In vitro grafting of cashew (Anacardium occidentale L.)

A successful micrografting technique in cashew was developed using in vitro germinated seedlings as rootstocks and axenic shoot cultures (shoot-tip and nodal cultures) established from mature tree source as microscions. In vitro germinated seedlings, which emerged 20–25 days after inoculation on absorbent cotton, were decapitated and used as rootstock. Mature tree explants initiated on hormone-free Murashige and Skoog [Physiol. Plant. 15 (1962) 473] (MS) modified medium were made into scion of 3–15 mm length for grafting. Micrografts could be easily cultured on hormone-free liquid half-MS medium and were potted out after 10–12 weeks of culture growth. Grafting success was dependent on the method of grafting and size of the scion. Shoot-tip grafting and side grafting were equally successful (79.5–100%). Length of scion shoot had significant effect on micrografting success. Graft success was high (79.5%) when the scion length was >5 mm and it was less (0.5%) when size of scion was small (3–5 mm). Scion presoaked in either water or 0.01% ascorbic acid and 0.015% citric acid (1:1) reduced phenolic browning and drying of scion. Micrografting techniques standardized could be used for rejuvenation of shoot explants of mature tree.     

Induction of lateral branches in tree fruit nursery stock with propyl 3-t-butylphenoxy acetate (MB 25, 105) and Promalin (GA4+7 + 6-benzyladenine)

Sprays with 250–2000 mg l^?1 propyl 3-t-butylphenoxy acetate (MB 25,105) and 250 and 500 mg l^?1 GA₄₊₇ + 6-benzyladenine (Promalin) were applied to scion growth of first nursery trees of ‘Bartlett’ pear (Pyrus communis L.), ‘Bing’ cherry (Prunus avium L.) and ‘Oregon Spur II Delicious’ apple (Malus domestica Borkh.) to stimulate lateral branching in the nursery. Most treatments significantly increased branching compared to untreated controls. Combination sprays of the two chemicals were usually better than either used alone. Chemical treatment usually produced greater branching and wider branch angles than mechanical heading. Both chemical and mechanical treatments reduced tree height and caliper, but the decrease was not always statistically significant.     

不同砧木对黄瓜产量、品质及南方根结线虫防治效果的影响

以7个南瓜砧木为试材,研究了砧木嫁接对黄瓜产量、品质和南方根结线虫防治效果的影响。结果表明：采用南瓜砧木嫁接,黄瓜春季增产4.1%～10.7%,秋季增产15.0%～104.2%,其中新动力嫁接的黄瓜产量最高,其次是黄砧3号。砧木嫁接对黄瓜果实中的可溶性蛋白含量没有显著影响|不同砧木品种和不同接穗品种嫁接黄瓜果实中可溶性糖、VC和硝酸盐含量比自根黄瓜有的增加,有的减少。砧木嫁接对黄瓜南方根结线虫具有较好的防治效果,春季为67.8%～79.7%,秋季12.7%～44.7%。综合来看,采用南瓜砧木新动力和黄砧3号嫁接的黄瓜,其产量较高,品质较好,对南方根结线虫的防治效果较好。     

Influence of rootstock on vegetative growth,fruit yield and quality in ‘Cuore di Bue’, an heirloom tomato

