Root and stem hydraulic conductivity as determinants of growth potential in grafted trees of apple (Malus pumila Mill.)

The anatomy of the graft tissue between a rootstock and its shoot (scion) can provide a mechanistic explanation of the way dwarfing Malus rootstocks reduce shoot growth. Considerable xylem tissue disorganization may result in graft tissue having a low hydraulic conductivity (k(h)), relative to the scion stem. The graft may influence the movement of substances in the xylem such as ions, water and plant-growth-regulating hormones. Measurements were made on 3-year-old apple trees with a low-pressure flow system to determine k(h) of root and scion stem sections incorporating the graft tissue. A range of rootstocks was examined, with different abilities of dwarfing; both ungrafted and grafted with the same scion shoot cultivar. The results showed that the hydraulic conductivity (k(hroot)) of roots from dwarfing rootstocks was lower compared with semi-vigorous rootstocks, at least for the size class of root measured (1.5 mm diameter). Scion hydraulic conductivity (k(hs)) was linked to leaf area and also to the rootstock on to which it was grafted, i.e. hydraulic conductivity was greater for the scion stem on the semi-vigorous rootstock. Expressing conductivities relative to xylem cross-sectional areas (k(s)) did not remove these differences suggesting that there were anatomical changes induced by the rootstock. The calculated hydraulic conductivity of the graft tissue was found to be lower for grafted trees on dwarfing rootstocks compared to invigorating rootstocks. These observations are discussed in relation to the mechanism(s) by which rootstock influences shoot growth in grafted trees.     

Control of scion vigour by kiwifruit rootstocks is correlated with spring root pressure phenology

Root pressure was measured continuously over spring in eight clonal kiwifruit rootstocks selected from seven Actinidia species (A. chrysantha, A. deliciosa, A. eriantha, A. hemsleyana, A. kolomikta, A. macrosperma, A. polygama), using pressure transducers and miniature compression fittings. Rootstocks that promoted scion vigour developed root pressures up to 0.15 MPa before or during scion budburst, whereas those that reduced scion vigour developed root pressure up to 0.05 MPa only after scion shoot expansion. When several seasons were compared, the date of onset of root pressure and the magnitude of pressure achieved were consistent for each rootstock. Root pressure was first recorded between late July and early September in vigour-promoting rootstocks, while scion budburst and initial shoot growth were in late August and early September. Vigour-reducing rootstocks did not develop significant root pressure until October. The date of onset was similar for the grafted rootstock and ungrafted plant of the same clone, but was not clearly related to the timing of shoot growth by the ungrafted plant. In the grafted plants the leaf and xylem water potentials of the scion were more negative, midday turgor was 0.3-0.5 MPa lower, and wilting was sometimes observed in developing shoots growing on low-vigour rootstocks, indicating that water stress was contributing to reductions in growth. Leaf turgor was correlated with average root pressure but not pressure measured during the day, suggesting that root pressure was not supporting transpiration during peak flows and was, instead, indicative of higher root hydraulic conductance. The rapid temporal rise in root pressure observed each spring in the various rootstocks was not accompanied by changes in xylem sap solute potential, but when rootstock clones were compared those that developed higher root pressures had higher sap solute potentials. Xylem sap solute potential varied between rootstocks from -0.07 MPa to -0.15 MPa, while root pressures measured at the same time varied between 0.0 MPa and 0.09 MPa, suggesting that an osmotic mechanism could account for the observed root pressure. Differences in phenology between the rootstocks and scion appeared to account for the rootstock effects on shoot growth, and changes in root pressure provided a useful indication of seasonal changes in root hydraulic properties and solute transport behaviour.     

