Spur Leaf Research Articles

Spur leaf and fruitlet seed phytohormones of biennial apple trees affect return bloom

Spur leaf and fruitlet seed phytohormones of biennial apple trees affect return bloom

Flowering and Non-Flowering Spur Leaf Characteristics of 'Amasya' Apple and Its Comparison with Other Cultivars

Understanding the attributes of spur leaves in apple trees is essential to gain more insight into the complex process of fruit development and quality. However, limited literature is available about the spur leaf characteristics of the 'Amasya' apple cultivar. In this work, the Soil Plant Analysis Development (SPAD) and leaf area were investigated in flowering and non-flowering spur leaves of 'Amasya' and six common apple cultivars. Significant differences among cultivars were observed for the SPAD and spur leaf area. The median SPAD readings in 'Amasya' were 32.63 and 26.23 for the flowering and non-flowering spurs, respectively, which were the relatively low values among studied cultivars. The maximum SPAD value was measured in flowering spurs of 'Cripps Pink' (45.03). SPAD values were found to be lower in non-flowering spurs compared with flowering ones for all the studied cultivars, which confirms that decline in chlorophyll content coincided with a gradual decline in productivity. A notably significantly lower spur leaf area was found in 'Amasya', whereas the highest spur leaf area was in 'Cripps Pink'. However, no statistical difference was observed between flowering and non-flowering spur leaf areas within the same cultivars. The present results provided a general framework of SPAD and spur leaf areas in 'Amasya' and other apple cultivars when spurs had flowers or not. Knowledge of these characteristics provides a basis for building a model related to yield elaboration of apple trees.

Screening Thermal Shock as an Apple Blossom Thinning Method. II. Pollen Tube Growth and Spur Leaf Injury in Response to Temperature and Duration of Thermal Shock

Blossom thinning can confer significant benefits to apple growers, including increased fruit size and annual bearing. However, current blossom thinning practices can damage spur leaves and/or fruit. We evaluated the use of short duration forced heated air treatments [thermal shock (TS)] as a blossom thinning strategy for ‘York Imperial’. Using a variable-temperature heat gun, TS treatments were applied to solitary blossoms 24 hours after pollination. Effects of output temperature (five levels) and treatment duration (four levels) were evaluated using a completely randomized design with a factorial treatment structure. Short duration treatments (0.5 and 1.0 seconds) were ineffective for arresting pollen tube growth in vivo. TS temperature required to inhibit stylar pollen tube growth was inconsistent across years. In 2014, TS temperatures ≥56 °C inhibited pollen tubes from reaching the style base at 2.0 and 4.0 second durations. However, in 2015, TS temperatures ≥81 °C at 4.0 seconds prevented pollen tubes from reaching the style base. Inconsistent effects of TS across years were attributed to treatments being applied too late due to optimal conditions for pollen tube growth during the intervening 24-hour period after pollination. Excessive injury to spur leaf tissue was observed at temperatures higher than 84 °C and 70 °C (2.0 and 4.0 seconds, respectively). Pollen tube growth was reduced or arrested at temperature and duration combinations that caused minimal visible injury to spur leaves. Identifying and exploiting structural differences between apple blossoms and vegetative spur leaves may provide insight for the future development of TS or other attempts at developing selective thinning technologies.

INFLUENCE OF PARTIAL SPUR LEAVES REMOVAL ON FRUITLET SHEDDING, FRUIT QUALITY AND SHOOT GROWTH IN APPLE TREES AS A BASIS FOR MECHANICAL THINNING

Knowledge of the physiology of natural fruitlet shedding is especially important to insure thinning efficiency in apple production. The effect of partial spur leaf removal on shedding, as well as on fruit quality and bourse shoot growth, was investigated. Removing spur leaves increased shedding, while there was no effect of partial leaf removal on mature fruit quality in terms of weight, firmness and sum of sugars, detected by HPLC-RI and resulted in lower contents of citric, fumaric and shikimic acids, detected by HPLC-UV. Growth of bourse shoots was poorer in treatments with leaf removal. To summarize, a decreased number of spur leaves caused more intensive fruitlet abscission and poorer bourse shoot growth but had no negative influence on fruit size. These results show the potential use of decreasing spur leaf area to stimulate more intensive natural shedding to support fruitlet thinning, which could be used in combination with prospective mechanical thinning.

