Reduced Fruit Size Research Articles

The rootstock effects on vigor, production and fruit quality in sweet cherry (Prunus avium L.)

BACKGROUND: New sweet cherries rootstocks and cultivars can be valorized on the market if they express improved plant yield efficiency and fruit quality, and also including highest content of antioxidant compounds (mainly anthocyanins but also significant amounts of phenolic acids and flavonols). OBJECTIVE: The goal of this study was to compare the effect of 10 new rootstock genotypes, now available for cherry, on plant growth and fruit quality of the cultivar “Sweetheart”, a very late auto-fertile sweet cherry cultivar. METHODS: Plants vegetative and productive parameters, as well as fruit sensorial quality, were measured during a 5-year cycle (2011–2015), while fruit nutritional quality was investigated for the last 3 years (2013–2015). RESULTS: For the agronomical traits, the vigorous rootstock Adara/Major and intermediate Gisela 6 stands out for the plant yield. From the qualitative point of view, the intermediate MaxMa 14 and Gisela 6, and the dwarf Gisela 5, differed for reduced fruit size but with optimal sugar/acid ratio. The higher fruit nutritional value were detected for “Sweetheart” trees grafted on Adara/Major (vigorous), the best MaxMa 14 (weaker) and Gisela 5 (dwarfing) rootstocks. CONCLUSIONS: There is not a univocal combination between the scion and rootstock equally valid for all the considered parameters. The rootstock capable of ensuring good yields, sensorial and nutritional quality is Adara/Major. From the productive and qualitative point of view, Gisela 6 is well adapted to these conditions, while MaxMa 14 rootstock stands out for nutritional quality, although induces a high reduction of vigor, poor vegetative renewal and low average fruit weight.

Flower traits change in response to infection with ‘Candidatus Phytoplasma mali’ in Nicotiana tabacum as model system

Flower traits such as flower colour, shape and volatile bouquet are shaped by a number of different factors, among them the interactions with pathogens. Infection with the ‘Candidatus Phytoplasma mali’ is associated with apple proliferation disease in Malus x domestica, a serious threat for commercial apple farming. Apple proliferation induces a range of symptoms on the leaves and a very reduced fruit size. However, the effects of this phytoplasma infection on floral traits are unknown. The phytoplasma presence was traced in different flower parts of the model system Nicotiana tabacum and changes in the floral reproductive tissue and other floral traits were explored. ‘Ca. P. mali’ was detected in floral tissues and seeds, and the floral traits changed in response to the infection. If this finding holds for M. domestica, pollinators may be able to discriminate between healthy and infected apple flowers, and their behaviour and thus pollination service may change as a consequence.

Canopy factors influencing sunburn and fruit quality of Japanese plum (Prunus salicinaLindl.)

High irradiance and high temperatures decrease Japanese plum (Prunus salicina Lindl.) quality by causing sunburn. We manipulated orchard conditions to determine how resultant light and temperature affected fruit quality and sunburn. In the 2013/14 season, early summer pruning, late pruning and a no pruning control were applied in an ‘African Delight’ plum orchard trained to a staggered V trellising system in the Western Cape Province of South Africa. In 2014/15, 20% shade net was incorporated during the hottest part of the season in a split plot design. Shade net and a no shade net control formed the main plots while pruning treatments were subplots. Photosynthetic photon flux (PPF), fruit surface temperature (FST) and sunburn were progressively assessed on two hourly intervals on typically hot days for upper, mid and lower canopy positions. PPF and FST generally decreased from top to bottom of the canopy. Upper canopy positions had bigger and softer fruit with higher sunburn incidence and higher total soluble solids (TSS). Fruit that developed sunburn received >50% PPF of full sun on average while average FST exceeded 35°C. Early summer pruning improved early light penetration but enabled vegetative regrowth for filtered light during the hottest part of the season resulting in bigger and redder fruit with higher TSS and low sunburn. Delayed pruning increased sunburn with no increase in fruit size, while the control delayed fruit maturity and reduced fruit size. The shade net reduced sunburn caused by delayed summer pruning. While it was apparent that proper timing of orchard light manipulation is essential, the use of shade net still has to be evaluated over the entire growing season to ascertain its full value.

