Biennial Bearing Research Articles

GENETIC ANALYSIS AND QTL DETECTION FOR BIENNIAL BEARING IN APPLE

ISHS XXVIII International Horticultural Congress on Science and Horticulture for People (IHC2010): International Symposium on Genomics and Genetic Transformation of Horticultural Crops GENETIC ANALYSIS AND QTL DETECTION FOR BIENNIAL BEARING IN APPLE

Varying leaf-to-fruit ratios affect branch growth and dieback, with little to no effect on photosynthesis, carbohydrate or mineral pools, in different canopy positions of field-grown coffee trees

Heavy bearing is a typical phenomenon on unshaded coffee ( Coffea arabica L.) trees and limits both the production and retention of leaves, leading to branch dieback, and, thus, results in a strong biennial bearing pattern. The major goals of this study were to investigate the physiological mechanisms that may be associated with the leaf-to-fruit ratio (LFR), branch dieback, biennial production and the relationships between carbohydrate and mineral fluctuations and branch dieback in coffee plants. The trees were grown in north–south-oriented hedgerows under conditions of full sunlight. Leaves and plagiotropic branches from the upper and lower strata of the east- and west-facing sides of the hedgerow were examined. A strong biennial pattern of coffee production was observed over three harvests. Overall, the east face of the hedgerow produced a more sellable crop than the west face, and this was associated with more light availability for the east-facing branches. The branch growth rate was higher with an increasing LFR during 2006–2007, regardless of the canopy position, and no compensatory increase in the photosynthetic rate was found in response to a decreasing LFR. Due to a relatively low fruit yield in 2007–2008, there was no branch dieback. The extent of branch dieback increased dramatically with decreasing LFR and was probably not closely related to changes in the concentrations of carbohydrates, amino acids and minerals. The extent of branch dieback was apparently unrelated to the differences in the photosynthetic rates per unit leaf area, carbon isotope composition, or oxidative stress, as was assessed by the electrolyte leakage from the leaf tissues. We discuss these responses in terms of the relative lack of branch autonomy in coffee trees.

Genetic control of biennial bearing in apple

Although flowering in mature fruit trees is recurrent, floral induction can be strongly inhibited by concurrent fruiting, leading to a pattern of irregular fruiting across consecutive years referred to as biennial bearing. The genetic determinants of biennial bearing in apple were investigated using the 114 flowering individuals from an F1 population of 122 genotypes, from a ‘Starkrimson’ (strong biennial bearer)בGranny Smith’ (regular bearer) cross. The number of inflorescences, and the number and the mass of harvested fruit were recorded over 6 years and used to calculate 26 variables and indices quantifying yield, precocity of production, and biennial bearing. Inflorescence traits exhibited the highest genotypic effect, and three quantitative trait loci (QTLs) on linkage group (LG) 4, LG8, and LG10 explained 50% of the phenotypic variability for biennial bearing. Apple orthologues of flowering and hormone-related genes were retrieved from the whole-genome assembly of ‘Golden Delicious’ and their position was compared with QTLs. Four main genomic regions that contain floral integrator genes, meristem identity genes, and gibberellin oxidase genes co-located with QTLs. The results indicated that flowering genes are less likely to be responsible for biennial bearing than hormone-related genes. New hypotheses for the control of biennial bearing emerged from QTL and candidate gene co-locations and suggest the involvement of different physiological processes such as the regulation of flowering genes by hormones. The correlation between tree architecture and biennial bearing is also discussed.