Summary

Heirloom tomatoes (Solanum lycopersicum L.) such as ‘Cuore di Bue’ are highly appreciated by consumers for their outstanding quality and flavour. Nowadays, they are often grafted onto vigorous rootstocks in order to overcome several soil-borne diseases. The present study was conducted in 2007 and 2008 in Southern Italy. Plants of ‘Cuore di Bue’, an heirloom ‘oxheart’ tomato, were grown in a greenhouse either as non-grafted plants, or grafted onto two inter-specific (S. lycopersicum S. habrochaites) rootstocks (‘Beaufort F₁’ and ‘Maxifort F₁’) in order to evaluate their effects on vegetative growth, marketable yield, fruit quality, and the sensory properties of ‘Cuore di Bue’ tomato fruit. Growth analysis revealed that ‘Maxifort F₁’ enhanced plant growth, particularly in terms of leaf area and leaf fresh weight. Grafted plants had higher leaf area ratios (by 13%) and higher leaf dry weight fractions (by 18%) compared to non-grafted ‘Cuore di Bue’ plants. Marketable yields increased by 20 – 25% in grafted plants in both years. However, total soluble solids (TSS) contents, titratable acidity (TA), and TSS/TA ratios were not significantly affected by grafting.Vitamin C contents decreased by 14 – 20% in both years in the fruit of plants grafted onto either rootstock. The sensory profiles of fruit were not modified by grafting, although taste panelists expressed a higher preference for purchasing fruit from plants grafted onto ‘Maxifort F₁’. These results confirm that, when using the appropriate rootstock/scion combination, grafting can improve plant growth and the marketable yield of heirloom tomato fruit without reducing the sensory quality of the fruit or its biochemical parameters. However, grafting can reduce vitamin C contents and, thus, nutritional quality.     

The effect of grafting on nitrogen use in determinate field-grown tomatoes

Grafting tomato (Solanum lycopersicum L.) onto disease resistant rootstocks has grown in use in North America over the past two decades. Rootstocks have traditionally been bred and used for their resistance packages to numerous soil-borne diseases but some rootstocks appear to improve scion yield and vigour in comparison to non-grafted plants in conditions lacking disease challenge. In this study, the tomato rootstocks ‘Maxifort’ or ‘RST-106’ were used to determine if vigour improved ‘Tribute’ scion traits, especially yield, and if marketable yield could be maintained in grafted plants at reduced nitrogen fertiliser inputs. Plants were grown in an open-field plasticulture production system at five rates of nitrogen from 0 kg ha^?1 to 224 kg ha^?1 applied via drip irrigation. Marketable yield was significantly affected by nitrogen rate and rootstock in both years. ‘Tribute’ grafted onto ‘Maxifort’ rootstock had the greatest, most consistent impact and increased marketable yield 15% and 30% in 2013 and 2014, respectively, compared to the non-grafted ‘Tribute’. Our findings suggest that some rootstocks can increase scion growth and yield but do not differentially respond to decreased nitrogen rates.     

The vegetative propagation of persimmon

Propagation of persimmon (Diospyros kaki L.) on D. lotus L. by veneer grafting, tongue grafting or budding was tested at 6 times from late June to the 3rd week in September. Grafting resulted in better success than budding. Success rates of 80–100% were obtained with veneer or tongue grafting between late June and the 3rd week of August.     

Stenting of roses; a method for quick propagation by simultaneously cutting and grafting

A method was developed for quick propagation of roses under conditions prevailing in The Netherlands, based on cutting and grafting in one action and called “stenting” (to stent), being a contraction of the dutch words “stekken” (to strike a cutting) and “enten” (to graft). A piece of stem of the cultivar with one leaf and a dormant bud is grafted on a single internode of the rootstock. Formation of the graft union and of adventitious roots occur simultaneously, resulting in a complete plant in 3 weeks.Absence of buds on the rootstock is essential to diminish wild suckering. Factors influencing the percentage of successful stentlings were investigated. With R. chinensis ‘Indica Major’ as a rootstock, the best results were obtained with mature internodes 6–8 mm in diameter after application of 5000 mg 1^?1 IBA. Pre-treatment of the rootstock internodes by application of IBA and storage at 4° C for 3 weeks improved rooting. Comparison of grafting by hand and by machine showed that machine-grafting offers good possibilities.The influence of the cultivar, after cutting or stenting, on root-formation and root-growth was studied. Grafting on seedling rootstocks (bench-grafting) and stenting proved to give similar results. In the first year after stenting, R. chinensis ‘Indica Major’ was a better rootstock for the cultivar ‘Cocktail 80’ than R. canina ‘Inermis’, while ‘Inermis’ was better for ‘Motrea’.Rose culture can be improved by using cultivars stented on a convenient rootstock. Stenting can be applied around the year, is ideal for screening new scion/stock combinations and to investigate the interaction between shoots and roots.     

