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A quick and accurate sampling method for determining yield in peach orchards could lead to better crop management decisions, more accurate insurance claim adjustment, and reduced expenses for the insurance industry. Given that sample size depends exclusively on the variability of the trees on the orchard, it is necessary to have a quick and objective way of assessing this variability. The aim of this study was to use remote sensing to detect the spatial variability within peach orchards and classify trees into homogeneous zones that constitute sampling strata to decrease sample size. Five mature peach orchards with different degrees of spatial variability were used. A regular grid of trees was established on each orchard, their trunk cross-sectional area (TCSA) was measured, and yield was measured as number of fruits/tree on the central tree of each one of them. Red Vegetation Index (RVI) was calculated from aerial images with 0.25 m&middot, pixel&minus, 1 resolution, and used, either alone or in combination with TCSA, to delineate sampling strata using cluster fuzzy k-means. Completely randomized (CRS) and stratified samplings were compared through 10,000 iterations, and the Minimum Sample Size required to obtain estimates of actual production for three quality levels of sampling was calculated in each case. The images allowed accurate determination of the number of trees, allowing a proper application of completely randomized sampling designs. Tree size and the canopy density estimated by means of multispectral indices are complementary parameters suitable for orchard stratification, decreasing the sample size required to determine fruit count up to 20&ndash, 35% compared to completely randomized samples.

Aim: An advance in grapevine phenological stages (including ripening) is occurring worldwide due to global warming and, in the hottest seasons, already results in a lack of synchrony between sugar and phenolic ripeness, leading to unbalanced wines. In order to cope with this fact, a general effort is being made by researchers and growers aiming at delaying ripening through cultural practices, particularly under warm growing conditions, where these effects are more deleterious. The aim of this work is to evaluate to which extent severe trimming and enhanced competition of laterals can delay ripening in Tempranillo vineyards under semiarid conditions.Methods and results: The experiment took place during two consecutive seasons in Traibuenas (Navarra, Spain) in a cv. ‘Tempranillo’ vineyard trained to a vertical shoot positioned (VSP) spur-pruned bilateral cordon. Severe mechanical pruning was performed ca. 3 weeks after fruit-set in order to reduce leaf-to-fruit ratio, and in the trimmed plants, three irrigation doses were applied until harvest aiming at enhancing lateral growth, hypothesized to compete with ripening. All measurements were performed in six 10-vine replicates per treatment. Trimming significantly reduced leaf area and yield, resulting in higher water availability in trimmed plants. The whole ripening process was delayed by trimming: mid-veraison was delayed by about 5 days, and the delay in sugar accumulation and acid degradation was longer, differences being more marked in malic than in tartaric acid concentration. The use of increased irrigation levels compensated the losses in yield caused by trimming, enhanced laterals’ growth and implied an additional delay in ripening.Conclusion: trimming and increased irrigation had an additive effect in terms of delaying ripening, and they can be used jointly when that delay is needed.Significance and impact of the study: this study proves the potentiality of the joint use of trimming and increased irrigation to delay ripening, although it is necessary to analyze the implications the obtained delay has on other quality aspects. The lower anthocyanin and phenolic values observed in trimmed vines were not solely due to delayed ripening, as lower values were observed even when data were compared for a given total soluble solid content.

Source to sink size ratio, i.e.: the relative abundance of photosynthetically active organs (leaves) with regards to photosynthate demanding organs (mainly bunches), is widely known to be one of the main drivers of grape oenological quality. However, due to the difficulty of remote sink size estimation, Precision Viticulture (PV) has been mainly based on within-field zone delineation using vegetation indices. This approach has given only moderately satisfactory results for discriminating zones with differential quality. The aim of this work was to investigate an approach to delineate within-vineyard quality zones that includes an estimator of sink size in the data-set. The study was carried out during two consecutive seasons on a 4.2 ha gobelet-trained cv. 'Tempranillo' vineyard. Zone delineation was performed using Normalized Difference Vegetation Index (NDVI), soil apparent electrical conductivity (ECa) and bunch number (BN) data. These variables were considered separately, in pairs, or the three altogether, using fuzzy k-means cluster analysis for combinations. The zones delineated based on single variables did not allow a sufficient discrimination for grape composition at harvest, NDVI being the only variable that by itself resulted in zones that to some extent differed in grape composition. On the contrary, when two variables were combined, discrimination in terms of grape composition improved remarkably, provided the sink size estimation variable (BN) was included in the combination. Lastly, the combination of the three variables yielded the best discriminating zoning, improving slightly on those provided by NDVI + BN and ECa + BN combinations. Thus, the relevance of including a variable related to sink size (in this case the number of bunches per plant) has been confirmed, which makes its consideration highly advisable for any PV work aiming at zone delineation for grape quality purposes. This work was funded by the Dpt. Innovación, Industria & Empleo of the Government of Navarra (MODELVID, Ref: IIM11879.RI.1), by the Centro para el Desarrollo Tecnológico Industrial CDTI (Ref: IDI-20100729, co-funded by the European Union ERDF as part of the Operational Programme I+D+i Technology Fund 2007-2013) and by Fundación Fuentes Dutor. The Spanish Ministry of Education funded I.U. stage in SupAgro, Montpellier (EDU/2719/2011).

