cultivars and this also supports the hypothesis"M. sieversii is probably the ancestor of M. domestica". However, 48 compounds that were not detected in M. sieversii were unique to M. domestica. Among them, six compositions (i.e., propyl acetate, (Z)-3- hexenal, 2-methyl-1-butanol acetate, pentyl acetate, 3-furanmethanol, and benzene acetaldehyde) belonged to character impact odors. This shows that in the domestication of M. domestica, introgression of other Malus species, except for M. sieversii, by interspecies hybridization is possible.(8) A cluster analysis for volatile compounds and their concentrations in 30 M. sieversii seedlings was performed. At 1.40 distance level, the 30 seedlings were divided to 7 groups, in which each of M67, M76, M13, M34, M5 and M61 formed one group, while the other 24 seedlings formed one group. A thorough analysis of these volatile components revealed that esters and alcohols play an important role in the subdivision of M. sieversii intraspecific types in volatile composition. The conclusion was supported by the results of the principle component analysis of volatile composition for 47 M. sieversii seedlings, 4 M. domestica cultivars and 4 Malus wild species.(9) There were 90 compounds unique to M. sieversii. Among them, acetals and lactones were not detected in M. domestica cultivars, and 7 components (i.e., 1-butanol, ethyl butanoate, 1-hexanol, ethyl hexanoate, 3-octen-1-ol, ethyl octanoate, and damascenone) belong to character impact odors. Furthermore, the principle component analysis of volatile composition for 47 M. sieversii seedlings, 4 M. domestica cultivars and 4 Malus wild species leaded to revealing of significant difference in volatile composition between M. sieversii, M. domestica and Malus wild species and the individuality in volatile composition for M. sieversii. Thus, the potential of M. sieversii in"utilization conservation"is enormous as a rare germplasm on genetic improvement of M. pumila cultivars.(10) Although the average total phenolics content of M. sieversii seedlings was higher than apple cultivar'Liaofu'and gingkgo, and was lower than'Fuji'and'Golden Delicious', and was much lower than green tea, the highest content of M. sieversii seedlings was 1.41~3.64 folds to those of apple cultivars and was 8.82 folds to the lowest content of M. sieversii seedlings. The coefficient of variation for total phenolics contents was 44% which revealed extensive variation in total phenolics contents. Gallic acid, chlorogenic acid, cinnamic acid, coumaric acid, ferulic acid, caffeic acid, phlorizin glucoside, myricetin, quercetin and catechin were identified by HPLC, in which phlorizin glucoside and myricetin existed in high contents, respectively. Proanthocyanidins also presented in high content, thus, phlorizin glucoside, myricetin and proanthocyanidins are main phenolics in M. sieversii leaf. There were extensive variations in contents of these phenolics and in total phenolics contents between M. sieversii seedlings which implyed high genetic diversity in phenolic content. The phenolic data of M. sieversii and apple cultivars was analyzed with PCA. There were significant variations between most M. sieversii seedlings in PC1. The result indicated large differences between M. sieversii seedlings and abundant genetic diversity in phenolic composition. A lot of previous studis conducted by other researchers had revealed that the phenolics intimately involve in resistance of plant to biotic and abiotic stresses. So, we suggested that there are perhaps difference for resistance to biotic or abiotic stresses between M. sieversii seedlings and perhaps some seedlings which possess high resistance. Nevertheless, more research work should been conducted.(11) DPPH radical-scavenging capacity, FRAP and TEAC results indicated abundant variation in antioxidant capacity of M. sieversii leaf. Although the mean value of antioxidant capacity of M. sieversii is lower than those of apple cultivar controls, because of abundant variation, such as FRAP values ranged from 35.17 to 184.61μmol/gDM, antioxidant capacities of several seedlings were higher than those of controls with five methods, respectively. So, M. sieversii is of potential for selection of elite seedling with high antioxidant capacity. The antioxidant capacities of phenolics extracts from M. sieversii were higher than VC, VE, BHT and 4-HR, and inhibition capacity of lecithin liposome oxidation of these extracts were higher than green tea, gingkgo, VC, VE, BHT and 4-HR. Comparison of these results with reports in other plant species, we found that the antioxidant capacity of M. sieversii leaf is higher than several general vegetables and several fruit trees in Rosacae. Thus, phenolics in M. sieversii leaf are perhaps of potential for natural antioxidant. More research should been conducted for the application of the phenolics.(12) The positive correlation at extremely significant level between total phenolic contents and antioxidant capacities was discovered in this study. A slight lower correlation at extremely significant level between proanthocyanidins contents and antioxidant capacities was also discovered in this study, which implied that proanthocyanidins is probably the main contributor for antioxidant capacity. The positive correlation at extremely significant level between proanthocyanidins contents and inhibition rate for PUFA peroxidation revealed that proanthocyanidins is probably of high inhibition effect on PUFA peroxidation. |
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