The effect of sprinkler and drip irrigation on lime-induced chlorosis of citrus

Trials were carried out on grapefruit (Citrus paradisi Macf.) ‘Marsh Seedless’ and orange (C. sinensis L.) ‘Valencia’, both on Sour orange (C. aurantium L.) rootstock. Shortening the interval between sprinkler irrigations increased the occurrence of lime-induced chlorosis (LIC), as indicated by reduced leaf chlorophyll and peroxidase enzyme activity. Drip irrigation, on the other hand, corrected LIC and increased leaf chlorophyll, peroxidase activity and photosynthesis.     

Cutting-grafts as a means to propagate greenhouse roses

A propagation method for rose nursery plants was studied by using a 2-node scion tongue-grafted on to an unrooted stock cutting. Uniform and disease-free nursery plants could be produced efficiently in a short period all the year round.Under greenhouse production trials, such cutting-grafts of ‘Sonia’ on R. multiflora ‘K-1’, R. indica ‘Major’, R. ‘Manetti’ and R. wichuraiana produced flowers of the same number and quality as when budded on to R. multiflora seedling root stock.     

Micropropagation of Darjeeling orange (Citrus reticulata Blanco) by shoot-tip grafting

Summary

Micropropagation of Darjeeling orange (Darjeeling mandarin) was done by shoot-tip grafting on the local rootstocks rough lemon, sour orange and Rangpur lime. Seedlings of these plants were raised in MS medium in standard conditions of temperature, light duration and plant age. Microbuds (0.2 mm long), aseptically excised from the scion, were grafted onto the decapitated rootstock seedlings. The micrografts in culture medium were grown under standard lighting. Rootstock seedlings showed optimum growth at 25–30°C. Optimum growth of the micrografts resulted from treatment in complete darkness for 4 d after grafting followed by exposure to 750 W for 16 h d^?1 for 15 d and 1500–2000 W for 16 h d^?1 for 39 d. The success of micrografting depended on the age of the rootstock seedling which was 21 d, 14 d and 14 d for sour orange, rough lemon and Rangpur lime respectively. The micrografts were then double grafted to the two year old rootstocks seedlings of the respective species and the age of the micrografts for the successful double grafts was also standardized. The survival rate was high with 40 d, 45 d and 45 d micrografts on sour orange, rough lemon and Rangpur lime respectively. The double-grafts were then indexed for tristeza virus and greening disease after six months’ growth in an insect-proof screenhouse and found to be free from these graft transmissible diseases.     

Investigations on Chlorosis of Fruit Trees.: III.—A Chlorosis of Plums Due to Potassium Deficiency.

Summary

Grafting is a suitable method to control soil-borne diseases in melon (Cucumis melo L.) crops. To date, several Cucurbita species and their inter-specific hybrids have been tested as rootstocks. However, graft-scion incompatibility and lower fruit quality have prevented their commercial use. The wild accession ‘Pat 81’ ssp. agrestis of C. melo is highly resistant to Monosporascus cannonballus Pollack et Uecker root rot, and develops a root system that is more suitable to withstand infested soils than that of cultivated melon. The potential of ‘Pat 81’ as a rootstock for melons (e.g., ‘Piel de Sapo’ type, C. melo ssp. melo) compared with the popular rootstock ‘RS 841’ (Cucurbita maxima Cucurbita moschata) has been evaluated here. The response of grafted plants to Monosporascus root rot disease, and rootstock effects on plant performance and fruit quality have been investigated using both classical methods and modern technologies (e.g., root image analysis and real-time PCR). The results indicate that, during infection, the root system of ‘Pat 81’ adapts to the needs of the aerial part of the ‘Piel de Sapo’ scion, displays a high level of resistance to M. cannonballus (similar to ‘RS 841’), and provides the plant with more healthy roots, with a higher root/vine biomass ratio compared with non-grafted ‘Piel de Sapo’. In addition, ‘Pat 81’ rootstock retains its favourable root structure (i.e., larger total length and root area) to withstand soil stress. In healthy soils, ‘Pat 81’ rootstocks had less effect on fruit quality than ‘RS 841’, leading to a lower percentage of non-marketable products. The high resistance of ‘Pat 81’, and its reduced effect on fruit quality, point to it as a good rootstock for the grafting of melons to resist M. Cannonballus infested soils.     