Relationships between xylem anatomy,root hydraulic conductivity,leaf/root ratio and transpiration in citrus trees on different rootstocks

The aim of the study was to determine the extent in which leaf and whole plant transpiration (Tp) were influenced by root hydraulic conductance (K_r), leaf to root ratio and leaf mass. Also, the relationships between the anatomic characteristics of roots and K_r were investigated. To this end, 9‐month‐old seedlings of the citrus rootstocks Cleopatra mandarin (CM), Poncirus trifoliata (PT), and their hybrids Forner‐Alcaide no 5 (FA‐5) and Forner‐Alcaide no 13 (FA‐13) and 15‐month‐old trees of Valencia orange budded on these four rootstocks were tested. The hybrid FA‐13 and PT had higher values of K_r and leaf transpiration rates (E) than FA‐5 and CM. There was a positive curvilinear correlation between E and K_r. Furthermore, E levels in the different types of plants decreased with increased leaf/root (L/R) ratios. Pruning of the roots and defoliation confirmed that transpiration rates were strongly influenced by the L/R ratio. However, variations in E because of differences in L/R ratios were less pronounced in trees budded on FA‐13 and PT than on the other two rootstocks. In addition, there was a positive correlation between Tp and leaf biomass, although differences between rootstocks may be attributed to differences in K_r. The average lumen diameter of xylem vessels was greater in rootstocks with high K_r. Size of epidermal and hypodermal cells of fibrous roots may also restrict K_r.     

Hydraulic conductance and rootstock effects in grafted vines of kiwifruit

Whole-plant hydraulic conductance, shoot growth, and leaf photosynthetic properties were measured on kiwifruit vines with four clonal rootstocks to examine the relationship between plant hydraulic conductance and leaf stomatal conductance (gs) and to test the hypothesis that reduced hydraulic conductance can provide an explanation for reductions in plant vigour caused by rootstocks. The rootstocks were selected from four species of Actinidia and grafted with Actinidia chinensis var. chinensis 'Hort16A' (yellow kiwifruit) as the scion. Total leaf area of the scion on the least vigorous Actinidia rootstock, A. kolomikta, was 25% of the most vigorous, A. hemsleyana. Based on shoot growth and leaf area, the selections of A. kolomikta and A. polygama are low-vigour rootstocks, and A. macrosperma and A. hemsleyana are high-vigour rootstocks for A. chinensis. Whole-plant hydraulic conductance, the ratio of xylem sap flux to xylem water potential, was lower in the low-vigour rootstocks, reflecting their smaller size. However, leaf-area-specific conductance (Kl) and gs were both higher in the low-vigour rootstocks, the opposite of the expected pattern. Differences in Kl were found in the compartment from the roots to the scion stem, with no difference between rootstocks in the conductance of stems or leaves of the scion. There was no evidence that the graft union caused a significant reduction in hydraulic conductance of vines with low-vigour rootstocks. Leaf photosynthetic capacity did not vary between rootstocks, but photosynthesis and carbon isotope discrimination (Delta13C) under ambient conditions were higher in the low-vigour rootstocks because gs was higher. gs and Delta13C were positively correlated with Kl, although the mechanism for this relationship was not based on stomatal regulation of a similar xylem water potential because water potential varied between rootstocks. For Actinidia rootstocks, changes in Kl do not provide a direct explanation for changes in vigour of the scion. However, depending on the rootstock in question, changes in hydraulic conductance, biomass partitioning, and crown structure are involved in the response.     

Effects of cultural treatments on the incidence of, and damage done by, tomato brown root rot