Morphological variability of Prunus lycioides Spach germplasm using multivariate analysis

Prunus lycioides Spach is an endemic Iranian species of the subgenus Amygdalus in family Rosaceae. The present investigation was carried out to evaluate morphological and fruit characteristics of this species from Markazi province in Iran. Some characters evaluated showed significant variabilities among the individuals studied. Branch leaf length ranged from 20.96 to 26.15 mm, while branch leaf width varied from 1.60 to 3.92 mm. In addition, spur leaf length ranged between 14.32 and 28.83 mm and spur leaf width varied between 1.96 and 3.51 mm. Nut length ranged from 9.04 to 13.24 mm and nut width varied from 6.54 to 9.26 mm. Nut weight ranged from 0.14 to 0.37 g with an average of 0.27 and kernel weight varied from 0.06 to 0.16 g with an average of 0.09. Full blooming date varied from 03 to 18 April and fruits were ripened from 28 June to 10 July. Kernel weight showed positive and significant correlations with nut and kernel dimensions. Principal component analysis (PCA) showed that the variables contributing to nut and kernel are more important in explaining the variation among the individuals. Ward dendrogram generated using Euclidean distance based on all morphological data separated the individuals into two major clusters. The current findings emphasize the usefulness of wild P. lycioides species in almond breeding programs and thus this valuable genetic resource must be conserved.

Sweet cherry collection composition and breeding value of Melitopol experimental station of horticulture

Aim. To evaluate the composition and breeding potential of a gene poolcollection of sweet cherry varieties of M.F. SydorenkoMelitopolResearch Station of Fruit Growing of the Institute of Horticulture, NAAS of Ukraine. Result and Discussion.The results of studying the morphological, economic and biological features of sweet cherry (Cerasusavium L. Moench) varieties from the gene pool collection of MelitopolExperimental Station of Horticulturenamed after M.F. Sidorenko of the Institute of Horticulture of NAAS are presented. The history of the collection creation and the genealogy of modern Ukrainian varieties were analyzed. We found that they were the 1st and 2nd generations of traditional Western European varieties. Major sweet cherry varieties that had been most often used in developing modern Ukrainian assortment, were identified. Analysis of the collection showed that 111 accessions of 129 were varieties bred in Melitopol, 40 of which are officially registered.The other accessions are elite forms, which failed the state variety trials or are being tested according to the competitive design. Among the latter, promising forms (candidates for varieties and pre-breeding forms) were distinguished, as they are sources of valuable economic traits. It was determined that the morphogenic process had contributed to the diversity in fruit quality features, which enabled building up a trait collection of sweet cherries for 20 traits with 82 levels of their expression. However, morphogenesis almost did not affect the growth power, fructification nature, generative organs, fructification time and resistance to diseases, therefore there are no significant differences in these features between the collection accessions bred at Melitopol Experimental Station of Horticulture named after M.F. Sidorenko of the Institute of Horticulture of NAAS. Most of the varieties grown on Magalebian cherry plantlet have extensive crowns, bear fruit on "May bouquets" and, after one-year growth, are winter hardy, tolerant to drought, moderately and highly resistant to spur blight and leaf spot as well as self-infertile. On this parent stock, most of the varieties come into fruition after 5-6 years and quickly increase their yields. It was established that enrichment of the gene pool collection with valuable introduced accessions and their wide involvement in hybridization were currently the key objectives aimed at expansion of morphogenesis limits to obtain competitive varieties with high adaptability, productivity and marketability. Conclusions. Modern Ukrainian varieties are the 1st and 2nd generations of traditional Western European varieties. German variety Drogansgelbeknorpelkirsche (DroganaZhyoltaya) with its clone Napoleon Belaya and Russian-Ukrainian variety Valeriy Chkalov were the most actively used in their development. 86% of the gene pool collection of MelitopolExperimental Stationof Horticulture named after M.F. Sidorenkoof the Institute of Horticulture of NAAS are varieties bred in Melitopol differing mainly in ripening time and fruit quality. The collection contains released varieties, a number of sources of valuable traits and, as a tool for the effective implementation of modern breeding programs, requires enrichment with varieties of other eco-geographical groups.

