Field evaluation of a plant growth promoting bacterium for enhancing the vegetative growth of Sri Lankan cinnamon (Cinnamomum verum)

This study investigated the effect of a local Plant Growth Promoting Bacterium (PGPB strain I-II) on the vegetative growth of Cinnamomum verum under field conditions. A field trial was conducted using a Randomized Complete Block Design (RCBD) in the Low Country Wet Zone of Sri Lanka. Three treatments were tested: an untreated control, the recommended dose of inorganic fertilizer, and the PGPB strain I-II. Four-month-old cinnamon plants were established in two blocks, with four replicates per treatment in each block. Inorganic fertilizer was applied twice a year according to standard recommendations. For the bacterial treatment, a suspension of PGPB strain I-II (10⁹ CFU mL-1) was sprayed on the foliage every two weeks. After 18 months, data were collected on plant height, stem circumference, number of leaves, internodal length, and chlorophyll content index (CCI). Plants treated with PGPB strain I-II did not differ significantly in plant height (104.13±7.31 cm) and CCI (42.73±1.96) compared to those treated with inorganic fertilizer (92.75±6.63 cm and 35.95±4.33, respectively; p>0.05). However, the total number of leaves in the PGPB strain I-II treatment (238.75±49.49) was significantly higher than that of the fertilizer (121.75±27.81) and control (118.38±35.29) treatments. The positive impact of PGPB strain I-II on vegetative growth enhancement suggests its potential as an alternative to inorganic fertilizer, warranting further validations across diverse cinnamon-growing regions.