Identification of the HAK gene family reveals their critical response to potassium regulation during adventitious root formation in apple rootstock

Adventitious root formation is a bottleneck during vegetative proliferation.Potassium(K^(+))is an essential macronutrient for plants.K^(+)accumulation from the soil and its distribution to the different plant organs is mediated by K^(+)transporters named K^(+)transporter(KT),K^(+)uptake(KUP),or high-affinity K^(+)(HAK).This study aimed to identify members of the HAK gene family in apples and to characterize the effects of K^(+)supply on adventitious root formation and on the expression of HAK genes and the genes that putatively control auxin transport,signaling,and cell fate during adventitious root formation.In this study,34 HAK genes(MdHAKs)were identified in the apple(Malus×domestica‘Golden Delicious’)genome.A phylogenetic analysis divided MdHAKs into four clusters(Ⅰ,Ⅱ,Ⅲ,andⅣ),comprising 16,1,4,and 13 genes,respectively.The syntenic relationships revealed that 62.5%of the total MdHAK genes arise from genomic duplication events.Chromosome location,domain structure,motif analysis,and physico-chemical characteristics were subsequently investigated.Furthermore,the application of K^(+)indicated the emergence of adventitious roots at 8 d and produced more adventitious roots at 16 d than the K^(+)-free control(CK)treatment.In addition,various MdHAKs showed root-specific expression in B9 apple rootstock stem cuttings and enhanced expression during the initiation and emergence stages of adventitious root formation in response to K^(+)treatment.Additionally,K^(+)treatment enhanced the expression levels of MdPIN1,MdPIN2,and MdAUX1.Further data indicated that a higher expression of MdWOX11,MdLBD16,and MdLBD29 and of cell cycle-related genes contributed to the auxin-stimulated adventitious root formation in response to K^(+).

Technical Studies of Controlling Jujube Witches Broom Disease with Resistant Rootstock

[Objectives]The paper was to screen and identify the control effect of resistant rootstock on jujube witches broom disease.[Methods]The seeds or branches of disease-free plants were collected from wild jujube bushes infected by witches broom disease,and 5434 seedlings were obtained by sowing or cutting.The virus was inoculated by grafting diseased bark.After 6 years of preliminary screening,40 plants with resistance to jujube witches broom disease were obtained.Taking these resistant plants as the rootstocks,the susceptible variety‘long red jujube’was grafted at a height of 40 cm.When the plants grew to appropriate thickness,diseased bark was grafted to‘long red jujube’and rootstock to transmit the virus.After 18 years of observation and judgment,4 rootstock strains with high resistance or immunity to jujube witches broom disease were finally determined,namely 90801,90803,90806 and 908011.The susceptible variety‘long red jujube’was grafted to 4 rootstocks and inoculated the virus through diseased bark grafting method.[Results]The resistant rootstock had obvious disease resistance effect.When the branches of 90801 and 90803 rootstocks were grafted to the trunk of diseased trees,the symptoms of jujube witches broom disease gradually alleviated till disappeared.[Conclusions]Using germplasm with high resistance or immunity to jujube witches broom disease as rootstock can effectively prevent the spread of jujube witches broom disease,and bridging the trunk of diseased trees with branches from resistant rootstock has certain therapeutic effect.

Effects of Different Dwarfing Rootstocks on Growth,Yield and Fruit Quality of‘Tianhong 2’Apple Trees

[Objectives]The paper was to provide a reference for screening dwarfing rootstock suitable for main spur-type Fuji cultivars in central and southern Hebei Province.[Methods]With spur-type Fuji‘Tianhong 2’as the material,the vegetative growth,yield and fruit quality of 8 different rootstock-scion combinations were compared.[Results]‘Tianhong 2’/SH6 as self-rooted rootstock had large average single fruit weight(256.33 g),large number of fruits per plant(188.68),the highest yield[(3250.08±23.42)kg/667 m ^(2)]and the highest colored area(93.5%),and the soluble solid content reached the requirement of high quality fruit(15.78%).[Conclusions]In central and southern Hebei Province,‘Tianhong 2’grafted on SH6 self-rooted rootstock has moderate growth,high yield and good fruit quality,so it can be considered as the preferred rootstock-scion combination in the local area.