Arabidopsis EOD3 homologue PaCYP78A6 affects fruit size and is involved in sweet cherry (Prunus avium L.) fruit ripening

Sweet cherry (Prunus avium L.) is an important commercial fruit crop cultivated in temperate areas. Fruit size is an influential agronomical trait in the modern horticultural breeding of sweet cherry because it directly affects the plant’s economic value. However, the genetic mechanisms underlying the control of fruit size are largely unknown. Here, we isolated and functionally characterized the sweet cherry cytochrome P450 gene CYP78A6, Arabidopsis EOD3/CYP78A6 homologue gene. Expression profiles showed that PaCYP78A6 was highly expressed in flowers and fruits. Silencing PaCYP78A6 using tobacco rattle virus-induced gene silencing (TRV-VIGS) reduced fruit size by decreasing mesocarp cell volume and expansion during fruit growth and development. In contrast, the overexpression of PaCYP78A6 in Arabidopsis resulted in increased silique and seed sizes, and PaCYP78A6 can recover the phenotype of cyp78a6 mutant. Silencing of PaCYP78A6 delayed fruit ripening and downregulated the ripening-related genes expressed in sweet cherry fruit. Moreover, PaCYP78A6 acts redundantly with PaCYP78A9 to effect fruit size. Thus, PaCYP78A6 appears to regulate the fruit size of sweet cherry during fruit growth and development and is involved in fruit ripening. This work provides new insights into the molecular mechanisms of a gene affecting fruit development and ripening in P. avium.

The Effect of Irrigation Frequency, Phosphorus Fertigation, and Cultivar on Levels of Phenolic Compounds in Sweet Cherries

This work examined the effect of irrigation frequency and phosphorus (P) fertigation on the levels of phenolic compounds present in two sweet cherry cultivars, ‘Skeena’ and ‘Cristalina’, over three growing seasons (2012–14). Two irrigation treatments were tested: a high irrigation frequency (I1) and a low irrigation frequency (I2). Both irrigation treatments applied the same quantities of water [100% evapotranspiration (ET)], but the high irrigation frequency applied water four times daily (0300, 0900, 1500, and 2100 hr) whereas the low irrigation frequency was applied at one time (0900 hr) every second day. Three soil management treatments were investigated, including 1) an unmulched control receiving no P, 2) a 10-cm waste wood mulch receiving no P, and 3) a treatment involving annual fertigation of 20 g P/tree at full bloom as ammonium polyphosphate. It was determined that cultivar was the most important factor affecting levels of phenolic compounds in sweet cherries, with generally greater levels associated with ‘Skeena’. The effect of different irrigation and fertilization strategies showed less promising results in terms of influencing levels of phenolic compounds. Both severe and mild water stress did not show an appreciable influence on increasing levels of phenolic compounds in cherries. Furthermore, severe water stress, which occurred during 2012, was associated with the lowest annual concentration of phenolic compounds and an economically unacceptable reduction in fruit size. Phosphorus fertigation influenced cherry phosphorus status positively by increasing leaf and fruit P concentrations consistently, yet these fruit exhibited lower levels of phenolic compounds.

English

Climate variability and change presents enormous risk to agricultural production globally due to the impacts on yields. While global scholarship on climate change impacts and adaptation measures on agriculture has been well-documented, little is known about climate and pineapple production. This study examined smallholder pineapple farmers experiences of climate variability and change on production, as well as ranked adaptation options using data from both primary and secondary sources. The primary data consisted of survey and focus group discussions in four major pineapple growing districts in Ghana. The analysis revealed that pineapple farmers experience climate variability and change evidenced mainly through irregular rainfall patterns and rising temperatures. These changes cause reduction in fruit size and yield, change in colour and taste, and consequently, reduction in income from pineapple production. Although diverisification of livelihood away from pineapple cultivation emerged as the main adaptation option employed by smallholder pineapple farmers studied, it has the potential to reduce pineapple production in Ghana. For improvement and sustainability of the pineapple industry in Ghana, future studies should investigate the vulnerability of the production system to changing climate to effectively identify exposure and sensitivity of pineapple production to climatic changes. This will in effect, enhance identification of measures that will improve production as well as promote adaptation of the smallholder production systems to climate variability and change. Key words: Climate variability, change, smallholder farmers, adaptation, pineapple production.