In soils naturally infested with Pyrenochaeta lycopersici, which usually occurs as a grey sterile fungus (GSF), symptoms of brown root rot (BRR) developed sooner and more extensively in the second year of cropping than in the first. The amount of BRR attributable to corkiness increased as plants aged but, at comparable stages of cropping, decreased in the second and third seasons, an effect associated inversely with the severity of early GSF attack. The larger amount of corkiness, 33 compared with 18 %, on two batches of plants in 1965, each with 53 % end-of-season BRR, was also attributed to a less severe early GSF attack on the former than on the latter, growing in soils unsteamed for 1 and 3 years respectively. The incidence of BRR decreased with increasing depth in infested soils but increased on plants grown in plots with partially sterilized topsoil. Partially sterilizing soils at the G.C.R.I. and Fairfield E.H.S. decreased the incidence of BRR and increased crop weights from about the second month of picking, but fruit quality was poorer. Seasonal yields from plants in untreated soil progressively decreased relatively to those from repeatedly steamed plots, from 93 to 65 % in successive years at Fairfield and from 65 to 56 and 43 % at the G.C.R.I. Steaming done in 1963 and 1964 temporarily retarded GSF attack in 1965 with corresponding yield increases. Increasing the amounts of sterilized propagating soil surrounding roots at planting from 0·4 to 1·01 per plant increased yields by c. 0·4 kg/plant, this being a relatively large increase for plants in infested soil, where this treatment significantly delayed the early incidence of BRR near stem bases. Grafting commercially acceptable scions to rootstocks that tolerated colonization by GSF (‘resistant’ rootstocks), temporarily checked growth, delayed picking and decreased fruit quality. Usually grafted plants, irrespective of soil treatment, yielded at least as much fruit as ungrafted plants in steamed soil. In one of five comparisons, soil steaming increased yields of grafted plants. When testing the effects of previous cropping it seemed that populations of GSF increased similarly in soils planted with grafted and ungrafted plants. In addition to GSF attack, roots at Fairfield E.H.S. were often colonized by Colletotrichum coccodes, microsclerotia (= black dots) being more numerous as plants aged. Although significantly more black dot developed on GSF-resistant rootstocks grown in untreated soil than on those grown in steamed soil, the differences were not associated with effects on yield. C. coccodes colonized GSF-susceptible and -resistant roots equally.     

Improving the Mineral Nutrition in Grafted Watermelon Plants: Nitrogen Metabolism

Watermelon (Citrullus lanatus [Trumb.] Mansfeld cv. Early Star), was used as scion grafted onto three cultivars of pumpkin (Cucurbita pepo L. cvs. Brava, Shintoza and Kamel) used as rootstocks and ungrafted Early Star plants were used as control. The rootstocks showed a high capacity for N uptake and transport to the scion where N reduction and assimilation improved growth of the scion in grafted plants with respect to the control.     

Anatomical Characteristics of Cherry Rootstocks as Possible Preselecting Tools for Prediction of Tree Vigor

An anatomical study of roots and stems of five self-rooted cherry rootstocks with different growth control potentials was performed to compare their structure and xylem anatomy. The aim was to correlate anatomical parameters with rootstock dwarfing potential and theoretical hydraulic conductance (k _h), and to evaluate the potential application of anatomical characteristics in the preselection process for prediction of ultimate tree vigor. One of the mechanisms of water transport efficiency reduction in dwarfing rootstock stems is from the rootstock xylem anatomy. Anatomical parameters of ??Gisela 5?? and ??Mazzard?? were typical for dwarfing and vigorous rootstocks, respectively, and were thus suggested as reference rootstocks. Significantly greater vessel diameter and frequency were found in invigorating and dwarfing rootstocks, respectively. Higher k _h was obtained in roots, compared to stems, due to significantly larger vascular elements. Dwarfing rootstocks had lower k _h due to small vessel lumens and percentage and, to a lesser extent, because of low wood/cortex ratios or percentage of wood. A higher percentage of wood or xylem in cherry roots and stems was not always positively correlated with their conductivity and vigor. Thus, these parameters cannot be reliably used in prediction of the ultimate vigor, although this method was previously suggested for some other fruit tree species. The most reliable anatomical parameters for that purpose proved to be vessel frequency, vessel lumen area, and percentage of vessels on wood cross section. These characteristics could thus be an effective way to estimate dwarfing capacity and could be applied in rootstock selection and breeding programs.     

嫁接对铜胁迫下黄瓜幼苗根系多胺代谢的影响

采用营养液栽培法,研究了嫁接(以黑籽南瓜为砧木)对铜胁迫下黄瓜幼苗根系活力及多胺代谢的影响.结果表明:铜胁迫下黄瓜幼苗根系活力下降,电解质渗漏率升高,而嫁接苗的变化幅度显著小于黄瓜自根苗;铜胁迫下黄瓜嫁接植株根系中除游离态腐胺(Put)含量显著低于自根苗外,结合态和束缚态Put、3种形态亚精胺(Spd)和精胺(Spm)含量均显著高于自根苗,嫁接苗根系中游离态Put含量及腐胺/多胺(Put/PAs)显著低于自根苗;铜胁迫下,嫁接苗根系精氨酸脱羧酶(ADC)、鸟氨酸脱羧酶(ODC)和S-腺苷蛋氨酸脱羧酶(SAMDC)活性高于自根苗,而二胺氧化酶(DAO)和多胺氧化酶(PAO)活性显著低于自根苗.表明嫁接黄瓜幼苗根系PAs的合成增加,降解减少,使PAs含量维持在较高水平,从而提高了黄瓜幼苗抗铜胁迫能力.     