[Background and aims] Viral diseases in grapevines result in reduced vineyard performance, but it remains unclear to which extent some of their effects are direct or indirect, or if both kinds of effects co-occur. The aim of this work is to evaluate the effect of three virus diseases (GFLV, GLRaV and GFkV) on cv. Tempranillo., [Methods and results] A wide dataset that comprised yield components and grape composition of 531 cv. Tempranillo accessions for seven years was used, comparing their performance depending on the presence of each virus. GFLV showed the highest deleterious effects, followed by GLRaV-3, whereas GFkV had no effect. GLRaV-3 and, especially, GFLV effects were very relevant., [Conclusions] Regression analyses demonstrated that GFLV increases soluble solids (TSS) and colour density (CD) independently of yield reduction or advanced ripening, and causes higher pH independently of TSS. Similarly, GLRaV-3 detrimental effect on CD is not caused only by delayed ripening, and higher pH is associated to imbalanced ripening., [Significance of the study] Our results highlight that a detailed analysis of a wide agronomic dataset allows a better understanding of virus diseases, unveiling to which extent some of their effects are direct or indirect., This work has been performed within the following projects: “Selección y mantenimiento en campo de fenotipos del cv. Tempranillo de la D.O.Ca. Rioja; estudio de su contenido fenólico y mejora de su extracción” (1998, CDTI/ADER) and “Creación de un banco de germoplasma de cv. Tempranillo de Rioja. Contenido fenólico de las variedades autóctonas, optimización de la extracción y estabilización”. VIN00-043-C3 (2000, INIA).

4 Pags.- 2 Tabls. Articles derived from XIV EUCARPIA Symposium on Fruit Breeding and Genetics (Bologna,Italy. June 14-18 2015) . The definitive version is available at: http://www.actahort.org/index.htm, The description of phenotypic traits in apple cultivars is generally performed using internationally agreed descriptors such as UPOV guidelines, which defines for each trait several states of expression. However, it is not always possible to classify a cultivar unambiguously using those guidelines, because in practice the states are not clearly enough defined or the example cultivars are not always available in the collections. This work presents the results of a harmonization project performed by the teams responsible of the main apple germplasm collections in Spain. The objective was to develop a standardized method for the 57 traits included in the TG/14/9 UPOV guidelines for apple characterization, defining their states of expression in a clear and unambiguous way for Spanish germplasm. Phenotypic data collected for more than 1,600 accessions from Spanish collections were used and the method to define each state depended on the type of expression. For quantitative traits the number of states and their limits were defined according to the variability that exists within and between accessions. For qualitative traits, high-resolution images clearly depicting each state were selected. A standardized characterization protocol for the 57 traits of apple germplasm has been provided, enabling to comparing properly the phenotypes of Spanish genetic resources., This Project has been funded by the Spanish Ministry of Science and Innovation/National Institute for Agricultural and Food Research and Technology (RF2011- 00017-C05-00).

The influence of the species in spring frost sensibility was determined for the Prunus species peach (P. persica (L.) Batsch), sweet cherry (P. avium L.), almond (P. dulcis (Mill.) Webb/P. amygdalus Batsch), japanese plum (P. salicina Lindl.), and blackthorn (P. spinosa L.). The confidence intervals for lethal temperatures of 10% (LT10) and 90% (LT90) bud injury were also determined. In 2000 and 2001, seven frost treatments were made for each one of the phenological stages comprised between B (first swell) and I (jacket split) in two cultivars per each species. The relationships between frost temperature and the proportion of frost damaged buds for each cultivar, year, and phenological stage were adjusted to linear regression models. The 95% confidence intervals were also calculated. The spring frost hardiness order of the species, from the least to most hardy, was as follows: sweet cherry, almond, peach, japanese plum, and blackthorn. Despite the highly homogeneous nature of the frost and bud characteristics, the temperature range for a given injury degree was quite broad, since the confidence interval's breadth for LT10 was as high as about 3 °C and as high as about 6 °C for LT90. Consequently, when critical temperatures are used in making decisions as to when to begin active frost protection, a prudent measure would be to take the temperature references from the upper limits in the confidence intervals.