Investigations into inconsistent and low bud-grafting success in Acer platanoides ‘Crimson King’

Causes of variable and inconsistent bud-grafting success in chip-budded Norway maple (Acer platanoides) were investigated using the red-leaved scion ‘Crimson King’. Large differences in bud-take were associated with the year of budding, which over a 14 year period ranged from 22 to 94%. The ‘year effect’ could not be explained by weather, or by differences in budding success found between commercial sources of red-leaved scions. Neither was incompatibility between the ‘Crimson King’ scion and individual genotypes among the seedling rootstocks implicated, although there were reasons why at first sight incompatibility was thought to be present. The size of rootstock when planted was not correlated with subsequent budding success, although large differences in the quality of rootstock growth at budding were associated with large differences in bud-take, but these were confounded with year and with the fields used for the experiments. The ‘year effect’ was best explained by the field in which budding took place. One field gave consistently poor results, associated with a readily compacting soil, pointing to the strong possibility that bud-take is determined by conditions which affect shoot and/or root growth during the budding season or specifically while the union is forming in late summer. It was shown also that the presence of the scion bud on the chip-graft contributed to union formation, and that infection of the rootstock with the soil-borne verticillium wilt disease depressed bud-take, but this did not explain the ‘field effect’.     

Shoot-tip culture and the eradication of viroid-RNA

Citrus exocortis viroid was eradicated from infected tomato plants (Lycopersicon esculentum Mill. ‘Rutgers’) by in vitro shoot-tip culture of axillary buds excised from greenhouse-grown plants. Plantlets developed from 23 of 67 shoot tips excised. The 6 plantlets that demonstrated normal root development were shown to be free of CEV by polyacrylamide gel electrophoresis and bioassay. Fully developed recovered plants showed the same characteristics as the ‘Rutgers’ seedlings.     

Long-term performance of ‘Ellendale’ mandarin on seven commercial rootstocks in sub-tropical Australia

‘Ellendale’ mandarin (Citrus reticulata Blanco) on seven commercially important rootstocks was assessed over a 26-year period on a site not previously planted to citrus. Tree yield data collected each season from 1969 to 1991 showed that yields were highest on ‘Lockyer’ rough lemon (C. jambhiri Lush) and lowest on ‘Emperor’ mandarin. Yields for the two citranges (C. sinensis (L.) Osbeck × Poncirus trifoliata (L.) Raf.), ‘Troyer’ and ‘Carrizo’, were intermediate, and somewhat higher than those for two selections of sweet orange (C. sinensis (L.) Osbeck), ‘Parramatta’ and ‘Joppa’. Linear regression was used to examine changes in yielding pattern across the 23 seasons of fruit production. This revealed that ‘Troyer’ was comparable with the rough lemon selections throughout most of the experiment and significantly higher than ‘Carrizo’ during certain periods in the middle of the experiment. Similarly, while ‘Joppa’ and ‘Parramatta’ produced near-identical results during most of the experiment, ‘Joppa’ out-performed ‘Parramatta’ toward the end of the experiment. ‘Emperor’ showed a low yield trend throughout the experiment, often more than 50 kg per tree per year less than the rough lemon and citrange selections. Detailed assessment of biennial bearing showed a significant pattern commencing when trees were approximately 15 years old and intensifying until the end of the experiment. However, rootstock had no effect on the biennial bearing behaviour of ‘Ellendale’ mandarin. Correlations of cumulative yields at each harvest date with the final cumulative yield (for 23 seasons of cropping) showed instability up until approximately the eighth year of cropping after which it increased steadily, suggesting that in similar experiments there may be only marginal value in assessing yields beyond about the 10th season. Fruit quality assessments made in two consecutive seasons showed expected trends, with rough lemon (both ‘Lockyer’ and ‘Mazoe’) producing the largest and heaviest fruit, with thicker rinds, lower juice content, and lower Brix. The citrange selections (‘Troyer’ and ‘Carrizo’) resulted in fruit quality comparable to the sweet oranges (‘Parramatta’ and ‘Joppa’), with ‘Troyer’ producing significantly higher Brix levels than any other rootstock. All rootstocks produced leaf nutrient levels close to the desirable range, with significant differences for the elements P, Mg, Ca, Mn, and B. These differences separated the seven rootstocks into categories consistent with their genetic relatedness.     