Physiological mechanisms of resistance to cold stress associated with 10 elite apple rootstocks

A study was conducted in attempting to identify the cold-resistant apple rootstocks and to establish a comprehensive evaluation system. In this study, 10 elite apple dwarfing rootstocks(GM256, JM7, M26, M7, SC1, SH1, SH38, SH6, M9, and T337) were employed for the experiment and the following parameters were investigated under different low temperature stress conditions(0, –15, –20, –25, –30, and –35°C): the changes of the relative electrical conductivity(REC), anthocyanin content, protein content, soluble sugar content, soluble starch content, proline content, malondialdehyde(MDA) content, superoxide dismutase(SOD) activity, and peroxidase(POD) activity of the dormant branches. The inflection temperature that could represent the plant tissue semi-lethal temperature(LT_(50)) was obtained by the measurements of REC. The LT_(50) was used to evaluate eight other indices. The results showed that there was no significant correlation between LT_(50) and POD activity as well as between the soluble sugar, protein and proline contents at 0 and –15°C. Soluble starch content at 0 and –15°C and anthocyanin content at –15–(–30)°C were significantly but negatively correlated to the LT50 and the MDA content at 0–(–20)°C was significantly positively correlated to the LT_(50). Statistical analysis based on principal component analysis and LT50 showed that cold resistant apple rootstocks in the decreasing order from high to low as GM256, SH6, SH38, SH1, SC1, M26, M7, JM7, T337, and M9.

Biochemical changes in grape rootstocks resulted from humic acid treatments in relation to nematode infection

Objective:To investigate the effect of humic acid on nematode infected,resistant and susceptible grapes in relation to lipid peroxidation and antioxidant mechanisms on selected biochemical parameters known as proactive substances.Methods:The grape rootstocks,superior,superior/ freedom and freedom were reacted differently to Meloidogyne incognita and Rotylenchulus reniformis according to rootstock progenitor.Two weeks after inoculation,two commercial products of humic acid were applied at the rate of(2,4 mL or grams/plant) as soil drench.After 4 months,nematode soil populations were extracted and counted.A subsample of roots from each plant was stained and gall numbers,embedded stages per root were calculated,final population, nematode build up(Pf/Pi),average of eggs/eggmass were estimated.Subsamples of fresh root of each treatment were chemically analyzed.Results:Freedom reduced significantly the nematode criteria and build up.Humic acid granules appeared to be more suppressive to nematode build up on superior and the higher dose on superior/freedom than liquid treatments.On freedom,all treatments reduced significantly the nematode build up regardless to the material nature.The higher dose was more effective than the lower one.As a result of humic acid applications,the malondialdehyde(MDA) and H_2O_2 contents were significandy reduced after humic acid treatments while the antioxidant compounds glutathione(GSH),ascorbic acid(ASA) and total phenol contents were significandy increased when compared with check.Antioxidant defense enzymes ascorbate peroxidase(AFX),superoxide dismutase(SOD),catalase(CAT) and polyphenol oxidase(PPO) showed significant increase in their specific activities in treated plants compared with nematode treated check.Conclnsions:Humic acid treatments improve we yield of grape by increasing the contents of antioxidant compounds and the specific activities of antioxidant enzymes.