Different alternatives for producing sprouts of avocado (Persea americana) rootstocks

In Chile, most avocado orchards have been planted using ‘Hass’ as the scion variety on seedling rootstocks. This has led to the presence of a large variety of individuals, some of which show, among other characteristics, high productivity and a low degree of biennial bearing cycle in the same growing conditions. The most common method used in other countries to propagate such rootstocks from trees involves severe topping; however, this technique is notably destructive, making it difficult to employ in commercial orchards. With the goal of developing alternate methods for forcing shoot production from the rootstock, we tested two different procedures in July 2002 and March 2003, respectively: wounding in conjunction with the application of 1.1 M or 2.2 M benzylaminopurine (BAP) and the removal of one half of the tree canopy (on a vertical plane) and girdling (at widths of 2 or 5 mm). The results indicate that, by removing the top layer of the soil, wounding and applying the BAP spray (1.1 M in July), it is possible to force the production of epicormic or basal sprouting from the rootstock. Additionally, vigorous shoots were obtained on both evaluation dates through the removal of half of the canopy or through girdling

A Theory of Blossom Thinning to Consider Maximum Annual Flower Bud Numbers on Biennial Apple Trees

Tree fruit growers use chemical and mechanical thinning techniques in an attempt to maintain regular annual flower production and maximum repeatable yields of varieties susceptible to biennial bearing. If the percentage of floral buds an apple tree could produce without causing yield depression in subsequent years was known, it would be possible to better manage crop-thinning regimes. This study proposes that thinning is a partial transfer of potential flower buds from one year to the next year and estimates the maximum repeatable sequence of flower buds without biennial bearing. The conceptual framework is tested on a 50-year simulation with 0% to 100% transfer of thinned flower buds. Results indicate that the maximum repeatable sequence of flower buds rises sharply when the final years of the orchard approach and declines when the percent transfer of thinned buds is near 0%.

THE DEVELOPMENT AND USE OF PLANT BIOREGULATORS IN TREE FRUIT PRODUCTION

The discovery of plant hormones and their ability to regulate all aspects of plant growth and development were defining moments in horticulture. Plant bioregulators (PBRs) were soon identified that could improve yield, quality and postharvest life. No where has their impact been more vividly chronicled than in tree fruit production. Tree fruit are considered high value crops and even small modifications in production efficiency, product quality or enhanced cosmetic appeal have the potential to significantly increase product value. Following the discovery of auxins, NAA was found to both to useful in counteract two of the most serious problems of apple production, biennial bearing and preharvest drop. NAA continues to be an important PBR. The discovery of gibberellins and cytokinins led to commercial uses of products in these hormone categories that include improved shape of fruit, enhanced market value by reducing blemishes, improved tree architecture that may be accomplished the by overcoming apical dominance. PBRs were later discovered that could either advance ripening or extend postharvest life, thus greatly expanding the effective period when high quality fruit could be harvested and marketed. Other areas of fruit production where PBRs are especially useful include prevention of preharvest fruit drop, control of vegetative growth, enhanced flower bud formation and control of fruit ripening. Future uses of PBR will emerge. Prohaxadione calcium, an inhibitor of gibberellin biosynthesis, not only retarded shoot growth but it can also alter plant metabolism to impart resistance to insects and diseases. The naturally occurring hormone abscisic acid is showing potential for overcoming plant stress and also enhancing early fruit drop. Recently 1-MCP, a competitive inhibitor of ethylene, has revolutionized storage of pome fruit by extending the postharvest life and improving storage quality of fruit. Recently, great progress in PBR use has come in areas of fruit thinning and retardation of preharvest drop. In these areas greater understanding of fundamental processes, the use of molecular biology techniques and continued empirical research has lead to more effective control of these important process in tree fruit production.

Post-harvest quality of ‘Green Gage’ European plum in integrated production: effects of year and fruit maturity

SummaryThe post-harvest quality of European plum (Prunus domestica L.) ‘Green Gage’ in integrated production was studied over three consecutive production years which varied in climatic conditions and fruit load. In each year, plums harvested at two stages of maturity at harvest, and during storage, were assessed for their weight, skin colour, fruit firmness (FF), total soluble solids content (TSSC), and titratable acidity (TA). The fruit load varied considerably from year-to-year, due to the effects of Spring frosts and biennial bearing. In general, year and harvest maturity affected most of the quality parameters analysed. The year fruit maturity interaction was highly significant only for TSSC at harvest. Changes in quality parameters during maturation and storage varied between years, with different crop loads, since fruit with a similar FF at harvest showed different levels of TSSC, TA, and colour. These parameters, and FF, developed differently during storage, depending on the year. In integrated production, the harvest period could be determined using FF and colour hue angle (hº), a parameter highly and positively correlated with FF at the end of storage. Thus, it may be possible to improve the ‘ready-to-eat’ quality of ‘Green Gage’ European plums at the end of storage, using FF and hº at harvest as selection criteria, regardless of crop load.