Comparison of Chemical Blossom Thinners Using ‘Golden Delicious’ and ‘Gala’ Pollen Tube Growth Models as Timing Aids

Reducing apple crop load during bloom can increase fruit size and promote annual bearing when compared with crop reduction at later timings. In this study, we compared the efficacy of chemical blossom-thinning strategies on ‘Golden Delicious’ and ‘Gala’ apple trees. Several blossom-thinning treatments were evaluated, including 1) unthinned control (control), 2) hand-thinned (HT) at bloom, 3) liquid lime sulfur + Stylet-Oil (LS + SO), 4) ammonium thiosulfate (ATS), 5) endothall (ET), and 6) naphthaleneacetamide (NAD). Chemical treatments were applied twice during bloom, using a predictive model to determine application timings. Blossom thinner effects on pollen tube growth, fruit set, and yield responses were evaluated. LS + SO and ATS reduced the number of pollen tubes that entered the style for ‘Golden Delicious’ by 75% and 63%, respectively. ET and NAD did not affect the number of pollen tubes that entered the style. In one of 2 years, LS + SO resulted in a near-ideal crop load and increased fruit weight. ATS was effective in reducing initial fruit set in ‘Golden Delicious’ and ‘Gala’, but did not reduce whole-tree crop density. ET reduced crop load in all experiments but caused excessive spur leaf injury and negatively affected fruit size of ‘Gala’ but not ‘Golden Delicious’. NAD had limited efficacy on ‘Golden Delicious’ at the concentrations and application timings used in this trial. When used as the sole method of crop load management, none of the chemistries evaluated over-thinned or increased fruit injury. However, ET caused excessive thinning when evaluated as part of a commercial crop load management program on ‘Gala’. Of the products evaluated, LS + SO provided the best overall thinning response.

Fruit load in almond spurs define starch and total soluble carbohydrate concentration and therefore their survival and bloom probabilities in the next season

Abstract Nonpareil almonds trees have compact shoots, known as spurs. Spurs are the main bearing structure of many fruit trees. However, in almonds, spurs show alternate bearing and low winter survival if fruit load is high or if leaf area is low at the spur level. To better understand the source sink relationships that govern the effects of fruit load on spur survival and return bloom, a total of 1920 spurs with varying fruit load (non-fruiting spurs, one fruiting spurs, two fruiting spurs, and one fruiting spurs de-fruited at 40 and 70 days after full bloom) were labeled and tracked for two seasons in fully mature trees. Spur variables such as leaf area, total soluble carbohydrates (TSC), starch concentration, winter survival and return bloom were collected and analyzed with generalized linear mixed models and structural equation models. Starch concentration in non-fruiting spurs (excluding de-fruited spurs) was twice as high as starch concentration of fruiting spurs. Similarly, in the following season, the probabilities of survival and bloom in non-fruiting spurs were 55% and 61% higher than fruiting spurs, respectively. Structural equation modeling suggests that starch concentration in a spur is correlated with spur leaf area, number of fruits, fruit weight, and TSC. Thus, this work improves our understanding of return bloom and winter spur survival.

A Method for Quantifying Whole-tree Pruning Severity in Mature Tall Spindle Apple Plantings