Transcriptome analysis reveals the effects of alkali stress on root system architecture and endogenous hormones in apple rootstocks

Soil alkalinity is a major factor that restricts the growth of apple roots.To analyze the response of apple roots to alkali stress, the root structure and endogenous hormones of two apple rootstocks, Malus prunifolia (alkali-tolerant) and Malus hupehensis (alkali-sensitive), were compared. To understand alkali tolerance of M. prunifolia at the molecular level, transcriptome analysis was performed. When plants were cultured in alkaline conditions for 15 d, the root growth of M. hupehensis with weak alkali tolerance decreased significantly. Analysis of endogenous hormone levels showed that the concentrations of indole-3-acetic acid (IAA) and zeatin riboside (ZR) in M. hupehensis under alkali stress were lower than those in the control. However, the trend for IAA and ZR in M. prunifolia was the opposite. The concentration of abscisic acid (ABA) in the roots of the two apple rootstocks under alkali stress increased, but the concentration of ABA in the roots of M. prunifolia was higher than that in M. hupehensis. The expression of IAA-related genes ARF5, GH3.6, SAUR36, and SAUR32 and the Cytokinin (CTK)-related gene IPT5 in M. prunifolia was higher than those in the control, but the expression of these genes in M. hupehensis was lower than those in the control. The expression of ABA-related genes CIPK1 and AHK1 increased in the two apple rootstocks under alkali stress, but the expression of CIPK1 and AHK1 in M. prunifolia was higher than in M. hupehensis. These results demonstrated that under alkali stress, the increase of IAA, ZR, and ABA in roots and the increase of the expression of related genes promoted the growth of roots and improved the alkali tolerance of apple rootstocks.

Resistant Evaluation of Kiwifruit Rootstocks to Root Zone Hypoxia Stress

In this thesis, 10 species of kiwifruit rootstocks were treated with hydroponics hypoxia to study their root zone hypoxia tolerance. The results were as follows: growth of all kiwifruit seedlings was inhibited. The max length of new root, plant height, plant biomass, root activity, relative growth rate of leaves, and content of chlorophyll in leaves under root zone hypoxia stress obviously declined comparing with control. MDA content, relative conductance in the leaves and roots all increased in 10 kinds of kiwifruit seedlings. The sensitivities of 10 kinds’ kiwifruit seedlings to hypoxia stress were obviously different. With the method of subordinate function and cluster analysis, the adversity resistance coefficient of 10 kinds’ kiwifruit seedlings, were comprehensively evaluated in order to appraise their hypoxia-tolerance abilities. According to the results, “Hayward”, “Qinmei”, “Jinxiang”, “Kuoye”, “Huayou” kiwifruit seedlings held higher tolerance to root zone hypoxia stress, while “Hongyang” kiwifruit seedlings were sensitive to root zone hypoxia stress. The others, including “Xixuan”, “Maohua”, “Jinhua”, “Shanli” kiwifruit seedlings kept moderate resistant intensity to root zone hypoxia stress. The kiwifruit seedlings’ resistance order from strong to weak was: “Hayward” > “Qinmei” > “Jinxiang” > “Kuoye” > “Huayou” > “Xixuan” > “Maohua” > “Jinhua” > “Shanli” > “Hongyang”.

Effect of Time, Cultivar and Rootstock on Success of Rose Propagation through Stenting Technique

An experiment was undertaken to study the effects of two grafting times (1st of June and end of September) as well as kind of rootstock on growth and rooting of rose stentlings. Two Rosa species i.e. R. canina and R. manetti were selected as rootstock and three different hybrid tea rose cultivars namely Avalanch, Peach Avalanch and Dolcevita were grafted on them as scion through omega and splice techniques. The growth parameters were collected 57 days after grafting. The highest average of rooting, healing percentage, numbers of root, shoot and leaves were seen in September grafted plants. In overall Rosa canina was the best rootstock for Avalanch cultivar. Other observations did not lead to any prominent result as it varied with time of grafting, scion and rootstock cultivars.

