PGPR (Plant Growth Promoting Rizobacteria) Benefits in Spurring Germination, Growth and Increase the Yield of Tomato Plants

There are microbes that are beneficial to plants. Among these, rhizobacteria, which functions as plant growth promoting rhizobacteria (PGPR) such as Pseudomonas spp. and Bacillus sp., can serve as fertilizer. These organisms have proven to accelerate germination and improve the yield of tomato plants. Colonization of rhizosphere by PGPR results in acceleration of plant growth and protection against plant pathogens. Soaking tomato seeds with Pseudomonas spp. and Bacillus sp. suspension accelerated germination by 2–3 days than the control without immersion with both bacteria. Soaking tomato seeds for 10–30 min in the suspension of Pseudomonas spp. yielded the same effect in tomato germination. Soaking in Bacillus sp. tends to cause faster growth as compared to immersion in Pseudomonas spp. suspension. Mixing these two bacterial suspensions had no significant effect in accelerating the germination of tomato seeds. Soaking tomato seeds for 20 min with a suspension of Pseudomonas spp. and Bacillus sp. at densities of 4 × 105 CFU and 8 × 105 CFU showed significant differences (p < 0.05) in plant height, leaf number, root length, number, and weight of tomato fruits. The highest fruit weight using Pseudomonas spp. and Bacillus sp. at 8 × 105 CFU was 491.7 g tomato plant−1 while the control average fruits weight was 100.0 g tomato plant−1.


Tomato and plant growth promoting rhizobacteria
Tomato is a potential horticultural crop for cultivation due to its high economic value. The production of the crop in Indonesia was 864,798 t/ha in 2008-2011, with an average productivity of 21.5 t/ha, which is below production levels of 100 t/ha in the United States and Europe.
Rhizobacteria of Pseudomonas spp. group are beneficial for plants, improving soil fertility, and function as biological control agents for plant pathogens and have the potential of increasing plant resistance (induced systemic resistance; ISR) [1]. Rhizobacteria plays an indirect role as a biological fertilizer and biological stimulant through the production of plant growth hormones, such as indole acetic acid (IAA), gibberellins, cytokinins, ethylene, and solubilizing minerals. These organisms also indirectly function to inhibit pathogenic microorganisms, through the formation of siderophores and antibiotics [1,2].
Rhizobacteria, such as P. fluorescens, P. putida, and P. aeruginosa, are beneficial to plants as plant growth promoting rhizobacteria (PGPR), with the ability to control plant diseases [3,4]. Research on the benefits of Pseudomonas spp. still continues to better understand its mechanism in spurring plant growth.
Bacillus sp. is a Gram-positive bacteria used in controlling root disease. These bacteria produce spores that can be stored for long periods and are easily inoculated into the soil. Previous research has shown that the bacteria Bacillus strains PRBS-1 and AP-3 proved to inhibit the growth of pathogenic fungi (Rhizoctonia solani, Colletotrichum truncatum, Sclerotinia sclerotiorum, Macrophomina phaseolina, and Phomopsis sp.) in soybean seeds and enhanced the growth of plants [5].
Rhizobacteria can be used as a bioprotectant that can suppress the development of plant pests/diseases, as a biostimulant that for production of indole acetic acid (IAA), cytokines, and gibberellin, and as a biofertilizer for increasing nutrient availability to plants [6].

Concentration levels of Pseudomonas spp. and Bacillus sp. in germination of tomato seeds
Soaking of tomato seeds in Pseudomonas spp. at a concentration of 8 × 10 8 CFU produced the highest germination percentage that of 91.7%, while germination in distilled water was at 41.6%. Concentrations of Pseudomonas spp. and Bacillus sp. significantly influenced tomato seed germination (Figure 1).
Soaking tomato seeds with bacterial suspension Pseudomonas spp. and Bacillus sp. gives a significant effect when soaked for 10-20 min at a concentration from 4 × 10 5 CFU, 8 × 10 5 , and 12 × 10 5 CFU (Figure 2). Tomato seeds soaked in a mixture of bacterial suspension of Pseudomonas spp. and Bacillus sp. showed significant effect when compared to distilled water. A previous study conducted by Widnyana et al. [7] involving the soaking of swamp cabbage (Ipomoea reptans Poir) seeds for 20 min with suspension of P. alcaligenes TrN2 resulted in 25% faster germination and increased fresh weight of stems up to 67.07%, compared to soaking of seeds in distilled water.