Genetic diversity of root anatomy in wild and cultivated Manihot species

An anatomical study of roots was conducted on two wild Manihot species, namely M. glaziovii and M. fortalezensis, and two cassava varieties, M. esculenta Crantz variety UnB 201 and M. esculenta variety UnB 122, to identify taxonomic differences in primary growth. Anatomical characters of cassava roots have been rarely investigated. Their study may help cassava breeders to identify varieties with economically important characters, such as tolerance to drought. We investigated tap and lateral adventitious roots of two specimens of each clone or species. Free-hand cross-sections of roots were drawn; these had been clarified with 20% sodium hypochlorite solution, stained with 1% safranin-alcian blue ethanolic solution, dehydrated in ethanol series and butyl acetate and mounted in synthetic resin. Anatomical differences among Manihot species and varieties were found in the epidermal and exodermal cell shape and wall thickness, content of cortical parenchyma, and number of xylem poles. Wall thickness of the epidermis and exodermis of tap root were similar in all species, while in the lateral root there were differences in cell shape and wall thickness. Epidermal cells with thick walls were found in the tap root of all species and in lateral roots of cassava varieties. This character is apparently associated with tolerance to drought and disease. The variation in the number of xylem poles of cassava varieties was larger (4-8) than in wild species (4-6), and appears to support the hybrid origin of cassava.     

Effects of mutual grafting on the cadmium accumulation characteristics of two ecotypes of Solanum photeinocarpum

Abstract

The effects of mutual grafting on the cadmium (Cd) accumulation characteristics of two ecotypes (farmland and mining) of the potential Cd-hyperaccumulator Solanum photeinocarpum were studied through a pot experiment for one month. Four treatments were used in the experiment: ungrafted farmland ecotype (F-CK), ungrafted mining ecotype (M-CK), the farmland ecotype as the scion grafted onto rootstocks of the mining ecotype (F-Scion), and the mining ecotype as the scion grafted onto rootstocks of the farmland ecotype (M-Scion). Mutual grafting increased the rootstock biomass of both S. photeinocarpum ecotypes. However, mutual grafting decreased the scion biomass of F-Scion compared with F-CK and M-CK, and the scion biomass of M-Scion was higher than that of M-CK and lower than that of F-CK. The Cd content in the rootstock of M-Scion increased compared with F-CK, and the Cd content in the rootstock of F-Scion increased compared with M-CK, but mutual grafting decreased the Cd content in scions of both S. photeinocarpum ecotypes. Mutual grafting increased Cd extraction by rootstocks of both S. photeinocarpum ecotypes, but decreased extraction by scions. Therefore, mutual grafting can increase Cd accumulation in S. photeinocarpum rootstocks but not increase Cd accumulation in S. photeinocarpum scions in a short period.     

铁胁迫对三种柑橘砧木的生长、生理特性及铁分布的影响

以枳壳、酸橙和红橘三种柑橘砧木实生苗为材料,采用溶液培养法研究了铁胁迫对其生长、生理特性及铁分布的影响.结果表明:缺铁胁迫(0 μmol·L-1)时,三种柑橘砧木的生长指标及叶片叶绿素含量均显著低于低铁(5 μmol·L-1)和适量铁(50 μmol·L-1)处理;三者叶片和根系的POD、CAT活性显著降低,SOD活性...     