Fingerprinting information can be used to elucidate in a robust manner the genetic structure of germplasm collections, allowing a more rational and fine assessment of genetic resources. Bayesian model-based approaches are nowadays majorly preferred to infer genetic structure, but it is still largely unresolved how marker sets should be built in order to obtain a robust inference. The objective was to evaluate, in Pyrus germplasm collections, the influence of the SSR marker set size on the genetic structure inferred, also evaluating the influence of the criterion used to select those markers. Inferences were performed considering an increasing number of SSR markers that ranged from just two up to 25, incorporated one at a time into the analysis. The influence of the number of SSR markers used was evaluated comparing the number of populations and the strength of the signal detected, and also the similarity of the genotype assignments to populations between analyses. In order to test if those results were influenced by the criterion used to select the SSRs, several choosing scenarios based on the discrimination power or the fixation index values of the SSRs were tested. Our results indicate that population structure could be inferred accurately once a certain SSR number threshold was reached, which depended on the underlying structure within the genotypes, but the method used to select the markers included on each set appeared not to be very relevant. The minimum number of SSRs required to provide robust structure inferences and adequate measurements of the differentiation, even when low differentiation levels exist within populations, was proved similar to that of the complete list of recommended markers for fingerprinting. When a SSR set size similar to the minimum marker sets recommended for fingerprinting it is used, only major divisions or moderate (FST>0.05) differentiation of the germplasm are detected. This study was funded by INIA, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (Project grant number RF2004-008-C03- 00) (JBR), for the consumables and SSR analyses, and internal University funding.

Early definition of oenologically significant zones within a vineyard is one of the main goals of precision viticulture, as it would allow an increase in profitability through the adaptation of agronomic practices to the specific requirements of each zone, and/or segregation of the harvest into different batches to produce wines with different qualities. The aim of this work was to evaluate whether early grape sampling is a relevant tool for within-vineyard zone definition. The study was carried out in 2010 and 2011 in a 4.2 ha vineyard, where a grid of 60 sampling points was defined. 300-berry samples were picked from each sampling point after veraison and at harvest, post-veraison information being used to define zones within the vineyard after fuzzy k-means analysis and subsequent application of a zoning procedure that took into account membership degree and neighbourhood criteria. Two variations of the zoning procedure were used, standard (StdZ) and top (TopZ) zoning. Each was designed to meet different requirements of wineries; StdZ gave the same oenological relevance to all the zones, and TopZ differentiated the zones producing 'top class' grapes, minimizing the within-zone variability in the top-class zone. Grape composition obtained at harvest from the zones delineated post-veraison was compared. Zone delineation using post-veraison data was proved to be oenologically relevant, provided sampling is performed once veraison is completed. The two zoning algorithms designed were shown to be suitable for objective zone delineation according to the goals intended for each. This work was funded by the Dpt. Innovación, Industria & Empleo of the Government of Navarra (MODELVID, Ref: IIM11879.RI.1), by the Centro para el Desarrollo Tecnológico Industrial CDTI (Ref: IDI-20100729, co-funded by the European Union ERDF as part of the Operational Programme I+D+i Technology Fund 2007-2013) and by Fundación Fuentes Dutor. I.U. The Spanish Ministry of Education funded I.U. stage in SupAgro, Montpellier (EDU/2719/2011).

11 Pags.- 6 Tabls.- 2 Figs., Isoenzymes from grapevine woody stems and shoots were evaluated for their use in identification of varieties and clones. Plant extracts were separated by polyacrylamide gel electrophoresis. Isoenzyme analysis was carried out for esterases, peroxidases, catechol oxidase, glutamate oxalacetate transaminase and acid phosphatase. The plant material was grown and sampled at two localities in Spain, with different climatic conditions. Sampling was carried out bimonthly for two consecutive years in order to find out the influence of the environment and time of the year. Each isozyme system had a pattern defined by ‘fixed’ bands, that were always present at both localities and during the resting period of the plant (fall—winter). Esterases had a pattern with very few ‘fixed’ bands. Catechol oxidase was the most polymorphic system, thus being highly discriminating. The studied isoenzyme systems gave differences among varieties, although not among clones of the same variety. The use of this methodology for identification of grapevine plant material is discussed., This study has been carried out with financial support provided by 'Comisión Interministerial de Ciencia y Tecnologia' (C.I.C.Y.T.), Project AGR 0070-91-C01-C02.