Timing of fruit removal affects concurrent vegetative growth and subsequent return bloom and yield in olive ( Olea europaea L.)

Olive ( Olea europaea) demonstrates a high tendency toward alternate fruit production, with significant negative consequences on the industry. Fruit load is one of the main cause-and-effect factors in the phenomenon of biennial bearing, often disrupting the balance between reproductive and vegetative processes. The objectives of the present study were to identify the time range during which heavy fruit load reversibly interrupts the reproductive processes of the following year. The linkage between timing of fruit removal, vegetative growth, return bloom, and fruit yield was studied. Complete fruit removal in cv. Coratina until about 120 days after full bloom (August 15) caused an immediate resumption of vegetative growth. The new shoots grew to twice the length of those on trees that underwent later fruit removal. Moreover, a full return bloom, corresponding with high subsequent yields, was obtained by early fruit removal, while poor or no bloom developed on late-defruited or control trees. Thus, the critical time to affect flowering and subsequent fruiting in the following year by fruit thinning occurs in olive trees even weeks after pit hardening—much later than previously suggested. Furthermore, the data indicate that flowering-site limitation, due to insufficient or immature vegetative growth during the On-year, is a primary factor inducing alternate bearing in olive.

Crop Load Overwhelms Effects of Gibberellic Acid and Ethephon on Floral Initiation in Apple

Potential strategies against biennial bearing in apple [Malus × sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] include promotion of return bloom with an “on”-year application of ethephon or inhibition of return bloom with an “off”-year application of gibberellic acid (GA), but the influence of initial crop load on the efficacy of these bioregulators is poorly understood. In 2004 and 2005, six total trials were initiated in which whole trees were manually adjusted shortly before anthesis to one of three levels of crop load (100%, 50%, 0%) in ‘Cameo’, ‘Honeycrisp’, and ‘Fuji’; GA4 + 7 was overlaid on trees of each crop level in four trials and ethephon in two. In all trials, initial crop load was the primary determinant of return bloom; proportional influence on flower density, fruit density, and yield was generally most pronounced at the 50% crop level. GA4 + 7 consistently reduced floral initiation, whereas ethephon promoted it. Flowering responses from a historically alternating ‘Cameo’ trial site showed greater sensitivity to ethephon and less sensitivity to GA4 + 7 than did responses from parallel trials established in an annually bearing ‘Cameo’ block, suggesting a predilection of nascent buds to a specific fate before the influence of exogenous bioregulators or gibberellins from seeds produced in developing fruit. Light crop loads and GA4 + 7 applications generally promoted shoot extension, whereas heavy crops and ethephon had the opposite effect.

Postharvest regulated deficit irrigation in ‘Summit’ sweet cherry: fruit yield and quality in the following season

We examined, over the postharvest seasons of 2005–2007, regulated deficit irrigation (RDI) for its potential of saving water and maintaining fruit yield and quality in ‘Summit’ sweet cherry. The postharvest irrigation treatments were: full irrigation (Control), receiving 80% of water in Control (RDI-80%), and receiving 50% of water in Control (RDI-50%). Midday stem water potential (Ψstem) was used for assessing plant water status. In 2006, trees produced a large crop and commercial fruit thinning had to be applied, whereas 2007 was a low crop year. The RDI treatment, first applied in 2005, reduced fruit set in 2006 and also reduced root winter starch concentration. In 2006, fruit set was lower in RDI-50% than in Control. But fruit thinning had still to be done with the final yield being the same among treatments. In 2007, RDI-50% produced more fruit and higher yields than Control. Relationship between postharvest Ψstem and crop load in the following season varied according to the year. They were negatively correlated in 2006 and positively correlated in 2007. Fruit firmness did not vary with irrigation treatments in any of the years. Fruit soluble solid concentration (SSC) and fruit relative dry matter (RDM) for RDI-50% was the highest in 2006 when RDI-50% trees had the lowest fruit set. In 2007, SSC and RDM for RDI-50% were the lowest with the trees having the highest fruit set and crop load at harvest. This study indicates that RDI-50% firstly applied in an “off” year, after crop has been harvested, can maintain fruit yield at similar levels to fully irrigated trees while saving water by 45%. Correction of biennial bearing and partial saving of thinning costs are additional advantages of this treatment.