Pruning is the cutting away of vegetation from plants for horticultural purposes. Pruning is known to reduce apple tree size, increase fruit size and quality, and decrease yield. Methods for studying the effects of varying degrees of severity of pruning on a whole-tree basis have used qualitative descriptions of treatments rather than repeatable whole-tree quantitative metrics. In this study, we introduce a pruning severity index calculated from the sum of the cross-sectional area of all branches on a tree at 2.5 cm from their union to the central leader divided by the cross-sectional area of its central leader at 30 cm from the graft union. This limb to trunk ratio (LTR) was then modified by successively removing the largest branches of ‘Buckeye Gala’ to achieve six severity levels ranging from LTR 0.5 to LTR 1.75, with lower values representing more extreme pruning with less whole-tree limb area relative to trunk area. Pruning treatments were applied for three consecutive years and tree growth and cropping responses were observed for the first 2 years. With increasing pruning severity the following characteristics increased after seasonal growth: number of renewal limbs, number of shoots, shoot length, number of shoot leaves, shoot leaf area, final fruit set, fruit size, yield of large fruit, crop value from large fruit, soluble solids, and titratable acidity. The following characteristics decreased: limb age, number of secondary limbs, number of spurs, number of spur leaves, spur leaf area, the ratio of spur leaf area to shoot leaf area, fruit count per tree, yield, yield efficiency, crop value from small fruit, overall crop value, and sugar:acid ratio. The LTR provides a measurable way to define and create different levels of pruning severity and achieve consistent outcomes. This allows a greater degree of accuracy and precision to dormant pruning of tall spindle apple trees. The use of the LTR to establish the level of pruning severity allows the orchard manager to set crop load potential through regulation of the canopy bearing surface. This metric is also a necessary step in the development of autonomous pruning systems.

The Role of Spur Leaves, Bourse Leaves, and Fruit on Local Flower Formation in Apple: An Approach to Understanding Biennial Bearing

Lack of consistent flower formation is the underlying cause of biennial bearing. Flower formation in apple (Malus ×domestica Borkh.) has been associated with different factors, such as leaf area, shoot growth, bourse length, crop load, and seed number. However, it is unclear how these different factors interact to promote or inhibit flower formation. The effect of spur defoliation, fruit removal, and their interaction were evaluated on spur flower formation and bourse length in annual-bearing ‘Gala’ and the biennial-bearing ‘Honeycrisp’. Eight different combinations of spur defoliation and fruiting treatments were applied in three consecutive springs, 2013–15. Bourse shoot defoliation and fruiting treatments inhibited spur flower formation in both cultivars, but in different patterns from year to year. In addition, spur leaf defoliation did not affect flower formation in either cultivar. Furthermore, local defoliation and fruiting treatments did not affect bourse length. We propose that bourse leaves play a major role in both producing and transporting flower formation signals, but the effect depends on cultivar.

Increases in leaf nitrogen concentration and leaf area did not enhance spur survival and return bloom in almonds (Prunus dulcis [Mill.] DA Webb)

Mature almond trees bear fruit mainly on short shoots called spurs, with only a small percentage of fruit produced laterally on long 1-year-old shoots. As a result, maintenance of large numbers of healthy spurs per tree is critical for fruit production. However, spurs that bear fruit have lower leaf area, leaf nitrogen content, and CO2 assimilation rate than non-fruiting spurs. This has been correlated with reduced percentages of spur survival and return bloom the following season. Thus, we hypothesized that spur leaf area, and ultimately spur health could be enhanced through application of foliar sprays and soil nitrogen treatments that would enhance leaf nitrogen content and spur leaf area. To test our hypothesis, we selected almond trees exhibiting significant yield differences as a consequence of differential soil rates of nitrogen fertilization (N rate) for three prior years (140, 224, and 392 kg/ha). In each tree, three spur types [non-fruiting spurs (F0); spurs with one fruit (F1); spurs with two fruit (F2)] were selected on the east side of the canopy and tracked for one complete season (2011–2012). Four foliar treatments (nutrient replacement, nutrient replacement with biostimulant, nitrogen, and non-spray) were directly applied to individual spurs in each N rate in the spring of 2011 and characteristic such as leaf nitrogen, and fruit quality were recorded throughout the season. In winter of 2012, spur survival and return bloom were addressed through individual visual inspection of the tagged spurs. In this experiment, soil and foliar N treatments effectively increased spur leaf area, fruit, and leaf nitrogen concentration. In the high N treatment, the leaf nitrogen values exceeded the critical nitrogen concentration established for almond trees and the critical leaf area for spur survival and blooming thresholds established by past research in this area. However, none of these positive changes in leaf N or leaf area improved spur survival and/or return boom of any spur type. Indeed, survival and hull + shell weight tended to be lower in the population of fruiting spurs with the highest leaf area and leaf nitrogen concentration and the return bloom probabilities were always lower in fruiting spurs than in non-fruiting spurs, independent of the nitrogen rate. These results and the relationship between nitrogen rate and spur survival are discussed.

