Effect of Foliar Application with Putrescine and Potassium Sulphate on Vegetative Growth, Fruit Set, Fruit Size, Fruit Quality and Yield of Washington Navel Orange

The present investigation was conducted during three successive seasons 2017, 2018 and 2019 years, respectively on Washington navel orange (Citrus sinensis L. Osbeck) twenty five years old budded on sour orange (Citrus aurantium L.) rootsock at Giza experimental station Agricultural Research center, Egypt. To study the effect of foliar application with Potassium sulphate K2SO4 at (2 and 3%), putrescine (PUT) at (50 and 100 ppm), a mixture of (putrescine (PUT) at 50 ppm + Potassium sulphate (K2SO4) 2%) and a mixture of (putrescine (PUT) at 100 ppm + Potassium sulphate (K2SO4)3%) compared with control treatment (untreated tree) on vegetative growth, fruit set, fruit size, yield, fruit quality of washington navel orange trees to improved fruit quality and yield in quantity and quality. The result showed that treatment with foliar application with a combination of (PUT) at 100 ppm + (K2SO4) 3% gave the highest values of vegetative growth (shoot length (cm), leaves number / shoot), fruit set (%) , fruits retention (%), yield /tree and yield T/ha, number of fruits/ tree, weight of fruits (g), Juice volume (cm), fruit pulp weight (g), fruit length (cm) and fruits size (cm) , peel thickness (mm), Chlorophyll (a) & (b) & (a + b) (mg/g fresh wt), vitamin C content (mg / 100mL juice), T.S.S%, and T.S.S /acidity %,Total protein (%),Total carbohydrates (mg/g), and total sugars (%), while, recorded the lowest fruits drop(%), softening (%), juice total acidity %, Moreover, increased leaf mineral contents (N, P, K, and Fe, Zn ppm)as compared with other treatments including control trees during three seasons. Foliar application of (PUT) at 100 ppm recorded the highest significant values of shoot diameter (mm), Carotenoids (mg/g fresh wt), peel weight (g), fruit set and decreased fruit drop percentage, softening (%), acidity % as compared with control trees. Foliar application with a combination of (putrescine (PUT) at 50 ppm + Potassium sulphate (K2SO4) 2%) gave the highest values of fruit diameter (cm), Mg % as compared with other treatments including untreated trees and significantly increased T.S.S %, T.S.S/acidity % also, decreased fruit drop percentage, acidity % as compared with control. Foliar application with K2SO4 (2% and 3%) increased most physical and chemical parameters of washington navel orange trees. For the interaction found that the combination between putrescine (PUT) and Potassium sulphate K2SO4 gave the best results in the most of taken characters.