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Hazelnut (Corylus avellana L.) is an important nut crop with clear mast seeding behaviour leading to alternate yield and, thus, to management issues. It was hypothesized that masting is associated to accumulation/depletion of carbon within storage tissues (i.e. stem, large branches, roots). We hypothesized that fruit yield depends both on carbon fixed by leaves on the same branch and carbon stored in the main stem. We therefore conducted a manipulation of carbon sink-source resources on fruit-bearing branches of C. avellana cv. ‘Tonda di Giffoni’ by combining girdling and defoliation on a set of branches. We measured the number and diameter of nuts and leaves, the dry weight of fruits and seeds and the amount of blanks over the growing season. We also estimated the whole tree leaf area by allometric equations and the tree yield by collecting all nuts separately on 15 trees at maturity. The average seed dry mass in the un-defoliated girdled treatment was significantly lower than the control (0.5 vs. 0.9 g) suggesting that the fruit-bearing branches need to import carbon from the main stem and that the carbon autonomy of fruit-bearing branches is not supported during kernel maturation process. We also observed that the correlation at whole tree level between leaf area and seed mass is strong in non-masting years, while it becomes weaker in masting years reinforcing the hypothesis that the productivity of masting yields also relies on stored resources.

Cross-pollen parents can affect fruit set and yield, and can influence fruit and seed characteristics of many tree crops. Available carbohydrates also limit fruit set and yield, and tree carbohydrates can be manipulated by girdling trees and by defoliation. We investigated how different macadamia cross pollen-parents and the availability of carbohydrates interact to modify macadamia fruit set, kernel yield and kernel size. We manipulated tree carbohydrates by selecting different branch sizes and girdling branches on macadamia cultivar ‘HAES 246’ (‘246’) maternal trees. We applied pollens from two different commercial cultivars, ‘HV A16’ (‘A16’) and ‘HAES 814’ (‘814’) in two experiments. In Experiment 1, two branch sizes, 150 leaves and 500 leaves were girdled. In Experiment 2, three branch sizes, 150 leaves, 300 leaves and 500 leaves were both girdled and ungirdled. Final fruit set and kernel yield per branch were significantly higher on the girdled 500 leaf branches compared with the girdled 150 leaf branches in both experiments (P

Fruit abscission is largely governed by carbohydrate supply, and carbohydrate shortage intensifies fruit abscission. Understanding cues from the starving fruit that activate the abscission zone (AZ) is an intriguing research subject and important for control fruit abscission. In this study, starvation stress generated by girdling and defoliating the bearing shoots was used to explore the cues from the starving fruit that triggers abscission in longan. The starving fruit abscised quickly within 5 days. However, removing the starving fruit induced even faster AZ activation with greater ethylene production in the pedicel. Abscission of the defruited pedicel was strongly suppressed by IAA, slightly by ethylene action inhibitor, silver thiosulfate (STS), but not by GA3 or zeatin. Both IAA and ABA concentrations in the starving fruit and the pedicel were significantly reduced compared with the control. IAA exudation from the starving fruit was significantly lower, while IAA oxidase activity in the fruit was higher. The activity of plasma membrane H+-ATPase (PM H+-ATPase) in the fruit and the pedicel was not significantly affected by carbohydrate starvation, while that of PM Ca2+-ATPase in both organs was significantly reduced by starvation. The results suggested that the starving fruit seems not send abscission-promoting signal e.g. ABA or ethylene, but sends weakened abscission-suppressing signal, IAA, to the AZ. The weakened capacity of starving fruit to export IAA is related to increase in IAA deactivation and reduction in PM Ca2+-ATPase activity. The reduced IAA in the AZ leads to increased sensitivity to ethylene synthesized in situ in the pedicel, which activates the AZ under starvation.

Girdling is a widespread agronomic technique to increase the fruit quality characteristics (e.g. size, solid soluble content [SSC] and colour). However, the information on the fruit metabolic changes related to this practice still remains unclear and fragmentary. Moreover, girdling duration and application time may greatly affect the plant/fruit metabolic responses producing sometimes counterproductive results. Fruit quality, metabolomic and antioxidant analyses were conducted to characterise the effects of two different girdling dates (4- and 2-weeks before the harvest, 4 W and 2 W, respectively) in skin and pulp of red-fleshed plum (Prunus cerasifera var. pissardii). Overall, the pulp metabolism was altered in both 4 W and 2 W Girdling by inducing accumulation of sugars (sucrose and trehalose), sugar alcohols (inositol and xylitol), organic acids (especially some TCA cycle intermediates such as α-ketoglutaric, citric, isocitric, fumaric and malic acid), amino acids (s-alanine and L-proline), anthocyanins and other phenols. In the skin only girdling 4 W showed major significant differences compared to the control increasing the fruit quality characteristics (size, SSC, dry matter and red colour) and showing greater metabolic changes with respect to the controls. Furthermore, the total antioxidant activity was also increased in both skin and pulp respect to other treatment only in Girdling 4 W. This approach could be used with both P. cerasifera plums as well as other red-fleshed fruit species in order to ensure red-fleshed fruits production with a uniform red colouration and higher content of bioactive compounds.

