Effect of chilling hours and fertilization methods in flowering budbreak and yield of some pear cultivars

This investigation was conducted at the Pome and grapevine Division in Sweida governorate during 2018-2019 seasons to study the influence of soil fertilization with potassium and foliar spray with the mineral elements boron and zinc and different levels of chilling hours (300-450-600-750-900-1050-1200) on Chilling Requirement Index (CRI) and Growing Degree Hours (GDH), and the influence of soil fertilization with potassium and foliar spray with the mineral elements boron and zinc on pollen grain viability, fertility, productivity, and fruit physical and chemical characters, leaf area and it's contact of some mineral elements and total chlorophyll, on four pear cultivar: Coscia, red coscia, bartlette, conference. Potasium fertilization was added to the soil with an average (700g/tree) at dormancy stage, while boric acid (2g/l) and zinc sulfate (2g/l) were added as foliar spray at bloom stage. The (CRI) increased by chilling hours' levels, and the level 1200 archived the highest (CRI) in the two seasons at 99%, also growing degree hours (GDH) reduced by chilling hours levels in the all studied cultivars, and conference had the highest (GDH) for both seasons 1594.34-1833.91 hours superior on other cultivars. Potassium fertilization and boron and zinc foliar spray had positive effect in CRI and GDH compared with the control in all cultivars. Soil fertilization and foliar spray increased the average of pollen grains viability significantly compared to the control in all studied cultivars, potassium fertilization and boron and zinc foliar spray had the highest average of pollen grains viability in both seasons 97.81-98.48% respectively. Result showed that fertilization treatments significant effect in percentage of fruits set compared to the control at level 95%, potassium fertilization and boron foliar spray achieved the highest percentage in fruit set in both seasons 36.3-37.32% respectively without significant differences with other treatments and superior on control. Fertilization and foliar spray increased productivity and average of fruit weight compared with control in all studied cultivars, bartlette had the highest average of productivity and fruit weight in both season. Also the added mineral elements had significant effect in leaf contact of total chlorophyll and leaf area compared with control, potassium fertilization and boron and zinc foliar spray had the highest total chlorophyll contact in both seasons 33.9-46.82 mg/100g respectively, and bartlette had the highest average of leaf area in both seasons 41.22-42.8 cm2 respectively superior in other cultivars. There were no significant differences between treatments and control in leaves content of mineral elements firmness of flesh fruits and fruits chemical characters.