Fast detection by loop-mediated isothermal amplification (LAMP) of the three begomovirus species infecting tomato in Panama

Potato yellow mosaic Panama virus (PYMPV), Tomato leaf curl Sinaloa virus (ToLCSiV) and Tomato yellow mottle virus (TYMoV) of genus Begomovirus (family Geminiviridae) are the only three begomovirus species detected infecting tomato (Solanum lycopersicum L.) in Panama. PYMPV, ToLCSiV and TYMoV induce symptoms of stunting, yellowing, curling, distortion of leaves and reduction of fruit size and cause important economic loses. A loop-mediated amplification under isothermal conditions (LAMP) assay was developed for the individual detection of these three begomovirus species by using a set of three primer pairs specific per each one of them. Amplification products were visualized by gel electrophoresis or direct Gel-Red staining of DNA into the reaction tube. PYMPV, ToLCSiV and TYMoV were detected in total DNA extracts obtained from different plant tissues such as leaves, stems, flowers, fruits and roots of infected tomato plants collected in different production regions of Panama. LAMP sensitivity was similar to that of conventional PCR but, the first procedure was faster and cheaper than the last one. Moreover, all three viruses were successfully detected by LAMP and not by conventional PCR from sap extracts obtained from leaf tissues of infected tomato plants which were embedded into 3MM Whatman paper and stored several days, facilitating the samples processing as well as the material movement among different laboratories. Therefore, LAMP is a specific, rapid and cheap procedure to detect all three begomoviruses infecting tomato in Panama and it is suitable for field surveys and sanitation programs.

Xylella fastidiosa: an examination of a re-emerging plant pathogen.

Bacteria; Gammaproteobacteria; family Xanthomonadaceae; genus Xylella; species fastidiosa. Gram-negative rod (0.25-0.35×0.9-3.5μm), non-flagellate, motile via Type IV pili-mediated twitching, fastidious. Xylella fastidiosa has a broad host range that includes ornamental, ecological and agricultural plants belonging to over 300 different species in 63 different families. To date, X.fastidiosa has been found to be pathogenic in over 100 plant species. In addition, it can establish non-symptomatic associations with many plants as a commensal endophyte. Here, we list the four distinct subspecies of X.fastidiosa and some of the agriculturally relevant diseases caused by them: X.fastidiosa ssp. fastidiosa causes Pierce's disease (PD) of grapevine (Vitis vinifera); X.fastidiosa ssp. multiplex causes almond leaf scorch (ALS) and diseases on other nut and shade tree crops; X.fastidiosa ssp. pauca causes citrus variegated chlorosis (CVC) (Citrus spp.), coffee leaf scorch and olive quick decline syndrome (OQDS) (Olea europaea); X.fastidiosa ssp. sandyi causes oleander leaf scorch (OLS) (Nerium oleander). Significant host specificity seemingly exists for some of the subspecies, although this could be a result of technical biases based on the limited number of plants tested, whereas some subspecies are not as stringent in their host range and can infect several plant hosts. Most X.fastidiosa-related diseases appear as marginal leaf necrosis and scorching of the leaves. In the case of PD, X.fastidiosa can also cause desiccation of berries (termed 'raisining'), irregular periderm development and abnormal abscission of petioles. In olive trees affected with OQDS, leaves exhibit marginal necrosis and defoliation, and overall tree decline occurs. Plants with ALS and OLS also exhibit the characteristic leaf scorch symptoms. Not all X.fastidiosa-related diseases exhibit the typical leaf scorch symptoms. These include CVC and Phony Peach disease, amongst others. In the case of CVC, symptoms include foliar wilt and interveinal chlorosis on the upper surfaces of the leaves (similar to zinc deficiency), which correspond to necrotic, gum-like regions on the undersides of the leaves. Additional symptoms of CVC include defoliation, dieback and hardening of fruits. Plants infected with Phony Peach disease exhibit a denser, more compact canopy (as a result of shortened internodes, darker green leaves and delayed leaf senescence), premature bloom and reduced fruit size. Some occlusions occur in the xylem vessels, but there are no foliar wilting, chlorosis or necrosis symptoms . USEFUL WEBSITES: http://www.piercesdisease.org/; https://pubmlst.org/xfastidiosa/; http://www.xylella.lncc.br/; https://nature.berkeley.edu/xylella/; https://ec.europa.eu/food/plant/plant_health_biosecurity/legislation/emergency_measures/xylella-fastidiosa_en.