Information about reproductive behavior of the olive trees (Olea europaea L.) in regions with lower occurrence of cold is fundamental to the expansion of its economic cultivation. Researches studding the adequacy of management techniques in order to promote flowering in these regions are important. Thus, this research was conducted to evaluated water restriction, girdling and paclobutrazol on flowering and production of olive cultivars. Three experiments were conducted in Federal University of the Jequitinhonha and Mucuri Valleys in Diamantina, Minas Gerais, Brazil. In the first experiment, ‘Arbequina’ olive trees were subjected to water restriction and two environmental conditions. In the second experiment, the girdled branches in different times on flowering and nutritional behavior of ‘Grappolo 541’ and ‘Barnea’ olive trees were evaluated. And in the third experiment, the application of paclobutrazol (PBZ) and the water restriction were studied in the vegetative growth and flowering of ‘Ascolana’ olive trees. The flowering of ‘Arbequina’ olive tree occurred with the averages of minimum temperatures varied from 8.4 to 11.7 °C, in autumn and winter. The girdling at different times did not influence the production of olive trees ‘Barnea’ and ‘Grappolo 541’. The girdled branches had a higher nutrient levels in leaves.The application of paclobutrazol in the soil promoted the reduction in vegetative growth of ‘Ascolana’ olive trees, with increase of flowering and fruiting. The water restriction did not favor the flowering of ‘Arbequina’ and ‘Ascolana’ olive trees and it reduced the effect of PBZ in ‘Ascolana’.

This study aimed to examine the effects of girdling on tomato (Solanum lycopersicum L.) plant growth and fruit development, and identify appropriate girdling time on tomato. Girdling was carried out on tomato main stems at four different girdling time: 0 days after anthesis of the last truss (0 DAA), 7 DAA, 14 DAA, and 21 DAA, respectively. Tomato plants that were not treated with girdling served as the control. Girdling altered carbohydrate allocation to different organs. With more carbohydrates partitioned to fruits, girdling significantly increased the fruit weight and yield, and advanced the commercial harvest time by approximately 10 days in comparison to the control. Due to a lack of carbohydrate supply, root biomass and carbohydrate concentration reduced in the girdled plants. No evident sink feedback inhibition of photosynthesis was observed in leaves after girdling. Considering plant growth and fruit development, the appropriate girdling time was approximately 2–3 weeks after anthesis of the last truss. Our results have demonstrated that the application of girdling on tomato plants can increase fruit size and accelerate fruit development, which provides an effective approach to regulate carbohydrate partitioning in tomato production.

Under non-inductive environmental conditions longan trees (Dimocarpus longan Lour.) were subjected to potassium chlorate (KClO3) applications, solely or in combination with shoot girdling or defoliation treatments, to induce flowering. Treated trees showed visible flower buds four weeks after treatment, while untreated reference trees remained vegetative. Trees treated with KClO3 solely and in combination with apical shoot defoliation flowered terminally at the shoot apex. KClO3 treatment in combination with girdling caused flowering exclusively at the lateral buds immediately below the girdle. Results from histological and hormone analyses are integrated with longan flowering gene expression data to build a comprehensive time course model for chemical flower induction in longan. The increased cytokinin concentration in shoot apex tissues, likely due to de novo biosynthesis and translocation, corresponds with transient up-regulation of the flower promoting gene Dimocarpus longan FLOWERING LOCUS 1 (DlFT1) in mature leaves after KClO3 treatment. Both occur during the presumed period of flower induction approximately at 10 days after treatment. Subsequently, and with some delay floral homeotic genes Dimocarpus longan APETALA 1 (DlAP1) are up-regulated in the buds indicating flower bud development, which coincides with visible floral meristems in histological specimen. The specific cytokinin accumulation and flowering gene expression pattern suggest a tight orchestration of hormonal and genetic pathways in chemically induced longan.