Las colecciones nucleares de plantas pueden formarse a partir de la información obtenida en caracterizaciones morfológicas, agronómicas o eco-geográficas, así como a partir de caracterizaciones bioquímicas o moleculares. Un aspecto poco estudiado de la formación y validación de colecciones nucleares es la capacidad de éstas para conservar la estructura y diversidad de la colección global en aquellos caracteres que no han sido empleados para formar la colección nuclear. En el presente estudio se determinaron tres colecciones nucleares para el Banco de Germoplasma de Manzano de la Universidad Pública de Navarra: para el primero se emplearon los datos de caracterización de 10 marcadores SSR, la segunda fue formada a partir de la caracterización hecha con 12 loci de isoenzimas, y la tercera se construyó a partir de la información proporcionada por 23 caracteres morfo-agronómicos. Se comparó la estructura y diversidad genotípica y fenotípica de las tres colecciones, entre sí y respecto de la colección original, para determinar el impacto que sobre dicha estructura y diversidad tenía el tipo de dato con que se formó la colección nuclear. Las tres colecciones conservaron una diversidad similar y no difirieron de la original en sus índices de Nei y Shannon-Weaver, y siempre se mantuvieron las frecuencias de las clases alélicas o fenotípicas. En conjunto, el tipo de caracterización empleada en la formación de la colección nuclear tuvo escasa influencia sobre la diversidad retenida, de lo que se concluye que en el manzano los microsatélites son especialmente adecuados para formar dichas colecciones. Various types of data have been used for sampling plant core collections, including morphological, agronomic and eco-geographical traits, and molecular and biochemical markers. However, little is known about the ability of woody perennial core collections to retain the diversity and structure of the whole collection for characters that were not considered in the selection, especially when molecular markers are used. In this study, three core subsets were established for the apple germplasm bank curated at the Public University of Navarre (UPNa, Spain): based upon the diversity found with 10 SSR markers, another based upon the diversity assessed with 12 isozyme loci; and a third based upon morpho-agronomic diversity evaluated by 23 morpho-agronomic traits. Comparisons between these three subsets and to the whole collection were assessed to determine the impact of the data used in the selection on phenotypic and genetic diversity and on their population structure. The three subsets had a similar diversity and they did not differ from the original collection, according to Nei and Shannon-Weaver indices. The allelic/class frequencies were also always maintained in the three subsets. Overall, the kind of data used to constitute a core collection had little influence on the phenotypic and genetic diversity retained, so in the case of apple collections the use of molecular markers is preferable for this task because they allow a rapid and reliable characterization. This study was funded by the Spanish Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA) grants Nº RF200400008-C03-00 and Nº RFP2004-00003-00-00.