根瘤蚜对不同抗性葡萄的选择性及葡萄根系挥发性物质的鉴定

为了探讨不同抗性水平砧木及品种对根瘤蚜吸引及驱避效应以及鉴定挥发性物质组分,采用离体根段培养法测定葡萄根瘤蚜Phylloxera viticola Fitch对砧木5BB,140Ru及栽培品种巨峰的选择性,发现根瘤蚜对栽培品种巨峰的根段具有很强的选择性,至接种后3 d,67.13％的根瘤蚜优先选择巨峰;而对5BB和140Ru的选择性却很差,分别有15.29％和17.58％的根瘤蚜选择5BB及140Ru。根瘤蚜在不同品种根段上的生长发育和繁殖也存在明显差异。对砧木5BB和巨峰根系的挥发性组分进行测定,发现2个品种挥发物独有组分数量均较高,巨峰独有组分为23个,占总成分数的48.94％,5BB的独有组分为32个,占总成分数的57.14％。5BB和巨峰的共有组分为24个,主要成分均为亚油酸甲酯和反油酸甲酯,但含量有所不同,其中,5BB以倍半萜类的丁香醇及脂肪酸甲酯类的亚油酸甲酯,反油酸甲酯,棕榈油酸甲酯含量较高,高于巨峰中相应物质含量的4.23%~6.46％,而巨峰以邻苯二甲酸二丁酯及胆甾烷含量较高,分别高于5BB相应组分含量的6.81％和1.07％。结果说明葡萄根瘤蚜对不同抗性水平砧木及品种确实存在不同的选择性,并且不同抗性水平的砧木及品种的挥发性物质存在显著差异。     

Changes in the anatomical structure of tree rings of the rootstock and scion in the heterografts of Siberian pine

The analysis of the anatomical characteristics of tree rings of the Pinus sibirica scions and Pinus sylvestris rootstocks is presented. The main anatomical features maintain the seasonal dynamics characteristic of the reference (ungrafted) trees of scion and rootstock, pointing to the stability of the genetic control of the xylem differentiation. However, various anatomical characteristics are reduced for rootstocks and increased for scions relative to the reference trees. A mechanism consistent with our results is that the graft union zone creates a barrier for the ascending and descending transport of substances, including phytohormones. The reaction of the scion and rootstock to climatic factors is weakened relative to the reaction of the reference trees. Thus, the presumed shift towards phytohormone disbalance reduces the influence of external factors on xylem differentiation. The interannual variation of the individual characteristics of the scions and rootstocks is increased relative to the reference trees, reflecting either the influence of the graft partners on each other or the non-uniform distribution of the growth regulators across the graft union. Thus, heterografts can be used to evaluate the interaction of the internal and external mechanisms of xylem differentiation.     

Rootstock effects on xylem conduit dimensions and vulnerability to cavitation of <Emphasis Type="Italic">Olea europaea</Emphasis> L.

Two clones of Olea europaea L. were studied for their potential impact on hydraulic architecture and vulnerability to xylem cavitation, when used as rootstocks. The clones used were “Leccino Minerva” (LM), showing vigorous growth and “Leccino Dwarf” (LD) with strongly reduced growth. Self-rooted LM and LD plants as well as their grafting combinations were compared, namely, LM/LD (Leccino Minerva grafted onto Leccino Dwarf rootstock) and LD/LM (Leccino Dwarf grafted onto Leccino Minerva rootstocks). Plants with LD roots (LD and LM/LD) showed significantly reduced leaf surface area compared with plants with LM roots. Xylem conduits of LD shoots were 25% more numerous than in LM shoots. When grafted onto LM rootstocks, however, LD shoots produced consistently wider and longer vessels than measured in LD self-rooted plants. This caused LD/LM plants to increase stem vulnerability to cavitation with threshold pressures for cavitation (P _c) of less than 0.5 MPa compared with LD self-rooted plants that had P _c of over 2.0 MPa. By contrast, although LD rootstocks caused some reduction of vessel diameter and length of LM scions, their influence on LM hydraulic architecture was too small to reduce vulnerability to cavitation of LM scions with respect to that measured for LM self-rooted plants. Our conclusion is that although dwarfing rootstocks effectively reduce grafted plant size, they do not necessarily confer higher resistance to xylem cavitation to scions which would improve plant resistance to drought.     

