RESPONSE OF GROWTH, YIELD AND FRUIT QUALITY OF "ANNA" APPLE TREES TO FOLIAR SPRAY WITH SOME PLANT GROWTH PROMOTING RHIZOBACTERIA AS A SUBSTITUTE TO SYNTHETIC BIOSTIMULANTS

Many synthetic biostimulants containing amino acids, macro- and micro-elements, humic acids and, sometimes, algae extractshave been used effectively for stimulating and increasing of fruit trees yield. The foliar spray with some PGPR (plant growth promoting rhizobacteria) has proved high potentiality in stimulating and increasing plant yield. The current study is concerned with the use of some PGPR types (Azospirillum brasilense, Pseudomonas fluorescens and Bacillis polymyxa) as an alternative to some commercial synthetic biostimulants i. e. Jisamar (J) and Furdos (F) in stimulating and improving yield of "Anna" apple trees.
The study field of apple trees (eight years old) was chosen at El-Bostan area, El-Behira Governorate, Egypt. The trees were sprayed twice with the different stimulators, the first was at fruit set and the second was done after 30 days from fruit set. The control trees were sprayed with water.
The microorganisms which were used for spray were counted in the plant phyllosphere and they showed heavy increase in the phyllosphere of the treated plants. The spray with the synthetic biostimulants showed remarkable improvement to the plant morphological characteristics, e. g. shoot length, shoot diameter, leaf area, leaf dry weight and leaf content of chlorophyll a, b and total chlorophyll. While, specific leaf weight (SLW) did not significantly change. Likewise, the spray with bacterial biostimulants proved similar potentiality as synthetic ones, and even, sometimes, surpassed them. The spray with Azospirillum brasilense gave the highest fruit yield; 45.1 and 41.2 kg/tree versus 33.5 and 32.0 kg/tree for control treatment in 2009 and 2010 seasons, respectively. The spray with Jisamar and Furdos gave 37.4 and 33.2 kg/tree and 36.5 and 34.7 kg/tree, respectively. The experimental treatments, raised the net return (£E/feddan) over that of control. Azospirillum brasilense spray attained the highest net return i. e. 21595 versus 16660, 16870 and 15650     £E/feddan for treatments of Jisamar, Fordose and control, respectively. Therefore, the substitution of synthetic biostimulant products with biological ones may be suitable for improving the plant growth, increasing productivity and raising the net return per feddan of Anna  apple  trees.