'XENIA', A NEW PEAR CULTIVAR FROM MOLDOVA, FIRST RESULTS IN THE NETHERLANDS

The pear cultivar `Xenia? (synonym `Noiabriskaia?) from Moldova is a selection from a cross between `Triomphe de Vienne? and `Nicolai Krier?. In The Netherlands, `Xenia? has been tested since 2001. So far, trees have given early and high yields and required little thinning. Up to now, a very low to moderate susceptibility to scab (Venturia pirinia) and a very low susceptibility to fruit tree canker (Nectria galligena) have been observed. The trees showed a medium vigour and there was a low tendency to biennial bearing. With the relatively young trees, the average fruit size of `Xenia? fruits at full crop was 250-300 g. The harvest window was wide. Fruits of `Xenia? had a green ground colour at harvest and were moderately bronzed. `Xenia? had a spherical pear shape. The fruits had a strong fruit skin. The firmness was higher than that of `Conference?. The juiciness varied from juicy to very juicy, depending on the maturity stage. `Xenia? had a good eating quality: fresh, slightly aromatic with a typical aroma. The storability of the fruits was very good and the shelf life of `Xenia? proved to be much better than of `Conference?. Summarizing, the first results show a good potential for commercial fruit growing.

Chemical and Defoliation Effects on Fruitset of \"Cox Orange\" and \"Elstar\" Apple Cultivars

Experiments were carried out at Klein Altendorf station in 2001 and 2002 with the objectives to reduce the number of fruits per tree, improve fruit quality and yield, overcome biennial bearing and investigate how photosynthesis and transpiration are affected by one of the chemical thinners (i.e. Azolon). At a dise of 10mg a.i/Li Ethrel (Flodimex) thinned better than at 5mg a.i/Li in 2001 while at 3 mg/Li in 2002 it achieved the required fruit set by thinning before June drop 62% and 15% after June drop compared to 49% of the unsprayed control and had 71% of the fruits in the class 1 fruit diameter size range of 75 to 90mm while yield per tree was reduced by 31% by Ethrel at 10mg a.i/Li but not Ethrel at 5gm a.i/li which had no effect on yield. Mean fruit weight was unaffected by the treatments. The foliar urea based fertilizer Azolon fluid at 75mg a.i/Li applied at full bloom, resulted in 61% fruit set before and 17% after June drop in 2002, slight leaf yellowing, killing and epinasty 7 days after treatment application which disappeared 14 days later but probably started earlier and a slight reduction in leaf photosynthesis and transpiration rates. However, Azolon fluid (i.e. methylene urea or urea formaldehyde) yielded smaller fruit than Ethrel (Flordimex), but larger fruits than the untreated control trees, without affecting fruit yield. The partial and gradual defoliation of selected primary spur leaves reduced fruit set to 50% before and 14% after June drop. These results provide evidence that reductions in photosynthetic rate or photosynthetic leaf area during the period of flowering is sufficient and can successfully induce thinning with a commensurate efficacy to chemical thinners. Keywords: Growth regulator, chemical application, full broom, fruitset, defoliation, natural and induced fruit drop, apple tree, photosynthesis, transpiration, yield, fruit drop, Azolon, Ethrel, Frodimex Discovery and Innovation Vol. 19 (1) 2007: pp. 56-59

Fruit thinning using NAA shows potential for reducing biennial bearing of 'Barnea' and 'Picual' oil olive trees