Girdling practice gained attention as a mean to increase crop yields particularly for alternate bearing plants. Data published for ligneous are controversial and mechanisms by which girdling regulates plant growth and photosynthesis for olive tree are still not well elucidated. The physiological modifications induced by shoots girdling, and their effects on the mobilization of assimilates, on the gas exchanges and on antioxidant activity were studied in olive leaves of Meski, Picholine, Chetoui and Koroneiki cultivars. From each ‘ON’ and ‘OFF’ trees, six shoots were selected, 3 of them were girdled and 3 were used as control. Total carbohydrates, alcoholic (Mannitol) and soluble (Glucose, Fructose and Sucrose) sugars, photosynthesis parameters, total protein and antioxidant activities in leaves of ‘ON’ and ‘OFF’ trees were analyzed. In girdled shoots a reduction of photosynthetic rate and a greater accumulation of both carbohydrates and antioxidant activities were observed. Girdling, breaking off the phloematic flow, caused a store of elaborated sap in leaves that inhibited the photosynthetic activity inducing an oxidative stress. Our results confirmed fluctuations in carbohydrates, gas exchanges and antioxidant activities as a direct consequence of girdling and of presence or absence of fruits, and showed clearly how each olive cultivar responds differently to girdling evidencing that the girdling effects are cultivar dependent.

In Australian macadamia ( Macadamia integrifolia Maiden and Betche, M . tetraphylla Johnson and hybrids) orchards, trees are generally side-hedged in early spring to maintain the inter-row for efficient orchard management. Hedging at this time increases fruit abscission and decreases yield due to competition for carbohydrates between fruit and post-pruning shoot growth, and to the loss of photosynthetic area. Girdling increases fruit set in many crops and the possibility that girdling might mitigate the effect of pruning on fruit abscission and yield was investigated in this study. Girdling was also investigated for its potential to control shoot growth and tree size. In the first experiment, in early spring around anthesis, trees were pruned (P), pruned and girdled (PG), or were left as unpruned and ungirdled control trees. Fruit per raceme over time, percent of racemes with fruit at 20 weeks post anthesis, fruit number per tree, nut weight, yield, and the shoot length and number of the post-pruning flush were measured. In a second experiment, trees were pruned (P) or pruned and girdled (PG) in autumn, and the shoot length and number of the post-pruning flush were measured. In a third experiment, trees were girdled at anthesis in 3 years over a 4-year period and shoot growth, tree height, yield, fruit number and nut weight were compared with ungirdled control trees. Girdling mitigated the effect of pruning on fruit abscission and yield but the mitigation was slight with PG trees producing 28% less yield than unpruned control trees. Girdling reduced shoot length and number but more so on unpruned branches (26% and 28%, respectively) than on pruned branches (10% and 14%, respectively). The tree height increment in girdled trees was around half that of ungirdled trees. In the 4-year study, girdling increased yield by around 10% in two out of four seasons, and decreased it in one season. Cumulative yields were similar for girdled and ungirdled trees. This study has shown that girdling was not useful in mitigating the effect of pruning on yield. However girdling was effective in controlling shoot growth and tree size, with no reduction in cumulative yield, and may be useful as a tree size control strategy. Further monitoring of long-term effects of repeat girdling is required to confirm this.

Polygalacturonase (PG), which degrades pectin in cell wall, was proposed to participate in the process of plant organ abscission. In an effort to understand the molecular mechanisms of lychee fruitlet abscission, a full-length cDNA encoding a polygalacturonase, termed as LcPG1, was isolated from lychee by using RT-PCR and RACEs. The LcPG1 cDNA was 1666 bp in length with an open reading frame (ORF) of 1443 bp, encoding a polypeptide of 481 amino acid residues. Homologous and phylogenetic analysis showed that the LcPG1 included three of the four typical domains conserved in PG proteins, and was clustered into the clade E of PG genes. Expression analysis in the fruitlet abscission zone (AZ) indicated that the expression of LcPG1 was positively correlated with the lychee fruitlet abscission, either induced by ethephon or inhibited by 2,4-dichlorophenoxyacetic acid (2,4-D). Moreover, the carbohydrate stress caused by the girdling plus defoliation was found to stimulate the fruitlet abscission, which was paralleled with an increase in LcPG1 expression level. All these results suggested that the LcPG1 played an essential role in the process of lychee fruitlet abscission. To our knowledge, it is the first case indicating that a PG gene, belonging to the clade E, is involved in organ shedding.