Penetration and Development of Meloidogyne arenaria on Two New Grape Rootstocks

Penetration, development, and reproduction of a virulent ''Harmony'' population of Meloidogyne arenaria was studied on two nematode-resistant grape rootstocks 10-17A and 6-19B. ''Cabernet Sauvignon'' was used as a susceptible control for comparison. Plants were inoculated with 100 freshly hatched second-stage juveniles (J2) of M. arenaria. Greater numbers of J2 penetrated roots of ''Cabernet'' than 10-17A, and none penetrated roots of 6-19B 4 days after inoculation (DAI). At 7 DAI, vermiform J2 advanced to sausage-shaped J2 in roots of ''Cabernet,'' penetrated roots of 6-19B, and had egressed from roots of 10-17A. Resistant rootstocks expressed hypersensitive responses to penetrating J2 along the root epidermis, among the cortical cells, and along the differentiating vascular bundles. At 13 DAI, 68% of the J2 had attained globose stage in roots of ''Cabernet,'' whereas there was no development of vermiform J2 in roots of the other two rootstocks. The nematodes reproduced only in roots of ''Cabernet.'' Lack of development of J2 in roots of the two resistant grape rootstocks might be the result of a hypersensitive response to J2 feeding.     

4-Desmethylsterol composition of citrus rootstocks of different salt exclusion capacity

Fibrous roots from seedlings of three citrus rootstocks (Rungpur lime, Kharna khatta and Etrog citron) grown hydroponically for 6 weeks in the presence or absence of 50 mM NaCl were analysed for their content of free, esterified, and glycosidic sterols. Leaf chloride analyses indicated that Rangpur lime was a good Cl- excluder and the other two rootstocks were Cl- accumulators.
On a dry weight basis and in the absence of NaCI only the free 4-desmethyIsterol levels showed significant rootstock differences. Kharna khatta had the highest, and Rangpur lime the lowest, free stcrol levels. Sitostcrol was the major component of all sterol fractions of Rangpur lime, the esterified fraction of the other rootstocks, and the glycosidic sterol fraction of Kharna khatta. The ratio of sitosterol to stigmasterol was highest in Rangpur lime and lowest in Etrog citron in all cases and the ratio of apos;more-planar apos; to apos;less-planar apos; free sterols was highest in Etrog citron and lowest in Rangpur lime.
Treatment with 50 mM NaCI resulted in an increase in free sterol levels in Rangpur lime and a decrease in Kharna khatta. Steryl ester levels were unaffected in Rangpur lime but were significantly reduced in the other rootstocks. In all three sterol fractions the sitosterol/stigmasterol ratio was decreased. A decrease in the ratio of apos;more-planarapos; to apos;less-planarapos; free sterols was observed only in Kharna khatta and, more notably, Etrog citron. Salt-induced changes in the apos;more-planar apos; to apos;less-planar apos; free sterol ratio correlated well with salt exclusion capacity.     

Effects of 4-month Fe deficiency exposure on Fe reduction mechanism, photosynthetic gas exchange, chlorophyll fluorescence and antioxidant defense in two peach rootstocks differing in Fe deficiency tolerance

Fe deficiency was imposed by omission of Fe (-Fe), or by inclusion of bicarbonate (supplied as 20 mM NaHCO3) in the nutrient solution in two contrasting peach rootstocks (GF-677; tolerant to Fe deficiency and Cadaman; sensitive to Fe deficiency) for 4 months. In the Fe-deprived leaves and roots, and especially in those treated with bicarbonate, a decrease in Fe concentrations was recorded. Omission of Fe resulted in an increase of the activity of root Fe(III)-chelate reductase (FCR) in both rootstocks, whereas FCR activity decreased in the bicarbonate-treated roots of Cadaman. The results obtained from the FCR assay were confirmed by an agarose-based staining technique used to localize FCR activity. Also, an agar-pH-test revealed that the roots of GF-677 exposed to (-Fe) treatment induced a strong H+ extrusion. In addition, Fe deficiency resulted in reduction of the total chlorophyll (CHL) content. Apart from the (-Fe)-treated leaves of GF-677, Fe deficiency caused a decline in the photosynthetic rate (P(n)) and stomatal conductance (g(s)), without changes of the intercellular CO2 concentration (C(i)), as well as a reduction in the maximum quantum yield of PSII (F(v)/F(m)) and the ratio between variable to initial fluorescence F(v)/F0. The above changes were particularly evident for the bicarbonate-treated leaves of Cadaman. On the other hand, Fe deficiency resulted in an increase of leaf superoxide dismutase (SOD) activity and a depression of catalase (CAT) activity in the leaves and roots, irrespective of the rootstock. Although the non-enzymatic antioxidant activity (FRAP values) was increased in the roots of both rootstocks exposed to -Fe treatment, however, FRAP values were stimulated in the (-Fe)-treated leaves of GF-677 and decreased in the bicarbonate-treated leaves of Cadaman. The H2O2 content was increased in Fe-deprived tissues except for the (-Fe)-treated leaves and roots of GF-677. As a result of Fe deficiency, peroxidase (POD) activity and isoform expression were diminished in the tissues of Cadaman. However, in the tissues of GF-677 subjected to -Fe treatment POD activity was increased whereas an additional POD isoform was detected in the roots suggesting that expression of POD isoforms might be an important attribute linked to the tolerance to Fe deficiency.     