Molecular evidence for the occurrence of tomato leaf curl New Delhi virus on chayote (Sechium edule) in southern India.

During 2012-2014, mosaic disease on chayote in the farmers field of Kodaikanal region (high altitude zone) of Tamil Nadu was observed. The disease was characterized with severe mosaic, cupping and enation on leaves with reduced fruit size. Disease was found to causes an yield loss of more than 60% with the maximum disease incidence of 100% for the past 5years consecutively. Preliminary serological and molecular screening indicated the association of begomovirus with the disease. Complete nucleotide sequence and phylogenetic analysis of DNA A revealed the identity of the virus as tomato leaf curl New Delhi virus (ToLCNDV). In recombination analysis study, the major parent was identified as ToLCNDV from Pakistan infecting tomato. Thus the present finding confirms expansion of new geographical region and host for ToLCNDV causing mosaic disease on chayote from Tamil Nadu. To our knowledge this is the first confirmed report for the occurrence of ToLCNDV on chayote in southern India.

Interaction of Maximum Daily Trunk Shrinkage and Fruit Quality in European Plum

Maximum daily trunk shrinkage (MDS) has been suggested as an appropriate indicator of plant water status because it is closely related to stem water potential. Interaction of MDS and fruit quality was studied in plum (Prunus domestica L. ‘Jojo’/Wavit and ‘Tophit plus’/Wavit) in temperate climate. According to the MDS data, trees were grouped as low MDS (LMDS) and high MDS (HMDS). Fruit quality was analysed during fruit development (95, 103, 117 DAFB for ‘Jojo’ and 99, 112, 121 DAFB for ‘Tophit plus’) before commercial harvest. Fruit picked at commercial harvest (137 DAFB and 140 DAFB for ‘Jojo’ and ‘Tophit plus’, respectively) were stored at 2 ± 0.5 °C (90 ± 2% RH) for 28 days, and 2 days shelf life at 20 °C providing 6 measuring dates postharvest. Results confirmed that MDS was positively correlated with water vapour pressure deficit also in the apparent temperate, semi-humid climate. Transpiration of fruit from high crop load and resulting HMDS trees, which can be assessed as physiologically drought, was low compared to that of fruit from LMDS trees. Furthermore, HMDS tree grown plums had enhanced soluble solids and dry matter contents with a tendency of reduced fruit size.

First Occurrence of Sternochetus mangiferae (Fabricius) (Coleoptera: Curculionidae) in Brazil.

Specimens of the mango stone weevil Sternochetus mangiferae (Fabricius) (Coleoptera: Curculionidae) were found in fruits of mango from a tree in the residential area of the Rio de Janeiro, RJ. This is the first report of the S. mangiferae in Brazil, currently regulated as an absent quarantine pest in the country. A taxonomist specialized in Curculionidae confirmed the identification based on morphological diagnostics characteristics. This detection is a relevant finding, because Brazil is a major producer and exporter of mango and the main areas of mango for exportation are located very far from this detection point. This pest damages seed and embryo of mango fruits and it causes reduction of fruit size and its premature dropping. The detection was notified to the Plant Health Department, division of the Brazilian Ministry of Agriculture, Livestock and Food Supply (MAPA), which is the National Plant Protection Organization of Brazil.

Influence of Irrigation Scheduling Using Thermometry on Peach Tree Water Status and Yield under Different Irrigation Systems

Remotely-sensed canopy temperature from infrared thermometer (IRT) sensors has long been shown to be effective for detecting plant water stress. A field study was conducted to investigate peach tree responses to deficit irrigation which was controlled using canopy to air temperature difference (ΔT) during the postharvest period at the USDA-ARS (U.S. Department of Agriculture, Agricultural Research Service) San Joaquin Valley Agricultural Sciences Center in Parlier, California, USA. The experimental site consisted of a 1.6 ha early maturing peach tree orchard. A total of 18 IRT sensors were used to control six irrigation treatments including furrow, micro-spray, and surface drip irrigation systems with and without postharvest deficit irrigation. During the postharvest period in the 2012–2013 and 2013–2014 growing seasons, ΔT threshold values at mid-day was tested to trigger irrigation in three irrigation systems. The results showed that mid-day stem water potentials (ψ) for well irrigated trees were maintained at a range of −0.5 to −1.2 MPa while ψ of deficit irrigated trees dropped to lower values. Soil water content in deficit surface drip irrigation treatment was higher compared to deficit furrow and micro-spray irrigation treatments in 2012. The number of fruits and fruit weight from peach trees under postharvest deficit irrigation treatment were less than those well-watered trees; however, no statistically significant (at the p < 0.05 level) reduction in fruit size or quality was found for trees irrigated by surface drip and micro-spray irrigation systems by deficit irrigation. Beside doubles, we found an increased number of fruits with deep sutures and dimples which may be a long-term (seven-year postharvest regulated deficit irrigation) impact of deficit irrigation on this peach tree variety. Overall, deployment of IRT sensors provided real-time measurement of canopy water status and the information is valuable for making irrigation management decisions.