Rootstock-scion interactions affect fruit flavor in grafted tomato

Vegetable grafting has become an important method for developing resistance to biotic and abiotic stresses and increasing potential yield in agronomic practice.To determine the effects of grafting on tomato taste,we examined the cultivated tomato‘Moneymaker’and the wild tomato Solanum pimpinellifolium,which have different fruit weights and qualities,to investigate the effect of grafting on sugars,acids,and volatiles in single-head and double-head grafted plants using GC-MS and LC-MS.We observed that the contents of sugars,acids and volatiles in heterografted tomato pericarps are influenced by rootstocks.Different metabolites exhibit distinct responses to the rootstock and might be associated with rootstock-scion interactions.Comparison of the metabolites in the heterogeneous fruit of the single-and double-head grafted plants indicates that the grafting method also influences the metabolic changes in grafted plants.Moreover,we also identified numerous mobile transcripts and determined that the mobile mRNAs are associated with metabolic processes in tomato leaves.Our work helps to elucidate the effect of genotype and graft method on fruit quality and may provide a basis for future research on rootstock breeding and selection in plants.

The effects of rootstocks on performances of three late-ripening navel orange varieties

Selection of rootstock is very important for citrus production. Besides its major role on resistance, the rootstock also can affect fruit production and quality. Currently, the main concerns on selection of rootstock for citrus production are compatibility and resistance, due to less information on the impacts of rootstock to the performance of scion varieties. This study aims to provide information on performances of navel orange varieties on different rootstocks. Three late-ripening navel orange varieties(Citrus sinensis var. Powell, Chislett and Banfield) grafted on seven rootstocks(Swingle citrumelo(C. paradisi× P. trifoliata), Carrizo citrange(C. sinensis×P. trifoliata), X639(C. reticulata×P. trifoliata), MXT(C. sinensis×P. trifoliata), Hongju(C. reticulata), Ziyang Xiangcheng(C. junos) and trifoliate orange(P. trifoliata)) were used as plant materials for comprehensive comparison of the performances on tree growth, fruit yield and quality in 21 scion–stock combinations. Investigation was carried out in these combinations in field nine years after planting. Vigorous growth of all the three late-ripening navel orange varieties was observed on Carrizo citrange with the largest canopy volume at 33.34 m3 and the highest yield at 29.43 kg per tree, but a low yield efficiency at 2.87 kg m–3. On the contrary, those on trifoliate orange had the smallest canopy volume at 10.79 m3 and the lowest fruit yield at 12.51 kg per tree, but the highest yield efficiency at 3.95 kg m–3. Rootstocks did not show significant effects on fruit size, fruit shape index, peel thickness and the edible rate of the fruits, but fruit quality was significantly affected by the rootstocks. Fruits from the trees grafted on trifoliate orange presented the best quality with significantly higher total soluble solids(TSS) content than those on Ziyang Xiangcheng and Hongju, and also the highest ratio of TSS/titratable acidity(TA). The TA content was observed from the fruits on X639 at 0.59 g 100 mL–1. Vitamin C(Vc) content of fruits on Hongju was the highest at 49.25 mg 100 mL–1. Growth vigor of the trees was positively correlated with fruit yield at an extremely significant level. The canopy volume was negatively correlated with yield efficiency, but positively correlated with compatibility index. Results of this study indicated that the rootstock has great impacts on the growth vigor of the tree, yield efficiency and quality of the fruit. In order to achieve good quality and yield efficiency for navel orange production, less growth vigor rootstock such as trifoliate orange is highly recommended.

Genotypic Effect of Rootstock and Scion on Grafting Success and Growth of Kola (Cola nitida) Seedlings