Biennial bearing is a major horticultural and economic drawback of olive (Olea europaea L.) cultivation, which particularly affects the olive oil industry under intensive production systems. The number of fruits per tree in an on-year is a primary determinant of the biennial cycle. While fruit thinning using NAA shortly after full bloom is commonly practiced to increase fruit size in table olives, the extent of its influence on biennial bearing is unknown. In the present study, the ability of that common naphthaleneacetic acid (NAA) treatment (100 mg/L, 10 days after full bloom) to alleviate biennial bearing in two oil olive cultivars, Picual and Barnea, was poor, although significant influence on the number of fruit was evident solely in Barnea. Picual seemed less susceptible than Barnea to biennial bearing. Consequently, the effect of a broad range of NAA concentrations (0–320 mg/L, 10 days after full bloom) on various yield parameters was investigated during a biennial cycle of Barnea trees. There was a gradual proportional decline in the on-year number of fruits from ~50 000 to 10 000/tree in response to increasing NAA concentrations. The number of return fruits in the off-year was reciprocal to the on-year fruit load, but remained relatively small, below 15 000/tree. The dynamic relationship between fruit load and fruit size in both on- and off-years was a significant compensation factor in fruit and oil yields. In both cultivars, an on-year fruit load smaller than 20 000/tree is likely to provide consistent yearly oil yields ranging from 10 to 12 kg/tree. The results demonstrate the possibility of using NAA post-bloom spraying to balance biennial bearing in oil olives.

Determination of the number of years in Arabic coffee progenies selection through repeatability

The purpose of this study was to estimate the repeatability coefficient of grain yield in Arabic coffee and to determine the minimal number of annual harvests required for a satisfactory level of reliability at the plant level. The experiment was conducted in Campinas (SP) in a randomized complete block design with 21 F3RC2 progenies of Icatu germplasm, for nine years, in nine replications. The repeatability coefficients were estimated by the method of analyses of variance, principal components based on correlation and covariance matrices and structural analyses based on correlation matrices. The selection of F3RC2 progenies of Icatu germplasm can be carried out with an accuracy of 80% in the three first harvests. The repeatability coefficient estimated by the covariance matrix method was the most adequate methodology to estimate this coefficient, since it minimizes the effect of biennial bearing.

Effect of Blossom Density and Crop Load on Growth, Fruit Quality, and Return Bloom in ‘Honeycrisp’ Apple

From 2003 to 2006, the blossom level and crop load of ‘Honeycrisp’ apple (Malus × domestica Borkh.) trees on M.26 rootstocks were adjusted to improve fruit quality and return bloom. The treatments consisted of manually removing flower clusters to 50, 100, and 150 per tree, then at ≈50 d after full bloom, the crop load was adjusted to 3, 6, and 9 fruit/cm2 trunk cross-sectional area (TCSA), respectively. All flower and crop load adjustment significantly increased TCSA and canopy volume compared with the control. Classic biennial bearing was observed on the untreated control trees and those thinned to 150 blossom clusters per tree and 9 fruit/cm2 TCSA and was mitigated for trees with 50 and 100 blossom clusters followed by crop load adjustment to 3 and 6 fruit/cm2 TCSA, respectively. Fruit color the “on” year was always lower on the control trees; no difference was found in the “off” year. The treatments increased fruit weight proportional to crop load except for the 2004 “off” year. This study illustrates that for trees with ≈1 m3 canopy volume, the combined effects of blossom and crop load adjustment to 100 blossom clusters/tree followed by fruitlet adjustment to 6 fruit/cm2 TCSA and below will induce consistent annual production for ‘Honeycrisp’.