The root system of plants derives all its energy from photosynthate translocated from the canopy to the root system. Canopy manipulations that alter either the rate of canopy photosynthesis or the translocation of photosynthate are expected to alter dry matter partitioning to the root system. Field studies were conducted to evaluate the effect of trunk girdling (2008 and 2009) and summer pruning (2009) on soil respiration, maximum quantum yield efficiency of photosystem II and leaf carbohydrate content. In apple trees, following trunk girdling there was increased soil respiration in association with a significant rainfall event suggesting rapid release of organic matter and subsequent microbial decomposition of the carbon. Soil respiration rates returned to baseline levels over time. Reduction in midday maximum quantum efficiency of photosystem II (RPSII) was increased by girdling when crop load was low and this reduction was not related to leaf carbohydrate levels. Girdling reduced leaf sucrose and sorbitol levels in both years, however, total leaf carbohydrates were not affected by girdling. Summer pruning increased soil respiration within 2 weeks of treatment in association with a significant rainfall event, also suggesting a release of organic matter and microbial decomposition of the carbon. Cultural practices that severely affect canopy sink source relationships such as girdling and summer pruning increase soil respiration, however these effects appear to be very short lived, 3–10 days, followed by recovery of the soil/root system to similar levels of soil carbon dioxide efflux. These cultural practices do not likely pose a long-term detrimental effect on root system efficiency because the effects are of short duration with apparent recovery.

The effect of girdling on abscisic acid, carotenoids content, xanthophylls cycle and non-photoquemical quenching was studied in leaves from different shoot types of containerized two-year-old ‘Loretina’ mandarin during spring flush period. Girdling increased abscisic acid in young leaves and decreased it in mature leaves. These changes were accompanied by a significant increase in leaf carotenoids, carotenoids:chlorophylls ratio, xanthophylls and xanthophylls cycle pool size and its de-epoxidation state in vegetative and multiflowered young leafy shoots. However, changes in de-epoxidation state did not correlate with the energy-dependent non-photochemical quenching. The role of carotenoids and abscisic acid as photoprotecting agents during the oxidative stress caused by girdling is discussed. In conclusion, this study provides evidence linking carotenoids-based photoprotecting mechanisms in the response to the stress induced by girdling in Citrus trees.

Information about citrus ethylene-responsive element binding factor (ERF) genes and their functions in fruit ripening or in stress tolerance is still scarce. In the present study, one of ERF genes, CitERF was isolated from fruit of Citrus unshiu with a maximal putative open reading frame encoding 207 amino acids. The deduced protein contains a region rich in acidic amino acids, an AP2/ERF domain and a KRRK nuclear localization signal. It belongs to group B of Class I in the ERF subfamily in which MdERF2 (Malus × domestica ethylene-response factor 2) and PsERF1b ( Prunus salicina ethylene-response factor 1b) were involved in the progress of fruit ripening. CitERF mRNA level in fruit peel and pulp increased obviously along with fruit ripening. However, its expression could be reduced significantly by treatments of total shading and fruit-bear-shoot girdling plus defoliation during fruit ripening. As for the response to abiotic stresses, CitERF expression was found to be induced continuously during the treatment of 10% polyethylene glycol. On the other hand, it could be induced to high level at 1 h after the treatment of 4 °C or 250 mM NaCl and then declined continuously. Taken together, the results suggested that CitERF may play an important role in some biological processes during fruit ripening and in improving tolerance to drought, low temperature and salt stress.

Trunks of 8-year-old vigorous ‘Fuyu’ persimmon ( Diospyros kaki Thunb.) were girdled to a 1 cm width on April 20 and June 10 2004. Tree growth and fruit characteristics were monitored for two years, with special emphasis on the carry-over effect in 2005. Girdling reduced trunk and shoot growth especially of April-girdled trees over two consecutive years. However, the most significant effect of girdling was in the occurrence of water sprouts: a control tree had 29.5 in 2004 and 27.3 in 2005, whereas the April-girdled trees had only 0.3 and 5.3, respectively. Girdling increased fruit set by nearly 50% and enhanced fruit colour in 2004 only. Girdling date did not significantly affect fruit size and soluble solids for two years. Fruit flesh of girdled trees in 2004, especially in the April-girdled trees, had lower N and P concentrations. The levels of starch, soluble sugars, and inorganic elements in flower-bearing distal buds measured just before new growth in 2005 were not significantly altered by the girdling in 2004.