Kola (Cola nitida) is an important economic cash crop for many West and Central African countries. It has several medicinal uses in the pharmaceutical industries and also plays a major role in traditional marriages among Islamic communities across West and Central Africa. The crop is extensively cultivated in Nigeria and Ghana. However, it exhibit signs of total and partial sterility as well as self incompatibility when propagated from seeds in most cases. Therefore, grafting is seen as a method of choice in addressing the problem stated above. Though grafting accounts for some degree of success, there is the need to assess genotypic and physiological factors that account for high or low grafting success. Genetic and physiological factors (such as rootstock age) affecting grafting success and growth in kola (C. nitida) were investigated in two separate experiments. In experiment I720 kola seedlings were raised from unselected kola nuts and sown at two monthly intervals. Four groups of seedlings (180/group) i.e. 6, 8, 10 and 12 months old were thus produced. Three different scions (A1, A12 and JB1) measuring (5-10 cm) were grafted onto the four age groups of rootstocks, namely, 6, 8, 10 and 12 months. Experiment II consisted of 540 seedlings raised from three main crosses (JX1/9 × JX1/11 * B1/142 × B1/151, JX1/9 × JX1/11 * B2/177 × B2/156 and JX1/9 × JX1/11 * GX1/46 × GX1/53). Grafting was done after six months using the same set of scions as described in experiment I. Experimental design used was 3 × 4 and 3 × 3 factorial designs in completely randomised design with three replicates for experiment I and II respectively. The fixed effects were the different genotype and age of rootstock at grafting whilst the response variable was the percentage of successful grafting two months as well as growth at six monthly intervals. Results from the study showed that grafting onto 6 months old stocks gave the highest percentage success and growth of grafts followed by 8, 10 and 12 months old rootstock in that order in both trial years. The study revealed also a significant rootstock and scion interaction (P < 0.05). We conclude that successful grafting in kola depends on rootstock genotype such as JX1/9 × JX1/11 * GX1/46 × GX1/53 and has been proven suitable for use in future kola propagation studies. Nonetheless, suitable rootstock with high grafting success does not translate into vigorous scion growth.

Rootstocks effect on plant nutrition concentration in different organ of grafted watermelon

In this study carried out in 2009 and 2010 growing seasons, effect of rootstocks on plant nutrition partitioning in grafted watermelon onto four gourd rootstocks was investigated. Ferro, RS841 (Cucurbita maxima x C. moschata) and Argentario and Macis (Lagenaria hybrid) were used as rootstocks. Crimson Tide and Crisby watermelon cultivars were used as scion. Grafted and ungrafted seedlings were produced by a commercial seedling company. Plants were grafted by one cotyledon grafting techniques. Experiment was conducted in Alata Horticultural Research Station inMersin. The grafted plants were planted under low tunnel in early spring and regular cultural practices for watermelon were applied. Plant nutrition concentrations were determined in leaf, fruit rind, fruit flesh and seeds. Leaf sample was taken at flowering stage, rind, flesh and seed sample were taken from fully mature fruit. Nitrogen concentration was determined by modified Kjheldahl methods. Phosphorous concentration was determined by vanadomolybdophosphoric acid method. K, Ca, Mg, Fe, Mn, Zn and Cu concentration of samples were determined by atomic absorption spectrophotometry. Plant nutrient concentration in leaf, rind, flesh and seed were significantly affected by rootstocks. Increase in concentration of N, P, K, Ca and Mg in leaves was not observed in grafted plant. Ungrafted plant had higher concentration of Fe, Mn, Zn and Cu in their leaves. Ca concentration in rind of fruits from grafted watermelon was higher than ungrafted control plant except Crimson Tide/Macis and Crimson Tide/Argentario graft combinations. Plant nutrition content of fruit flesh was significantly affected by rootstocks and scion. Magnesium, Fe, Zn and Mn concentration of seed was not significantly influenced by rootstocks and scion while other plant nutrient content was significantly affected rootstocks and scion.

Effects of Different Rootstocks on Plant Growth and Fruit Quality of Watermelon

[Objectives] This study was conducted to explore the effects of different rootstocks on plant growth and fruit quality of watermelon. [Methods] The scions of two different watermelon varieties Qianmei No. 1,which has yellow flesh,and Qianli No. 1,which has red flesh,were grafted onto six different rootstocks of Lagenaria and Citrullus. Then,the seedling survival rate,growth potential and fruit quality in different rootstock-scion combinations were investigated.[Results]Rootstock type showed an extremely significant correlation with the survival rate of grafted watermelon plants. The watermelons grafted onto Lagenaria rootstocks had higher survival rate and better fruit quality than those onto Cucurbita rootstocks. Among them,Jingxinzhenguan was more suitable for red-fleshed watermelon variety,and bottle gourd rootstock was more suitable for yellow-fleshed watermelon variety. There were significant correlations between rootstock type and the number of leaves,the number of branches and the length of main vine of grafted plants. The number of leaves per seedling of all grafted plants was higher than that of non-grafted plants. There were no significant differences in sugar content at the center part of flesh and total soluble sugar content of fruit between the grafted and non-grafted watermelons. In addition,the interaction between rootstock type and watermelon variety had no significant effect on vegetative growth and fruit quality of grafted watermelon. [Conclusions] This study provides a theoretical basis for the grafting of watermelon.