Nitrogen Fertilizer Influences Fruit Quality, Soil Nutrients and Cover Crops, Leaf Color and Nitrogen Content, Biennial Bearing and Cold Hardiness of ‘Golden Delicious’

ABSTRACT Four rates of ammonium nitrate (NH4NO3) (0, 151, 454, and 908 g actual N/tree) were applied each spring for 6 years to ‘Golden Delicious’ (Malus domestica) apple trees. High rates of nitrogen (N) increased N concentration of Orchardgrass (Dactylis glomerata) blades and increased cover-grass growth whereas various legume species were prevalent at the low rates. Leaf N in spur or mid-terminal leaves increased yearly, and was related to leaf color by visual comparison and reflectance. Fruit from the higher N rates had greener peel and lower firmness, soluble solids content and titratable acidity. In vitro freeze tests indicated trees fertilized with lower rates of N were more cold hardy during the fall, winter and spring than those receiving the higher rates. In a similar long-term study on ‘Delicious,’ cold hardiness was related not only to seasonal temperature cycles and shoot dry matter, but to total sugars and sorbitol content in wood or sap.

Effect of Leaf Number and Area on the Fruit Growth of Regular and Biennial Bearing Mango (Mangifera indica L.) Grown Under North Indian Conditions

The optimum leaf number required for normal fruit growth in the regular bearing mango cultivar ‘Amrapali’ and the biennial bearing cultivars ‘Chausa’, ‘Dashehari’ and ‘Langra’ were studied by isolating individual fruits with known numbers of supporting leaves by shoot girdling at the time of fruit set. There were significant differences in the leaf area (249.01-1817.10 cm2), fresh weight (7.0-77.0 g) and dry weight (3.7-50.0 g) of leaves on shoots having 30, 20, 10 and 5 leaves as compared with control in different cultivars. In both types of cultivars, there was a progressive reduction in fruit size in terms of total fruit, pulp, peel, and seed weight with decreasing numbers of supporting leaves, however, a minimum reduction (2.4%) in fruit growth in ‘Amrapali’ was noticed with 30 supporting leaves. A nonsignificant difference in photosynthetic rate with varying number of leaves was found but its efficiency in leaves was higher in ‘Amrapali’ as compared with biennial bearing cultivars. Starch accumulation in the leaves was reduced by shoot girdling. The stomatal resistance of the leaves of girdled shoots was comparable with that of leaves on control shoots. In all the cultivars except ‘Amrapali’ it was observed that 30 leaves, the maximum retained on a shoot, could not support the growth of a single fruit to normal size. The data on rate of photosynthesis in different pool size of leaves and fruit growth in girdled and nongirdled shoots clearly show that fruit development depends not only on the current assimilates but also to a great extent on reserves. A 14CO2 feeding experiment showed a higher rate of carbon fixation in the leaves of girdled shoots than in the control shoots, but the translocation of 14C assimilated to the developing fruits on the girdled and control shoots was comparable. The results also indicated that developing fruits are major sinks for current photosynthates as more than 60 percent of the 14C exported from the treated leaf was found in the fruit in all instances.

ORGANIC FRUIT PRODUCTION IN EUROPE: SUCCESSES IN PRODUCTION AND MARKETING IN THE LAST DECADE, PERSPECTIVES AND CHALLENGES FOR THE FUTURE DEVELOPMENT

The organic market has grown exponentially in Europe during the last ten years. However, the organic fruit industry in European states still has a relatively low market share of less than 1-5% compared with organic vegetables, milk and eggs that have achieved market shares of close to 10% of the total market. As well, conventional fruit growers still hesitate to respond to the generally good organic market demand. A major reason for this behaviour is the continuing high production risk due to less availability of effective management tools for the control of pests, diseases, weed and biennial bearing. The key pests and diseases in apple and pear include scab, sooty blotch, and fire blight as well as rosy apple aphid, pear sucker and codling moth, as well as post-harvest diseases like Gloeosporium rot. Another reason that holds up organic fruit expansion is that in fruit production, in contrast to milk or wheat, new and organic-specific marketing attempts are necessary for organic cultivars, less cosmetic “beauty”, etc.) but are presently scarce. In an ideal organic production system, all possible measures that lead to improved stability and self-regulation of the agro-ecological system have to be implemented (e.g. resistant cultivars, bio-diversity areas, lower planting densities, measures to avoid inoculum build-up, soil fertility). At present, most organic orchards have almost the same design as found in conventional production and often do not include system stabilising elements. Therefore, organic fruit production still depends largely on direct pest and disease control methods. In the last decade effective compounds and techniques have been developed such as Neem preparations, granulosis viruses, and mating disruption to control pests. Some new plant protection techniques e.g. clay powders, resistance inducers, better spray technique and spray timing models have been introduced. The introduction of new equipment, compounds, cultivars and decision support systems will further improve yield stability. However, for other limiting factors, such as weed competition, crop load regulation and market demands in respect to quality, innovative solutions have to be developed. The challenge for the future is to build up a credible (“true-organic”) and high quality multi-factor oriented organic fruit production that combines single factor solutions to a self-regulating, and possibly even organic pesticide-free, production system. Progress in this direction will lead to innovative organic production and marketing concepts that are clearly different from conventional ones. To achieve these goals, creative efforts along the whole chain involving producers, consumers, retailers, advisory services and researchers are essential.