Yield in almond is related more to the abundance of flowers than the relative number of flowers that set fruit

Almond tree yield is a function of the number of flowers on a tree and the percentage of flowers that set fruit. Almonds are borne on spurs (short proleptic shoots that can have both leaves and flowers). Almond tree spur dynamics research has documented that previous year spur leaf area is a predictive parameter for year-to-year spur survival, spur flowering and to a lesser extent spur fruiting, while previous year fruit bearing has a negative impact on subsequent year flowering. However, a question remained about whether yields are more dependent on flower numbers or relative fruit set of the flowers that are present. The aim of the present work was to compare the importance of flower abundance with that of relative fruit set in determining the productivity of a population of tagged spurs in almond trees over a 6-year period. Overall tree yield among years was more sensitive to total number of flowers on a tree rather than relative fruit set. These results emphasize the importance of maintaining large populations of healthy flowering spurs for sustained high production in almond orchards.

The influence of temperature and water supply on apple fruit growth and the development of orchard-grown trees

SummaryThe growth of ‘Cox’s Orange Pippin’ apples in an orchard was studied in relation to temperature and irrigation. Temperature around a number of trees was raised by the use of polythene tunnels from bloom in May until harvest in September. These trees within the polytunnels received irrigation, while for comparative purposes some trees outside did not. Continuous measurements of the canopy environment, particularly temperature, were made until harvest. Throughout the growing season fruit size was repeatedly measured, non-destructively, on a large number of selected fruit. Despite differences in mean temperature and accumulated day-degrees between trees inside and outside the polytunnels, there was no benefit to fruit size from raised temperatures. Supplemental irrigation did have a number of effects; spur leaf area was enhanced without significant change in total leaf area, while in the absence of irrigation, final shoot length was greater. This greater shoot production was however associated with a ...

Mechanical blossom thinning of apples and influence on yield, fruit quality and spur leaf area

McClure, K. A. and Cline, J. A. 2015. Mechanical blossom thinning of apples and influence on yield, fruit quality and spur leaf area. Can. J. Plant Sci. 95: 887–896. Apple (Malus×domestica Borkh.) trees tend to crop heavily, which often makes crop load adjustment necessary. This can now be achieved as early as bloom by mechanical removal/thinning of blossoms. High-density Empire/M.26 and Royal Gala/M.26 apple trees were mechanically (MBT) and hand blossom thinned (HBT) in 2010 and 2011, respectively, and their effects on fruit set, subsequent hand thinning, final crop load, and spur leaf area were measured. In both years, MBT effectively thinned trees and reduced fruit set, but did not reduce the requirement for follow-up hand fruitlet thinning after June drop in 2011. In 2010, harvest yields for MBT treatments decreased, while weight and diameter increased. In 2011, most harvest and fruit quality parameters were unaffected by thinning. Trees that were mechanically thinned had significantly reduced spur leaf area, but were similar to unthinned control trees with respect to many of the yield and quality parameters measured. Mechanical blossom thinning is a new crop load management option for apple growers looking to supplement more traditional chemical and hand thinning techniques.

Spur Fruit Set Is Negatively Related with Current-year Spur Leaf Area in Almond

Almond spurs are known to be the primary bearing unit in almond tree and are subject to alternate bearing. Fruits are a strong sink in bearing spurs and can influence spur leaf growth. At the same time the percent of flowers that set fruit on a spur (spur relative fruit set) could be influenced by the competition among multiple flowers/fruits borne on the same spur as well as by limited leaf area on the same spur. The aim of the present work was to investigate the relationship between current-year spur leaf area and spur absolute and relative fruit set. Approximately 2400 spurs were tagged and followed over 6 years and data concerning spur leaf area, number of flowers per spur, and number of fruits per spur were collected. Spur leaf area was reduced in fruiting spurs in comparison with non-fruiting spurs according to the number of fruits borne by each spur. This phenomenon contributes to spur alternate bearing because spur flowering and survival in the next year are a function of the leaf area in the current year. Relative fruit set in almond appears to be negatively associated with current-year spur leaf area. Competition among fruits on the same spur did not appear to influence spur relative fruit set.

