Heat Unit Requirements of "Flame Seedless" Table Grape: A Tool to Predict Its Harvest Period in Protected Cultivation.

Greenhouse cultivation of table grapes is a challenge due to difficulties imposed by their perennial habit and chilling requirements. Despite difficulties, greenhouse cultivation allows ripening long before that in the open field. Nonetheless, for harvesting "Flame Seedless" in the most profitable periods, a cultural practices timetable has to be established. In this context, an estimation of development rate as a function of temperature becomes essential. This work puts forward a procedure to determine "Flame Seedless" threshold temperatures and heat requirements from bud break to ripening. "Flame Seedless" required an average of 1633 growing degree days (GDD) in the open field with a base temperature of 5 °C and an upper threshold temperature of 30 °C. Strikingly, only 1542 GDD were required within the greenhouse. This procedure forecast "Flame Seedless" ripening with an accuracy of three and six days in the open field and greenhouse, improving predictions based on the average number of days between bud break and ripening. The procedure to predict oncoming harvest date was found satisfactory, just four days earlier than the real date. If we used the typical meteorological year instead of the average year, then the prediction was greatly improved since harvest was forecast just one day before its occurrence.

Postveraison Deficit Irrigation Effects on Fruit Quality and Yield of "Flame Seedless" Table Grape Cultivated under Greenhouse and Net.

Lack of color in the skin of red table grape varieties is a serious problem in areas of warm climate. This problem is often addressed by the application of ethylene release products such as ethephon. Strict regulation in the use of this product in EU forces European grape producers to look for suitable alternatives. With the aim to increase red skin color, we applied regulated deficit irrigation (RDI) strategies from veraison until harvest on "Flame Seedless" table grape vines cultivated under nets and under a plastic greenhouse in South East Spain, and compared yield and fruit quality with vines fully irrigated under the same net and plastic greenhouses. Our results show a modest improvement in the percentage of commercial clusters with better skin color, probably because the short duration of the deficit irrigation period only caused a slight decrease in soil water content and a mild water stress in RDI vines. Larger differences were observed under the more limiting conditions of the plastic greenhouse for light environment, especially when berry skin color was measured by CIRG (color index of red grape). More noticeable effect of RDI was noted on fruit earliness. Water savings were also remarkable. Negative effects of RDI on berry size or total soluble solid content were not perceived. Our results suggest that RDI is a suitable strategy to save irrigation water without substantial negative effects on yield and berry size. However, the effects on skin color were insufficient in the trial conditions.

Harvest prediction in 'Algerie' loquat.

Plant phenology is in great measure driven by air temperature. To forecast harvest time for 'Algerie' loquat accurately, the growing degree days (GDD) needed from bloom to ripening were determined using data from nine seasons. The methods proposed by Zalom et al. (Zalom FG, Goodell PB, Wilson LT, Barnett WW, Bentley W, Degree-days: the calculation and use of heat units in pest management, leaflet no 21373, Division Agriculture and Natural Resources, University of California 10 pp, 1983) were compared as regards their ability to estimate heat summation based on hourly records. All the methods gave remarkably similar results for our cultivation area, although the double-sine method showed higher performance when temperatures were low. A base temperature of 3 degrees C is proposed for 'Algerie' loquat because it provides a coefficient of variation in GDD among seasons of below 5%, and because of its compatibility with loquat growth. Based on these determinations, 'Algerie' loquat requires 1,715 GDD from bloom to harvest; under our conditions this heat is accumulated over an average of 159 days. Our procedure permits the 'Algerie' harvest date to be estimated with a mean error of 4.4 days (<3% for the bloom-harvest period). GDD summation did not prove superior to the use of the number of calendar days for predicting 'Algerie' harvest under non-limiting growing conditions. However, GDD reflects the developmental rate in water-stressed trees better than calendar days. Trees under deficit irrigation during flower development required more time and more heat to ripen their fruits.