Lettuce seed pelleting with Pseudomonas sp. 31-12: plant growth promotion under laboratory and greenhouse conditions

Plant growth promotion by Pseudomonas sp. 31-12 incorporated into a lettuce seed pelleting matrix was studied. We examined (1) the effect of five rhizosphere derived bacterial strains on green oak lettuce ( Lactuca sativa L.) seed germination, root and shoot growth, as a strain selection step for seed coating and seed pelletizing studies, (2) population stability of Pseudomonas sp. 3112 incorporated into a pelleting matrix on lettuce seed stored three months at 4 degrees C, and (3) lettuce growth promotion in the laboratory and greenhouse by Pseudomonas sp. 31-12 coated and pelletized seed. A spontaneous streptomycin mutant of Pseudomonas sp. 31-12 (str) was used to determine population size on seed and roots of 15- and 30-day-old lettuce. The population of Pseudomonas sp. 31-12str on coated and pelleted seed decreased from 104 4 cfu/seed to 103 3 cfu/seed after 3 months storage at 4 degrees C. However, the population exceeded 104 4 cfu/g root dry mass and 105/g 5 /g root dry mass after 15 days and 30 days in the greenhouse. Leaf fresh mass was significantly increased (P P <= 0.05) with Pseudomonas sp. 31-12 seed treatment as compared to noninoculated seed. In conclusion, pelletized lettuce seed with Pseudomonas sp. 31-12 promoted growth and yield in the greenhouse.