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Apple trees produce many more flower clusters than needed for a full crop, but natural early season flower and fruitlet abscission drastically reduce the final fruit number. Natural fruit abscission varies significantly year to year. There have been attempts to try to model apple fruit abscission in the past. However, due to the great complexity of a perennial crop system in a dynamic environment with significant plant manipulations, regulatory processes and controlling environmental variables have been difficult to elucidate. In 1995, a field trial was planted at the New York State Agricultural Experiment Station in Geneva, New York with 3 apple cultivars ('Delicious', 'Gala', and 'McIntosh'). Beginning in 2000 and for 18 years thereafter, we recorded the natural whole-season fruit abscission of untreated trees that received no chemical or hand thinning. We also estimated early season patterns of carbohydrate supply-to-demand each year with a carbon balance model. These data were used to correlate tree carbon balance status and other environmental variables with natural fruit abscission responses. In general terms, natural set, defined as final fruit/flower cluster, of 'Gala' averaged ~1 fruit for each flower cluster (fruit set = 0.9), whereas fewer fruits were set on 'Delicious' and 'McIntosh' (fruit set = 0.7 and 0.6, respectively). Fruit set of 'Gala' was less variable than of 'Delicious' or 'McIntosh', and there was a clear pattern for decreasing fruit set when the number of initial flower clusters per tree increased.Fruit weight was less dependent on fruit number for 'Delicious' and 'McIntosh' than for 'Gala'.Multiple regression models indicated that number of flower clusters per tree and average carbohydrate balance between 0-60 degree days (DD) after bloom and 300-360 DD after bloom were the main significant variables that explained 60-80% of the variability in natural fruit set or final fruit number. For 'Delicious', temperatures of the previous fall also explained a significant amount of variation in final fruit set and final fruit number. For 'Gala', carbon balance from bloom to shortly after petal fall and when fruits were about 18 mm were the two main periods, which were more sensible to carbohydrate deficiency triggering fruit abscission. A later susceptible period was also observed for 'McIntosh', suggesting a larger thinning window for this cultivar.

SUMMARYThis study tested the relationship between stem water potential (ψ stem ) and vapor pressure deficit (VPD) in order to evaluate its use as reference for irrigation control of table grape (Vitis vinifera) cvs. Thompson Seedless and Redglobe. Two trials were carried out on consecutive seasons. In the first season the treatments consisted of four different irrigation regimes: T1, plants irrigated at 100% of ETc; T2, irrigated until fruit set the same as T1 but after fruit set every other time T1; T3, plants with no irrigation from fruit set to harvest; and T4, plants irrigated at 50% of ETc throughout the growing season. Vines from T1 always showed a higher ψ stem for a wide VPD range, therefore the ψ stem and VPD relationship was established using T1 vines, obtaining a logarithmic function with a high determination coefficient (R 2 =0.85). The following season this relationship was used to control irrigation frequency on two table grape cvs. Irrigation started when vines had 20 cm shoots and then the irrigation amount was set to replenish 10% of soil available water. Trial 1 was conducted on cv. Thompson Seedless and consisted of two treatments: T1 plants irrigated to satisfy 100% ETc and T2 plants irrigated according to the previously obtained ψ stem -VPD reference line. Trial 2 was established with Redglobe cv. plants using three treatments: T1 plants irrigated to satisfy 100% Etc; T2, plants irrigated the same as T1 but after fruit set every other time T1; and T3, plants irrigated according to the ψ stem -VPD reference line previously obtained. Irrigation frequency determined using the ψ stem -VPD relationship reduced total water volume compared to T1 on both trials, with no effects on yield or quality, showing the feasibility of using this relationship to control irrigation frequency. RESUMOEste trabalho incidiu na análise da relação entre o potencial hídrico xilemático (ψ stem ) e o déficit de pressão de vapor (VPD), para utilizá-la como referência na programação de irrigação em uva de mesa (Vitis vinifera) das variedades Thompson Seedless e Redglobe. Foram realizados dois ensaios em temporadas consecutivas. Na primeira temporada os tratamentos consistiram em quatro regimes de irrigação: T1, plantas irrigadas com 100% de ETc; T2, plantas irrigadas igual ao T1 até a frutificação e depois uma vez a cada duas irrigações deT1: T3, plantas sem irrigação entre a frutificação e a colheita; e T4, plantas irrigadas com 50% de ETc durante toda a temporada. As plantas de T1 apresentaram sempre valores mais altos de ψ stem para uma ampla gama de VPD, portanto, a relação ψ stem -VPD foi estabelecida utilizando plantas de T1, obtendo uma função logarítmica com um alto coeficiente de determinação ((R 2 =0.85). Na subsequente temporada esta relação foi utilizada para controlar a frequência de irrigação em duas variedades de uva de mesa. A quantidade de irrigação foi estabelecida para repor 10% de humidade aproveitável. O ensaio 1 foi realizado na variedade Thompson Seedless e baseou-se em dois tratamentos: T1, plantas...

Apple trees naturally set many more fruits than desired thus requiring active crop load management to achieve optimum fruit size and to ensure adequate return bloom. Chemical thinning is the primary method used to reduce crop load but despite 50 years of experience, it remains an unacceptably unpredictable part of apple production with large variation from year to year and within years. Our research suggests the variability in chemical thinner efficacy is related both to stage of fruit development and carbohydrate availability to support fruit growth. There is low sensitivity to chemical thinners when fruits are small at petal fall (about 4 mm diameter) followed by high sensitivity of rapidly growing fruits between 8-15 mm and then low sensitivity once fruits reach 20 mm. The basis for the differing sensitivity is not clear. A second source of variability is the availability of carbohydrates to support fruit development. Weather has strong effects on carbohydrate production and utilization. We have estimated carbohydrate supply and demand for fruit growth using the Cornell MaluSim carbohydrate prediction model and have related the carbohydrate balance to chemical thinning efficacy. Simulations over several years showed that there are often periods of particularly negative or positive carbon supply:demand balance, which were associated with severe thinning or mild thinning. We have also related the growth rate of fruits to fruit abscission. We have developed an integrated method to more precisely manage chemical thinning that utilizes estimated carbohydrate supply to the fruits and actual fruit growth rate measurements to provide real time information to fruit growers to manage thinning.

-Introduction. Texture parameters are important factors for characterizing the sensory quality of raw almonds; nevertheless there is scarce literature that explores sensory differences among cultivars. The aim of this study was to characterize quality attributes of different raw almond cultivars. Materials and methods. The almond cultivars 'Nonpareil', 'Mission', 'Supernova', 'Tuono', 'Ferragnès' and 'Marcona' were used to characterize their industrial and sensory quality attributes. A panel of 14 assessors with previous experience in testing stone fruit was specifically trained on descriptive analysis for determining quality and particularly texture of raw almonds. Results and discussion. A direct relationship was observed between kernel yield and shell fracture resistance; the American cultivars 'Nonpareil', and 'Mission' showed more minor shell fracture resistance than the European. 'Tuono' stood out for being tasty, crunchy and hard, whereas 'Marcona' was noted for its color intensity, crispness and hardness; but it lacked taste. 'Supernova' was described as tasty. Conclusion. A 5-h training period proved to be adequate for characterizing raw almond cultivars. The panel was able to discriminate between cultivars and segregate 'Nonpareil' and 'Mission' from the other cultivars in terms of texture attributes.