Biomass accumulation, plant biometrics and fruit production of watermelon according to changes in source/drain relations

O objetivo deste estudo foi avaliar o acúmulo de biomassa, biometria de plantas e produção de melancia submetida a mudanças nas relações de fonte e dreno. O experimento foi conduzido na área experimental do CCTA / UFCG, PB, Brasil, no período de setembro a dezembro de 2013. Foram utilizadas sementes da cultivar "Sweet carmesim" e os tratamentos foram distribuídos em parcelas divididas em 2x4, com quatro Repetições. As parcelas foram constituídas por plantas cultivadas com diferentes números de frutos (1 e 2) e as subparcelas com poda dominante em diferentes estações de cultivo (25, 30, 35 e 40 dias após o transplante - DAT). As características de crescimento foram avaliadas. As modificações induzidas nas melancias por poda dominante do caule e desbaste do fruto proporcionaram mudanças nas partições de fotoassimilados e na produção de plantas. As modificações induzidas nas melancias pela poda dominante do caule e desbaste do fruto proporcionaram mudanças no acúmulo de biomassa, na biométrica e na produção de melancia nas frutas. O desbaste do dreno da planta (fruto) resultou em maior acúmulo de folhas de folhas quando comparado com o fruto, proporcionando uma massa seca total maior. As plantas cultivadas com duas frutas apresentaram o maior índice de colheita ea maior produção, com tamanho de fruto reduzido. A poda de mudas de mudas aos 40 dias após o transplante promoveu maior crescimento e produção de frutos de melancia.

Nitric Oxide Overproduction in Tomato shr Mutant Shifts Metabolic Profiles and Suppresses Fruit Growth and Ripening.

Nitric oxide (NO) plays a pivotal role in growth and disease resistance in plants. It also acts as a secondary messenger in signaling pathways for several plant hormones. Despite its clear role in regulating plant development, its role in fruit development is not known. In an earlier study, we described a short root (shr) mutant of tomato, whose phenotype results from hyperaccumulation of NO. The molecular mapping localized shr locus in 2.5 Mb region of chromosome 9. The shr mutant showed sluggish growth, with smaller leaves, flowers and was less fertile than wild type. The shr mutant also showed reduced fruit size and slower ripening of the fruits post-mature green stage to the red ripe stage. Comparison of the metabolite profiles of shr fruits with wild-type fruits during ripening revealed a significant shift in the patterns. In shr fruits intermediates of the tricarboxylic acid (TCA) cycle were differentially regulated than WT indicating NO affected the regulation of TCA cycle. The accumulation of several amino acids, particularly tyrosine, was higher, whereas most fatty acids were downregulated in shr fruits. Among the plant hormones at one or more stages of ripening, ethylene, Indole-3-acetic acid and Indole-3-butyric acid increased in shr, whereas abscisic acid declined. Our analyses indicate that the retardation of fruit growth and ripening in shr mutant likely results from the influence of NO on central carbon metabolism and endogenous phytohormones levels.