Influences of rootstock and agro-climatic condition on physico-chemical and bioactive compounds of Gunda Gundo orange(Citrus sinensis L.Osbeck)in the Northern Ethiopia

Rootstocks have a significant influence on adaptation to biotic and abiotic stress conditions and quality of fruit.So,choice of rootstock for a specific growing region is an important decision for a grower to make when establishing a commercial citrus orchard.This study was undertaken to assess effects of rootstock and location on quality of orange fruit.The study was conducted over two consecutive years(2017/18 and 2018/19).Scions from the Gunda Gundo orange grove were grafted on rough lemon and sour orange rootstocks and planted in Tigray and Afar,Ethiopia at four sites(Abala,Agulae,Adiha and Rama).The experiment was laid out in Randomized Complete Block Design(RCBD)with four replications.Data on different physico-chemical and bioactive compounds were collected and analyzed using R software(version 4).Compared to sour orange,rough lemon rootstock revealed higher fruit mass(151.96 g,195.38 g),fruit length(62.27 mm,68.88 mm)and fruit diameter(65.58 mm,71.3 mm),in 2017/18,2018/19,respectively.Among the four locations(Abala,Agulae,Adiha and Rama),higher juice percentage was found in Adiha(43.47%in 2017/18)and Abala(49.87%,in 2018/19).In 2017/18 higher total soluble solid(TSS,13.87%),TSS/acid ratio(19.18)and fruit rag(32.77%),were obtained at the Rama site.On the one hand,higher vitamin C(826.6 mg·kg^(-1))and total phenolic content(208 mg·kg^(-1 )GAE)were recorded at Agulae than Abala,Adiha and Rama sites from sour orange rootstock.High TSS,TSS/acid ratio and antioxidant were recorded from orange fruits at Rama site.This was expected to have resulted from hot climate conditions at the site.Besides,at a relatively cooler condition of the Agulae site,high phenolic,reduced ferric power and high vitamin C were recorded.Rough lemon rootstock improved fruit size,while rootstock did not affect the contents of TSS,TSS/acid ratio across the sites in both harvesting years.

Evaluation of Propagation of Chinese Hibiscus (<i>Hibiscus rosa-sinensis</i>) through Stenting Method in Response to Different IBA Concentrations and Rootstocks

Stenting is a vegetative propagation method, based on cutting and grafting in one action. The question addressed in this study is whether indole-3-butyric acid (IBA) concentration is able to impress success of Chinese hibiscus propagation when grafted onto two kinds of rootstocks. The used IBA concentrations include: 0, 1000, 3000 and 5000 ppm and two cultivars of Hibiscus syriacus (“Blue Stain” and “Jeanne d’Arc”), which have been used as rootstock. Results indicated that, all the cultivars were superior for most of the measured parameters when IBA treatments were used compared to control plants except for average of the longest root size. The highest healing percentage resulted in stentlings (plant which has been propagated by stenting method) with 5000 ppm of IBA treatment. All IBA treatments significantly increased rooting percentage compared with the control plants. Stentlings that were treated with 3000 and 5000 ppm of IBA, produced the greatest leave number. In Chinese hibiscus/“Jeanne d’Arc” combination, higher root number and dry weight of roots were observed. Interactions of kinds of rootstock and IBA concentration showed that the highest healing percentage was obtained in “Blue Stain” in concentration of 5000 ppm and the highest root number were seen in stentlings with “Jeanne d’Arc” in 3000 ppm and “Jeanne d’Arc” in 5000 ppm.