A collection of 141 old and local Spanish accessions of pear (Pyrus communis) from the Escuela Tecnica Superior de Ingenieria Agraria-Universidad de Lleida (ETSIA-UdL) Pear Germplasm Bank in Lleida, Spain, were studied using a set of eight microsatellite markers to estimate the genetic diversity of the collection, to identify the genetic structure and relationships among its accessions, and to establish a representative core collection. An additional set of 13 well-known pear cultivars, currently grown in Spain and which represent a wide genetic diversity, were added as reference. The eight simple sequence repeat (SSR) loci amplified 97 alleles, with nine to 15 alleles per locus, and with the expected heterozygosity ranging from 0.65 to 0.89. All of the accessions except for 16 had at least one of the 48 rare alleles (frequency < 0.05) identified, and seven unique alleles were found in six accessions. Fifteen accessions were identified as synonyms and were excluded from the analysis. Genetic analyses performed by hierarchical clustering, Bayesian modelbased clustering, and factorial correspondence analysis supported the existence of three groups among the accessions with moderate [fixation index (FST) = 0.074], but significant, differentiation. As a whole, most of the germplasm (about 75%) curated at the collection showed its genetic distinctness with respect to the main pear cultivars used in European orchards. In fact, most reference cultivars were included in one single cluster that, moreover, had the lowest genetic diversity and allelic richness, in spite of having been chosen as heterogeneous material from different origins. The obtained results were also used to create a core collection with 35 accessions constituting an efficient and accessible entry point in the ETSIA-UdL pear collection for breeding and research communities. Pear (Pyrus spp.) is one of the most important fruit crops of the Rosaceae family, ranking second to apple (Malus ·domestica) in world and European production of pome fruit tree species (Food and Agriculture Organization of the United Nations, 2010). Pyrus communis is the most commonly cultivated pear species in Europe, America, and Africa, whereas Pyrus pyrifolia is the main cultivated species in Asia (Bell, 1991). Worldwide production of P. communis pears is based upon relatively few cultivars, most of them selected in late 18th and 19th century, or derived from those. Furthermore, the genetic base of cultivated pear in western Europe has significantly narrowed in the last few years. In 1986, seven cultivars accounted for 58% of pear production in western Europe (Bell, 1991), but nowadays, seven cultivars account for 75% of the production (World Apple and Pear Association, 2009). ‘Conference’ has become predominant in most European producing countries, and accounts for nearly one-third of European Union production. The reasons for this concentration are varied, but include economic and market factors, changes in consumption patterns, and biological aspects, such as productivity, storage ability, and susceptibility to pests and diseases (Bell, 1991). As a consequence, many of the traditional or local cultivars have been considered obsolete and replaced, leading to a dramatic loss of genetic diversity. The recognition of the need for the collection and preservation of endangered fruit germplasm has encouraged the establishment of genetic resource conservation programs. In 1986, a germplasm bank of old and local pear cultivars was established by the Horticulture section of the ETSIA-UdL. This germplasm bank currently maintains 114 Malus and 169 Pyrus accessions, collected at 12 northern Spanish provinces (Urbina et al., 2007), at the Estacion Experimental de Lleida of the Institut of Recerca i Tecnologia Agroalimentaria (IRTA) in Lleida, Spain. In 2002, a research program was launched to evaluate the genetic diversity of the collection through detailed morphological and agronomical description, and fingerprinting analysis based upon molecular markers was initiated in 2005. Microsatellite or simple sequence repeat (SSR) markers have been favored over other methods in establishing unique genetic identities or fingerprints and in assessing genetic diversity within a collection due to their high polymorphism level, reproducibility, and relative ease of analysis (Schlotterer, 2004). Moreover, SSR have also proven useful in creating core collections that represent not only the genetic structure of germplasm collections, but also their phenotypic structure (Santesteban et al., 2009). The SSR markers used in the earliest studies in pear were derived from apple (Yamamoto et al., 2001; Hemmat et al., 2003), as apple proved to be highly conserved in pear. However, after the development of SSR derived from asian pear (P. pyrifolia) and Received for publication 10 May 2010. Accepted for publication 28 June 2010. Financial support for this work was provided by INIA, Instituto Nacional de Investigacion y Tecnologia Agraria y Alimentaria (project grant nos. RF2004008-C03-00, RFP2004-009, and RFP-0000-68). Corresponding author. E-mail: carlos.miranda@unavarra.es. 428 J. AMER. SOC. HORT. SCI. 135(5):428–437. 2010. Table 1. Pear accessions maintained by the Escuela Tecnica Superior de Ingenieria Agraria Universidad de Lleida (ETSIA-UdL) Germplasm Bank and reference cultivars that were included in the study, in alphabetical order. Accessions selected to constitute the core collection are indicated in bold. Collection information includes accession name and bank code, site of collection, specific latitude and longitude, approximate elevation, and collecting source code according to Food and Agriculture Organization of the United Nations/International Plant Genetic Resources Institute (FAO/IPGRI, 2001) multicrop passport descriptors. Accession name Accession code Site of collection in Spain Latitude Longitude Elevation (m) Collecting source Agramunt 1 PRF-135 Puigvert d’Agramunt, Lleida 41.78 1.13 360 23 Agua PRF-030 Nalda, La Rioja 42.33 –2.48 530 23 Agua Iglesia PRF-028 Lardero, La Rioja 42.42 –2.45 435 23 Agua Magistral PRF-029 Lardero, La Rioja 42.40 –2.47 460 23 Aguilar 1 PRF-011 Aguilar de Campoo, Palencia 42.78 –4.25 900 23 Almenar 1 PRF-071 Almenar, Lleida 41.77 0.62 270 62 Angelina PRF-141 Isona i Conca Della, Lleida 42.08 1.12 1000 23 Areny 1 PRF-091 Areny de Noguera, Huesca 42.25 0.73 670 62 Areny 2 PRF-092 Areny de Noguera, Huesca 42.25 0.73 675 62 Areny 3 PRF-093 Areny de Noguera, Huesca 42.25 0.73 675 62 Areny 4 PRF-113 Areny de Noguera, Huesca 42.25 0.72 750 23 Azucar verde 1 PRF-007 Albelda de Iregua, La Rioja 42.37 –2.47 490 21 Azucar verde 2 PRF-008 Albelda de Iregua, La Rioja 42.37 –2.47 490 21 Balaguer 1 PRF-066 Balaguer, Lleida 41.75 0.77 220 23 Balaguer 2 PRF-067 Balaguer, Lleida 41.75 0.77 220 23 Balaguer Flix 1 PRF-046 Balaguer, Lleida 41.73 0.93 290 62 Balaguer Flix 2 PRF-047 Balaguer, Lleida 41.73 0.93 290 23 Balaguer Flix 3 PRF-048 Balaguer, Lleida 41.73 0.93 290 23 Balaguer Flix 4 PRF-049 Balaguer, Lleida 41.73 0.93 290 23 Balaguer Flix 5 PRF-050 Balaguer, Lleida 41.73 0.93 290 23 Balaguer Flix 6 PRF-051 Balaguer, Lleida 41.73 0.93 290 23 Balart PRF-070 Almenar, Lleida 41.77 0.58 280 23 Benavent de la Conca 1 PRF-142 Benavent de la Conca, Lleida 42.08 1.12 985 23 Bergamota PRF-112 Sopeira, Huesca 42.33 0.73 780 23 Bescano 1 PRF-121 Bescano, Girona 41.97 2.75 110 23 Bescano 2 PRF-122 Bescano, Girona 41.97 2.72 110 23 Biscarri 1 PRF-143 Biscarri, Lleida 42.12 1.12 920 23 Blanca d’aigua PRF-079 Baix Pallars, Lleida 42.33 1.0

