[Prediction of the size and evolution of maturity of plums, cv. D'Agen]

The present study was undertaken to predict the size of dried prune, cv. D'Agen, and to know its optimum harvest time with greater accuracy. Fruit growth of the European prune was described. The observations were carried out in two orchards, one in Pirque and the other in Calera de Tango. Four trees were chosen on each farm. Twenty-five fruits per tree were selected for measurements of suture and cheek diameters every 7 days. Growth for both diameters described a sigmoid double curve. Suture diameter was greater than cheek diameter until about 85 days after full bloom when cheek diameter became greater. Dates for the different stages of fruit development were determined; among them, 51 to 54 days after full bloom at which 80 to 90 percent of the fruit showed visible endosperms should be highlighted as a reference date for size prediction. To evaluate the foreign methodology to predict dried prune size under the local conditions, 18 orchards were chosen from the V to the VIII Regions and within each orchard 30 trees were randomly selected to determine fruit size at the reference date and at harvest time by weighing 20 fruits per tree. Subsequently, lineal regression between both sizes was estimated. It was found that most orchards presented a determination coefficient (R2) of 20 to 50 percent without a high relationship between both sizes. Only three orchards showed an R2 superior to 60 percent; these orchards were characterized by a good management and their sampled trees had a wide range of fruit sizes. In analyzing the relationship between fruit at the different development stages and its final size it was found that the moment of highest correlation coincides both with the beginning of embryo growth and minimum fruit growth. The trees selected to measure fruit growth were also used to describe maturity evolution. This, from the first week of January and every seven days six fruits per tree were collected to determine pulp firmness and soluble solids content. Pulp resistance to pressure reached 3 to 4 pounds at 148 days after full bloom (February 15) when the fruit achieved its final size; at this same time soluble solids accumulated 23.75 and 21.5 deg Brix in the evaluated orchards