Girdling is widely used for many crops, mainly in order to improve the fruit set, size, and quality and to increase the yield of flower buds. However, girdling may damage trees, and permanent injury can occur if callus bridges are not formed across the ring. We determined the regeneration of vascular bundles and the healing process of wounds caused by surgical treatments. It occurred as follows: necrosis of some cell layers on the edge of the cut, callus formation and dedifferentiation of the parenchyma cells, callus proliferation, contact between callus pads, callus bridge formation, and differentiation into the mature vascular bundle; however, the innermost callus cells remained undifferentiated. At 3 days after treatment (DAT), several phloem parenchyma cell layers showed symptoms of necrosis. At 10 DAT, callus formation started in the phloem tissue below the periderm. Initially, the callus cells were uniform; however, the callus tissue pad was distinguished into 2 layers based on color and firmness. After callus bridge formation, the inner callus differentiated into the mature xylem and the outer callus, into mature phloem. In strangulation, xylem elements were formed from the inner callus pad before callus bridge formation. The callus bridge formed within 6 weeks, 20-25 days, and 14 weeks after girdling, scoring, and strangulation, respectively.

The influence of girdling, deficit irrigation, and a combination of girdling and deficit irrigation on fruit quality of ‘Marisol’ Clementines was investigated over two seasons, 1998 and 1999, at two different sites in South Africa. Girdling increased the total soluble solids (TSS) by 2–10%, however, the effect was not always significant. There were no trends observed for external fruit colour, fruit diameter, juice content (%), titratable acidity (TA) and TSS:TA ratios due to girdling. Deficit irrigation increased the TSS (by 2–17%) and the TA levels (by 9–13%) in both seasons and at both sites, increased the TSS:TA ratio at Citrusdal in 1998 (4–8%), and decreased the TSS:TA ratio (by 7%) in the second season (1999) at both sites due to the increased acidity levels (by 11–13%). Deficit irrigation had no major effects on external fruit colour and juice content in 1999, but decreased fruit diameter (by 10%) at Citrusdal. According to these results, deficit irrigation, summer trunk girdling, or a combination of both, can be used as cultural practices to improve internal fruit quality. The combination of girdling and deficit irrigation increased the TSS more than when the practices are executed on their own.

Plant hormones (IAA, ABA, GA1/3, GA4/7) contents in the leaves of satsuma mandarin trees (Citrus unshiu Marc. `Okitsu') were measured to elucidate the relationship between endogenous plant hormones and flower buds formation. The ringing treatment to lateral branch in October enhanced the percentage of leafless inflorescence and number of flowering shoots in the following spring. While, more vegetative spring shoots were formed on bearing shoots which were left the fruit load in the previous autumn to winter. GA1/3 were the dominantly detected GAs in the leaves. Their content was higher in the leaves of the bearing shoots than in that of the vegetative shoot but was not affected by the ringing treatment. Ringing increased the percentage of leafless inflorescence and the contents of IAA and ABA in December. These results suggested that flower bud formation was inhibited by GA1/3 in October, and that high IAA and ABA content in December also promote the percentage of leafless inflorescence and the number of flower buds per node. The relationship between endogenous plant hormones and flower bud formation was discussed.

Seasonal changes of sucrose, glucose and fructose were monitored in the bark (phloem) and xylem in Ponkan mandarin (Citrus reticulata Blanco cv. Yoshida). Sucrose was the most abundant sugar. A decline in bark sucrose content coincided with the major fruit abscission period. Stem girdling was carried out at anthesis (May), end of June drop (July), start of autumn (September) and in early winter (November). Girdling in July and September slightly increased leaf sugar content. At peak starch content (in winter), the September girdled treatment had the highest starch content. May girdling increased fruit set significantly and also improved fruit color. July and September girdling improved fruit size, but late girdling (November) had no effect on fruit size. Flowering and fruit set in the following year were closely related to starch content in the previous winter: they were highest in September girdled trees and lowest in May girdled trees.

‘Nova’ mandarin hybrid is prone to stylar-end fruit splitting when produced in solid, isolated blocks. In addition, self-incompatibility and weak parthenocarpy result in poor fruit set. Calcium nitrate application during flowering reduced fruit split, while girdling using a Spanish girdling tool increased fruit set dramatically. A strategy to increase export packout is presented.

