Effectiveness of plant growth-promoting Rhizobacteria (PGPR) to control gall rust of Falcataria moluccana under field conditions

Abstract

Gall rust caused by Uromycladium spp. is a most devastating disease of Falcataria moluccana plantations in Indonesia since a decade. There is no effective control measures to suppress rust gall disease. The objectives of the research was to investigate the effectiveness of PGPR on seedlings growth, gall rust severity and growth of young Falcataria moluccana trees. Talc-based powder formulation of PGPR mixtures of Pseudomonas fluorescens, Bacillus polymixa and Rhizobium spp. was used. First experiment consisted of testing as a seed treatment by PGPR using four concentrations of PGPR i.e. 0 (untreated), 2.5 g/L, 5 g/Land 10 g/L equal to 1.25 x 106 cfu/L, 2.5 106 cfu/L and 5 x 106 cfu/L. Emergence rate and seedlings growth were evaluated. Second experiment was a field trial using young three months age-seedlings trees under pathogen natural infestation, designed as a complete randomized block design with six replications. Treatments were PGPR 2.5 106 cfu/kg and 5 x 106 cfu/kg, untreated and mancozeb fungicide. Powder formulation of PGPR was mixed with granule NPK fertilizer and applied as soil incorporation at planting date and 42 days after transplanting. Disease severity, plant height and stem diameter were observed weekly at 1 to 11 week after transplanting. Seed treatment with all concentration of PGPR did not affect germination rate, but increased seedlings growth. Moreover, field application of PGPR at the rate of 5 x 106 cfu/kg in PGPR-NPK fertilizer mixture was the best treatment to control galll rust of young plants under field conditions with an effectiveness rate of 42.28%, compared to fungicide treatments which has effectivenes rate of 34.39%. The treatments also enhanced the growth of young plants.