BIOSTIMULATORS EFFECT ON GROWTH AND FRUITING PROCESSES OF TWO SWEET CHERRY CULTIVARS GRAFTED ON GISELA 3 ROOTSTOCK

The present study followed in the period 2020-2022 the effect that the supplementation of basic, mineral fertilization with three biostimulators had on the growth and fruiting processes of two cherry cultivars grown at ICDP Pitesti, Arges, in the southern area of Romania, in a temperate continental climate, with multiannual average temperature of 10.1 °C (extreme temperatures of -24.4 °C and 38.8 °C, respectively), total precipitation of 662.6 mm and sunshine of 2273.1 hours. The study was carried out in a demonstration batch of cherry (cultivars 'Regina' and 'Kordia', grafted on Gisela 3 rootstock) established in 2017, with planting distances of 4x1 m, in which the necessary water and nutrients were provided through an automatic fertigation system. Fertilization of the trees was supplemented with three biostimulators, two foliar (applied in the phenological stages BBCH 53-green tip, BBCH 69-petal fall and BBCH 72-sepals beginning to fall), BSA, containing amino acids - most of which are arginine, proline, threonine, lysine - N, C, B, Mn, Zn and BSB respectively, containing amino acids, proteins, betaine, vitamins, N, C, K and a root bio-stimulator (BSC), containing salts of humic and fulvic acids, amino acids, micro and macro-elements, living bacteria) applied in a single phase, in the BBCH 53 phenological stage. The index of leaf chlorophyll content, indicators of growth and fruiting processes and those of fruit quality were recorded, which were later compared both with each other, as well as with the blank version. Data were statistically analysed (descriptive analysis, ANOVA analysis of variance, and Duncan Multiple range test, p ≤0.05). The results indicated that CCI registered significant increases compared to the Control as early as May in all variants treated with biostimulators (from 18.28 to 19.54-19.98 in May, from 23.12 to 26.59- 29.18 in June and from 25.18 to 27.36-30.05 in July). Later, significant differences were also revealed between treatments with biostimulators, BSC stood out, with the highest CCI values both at the June and July determinations (29.18 and 30.34, respectively). The same soil applied BSC stimulated the annual increase of TCSA (6.78 cm2 compared to 4.76 cm2 in the Control), although smaller but still statistically assured effects were recorded for the two foliar biostimulators (5.50 BSB and 5.67 BSA respectively). However, high fruit yield for high annual increases of TCSA (7.2-11.7 cm2) was obtained in the foliar treatment with BSA (15-24.5 kg/tree). For all three biostimulators, significant increases compared to the Control were observed regarding fruit weight (by a maximum of 19% in 'Regina' and 8% in 'Kordia') and total soluble content (on average by a maximum of 4%). Also, in these variants, and especially for BSB, fruit firmness increased significantly from 52.3 to 56.9 HPE-II-FFF Bareiss units. BSB was also the biostimulant for which the lowest TTA was determined (0.46% compared to the Control with 0.57%). Last but not least, BSA and BSB increased both TSC (from 13.6 to 14.5 and 14.8%) and vitamin C content (from 15.8 to 16.1 and 16, 6 mg/100 g respectively). Therefore, supplementing basic, mineral fertilization with biostimulators containing humic acids, humic acids, fulvic acids, amino acids, micro and macro elements, and live bacteria (BSC) applied to the soil stimulated the accumulation of photosynthetic pigments and vegetative growth, while the foliar one, BSA, stimulated both vegetative growth and fruit yield. All three biostimulant increased fruit weight, firmness, and TSS, while low acidity and high sugar and vitamin C levels were recorded only in foliar treated sweet cherry.