Effects of flooding on grafted annona plants of different scion/rootstock combinations

Annona atemoya Hort cv. African Pride (AP) is highly valued due to its high quality and unique flavor, but highly susceptible to water-logging. Prevalence of root diseases in saturated soils is one of the main problems in production, which restricts the development of AP in south China, where flooding frequently occurs in rainy seasons. However, some annona species, e.g. A. montana, A. glabra and A. muricata, are relatively tolerant to continuous flooding and periodic water-logging conditions, but of limited commercial value. Yet, the potential may exist to increase flood tolerance of commercial annona varieties by the use of flood tolerant rootstocks. An experiment was conducted with the aim to study the effects of continuous or periodical soil flooding on tree performances of four different annona scion/rootstock combinations: AP/AR/G (scion/interstock/rootstock), AR/G (scion/rootstock), AP/AR/M and AR/M, where AP stands for Annona atemoya Hort cv. African Pride, AR for the hybrid of “AP” atemoya × A. reticulata, used as an interstock, G for pond apple (A. glabra), and M for mountain soursop (A. montana). Plant growth, leaf net photosynthetic rates and chlorophyll fluorescence parameters were measured regularly after flooding treatments were applied. Flooding treatments reduced shoot extension, leaf production, net photosynthetic rates and maximum quantum efficiency of photosystem II (Fv/Fm) in plants of AP/AR/M and AR/M, which displayed wilting within 2 weeks of flooding, with a higher wilting percentage in AP/AR/M than in AR/M. The wilted plants shed all leaves but remained alive and sprouted new but weak shoots after 16 weeks of flooding. Long term flooding did not suppress but enhanced photosynthesis as well as tree growth in AP/AR/G and AR/G, with vigorous growth of adventitious roots. Thus, we suggest the use A. glabra instead of A. montana as a rootstock and AR as an interstock to increase flood tolerance of commercial annona varieties.

Comparison of leaf morphological,anatomical,and photosynthetic responses to drought stress among eight apple rootstocks

The drought resistance of eight commonly used apple rootstocks under natural drought conditions was examined to provide clues for the selection,promotion,and utilization of drought-resistant apple rootstocks.The ultrastructural differences and physiological and biochemical characteristics of the leaves of eight apple rootstocks under drought stress were observed.The index changes were used to rank drought resistance by the membership function method comprehensively.The results showed that the leaf thickness,palisade tissue thickness,sponge tissue thickness,net photosynthetic rate,and chlorophyll content were significantly higher in‘Fupingqiuzi'than those of other rootstocks at various stress conditions.The leaf water content and water use efficiency of'Qingzhen 1'were significantly higher than those of other rootstocks under different stress conditions.The root vigor of‘B.9'was significantly higher than that of other rootstocks.The results of membership function analysis showed that the drought resistance of different rootstocks was in the order:‘Fupingqiuzi'>‘Qingzhen 1'>‘B.9'>‘MM.111'>‘GM256'>‘MM.106'>‘M.26'>‘M.9-Nic29'.‘Fupingqiuzi'had the strongest drought resistance,and‘Qingzhen 1'and‘B.9'were also relatively droughtresistant.These rootstocks can be used as raw materials for drought-resistant apple rootstock breeding and are propagated and utilized in arid areas.