Drought tolerance of apple rootstocks: Production and partitioning of dry matter

The drought tolerance of the commercial apple ( Malus domestica Borkh.) rootstocks M9, M26, M27 and MM111, and some new selections from the rootstock breeding programme at HRI-East Malling (AR69-7, AR295-6, AR360-19, AR486-1 and AR628-2), was assessed using potted, glasshouse-grown, unworked rootstocks. After an initial period of growth under well-watered conditions the amount of irrigation was gradually reduced, for some treatments, to simulate natural drying in the soil. At the end of a six-month growth period, the rootstocks were harvested and the production of dry matter and its partitioning to various plant parts determined. The rootstocks exhibited large differences in shoot and root dry matter, and root length but not all the rootstocks showed declines in root mass or length in response to the droughting treatment. The dwarfing rootstocks tended to have smaller amounts of both coarse (>2 mm diameter) and fine roots (<2 mm diameter), than the more vigorous rootstocks. Irrespective of rootstock or irrigation treatment there was a close linear relationship between coarse and fine root. There was also no change in the length/weight relationship for fine roots irrespective of rootstock or irrigation treatment, i.e. 42 m of fine root weighed 1 g dry weight. In some cases the amount of root produced could be directly correlated with the rootstock known potential to control scion vigour, but this was not true for all the rootstocks examined. The absence of this relationship was particularly evident in some of the new selections of rootstock. The possible causes for these differences, compared with commercially used rootstocks, is discussed in relation to the origin and parentage of the rootstock selections. Despite this lack of a root length/vigour relationship, the amount of dry matter partitioned to shoot growth reflected the rootstocks' known vigour. The different responses of these rootstocks to drought are discussed along with their implications for understanding the mechanisms by which rootstocks are thought to dwarf scion shoots.     

Grafting helps improve photosynthesis and carbohydrate metabolism in leaves of muskmelon

The most important quality for muskmelon (Cucumis melo L.) is their sweetness which is closely related to the soluble sugars content. Leaves are the main photosynthetic organs in plants and thus the source of sugar accumulation in fruits since sugars are translocated from leaves to fruits. The effects of grafting muskmelon on two different inter-specific (Cucurbita maxima×C. moschata) rootstocks was investigated with respect to photosynthesis and carbohydrate metabolism. Grafting Zhongmi1 muskmelon on RibenStrong (GR) or Shengzhen1 (GS) rootstocks increased chlorophyll a, chlorophyll b and chlorophyll a+b content and the leaf area in middle and late developmental stages of the plant compared to the ungrafted Zhongmi1 check (CK). Grafting enhanced the net photosynthesis rate, the stomatal conductance, concentration of intercellular CO(2) and transpiration rate. Grafting influenced carbohydrates contents by changing carbohydrate metabolic enzymes activities which was observed as an increase in acid invertase and neutral invertase activity in the functional leaves during the early and middle developmental stages compared to CK. Grafting improved sucrose phosphate synthase and stachyose synthase activities in middle and late developmental stages, thus translocation of sugars (such as sucrose, raffinose and stachyose) in GR and GS leaves were significantly enhanced. However, compared with CK, translocation of more sugars in grafted plants did not exert feedback inhibition on photosynthesis. Our results indicate that grafting muskmelon on inter-specific rootstocks enhances photosynthesis and translocation of sugars in muskmelon leaves.