Influence of Mechanical String Thinning Treatments on Vegetative and Reproductive Tissues, Fruit Set, Yield, and Fruit Quality of ‘Gala’ Apple

The objectives of this experiment were to test the efficacy of a mechanical string thinner (Darwin PT-250; Fruit-Tec, Deggenhauserertal, Germany) on apple and to identify an optimal range of thinning severity as influenced by spindle rotation speed. Trials were conducted in 2010 and 2011 at the Pennsylvania State University Fruit Research and Extension Center in Biglerville, PA, on five-year-old ‘Buckeye Gala’/M.9 apple trees that were trained to tall spindle. A preliminary trail on five-year-old ‘Cripps Pink’/M.9 was conducted to determine the relationship between string number and thinning severity. As the number of strings increased, the level of thinning severity increased. A range of spindle speeds (0 to 300 rpm) was applied to the same trees for two consecutive years. As spindle speed increased, blossom density (blossom clusters per limb cross-sectional area) was reduced as was the number of blossoms per spur. In 2010, leaf area per spur was reduced 9% to 45%. In 2011, the fastest spindle speed reduced leaf area per spur 20%. Although increased spindle speed reduced cropload, injury to spur leaves may have inhibited increases in fruit size. The largest gain in fruit weight was 28 g (300 rpm) compared with the control. In both years, the most severe thinning treatments reduced yield by more than 50%. There was no relationship between spindle speed and return bloom. Severe thinning treatments (240 to 300 rpm) caused significant reductions in spur leaf area, yield, and fruit calcium and did not improve fruit size or return bloom. Spindle speeds of 180 and 210 rpm provided the best overall thinning response and minimized injury to spur leaves, but cropload reduction was insufficient in years of heavy fruit set. Therefore, mechanical blossom thinning treatments should be supplemented with other thinning methods. Mechanical string thinning may be a viable treatment in organic apple production, where use of chemical thinners is limited.

Comparison of leaf population of sweet cherry (Prunus avium L.) trees on different rootstocks

In a series of investigations, undertaken to find the optimal leaf area index (LAI) within the canopy of high density cherry orchards (Prunus avium L.) we studied the characteristics of the leaf population from sweet cherry trees on different rootstocks and their impacts on LAI. Our study involved measuring leaf surfaces, weighing and counting the leaves as well as calculating different indexes to evaluate the distribution of the leaf population. The investigations were carried out five (2008) and six (2009) years after plantation, on ‘Petrus’ and ‘Rita’ sweet cherry trees budded on the following rootstocks. ‘Petrus’ on two clonal Mahaleb rootstocks: ‘Bogdány’, ‘Magyar’ and also on two interspecific hybrids: ‘Gisela 6’ and ‘Prob’. ‘Rita’ trees were grafted on Prunus mahaleb seedlings: ‘Korponay’, P. avium seedlings and on ‘Gisela 6’ rootstocks. The average single leaf area (SLA) of both cultivars was larger on extension shoots compared to spurs. This large single leaf size difference impacts the total leaf area (TLA) of the tree. Leaves from trees on dwarfing rootstocks usually show larger specific leaf weight (SLW), while on vigorous rootstocks the SLW on both shoot type was smaller. On the other hand, there is a tendency that spur-leaves show lower SLW compared to extension shoots. The rootstock vigor strongly influenced the LAI and so the leaf density within canopy space. Both ‘Rita’ and ‘Petrus’ trees tend to develop a proportionally larger spur leaf canopy on dwarfing rootstocks, and this tendency is even stronger after heading the trees (Table 6), while trees on ‘Magyar’ and ‘Bogdany’ rootstocks have consistently low SPLA rates.