Effects of grafting height of MM106 rootstock on growth,lateral shoot formation and yield in apple trees

Summary

Between 2004 and 2008, the effects of different grafting heights on sylleptic shoots were tested in the apple (Malus domestica Borkh.) cultivars ‘Granny Smith’ and ‘Gloster’, and cumulative fruit yields were evaluated. MM106 apple rootstocks were grafted 10, 20, 40, or 60 cm above soil level in August 2004. The results showed that an increased grafting height significantly decreased tree height in both cultivars. The tallest and shortest trees were observed at grafting heights of 10 cm (153.0 and 170.0 cm) and 60 cm (141.3 and 143.5 cm) in ‘Granny Smith’ and ‘Gloster’, respectively.Among the various grafting heights tested, 60 cm in ‘Granny Smith’ and 20 cm in ‘Gloster’ gave the largest stem diameters (17.6 mm and 16.8 mm, respectively). The number of lateral shoots increased significantly with increased grafting height in both cultivars. The largest numbers of lateral shoots in ‘Granny Smith’ (10.75) and ‘Gloster’ (2.00) were obtained from a grafting height of 60 cm, while 2.55 and zero lateral shoots occurred at 10 cm grafting height in ‘Granny Smith’ and ‘Gloster’, respectively. Shoot lengths decreased significantly by increasing the grafting height. Grafting heights of 10 cm and 60 cm resulted in the tallest and shortest shoots in both cultivars. Cumulative fruit yields were significantly affected by grafting height in both cultivars. The highest yield was found for a 60 cm grafting height in both ‘Granny Smith’ (11.295 kg tree^–1) and ‘Gloster’ (4.818 kg tree^–1).The results of this study suggest that grafting heights of 40 cm and 60 cm have the potential to promote branching and early bearing for apple fruit production in sustainable and organic agricultural systems.     

The Response of Soilless Grown ‘Michele Palieri’ (<Emphasis Type="Italic">Vitis vinifera</Emphasis> L.) Grapevine Cultivar to Deficit Irrigation Under the Effects of Different Rootstocks

Global warming, altering the physiology and irrigation demand of grapevines, has already been perceived in certain premium viticulture regions across the world. Selection of proper rootstocks for especially new cultivars has vital role for a sustainable viticulture under water-deficit conditions. The grapevine cultivar ‘Michele Palieri’ has been finding a good reception on the global markets. The objective of this study was to determine the response of ‘Michele Palieri’ cultivar to deficit irrigation using different rootstocks with distinct genetic origins. Two irrigation regimes (Full Irrigation [FI] and Deficit Irrigation [DI]) were applied to the vines of different grafting combinations of ‘Michele Palieri’ with Kober 5 BB, Richter 99, Richter 110, 140 Ruggeri, 44–53 Malégue or grown on own roots. Two years old vines were cultivated in 60?L pots containing sterile peat under controlled glasshouse conditions. Irrigations were regulated according to soil water matric potential (Ψm) levels using tensiometers. The volume of the irrigation water that has to be applied to attain 100% field capacity was performed as FI, while 50% of FI was considered as DI. The water was transported directly into the pots by micro-irrigation systems consisting of individual spaghetti tubes. The vines of DI treatment showed visible symptoms of mild water stress (e.?g., loss of turgor in shoot tips), but no defoliation or leaf necrosis occurred. DI treatment reduced the gs of ‘Michele Palieri’ scion cultivar in varying levels depending on the rootstock. DI treatment also affected vegetative growth of the scion cultivar in different levels. For example, the greatest decrease (26.7%) in shoot length resulting from DI was determined in ‘Michele Palieri’/5 BB grapevines, followed by own rooted vines (13.1%), while the lowest change (2.4%) was found in vines grafted on 110?R. Overall findings of this study imply that the rootstocks originating from V. berlandiery?×?V. rupestris hybrids (110?R, 99?R, 140?Ru and 44–53?M) better performed in a similar genetic aptitude under deficit irrigation regime while the rootstock 5 BB (V. berlandiery?×?V. rupestris) showed more susceptible responses. On the other hand, the general response of own rooted vines were better than those grafted on 5 BB. Therefore, the use of one of V. berlandiery?×?V. rupestris hybrids may be a better choice for viticulture under semiarid regions.     