Nitrogen Fertilization Strategies for the ‘Hass’ Avocado that Increase Total Yield Without Reducing Fruit Size

Effects of nitrogen (N) fertilizer application times and rates on ‘Hass’ avocado (Persea americana) yield and fruit size were determined to resolve whether a single dose of soil-applied N [1x N (25 lb/acre)] at each of the five key stages of tree phenology (January, April, July, August, and November) (control) was as efficacious as soil-applied 2x N (50 lb/acre) at one or two key stages or soil- or foliar-applied 3x N (75 lb/acre) at only one stage. All trees received soil-applied N at 125 lb/acre as ammonium nitrate (NH4NO3) annually; trees receiving 2x or 3x N received the remaining N divided evenly at the same phenological stages (months) as trees receiving five 1x N applications. The importance of supplying N during the summer, when June drop, exponential fruit growth, vegetative shoot growth, and floral initiation occur, was determined by testing soil-applied 0.8x N in July plus August only (40 lb/acre N as NH4NO3 annually). Application time proved an important determinant of total yield. Yield of commercially valuable size (CVS) fruit was correlated with total yield (r = 0.80, P < 0.0001). Four-year cumulative total yields were equal for trees receiving soil-applied 1x N at five key phenological stages and trees receiving soil-applied 2x N in April and 18.75 lb/acre N at the four other stages (months). However, trees receiving soil-applied 2x N in April plus November and only 8.3 lb/acre N in the three other months, in particular July and August, had significantly lower 4-year cumulative total yields (P = 0.0362). Additional evidence of the importance of meeting avocado tree N demand in the summer is that trees receiving only 40 lb/acre N split in July plus August produced 4-year cumulative total yields equal to trees receiving 25 lb/acre N at the five key phenological stages; lower annual N would reduce fertilizer expense and protect the environment.

Interference of spray volume, fruit growth and rainfall on spray deposits in citrus black spot control periods

ABSTRACT: Citrus black spot (CBS) caused by Guignardia citricarpa is one of the most serious Brazilian citrus diseases. This study aims to assess the interference of three application volumes in spray deposition citrus fruit, as well as fruit growth and rainfall effects on spray deposit reduction during the CBS control period. The experiment was carried out in a commercial citrus orchard, with sixteen-year-old trees of the Valencia variety, in Mogi Guaçu, São Paulo State, Brazil. The spray volumes were: 3.5 (1333L ha-1), 4.5 (1714L ha-1) and 8.5 (3238L ha-1) litres per tree, sprayed by an airblast sprayer using fungicides at recommended periods for disease control. The spray deposition quantification and residue was done by spectrophotometry using a copper oxychloride tracer. Samples were collected in three height zones of the tree (top, middle and bottom) and placed between trees on line plantation. Spray depositions were significantly smaller in the first application as a consequence of reduced fruit size. The spray losses on average for each day of rainfall ranged from 4.0 to 5.7%. There was no significant difference between application volumes regarding spray deposition on citrus fruit,which makes possible the reduction of application volumes, however, it is necessary to improve spraying techniques for the top zone of the citrus tree.

How microRNA172 affects fruit growth in different species is dependent on fruit type

ABSTRACTmicroRNA172 (miR172) expression has been shown to have a positive effect on Arabidopsis fruit (siliques) growth. In contrast, over-expression of miR172 has a negative influence on fruit growth in apple, resulting in a dramatic reduction in fruit size. This negative influence is supported by the results of analyzing a transposable element (TE) insertional allele of a MIR172 gene that has reduced expression of the miRNA and is associated with an increase in fruit size. Arabidopsis siliques are a dry fruit derived from ovary tissues, whereas apple is a fleshy pome fruit derived mostly from hypanthium tissues. A model has been developed to explain the contrasting impact of miR172 expression in these two plant species based on the differences in their fruit structure. Transgenic apple plants with extremely high levels of miR172 overexpression produced flowers consisting of carpel tissues only, which failed to produce fruit. By comparison, in tomato, a fleshy berry fruit derived from the ovary, high level over-expression of the same miR172 resulted in carpel-only flowers which developed into parthenocarpic fruit. These results further indicate that the influence of miR172 on fruit growth in different plant species depends on its fruit type.

Effects of applying variable temperature conditions around inflorescences on fertilization and fruit set in date palms