The effects of girdling and etiolation on the anatomical structure and adventitious rooting of hybrid chestnut ( Castanea sativa × Castanea crenata ) cultivar ‘Marigoule’ shoots are reported and discussed. The treatments were: (1) shoot girdling (2–3 cm above stool-insertion point); (2) etiolation (covering stoolbed with soil); (3) girdling and etiolation; (4) untreated control. Only the shoots of treatment (3) formed adventitious roots (70% rooting). Etiolation induced no substantial differences in shoot anatomy in comparison with the control, except for a greater accumulation of starch grains. The two girdling treatments stimulated cell division and growth, particularly evident in the swelling of the cortex just above the girdle, and the production of multi-seriate xylem rays, especially notable in treatment (3). This latter treatment also evinced diminished shoot-tissue differentiation compared with treatments (2) and (4), and poorly differentiated cortex sclerenchyma cells, which were arranged not as rings but in irregularly shaped groupings. Root primordia in the early formation stages were found next to the multi-seriate xylem rays in the youngest phloem of the treatment (3) shoots. These findings indicate that root formation occurs over a fairly lengthy period and is associated with anatomical changes in the involved shoot zones. The effects of etiolation and girdling in treatment (3) could not be separated, suggesting their synergistic influence on rooting in chestnut.

Abscission of flower buds was not observed when plants or harvested flowers of rose cultivars ‘Nubia’ and ‘Celica’, grown for cut flowers were kept for 3 weeks at 22°C in the dark. However, all young buds of the miniature rose cultivar ‘Orange Meillandina’ abscised after 6 days of darkness. Removal of buds at early stages of development resulted in abscission of peduncles left intact on the plant in all cultivars examined. Girdling of the stem combined with defoliation postponed the abscission of decapitated peduncles of ‘Nubia’ in situ. The time to abscission of decapitated peduncles in explants was similar to that on the plants in situ. Abscission of peduncles, although delayed, was also present in non-decapitated explants of ‘Nubia’, ‘Celica’, and ‘Yellow Meillandina’ with young buds. In contrast, in the whole plant, darkness did not induce abscission in non-decapitated explants of ‘Orange Meillandina’. Abscission of decapitated peduncles of ‘Nubia’ on the plant was postponed by application of either indoleacetic acid (IAA) or gibberellin (GA3), while only IAA applied to the distal end of the peduncle inhibited peduncle abscission in explants. The abscission of decapitated peduncles in explants was promoted by abscisic acid (ABA) and in non-decapitated explants by application of 2,3,5-triiodobenzoic acid (TIBA) as a lanolin ring beneath the bud. The possible involvement of three components originated in flower buds, leaves or roots in the phenomenon of flower bud abscission in rose plants is discussed.

Fruit set, fruitlet and young leaf growth at an early stage of fruit ontogeny were promoted significantly by girdling at the base of autumn-shoots of the preceding year on Day 10 pre-full bloom. In contrast, defoliation or darkening of the old leaves on the autumn-shoots aggravated fruit drop and inhibited fruitlet and young leaf growth. During this period the net photosynthetic rate (Pn) of old leaves rose sharply. These observations clearly indicate that assimilate supply to fruitlets and young leaves of Citrus unshiu during this period is mainly affected by the current photosynthates from the old leaves instead of from the remobilization of stored reserves within the trunks. On Day 20 after full bloom the young leaves reached 48% of their final area and increased their Pn rapidly. Subsequently, the Pn of old leaves began to decrease dramatically. The impeding effect of darkening of old leaves on fruit growth from Day 20 after full bloom was absent. The results show that the young leaves gradually substitute for the old leaves to supply photosynthates to the developing fruits from about Day 20 after full bloom.

The abscission of young fruit occurring in apple trees was measured under various conditions in order to locate the possible source of the signal that induces fruit drop. The effect on fruit abscission of shading of leaves, girdling of conducting tissue, extracting seeds and defruiting pedicels was investigated. Complete shading of whole trees for 5 days, steam girdling of defoliated fruiting wood proximal to the abscission zone and removal of seeds from attached fruit resulted in 100% fruit drop when treatment was carried out prior to the June drop period. When the same treatment was applied after June drop no fruit abscised. However, fruit abscission took place before and after June drop when steam girdling was applied to the pedicel distal to the abscission zone. The same effect was observed in defruited pedicels, which always abscised after fruit removal throughout fruit development. The results show that during the pre-June drop period, abscission can be induced by treatments which reduce or block nutrient supply to the abscission zone of fruit. After that period the growing fruit becomes a sugar storage organ which is resistant to abscission. It is though likely that inhibition of abscission is related to the presence of stored carbohydrates already accumulated in the young fruit. An indication for the involvement of the sugar level, in particular glucose, in the control of the abscission process was provided by the results of measurements of individual sugar levels in conducting tissue distal and proximal to the abscission zone. It was found that during fruit development, glucose concentration in the pedicel was normally above the concentration found in fruiting wood proximal to the abscission zone. However, when abscission during the June drop period was induced, the glucose level dropped to a minimum in the pedicel, reaching the same value as in the fruiting wood. It is suggested that the glucose level in the pedicel of growing fruit may therefore be a factor in the control of the abscission process in young apple fruit, abscission occuring only in those fruit in which the glucose content in the pedicel is below a critical level. Fruit which remain on the tree have most likely reached a stage in their development at which sufficient amounts of sugar have accumulated to prevent abscission.

