Improvement of seed germination and early growth of Caucasian whortleberry (Vaccinium arctostaphylos L.) by plant growth promoting rhizobacteria and cold stratification

Vaccinium arctostaphylos is a threatened species in Caspian forests of Iran that its seeds germinate in a long time due to internal dormancy. The purpose of this research was to investigate the effects of plant growth-promoting rhizobacteria and the cold stratification periods on seed germination of Vaccinium arctostaphylos. The seeds were inoculated with growth-promoting bacteria including Bacillus subtilis, Enterobacter cloacae, and Pseudomonas putida and combination (co–inoculation) of all strains. Then they were subjected to cold stratification in a refrigerator at 4 ± 1°C for 0, 1, 2, 3, 4 and 5 months. At the end of periods, seeds were sown in polyethylene bags (15 cm×8 cm) containing cocopeat, perlite, and sand (1:1:2) and were placed in greenhouse with temperature of 22 and 25°C, and relative humidity of 60% and 70%, respectively. After 40 days, germination percentage, germination speed, and seed vigor index (SVI) were calculated. Results showed that, bacteria inoculation and their interactions affected germination traits. Germination percentage ranged from 0 to 58.50%. Both inoculation and CS had positive effect on Germination percentage. The highest percentages of seed germination (57.50–58.50%) and speed of germination (2.26 n/d) belonged to co-inoculated seeds by the combination of all bacterial along with 4 and 5 months of cold stratification periods, respectively. The maximum shoot length (23. 25 mm), root length (17.98 mm), and seed vigor index (24.12) were recorded for co-inoculated seeds by the combination of all bacterial inoculants and five months of cold stratification. The results confirmed to overcome seed dormancy, increase of seed germination components, and early seedling growth of V. arctostaphylos , Plant growth promoting rhizobacteria is better to be applied in combination with cold stratification.