Control of pollination and fertilization in date palm is essential for the development of high-quality fruit. Pollen is harvested from male trees and mechanically applied to inflorescences on female trees. An overly high rate of fruit set may cause excessive fruit load, requiring expensive fruit thinning to prevent reduction in fruit size and marketability. On the other hand, inefficient pollination results in lower yield. Although the female flower has three separate carpels, only one develops into a fruit; the others degenerate. Non-fertilized flowers may develop into parthenocarpic singlet or triplet fruit, which have no commercial value. Environmental conditions affect fertilization and fruit development. The current study characterizes fertilization and early fruit development in date palm under different temperature conditions. The date palm is a very large tree. To study environmental effects on its reproductive biology, special units, termed “modular phytotrons”, were designed for this research. They were assembled on pollinated inflorescences of whole ‘Medjoul’ date trees in the orchard, enabling modification of temperature regimes in planta. Pollen-tube growth, fertilization, fruitlet formation and carpel degeneration, as well as early development of parthenocarpic fruit were defined and characterized by macro- and microscopic analyses. Relatively low temperatures applied during plant fertilization significantly decreased pollen germination rate, enhanced formation of parthenocarpic fruit and reduced normal fruit development. The significance of these results to horticultural practices during fertilization and fruit thinning is discussed.

EVALUATION OF KRYMSK®5 (VSL-2) AND KRYMSK®6 (LC-52) AS ROOTSTOCKS FOR SWEET CHERRY 'KORDIA'

During a 6-year period the growth and production of trees of sweet cherry ‘Kordia’ grafted on rootstocks Krymsk®5 (VSL-2), Krymsk®6 (LC-52) and GiSelA 5 were compared. Shoot growth, increase in trunk diameter and intensity of flowering of ‘Kordia’ were almost similar on all three stocks. Fruit production per tree was significantly higher for ‘Kordia’ on rootstocks Krymsk®6 and GiSelA 5, while that on Krymsk®5 was similar to that on GiSelA 5. Both Krymsk rootstocks gave a small reduction in fruit size, and a slightly lower sugar and acid content. With Krymsk®6, smaller fruit size was related to the higher fruit load of the trees and may be avoided by thinning the tree to the optimum crop load. With Krymsk®5, the reduction in fruit size could not be attributed to overcropping. Fruit cracking, a big problem for cherry growers in areas with high risks of rain in the harvest period, occurred less on Krymsk®6 than on GiSelA 5 or Krymsk®5. Both Krymsk rootstocks produced significantly more root suckers than GiSelA 5. The highest numbers were observed for Krymsk®5, which produced on average 3.3 suckers per tree per during the first 6 years in the orchard. Krymsk®5 also developed burrknots. From this trial it is concluded that Krymsk®6 can be a good alternative rootstock to GiSelA 5, especially for less well drained soils and because its effect on reducing the occurrence of fruit cracking. However, because of its tendency to reduce fruit size, overcropping should be prevented. Therefore, Krymsk®6 is probably less suited for self-compatible cultivars than for cultivars setting fruit only after cross pollination.

A COMPARISON OF AGRONOMIC TREATMENTS TO IMPROVE AVERAGE BERRY SIZE IN EVERBEARING STRAWBERRIES (FRAGARIA × ANANASSA)

The total area of strawberry grown in the UK is nearly 5000 ha producing 110,000 t (DEFRA Basic Horticultural Statistics, 2011) of which approximately 40% is of everbearing cultivars. As everbearers are a very important component within the UK strawberry industry, it is essential to maximise the yield of class 1 berries for the growers. In many everbearer cultivars the average fruit size decreases as the season progresses. In 2010 and 2011 two trials were conducted to determine whether agronomic treatments could improve the average fruit size at harvest. The cultivar used for the study was ‘Finesse’, which is a recent release from East Malling Research that is becoming an important cultivar in the UK market place. Study 1 conducted in 2010 was designed to determine whether the removal of leaves and/or the removal of blooms could influence fruit size in the latter stages of harvest. In this study the oldest leaves of ‘Finesse’ were removed to a leaf area index (LAI) of 3.0 in an attempt to eliminate older, less-efficient leaves thereby diverting assimilates to enhance fruit size, while maintaining a full canopy of newer and more productive leaves. There was anecdotal evidence from UK growers that this treatment had been effective in some everbearing cultivars but this study concluded that a LAI of 3.0 and de-blooming three weeks after planting had the effect of reducing overall yield, due to a reduction in fruit size. Based on the same principle of relocating assimilates, study 2 conducted in 2011 compared four further treatments, which included a control, de-flowering at planting, picking only large berries followed by truss removal, and removing whole trusses from the plants. Harvesting continued until end of October 2011. Results showed that not harvesting the smaller berries increased significantly the percentage of larger fruit (above 45 mm) produced per plant. The production of larger berries in that treatment was also shifted towards the end of the harvest but that result was not consistent across the four replications.