The effects of gibberellic acid (GA3), ethephon or trunk girdling on raceme production and fruit set of Macadamia integrifolia Maiden & Betche, Proteaceae, when applied at the onset of the flowering season were evaluated. A single application of GA3 at 200 or 1000 mg l−1 inhibited flower production. Trees treated with 100 or 500 mg l−1 ethephon had an earlier first flowering peak and a reduction in racemes with fruit set per tree. Girdling increased the cumulative number of racemes with unopened flower buds and with flowers at anthesis when counted at 2-week intervals during the flowering season. This resulted in an increase in racemes with fruit at the conclusion of the flowering season.

A single GA 3 -spray at petal-fall to the entire tree enhanced initial set in the ‘Navelate’ sweet orange ( Citrus sinensis L. Osbeck), but this effect was transient and in most cases final yield was not increased. When followed by girdling, final yield was increased even in the most productive orchards, this effect being due to an increase in fruit number while fruit size was unaffected. The response was markedly dependent on the GA 3 concentration, 5 mg l −1 giving the best results. Higher concentrations up to 20 mg l −1 even reduced yield compared to the untreated control trees. Chlormequat reduced the number of fruits finally cropped without affecting their size, an effect which may be explained through a reduction in the endogenous gibberellin levels.

Different patterns of assimilate translocation were demonstrated in the kiwifruit vine, such that any shortage in the local supply of carbohydrate for fruit growth within a lateral was readily met by surplus carbohydrate from other fruiting or non-fruiting laterals. Assimilate transport occurred in either a basipetal or acropetal direction, depending on the relative positions of the regions of carbohydrate surplus and shortage. Translocation over 7 nodes distance in 1-year-old stems was observed. Fruit on laterals with low leaf-fruit ratios (1:1) imported the most 14C label from neighbouring laterals. The partitioning of 14C assimilate towards these fruit increased with the physical proximity of the laterals. A non-equivalence between girdled and non-girdled shoots was observed. While fruit growth was increased by the presence of non-fruiting laterals in girdled canes, fruit size was reduced by large leaf numbers on non-girdled canes.

Girdling, growth retardant succinic acid 2-2-dimethyl hydrazide (Alar), 2-naphthoxyacetic acid (NOA), and Gibberellic acid (GA3) were tested as a fruit-setting agent in 1975 for ‘Yaghooti’, a stenospermocarpic cultivar of Vitis vinifera grape. Bloom Alar spray at 7500 p.p.m. increased the number of berries per cluster and the cluster weight. Bloom auxin spray did not effectively increase fruit set, while gibberellin had a depressing effect. Girdling also increased fruit set and a combination of Alar and girdling had the most pronounced effect on fruit set. None of the treatments significantly altered soluble solids and/or vitamin C content of the berries.

Yields of ‘Topaz’ mandarin, a self-incompatible local selection of ‘Ortanique’, were substantially increased by spraying with 20 p.p.m. gibberellin or by girdling at blossom time. The number of seeds increased with decreasing distance from ‘Minneola’ pollinizers, while fruit size and yields were not clearly affected.

A study of the daily changes in fruit volume was carried out in an attempt to analyse the suitability of the apparent fruit growth (AFG) rate as an indicator for timing of irrigation in grapefruit. Three distinct fruit growth phases could be distinguished within an irrigation cycle. Phase 1, lasting about 3 days, was characterized by a relatively rapid volume increment rate owing to both turgor-attributed physical swelling of the fruit and its normal growth; Phase 2, with a moderate volume increment rate, defined as normal growth; Phase 3, in which fruit volume growth stopped altogether, sometimes even showing some fruit shrinkage. Even though no changes in fruit volume were discernible during Phase 3, it is proposed that some growth did take place, being counterbalanced by an equivalent amount of shrinkage. Comparison of the growth patterns of fruits from moisture stressed (S) and regularly irrigated (RI) trees showed that, after irrigation was renewed, the fruits from S trees swelled and grew faster for longer periods. This more rapid growth could compensate for most or all of the growth lost during the stress period. Girdling of branches was effective in prolonging the period of faster fruit growth rate in S trees. These observations argue against using the AFG rate as an indicator for timing of irrigation. They also lead to the question as to the nature of the factor(s) which promote the faster growth of fruits from S trees after irrigation renewal.