The lowest flower in the pear (Pyrus communis L.) cluster usually develops and blooms first and also has a greater sink potential. For this reason, resources are preferentially utilized by the lowest fruit, and this is also one of the reasons why most thinning practices tend to favor their set. However, it is not always possible to perform selective thinning. This study was undertaken to determine if hindering pollination in the most developed flowers in the cluster influences yield or quality compared to that obtained in a whole open-pollinated cluster. The treatments were made in `Blanquilla' (Spadona, Agua de Aranjuez) and `Conference' pear within a wide range of flower densities for each cultivar. Pollination was hindered by cutting off the flower styles. The factor tested was style removal intensity (SRI). Treatments consisted in removing the styles of two, four(always the most developed), or all flowers in each cluster. Flower density was used as a covariate in an analysis of covariance to account for differences in flower densities in response to SRI treatments. In all experiments the covariate was not significant; therefore, SRI effect was not affected by flower density. `Blanquilla' and `Conference' had similar responses to treatments, so that when at least three flowers are susceptible to be openly pollinated, fruit set, seed content, and cluster yield were similar to control clusters, therefore the growth potential of fruit from partially damaged clusters in their most developed flowers is similar to undamaged open pollinated clusters. The reduced set of parthenocarpic clusters implies yield reductions ranging between 40% and 60% in `Conference', and up to about 60% in `Blanquilla'.

The apical or king (K) flower in the apple (Malus ×domestica L. Borkh.) cluster usually develops and blooms first and also has a greater sink potential. For this reason, resources are primarily used by the K fruit, and this is also one of the reasons why most thinning practices tend to favor K fruit set. However, it is not always possible to retain the K flower and remove the lateral ones. This study was undertaken to determine if the removal of the most developed flowers in the cluster influences yield or quality compared to that obtained in a whole cluster. The treatments were made in `Golden Delicious' and `Royal Gala' apple cultivars, within a wide range of flower densities for each cultivar. The factor tested was the intensity of flower removal (FRI); the treatments consisted in removing one, two, or three flowers in each cluster. Flower density was used as a covariate in an analysis of covariance to account for differences in flower densities in response to FRI treatments. In all experiments the covariate was not significant; therefore FRI effect was not affected by flower density. `Golden Delicious' and `Royal Gala' had similar responses to flower removal, so that when at least three flowers in a cluster remained, fruit set and cluster yield were similar to whole clusters. Only when two or fewer poorly developed flowers remained after FRI treatments, yield was reduced by as much as 25%. Fruit from FRI clusters were even heavier than those from whole clusters, due to reduced competition among the fruit, so that the growth potential of fruit from the first and second lateral flowers was similar to clusters with K fruit, in clusters where the K flower had been removed.