Foliar Applications of Urea Affect Nitrogen Reserves and Cold Acclimation of Sweet Cherries (Prunus avium L.) on Dwarfing Rootstocks

Seasonal uptake, storage, and remobilization of nitrogen (N) are of critical importance for plant growth. The use of N reserves for new growth in the spring is especially important for sweet cherry (Prunus avium L.), for which new shoot and fruit growth is concomitant and fruit development occurs during a relatively short bloom-to-ripening period. Sweet cherries grafted on precocious, dwarfing rootstocks such as the interspecific (P. cerasus × P. canescens) hybrids Gisela® 5 and 6 tend to produce large crops but smaller fruit when crop load is not balanced with adequate leaf area. Study objectives were to: 1) characterize natural N remobilization during fall and winter to canopy reproductive and vegetative meristems; 2) determine the effect of fall foliar urea applications on storage N levels in flowering spurs; 3) determine whether differential storage N levels influence spur leaf formation in spring; and 4) determine whether fall foliar urea applications affect the development of cold-hardiness. During fall, total N in leaves decreased by up to 51% [dry weight (DW)] and increased in canopy organs such as flower spurs by up to 27% (DW). The N concentration in flower spurs increased further in spring by up to 150% (DW). Fall foliar applications of urea increased storage N levels in flowering spurs (up to 40%), shoot tips (up to 20%), and bark (up to 29%). Premature defoliation decreased storage N in these tissues by up to 30%. Spur leaf size in the spring was associated with storage N levels; fall foliar urea treatments increased spur leaf area by up to 24%. Foliar urea applications increased flower spur N levels most when applied in late summer to early fall. Such applications also affected the development of cold acclimation in cherry shoots positively during fall; those treated with urea were up to 4.25 °C more cold-hardy than those on untreated trees.

Spur behaviour in almond trees: relationships between previous year spur leaf area, fruit bearing and mortality

In mature almond (Prunus dulcis) orchards, the majority of crop is borne on spurs (short, proleptic shoots) that can live for several years and can produce from one to five fruits. Previous research has led to the hypothesis that spur longevity is related to spur light exposure, cropping and age. However, limited quantitative data are available to substantiate these hypotheses. The objective of this study was to determine spur characteristics that were most highly correlated with spur productivity and longevity in mature, bearing almond trees. Previous year spur leaf area was strongly related to spur viability and flowering; the greater the leaf area in the previous year, the higher the probability of spur survival into the next year and the higher the probability for the spur to bear one or more flowers. Previous year bearing also appeared to influence viability and return bloom, especially in spurs with low leaf area. These results suggest that spur source-sink balance is basic to the life cycle of almond spurs. Furthermore, the results are consistent with the hypothesis that spurs are semi-autonomous organs with respect to carbohydrate balance for much of the growing season. Finally, this information provides general thresholds for maintaining spur viability and productivity that will be useful for developing and evaluating tree training systems and orchard management practices.

Effects of Nitrogen Supply on Source-sink Balance and Fruit Size of ‘Gala’ Apple Trees

The objective of this study was to determine how nitrogen (N) supply affects the source-sink balance and fruit size of ‘Gala’ apple when crop load was controlled at a moderate level. Five-year-old ‘Gala’/‘M.26’ trees grown in sand culture and trained in tall spindle received a total of 3.3, 10.0, 20.0, or 40.0 g actual N through fertigation using Hoagland's solution from bloom to 3 weeks before harvest. The crop load of these trees was adjusted to 6.5 fruit/cm2 trunk cross-sectional area by hand thinning when the diameter of the largest fruit was 10 mm. As N supply increased, total shoot leaf area in the canopy increased, whereas total spur leaf area remained unchanged. Both single leaf and whole canopy net CO2 assimilation rates increased with increasing N supply. The net dry matter gain of the whole tree from budbreak to fruit harvest increased ≈74% from the lowest N supply to the highest N supply, but the proportion of net dry matter gain partitioned to fruit (harvest index) decreased from 83% to 70%. Both leaf area to fruit ratio and average final fruit size increased with increasing N supply, and a linear relationship was found between leaf area to fruit ratio and final fruit size. The number of cells per fruit increased with increasing N supply, whereas average cell size remained unchanged. As N supply increased, fruit soluble solids concentration increased, whereas fruit firmness decreased slightly. These results indicate that 1) apple trees grown under low N supply are source-limited; and 2) within the range of N supply used, increasing N supply improves leaf N status, leaf and whole tree photosynthetic capacity, and leaf area to fruit ratio, leading to more cells per fruit, larger fruit, and higher soluble solids.