Naphthaleneacetic Acid, Ethephon, and Gibberellin A4 + A7 Have Variable Effects on Flesh Firmness and Return Bloom of Apple

Experiments were conducted in commercial apple (Malus ×domestica) orchards in the southeastern U.S. between 1998 and 2006 with the primary objective of evaluating the effects of naphthaleneacetic acid (NAA) and ethephon on return bloom. NAA increased return bloom in six of 10 experiments, whereas ethephon increased return bloom in four of seven experiments. Four biweekly applications of 5 ppm NAA during June and July (early summer NAA) increased return bloom more consistently than fewer applications. Four weekly preharvest applications of 5 ppm NAA increased return bloom of ‘Delicious’ and ‘Golden Delicious’ as effectively as early summer applications. Combining NAA and ethephon in early summer sprays did not consistently increase return bloom compared with either material alone. The flower cluster density of ‘Golden Delicious’ in the year of treatment had a negative effect on return bloom that was more pronounced on control trees than trees sprayed 5 weeks after bloom with 444 ppm ethephon (48 fl oz/acre Ethrel). Combining four early summer sprays of 316 ppm ethephon (24 fl oz/acre Ethrel) with 15 ppm gibberellin A4 + A7 (GA4+7) increased return bloom of ‘Cameo’ but had no effect on return bloom of ‘Mutsu’ or ‘Golden Delicious’. Growth regulator treatments did not have a consistent effect on fruit firmness in the year of treatment. Naphthaleneacetic acid or ethephon treatments in the on year of a biennial bearing cycle can promote return bloom of apple spurs. However, the positive effect on return bloom may be minimal in cultivars with a strong natural tendency toward biennial bearing or when bloom or initial fruit set are heavy in the year of treatment.

Seven-year orchard performance of eleven new apple cultivars from Holovousy in comparison with some commonly grown ones

 In an orchard trial that was established in the spring of 1999 on M 9 rootstock at the spacing of 4 × 1 m, eleven new apple cultivars bred in Holovousy (Angold, Julia, Nabella, Primadela, Produkta, Resista, Rubinstep, Rucla, Selena, Vysočina and Zuzana) were evaluated in comparison with three standard varieties (Gala, Golden Delicious and Jonagold) and another two with resistance to scab (Rosana and Topaz). In the first three years, the incidence of scab and mildew was evaluated under limited chemical protection. In 2000–2005 on each of 10 randomly selected trees of each cultivar, the time of flowering and optimum harvest ripening were recorded, flower set and fruit sets were rated, yield per tree and weight of 10 fruit samples were measured. Trunk diameter was measured between 2002 and 2005. The early summer apple Julia had the healthiest state and it was recommended for organic growing. Selena was the most precocious, the least vigorous and had the highest crop efficiency. The highest annual yields per tree were recorded with Produkta, but this cultivar had the highest proportion of trees with biennial bearing. Primadela achieved the highest cumulative yields, whereas Angold brought the largest fruits on average. With the obtained results, the evaluated cultivars were characterised by some important features or recommendations for growers.