Effectiveness of Pelleting for Inoculating Plant Growth-Promoting Rhizobacteria on Small Seeds

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The effectiveness of pelleting for inoculating small seeds with plant growth-promoting rhizobacteria (PGPR) was studied. Seeds of sesame cv. Yangbaeckkae and perilla cv. Namcheon were inoculated with Bacillus sp. KR083 and Pseudomonas sp. RRj228 with pelleting material, ‘DPA’ (contained 70% diatomite, 14% perlite, 5% appetite, 5% cow dung, 3% peat, and 3% pea) and stored at refrigerator temperature of 4°C or room temperature of 18 - 20°C for 2 to 7 weeks. While 4°C modestly improved strain survival and growth, crop by strain interaction was substantial. Strain KR083 numbers grew 10 to 13 fold on sesame in 2 to 7 weeks but declined by as much as 78% on perilla across both temperatures. In contrast, strain RRj228 numbers grew 1.7 to 11 fold on perilla but only maintained its numbers on sesame across temperatures and storage times. Strains impacted seed viability differently; while KR083 had no effect, RRj228 decreased germination rate of both sesame and perilla by as much as 20% after 2 weeks of storage of pelleted seeds at 18 - 20°C. Strain KR083 significantly improved root elongation of both crops, but only of sesame when co-inoculated with RRj228. On the other hand, KR083 had lower colonization ability than RRj228 on roots, 19 and 83 % lower on sesame and perilla, respectively. Mixed inoculum, however, significantly improved colonization of both strains on both crops. In field trials, sesame co-inoculated with KR083 and RRj228 yielded 18% higher than non-inoculated control while reducing phytophthora blight infection by 10 and 20% in silty loam and sandy loam soils, respectively. Likewise, Perilla yielded 29% more leaf with mixed inoculation than the non-inoculated, diatomite-pelleted control in the same silty loam soil. Results indicate DPA pelleting as an effective method for small seeded crops when compatible PGPR strains are used as inocula. Images of microscopic transverse section (50 fold magnification) of a sesame seed pelleted with ‘DPA’ material together with a mixture of PGPR strain Bacillus sp. KR083 and Pseudomonas sp. RRj228 (Left), a sesame seedling from the seed pellet (Center) and its growing status in ‘growth pouch’ (Right).