Differential tolerance to iron deficiency of citrus rootstocks grown in nutrient solution

We studied the effects of Fe deficiency on physiological parameters of citrus rootstocks grown in nutrient solution. Three 4-week old rootstocks (‘Troyer’ citrange – Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf., Citrus taiwanica Tan. and Shim., and ‘Swingle’ citrumelo – Poncirus trifoliata (L.) Raf. × Citrus paradisi Macf.) were grown in nutrient solutions with 0, 5, 10, 15 and 20 μmol Fe dm⁻³. Calcium carbonate (1 g dm⁻³) was added to all solutions to mimic the natural conditions in calcareous soils. For each rootstock, shoot length, number of leaves, and root and shoot dry weights were measured at the end of experiment. Chlorophyll concentration was estimated using a portable SPAD-502 meter calibrated for each rootstock. The amount of nutrients (P, K, Mg, Ca, Fe, Zn, Mn, and Cu) was determined in shoots. Chlorophyll fluorescence parameters (F₀: basal fluorescence; F_m: maximum fluorescence; F_v = F_m − F₀: variable fluorescence) were measured with a portable fluorimeter. ‘Troyer’ citrange rootstock was the most tolerant to Fe deficiency. These plants grew more and accumulated more chlorophyll and nutrients than the others in the presence of low levels of Fe (10 μmol Fe dm⁻³). ‘Swingle’ citrumelo plants needed 20 μmol Fe dm⁻³ in the nutrient solution to secure adequate growth. ‘Taiwanica’ orange rootstock had an intermediate behaviour, but could be distinguished from ‘Troyer’ citrange based on fluorescence parameters, since there was a variation in the basal fluorescence in the former, whereas in ‘Troyer’ citrange the basal fluorescence was not affected by the supply of Fe.     

Effects of high-humidity storage on quality,decay and storage life of cherry,lemon and peach fruits

Sweet cherries (Prunus avium (L.) ‘Lambert’ and ‘Blackboy’), lemons (Citrus limon (L.) Burm. f. ‘Lisbon’) and peaches (Prunus persica (L.) Batsch, ‘Summerset’) were stored at 77–83, 90–94 and 95–99% RH (high humidity) at near-optimal storage temperatures after harvest and treatment with fungicides. High-humidity storage did not increase the storage life of peaches held at 0°C, but the life expectancy of cherries (both cultivars) was extended by 7–10 days at 0°C, and of lemons by at least 4 weeks at 10°C when fruit were stored at 95–99% RH compared with levels below 95%. The beneficial effects of high humidity were attributed to retardation of peel desiccation and associated reductions in fruit deformation, peel de-greening, chilling-injury and decay in lemons and to the maintenance of a fresher stalk and a firmer, less shrivelled fruit in cherries. High humidity had no effect on decay in cherries or peaches, but it significantly reduced weight loss and delayed the appearance of shrivel in peaches stored at 0°C. However, after storage at high humidity for 4 weeks, peaches ripened with low rates of C₂H₄ evolution and showed severe low-temperature injury, slight peeling-injury and a poor flavour ex-store.     