The fruit yield of the sexually self-incompatible citrus ‘Ortanique’ can be successfully increased, firstly by the introduction of ‘Valencia’ sweet orange trees for the purpose of cross-pollination, and secondly, by girdling. ‘Valencia’ cross-pollination results in fairly low seed counts in the ‘Ortanique’ fruits, the averages in two successive seasons being 3 and 5 seeds. ‘Minneola tangelo’ is a highly effective pollen source, but induces large numbers of seeds per fruit. The pollen from ‘Tomango’ and ‘Shamouti’ sweet orange is ineffective.

Decapitation of young Brussels sprout plants (Brassica oleracea L. var. gemmifera) which had just produced axillary buds stimulated the development of the upper axillary buds, but this was partially prevented by application of auxin to the decapitated stem. Removal of leaves also stimulated axillary bud outgrowth, even in the absence of decapitation, but only when some of the leaves were left attached. Removal of leaves from the top half of the stem was very effective in stimulating bud outgrowth, whereas removal of basal leaves was ineffective. Steam-girdling the middle of the stem resulted in enhanced axillary bud growth below the girdle and was more effective in defoliated than in leafy plants. The role of the leaves and stem apex in controlling the movement of nutrients and hormones to axillary buds is discussed.

Mature macadamia (Macadamia integrifolia Maiden and Betche) cultivar ‘Own Choice’ trees were subjected to growth manipulation to show the extent to which new vegetative and/or reproductive growth depleted carbohydrate reserves in trunk tissues. Ethephon at 1.6 ml l−1 was applied in winter and early spring to abort racemes (RR). Those which developed subsequently were removed by hand. Vegetative growth was suppressed (RV) by applying 10 sprays of 0.1 ml l−1 paclobutrazol (PP333) at 2-weekly intervals from mid-winter to early summer. Also, a combination of these two treatments (RR/RV) was applied and tree trunks were cinctured (girdled) to promote the accumulation of carbohydrates. In control trees, storage carbohydrate levels declined with the onset of spring flush and flowering in September, and remained low until mid-December (summer) after rapid nut growth had ceased. Similar patterns occurred in cinctured and RV trees. In contrast, carbohydrate levels in RR trees remained relatively constant over this period, whereas RR/RV treatments produced an intermediate effect. It is concluded that the decline in carbohydrate reserves was due to demand by the developing crop rather than that of the small spring vegetative flush. In the following year, flowering was more advanced and intense on trees which were prevented from cropping, but this was not reflected in higher yields.

Fruit size of kiwifruit was not reduced at low leaf-fruit ratios (less than 2:1) on non-girdled laterals because translocation from other parts of the vine could meet any shortfall in the local supply of carbohydrate in the fruiting lateral. However, girdling and 14 C-tracer studies showed that the minimum leaf:fruit ratio that is required to support fruit growth in the kiwifruit lateral, without import of carbohydrate, is 2:1, or approximately 225 cm 2 of leaf area per fruit. Fruit load did not affect the specific leaf weight, photosynthetic rate or stomatal resistance of the leaves on either intact or girdled laterals. Indications of an inhibitory effect on fruit growth by large leaf areas on intact laterals, which was reversed when girdling treatments were applied, may relate to the interactions of growth substances in determining sink strength.

Girdling in October of small or large fruitless branches increased 2–3-fold both starch content of leaves and flower numbers as compared with ungirdled ‘Murcott’ mandarin trees. Autumn girdling and GA 3 treatments were both effective and additive in increasing starch contents of leaves and twigs of ‘Shamouti’ orange trees. GA 3 , however, had the expected effect of depressing the reproductive inflorescences in both girdled and ungirdled branches, while girdling had the opposite effect. Girdling and fruit removal in October also additively and dramatically increased flower production in ‘Murcott’. Lowtemperature regimes in a phytotron caused young ‘Minneola’ budlings to flower earlier in the season and more profusely, while having no effect on starch content of leaves and twigs. The interactions of increased carbohydrate content and gibberellin in the control of flower formation in citrus are discussed.

Girdled limbs of ‘Fuerte’ avocado produced a bigger crop than controls for 3 consecutive years. Limbs girdled for 4 consecutive years yielded the same as the control, but healed slowly. Yield was maintained in the year after girdling was stopped. The number of seedless fruit was not increased by girdling.