Comprehensive evaluation of tolerance to alkali stress by 17 genotypes of apple rootstocks

Alkaline soils have a great influence on apple production in Northern China. Therefore, comprehensive evaluations of tolerance to such stress are important when selecting the most suitable apple rootstocks. We used hydroponics culturing to test 17 genotypes of apple rootstocks after treatment with 1:1 Na2CO3 and Na HCO3. When compared with the normally grown controls, stressed plants produced fewer new leaves, and had shorter roots and shoots and lower fresh and dry weights after 15 d of exposure to alkaline conditions. Their root/shoot ratios were also reduced, indicating that the roots had been severely damaged. For all stressed rootstocks, electrolyte leakage(EL) and the concentration of malondialdehyde(MDA) increased while levels of chlorophyll decreased. Changes in root activity(up or down), as well as the activities of peroxidase(POD), superoxide dismutase(SOD), and catalase(CAT) were rootstock-dependent, possibly reflecting their differences in alkali tolerance. Using alkali injury index(AI), adversity resistance coefficients(ARC), cluster analysis, and evaluation of their physiological responses, we classified these 17 genotypes into three groups:(1) high tolerance: Hubeihaitang, Wushanbianyehaitang, Laoshanhaitang Ls2, Xiaojinbianyehaitang, and Fupingqiuzi;(2) moderate tolerance: Pingyitiancha, Laoshanhaitang Ls3, Hubeihaitang A1, Deqinhaitang, Balenghaitang, Maoshandingzi, Shandingzi, and Xinjiangyepingguo; or(3) low tolerance: Pingdinghaitang, Hongsanyehaitang, Xiaojinhaitang, and Sanyehaitang. These results will significantly contribute to the selection of the most suitable materials for rootstocks with desired levels of tolerance to alkali stress.

Dwarfi ng apple rootstock responses to elevated temperatures: A study on plant physiological features and transcription level of related genes

The aim of this study was to investigate the impact of heat stress on physiological features, together with endogenous hormones and the transcription level of related genes, to estimate the heat resistance ability and stress injury mechanism of different dwarfing apple rootstocks. Among the six rootstocks, the rootstocks of native Shao series(SH series) showed better heat stress resistance than those of Budagovski 9(B9), Cornell-Geneva 24(CG24), and Malling 26(M26) from abroad. Among SH series rootstocks, SH1 and SH6 showed higher heat stress resistance than SH40. M26 demonstrated the lowest adaption ability to heat stress, showing higher leaf conductivity and lower liquid water content(LWC) with the increase in temperature. Heat stress also resulted in the suppression of photosynthesis, which showed no significant restoration after 7-day recovery. It should be noted that although a higher temperature led to a lower LWC and photosynthetic efficiency(P_n) of CG24, there was no significant increase in leaf conductivity, and 7 days after the treatment, the P_n of CG24 recovered. The extremely high temperature tolerance of SH series rootstocks could be related to the greater osmotic adjustment(OA), which was reflected by smaller reductions in leaf relative water content(RWC) and higher turgor potentials and leaf gas exchange compared with the other rootstocks. Determination of hormones indicated multivariate regulation, and it is presumed that a relatively stable expression levels of functional genes under high-temperature stress is necessary for heat stress resistance of rootstocks.

Differences in the Efficiency of Potassium(K) Uptake and Use in Five Apple Rootstock Genotypes

Plants that grow well while accumulating and transporting less potassium(K) perform better than more-sensitive plants when under deficiency conditions, which makes low-K-input and environmentally friendly agriculture possible. We conducted hydroponics and sand culture experiments to evaluate the efficiency of various apple(Malus domestica Borkh) rootstocks in their K uptake and utilization. Five genotypes were selected which are widely used in China- M. hupehensis Rehd, M. prunifolia Borkh, M. robusta Rehd, M. sieversii Roem, and M. rockii Rehd. Plant heights, root and shoot dry weights, and K concentrations were recorded. These genotypes differed markedly in dry weights, absolute and relative K concentrations, absolute and relative K accumulations, and their K efficiency ratio under deficient K conditions. The last parameter, expressed as relative shoot dry weight, was strongly and positively correlated with the other four parameters in each genotype. Therefore, we suggest that this parameter could serve as an index when selecting K-efficient genotypes. In this study, we have determined that M. sieversiiand M. rockii are K-inefficient genotypes; M. prunifolia is K-efficient genotype; M. hupehensis and M. robusta have moderate levels of potassium efficiency.