Effect of immersion of tomato seeds in Pseudomonas spp. and Bacillus sp. on plant height and number of leaves
Soaking tomato seeds with Pseudomonas spp. suspension and Bacillus sp. can increase the growth of tomato plants. This is evidenced in Table 1, with the increase in plant height followed by the increase in number of tomato plant leaves. The positive effect of soaking the tomato seeds is obtained on population density of Bacillus sp. and Pseudomonas spp. which is  a minimum of 4 × 10 5 to 12 × 10 5 CFU. The application of Pseudomonas spp. suspension with concentration of 5 × 10 5 CFU through seed immersion showed significant difference in tomato plant height, with average tomato height in the first and fourth week at 2.7 cm and 8.5 cm, respectively [8] ( Table 2).
Tomato plants treated with rhizobacteria have higher productivity caused by the ability of PGPR in spurring plant growth and inhibiting the growth of pathogens. This is in accordance with Hatayama et al.'s [9] study that plants treated with PGPR bacteria have higher yields than controls. One of the PGPR product compounds that inhibit the growth of pathogens is siderophore. Siderophore serves as a systemic booster of plant resistance by inducing plants to form salicylic acid at higher level. Mukaromah [10] stated that salicylic acid acts as a signal transduction gene that activates the systemic inducing receptor in plant tissue. Bacillus sp. and Pseudomonas sp. are antagonistic microorganisms that are able to suppress soil pathogens by forming antibiotic compounds such as chitinase enzymes that can hydrolyze fungal cell walls and form siderophores and other antibiotics [11,12]. tomato germination. This indicates that the soaking of tomato seeds with suspensions of bacterium Pseudomonas spp. and Bacillus sp., or suspense mixture of both types of bacteria is very useful in spurring the growth of tomato seeds when the soaking treatment lasts 20-30 min.

Tomato seed immersion treatment on growth and yield of tomato plants
Treatment of tomato seeds with Pseudomonas spp. bacterial suspension in addition to spurring the germination of tomato seeds also has an impact on the growth and yield of tomato fruit [13]. Significant differences were observed (P ≤ 0.01) among plant height and leaf numbers for P. alcaligenes bacteria isolate and the application method used ( Table 3). Also significant differences were observed (P ≤ 0.01) among fruit number, total fruit weight per plant, and weight per tomato fruit for P. alcaligenes bacteria isolate and the application method used ( Table 4).
Soaking tomato seeds with P. alcaligenes suspension yielded a significant effect on the number of tomato leaves, where the number of leaves reached 192.11 strands on immersion with P. alcaligenes TmA1, followed by P. alcaligenes TrN2 where the number of leaves reached 182.4 strands. There were 161.6 strands on soaking the seeds with P. alcaligenes KtS1, whereas in soaking the seeds with distilled water, the number of leaves was only 78.6 strands. Soaking tomato seeds with P. alcaligenes suspension also yields a significant effect on tomato plant height. The highest tomato plant reached 120.4 cm in tomato seed immersion with suspension P. alcaligenes TmA1, followed by 116.3 cm with P. alcaligenes TrN2, and 114.1 cm with P. alcaligenes KtS1, while in soaking the seeds with distilled water, tomato plant height was Notes: Values followed by the same letter in the same column are not significantly different at 5% DMRT. only 36.1 cm. The abovementioned data indicate that the seed-soaking treatment is the best application method when compared to soaking the roots of the seedlings or watering the tomato seeds (Table 3) Soaking tomato seeds with P. alcaligenes suspension has a significant effect on the number of fruits per plant, fruit weight per plant, average weight per fruit unit, and fruit weight in hectare. On the weight parameters of tomato per plant, the average weight per fruit unit, and the weight of tomato per hectare, it was found that soaking the tomato seeds with a suspension of P. alcaligenes TmA1 had a significant effect and was significantly different with all other treatments. The highest weight of tomatoes per plant, weight per fruit unit, and fruit weight per hectare was found in tomato seed immersion treatment with P. alcaligenes TmA1 suspension that are 451.9, 7.2, and 20.3 tons, respectively. This value differs significantly with all other treatments ( Table 4).

Conclusion
1. Soaking tomato seeds in a suspension of Pseudomonas spp. and Bacillus sp. can accelerate germination by 2-3 days than when not being immersed in both bacterial suspensions.
2. Soaking the tomato seed for 10-30 min in Pseudomonas spp. suspension yields the same effect on the speed of germination of tomato seeds. Notes: Values followed by the same letter in the same column are not significantly different at 5% DMRT.