Determination of graft compatibility in sweet cherry by a co-culture method

Summary

Cell suspensions of two sweet cherry cultivars (Prunus avium L.) ‘Sam’ and ‘Sweetheart’, and four cherry rootstocks: ‘Edabriz’ and ‘Weiroot 10’ (P. cerasus L.), ‘P. avium seedlings’ (Alkavo selection) and ‘Gisela 5’ (a P. cerasus P. canescens hybrid) were co-cultured for 14 d and their mass increase used to calculate an affinity index and the degree of compatibility between pairs of genotypes. Synergistic as well as antagonistic growth responses were observed among the various genotype combinations. The effect on growth was never significantly negative, or resulted in cell mortality. Co-culture of ‘P. avium seedlings’ and ‘Sweetheart’ had a significantly positive influence on the growth of ‘P. avium seedling’ cell suspensions, and co-culture with either of the sweet cherry cultivars had a very positive effect on the growth increase (GI) of ‘Edabriz’ cell suspensions. The GI of the sweet cherry cultivar ‘Sam’ was positively influenced by the presence of both ‘Weiroot 10’ and ‘Gisela 5’ in the co-culture chamber. The GI for the combination of ‘Sweetheart’ with ‘Gisela 5’ or ‘Edabriz’ was significantly lower than in the control, and none of the combinations with ‘P. avium seedlings’ or ‘Weiroot 10’ gave an increase in GI greater than controls of the scion cultivar ‘Sweetheart’ alone. The calculated degree of compatibility (DC_cc) showed that the cultivar ‘Sam’ had no compatibility problems with the four rootstocks tested, whereas the combination of ‘Sweetheart’ and ‘Gisela 5’ had the lowest DC_cc (= 0.80) which was concluded to be on the border between a compatible and an incompatible relationship. It was therefore concluded that a calculated value of DC_cc < 0.80 would indicate an incompatible combination, and that values of DC_cc > 1.00 would indicate healthy and strong combinations.Virus-induced incompatibility appeared to play a much larger role in explaining unsuccessful grafts observed in the nursery than previously assumed.     

The effects of low boron on growth,gas exchange,boron concentration and distribution of ‘Newhall’ navel orange (Citrus sinensis Osb.) plants grafted on two rootstocks

The effects of low boron (B) on plant growth, photosynthesis, B concentration and distribution of ‘Newhall’ orange (Citrus sinensis Osb.) plants grafted on either Trifoliate orange (Poncirus trifoliata (L.) Raf.) or Carrizo citrange [C. sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.] rootstocks were investigated. One-year-old plants of the two scion-rootstock combinations were grown for 183 days in sand:perlite (1:1, v/v) medium under greenhouse conditions. The plants were irrigated with half-strength Hoagland's nutrient solutions containing four B concentrations (0.01, 0.05, 0.10 and 0.25 mg l⁻¹). The growth of root, stem of scion and leaves was less affected by low B treatments when ‘Newhall’ scion was grafted on Carrizo citrange than on Trifoliate orange. Thus, the growth of scions under low B conditions was mainly depended on the rootstock used, i.e., Carrizo citrange-grafted plants were more tolerant to low B compared to the plants grafted on Trifoliate orange. Boron concentrations in all plant parts decreased significantly by decreasing the B supply in the nutrient solution. Leaves were the dominant sites of B accumulation and showed the greatest reduction in B concentration compared to the other plant parts, as B concentration in the nutrient solution decreased. Irrespective of the rootstock, B levels in the upper–younger leaves were substantially higher than in basal-older leaves when plants were exposed to low B concentrations (≤0.05 mg l⁻¹), suggesting that under such conditions B was preferentially translocated to upper–younger leaves to support their growth. Furthermore, B distribution in different plant parts indicated that there was a restriction in translocation of B from root to scion tissues (stems and leaves of scion) under conditions of limited B availability. In addition, low B treatments decreased leaf photosynthetic rate, stomatal conductance and transpiration rate but increased intercellular CO₂ concentration in the leaves of ‘Newhall’ plants, irrespective of the rootstock used.