Biostimulants Enhanced Seedling Root Growth and Bulb Yields of True Seed Shallots (Allium cepa var aggregatum L.)

The objective of this research was to investigate the effects of biostimulan (PGPR) on root growth of seedlings and bulb yields of true seeds shallo ts (TSS). The research was conducted in the glasshouse in Tangtu village, Badung regency,Bali province of Indonesia, from April until October 2018. Complete randomized block design was used with 4 replications. Three kinds of biostimulants (B, C, D) and one control, and two TSS varieties (Sunren F1 and Tuktuk) were the treatments imposed. Results of experiment showed that biostimulants as well as TSS variety significantly (P<0.05) increased germination percentage, root length of TSS seedlings, leaf chlorophyll content, bulb diameter, bulb number, leaf and bulb fresh weight per pot. However there was no significant different effect between types of biostimulant. Interaction effect between biostimulants and TSS variety was only significant on leaf chlorophyll content. Biostimulant application could be expected to increase growth and yields of TSS. Keywords—Biostimulants, bulbs, roots, true seed shallots.


I. INTRODUCTION
The use of true shallot seeds (TSS) is increasing particularly in Indonesia due to its advantages compared to seed bulbs (Basuki, 2009). The benefits of TSS are free from pathogen, small amounts of planting materials, easier transporting and storaging, producing healthier crops and bigger bulbs (Ridwan et al., 1998;Permadi, 1993;Sumaratne et al., 2005. The use of TSS ia economically beneficial due to doubling the yields compared to seed bulb crops van den Brink and Basuki, 2011). However, the slow growth of seedlings in the nursery takes 21-25 days to be able to transplant into the field resulted in longer time in producing bulbs compared to seed bulb crops. Seed priming has been proved to increase seed germination and reduce abnormal seedlings of onions ((Allium cepa cv. aggregatum L.) (Caseiro et al., 2004;Sevarani and Umarani, 2011;Jagosz, 2015). Biostimulant or plant growth promoting rhizobacteria (PGPR), is a group of beneficial bacteria actively colonizing the rhizosphere and important in increasing plant growth (Rahni, 2012). Research results showed that bacteria of Pseudomonas, Azotobacter, Bacillius dan Serratia genus were identified as phytohormone producers such as auxin, cytokinin, gibberellin, ethylene and absisic acids that were able to enhance the growth and yield of plants (Rahni, 2012). GA 3 significantly enhanced seed germination, index of seedling vigour and the speed of seedling emergence of true seed shallots variety Tuktuk compared to KNO3 (Agung and Diara, 2017). Steptomyces griseoviridis was also reported to produce auksin and IAA invitro which is able to stimulate plant growth (Fitrah-pratiwi et al., 2017). Biostimulants that contain Pseudomonas fluorescens colonize the rooting zones of bamboo were reported to increase the solubility of soil phosphorus . Some strains of Pseudomonas fluorescens can avoid the infection of soil pathogen fungi and is used as biocontrol agents commercially in the glasshouse and in the fields (Arshad and Frankenberger, 1997).

II. METHODOLOGY
The research was conducted in the glasshouse in Tangtu village, Badung regency,Bali province of Indonesia, from April until October 2018. The objective of this research was to investigate the effects of biostimulan (PGPR) on root growth of seedlings and bulb yields of true seeds shallots (TSS). Complete randomized block design was used with 4 replications. Three kinds of biostimulants (B, C, D) and one control, and two TSS varieties (Sunren F1 and Tuktuk) were the treatments imposed. Biostimulant B consisted of Rhizobia, Azospirillum sp., Bacillus subtilis, Aspergilus niger, Lactobacillus sp, Pseudomonas putida. Biostimulant C consisted of total bacteria, Azosprillum sp., Azotobacter sp. and N fixed bacteria. Microorganisms in biostimulant D were Pseudomonans fluorescence, Trichoderma, Aspergillus niger, Azotobacter, Azospirilum and Rhizobium. After soaking in each biostsimulant for 24 hours, 25 seeds were germinated in petridshes as well as on moistened tissues wrapped with transparent plastic sheets. Seedlings were then transplanted into 20 cm diam pots. Germination percentage of seeds, root length of seedlings, leaf chlorophyll content, bulb diameter, bulb number, leaf and bulb fresh weight per pot were the variable measured.

III.
RESULTS AND DISCUSSION 3.1 Germination Percentage Biostimulants as well as variety significantly (P<0.05) increased the germination percentage of TSS. Biostimulants resulted in 41.37% higher germination than control (Table 1). There was no difference effect between types of biostimulants. Sunren F1 variety had 41.67 % higher germination than Tuktuk variety (Table  1). There was no effects of interaction between types of biostimulant and TSS variety on germination percentage.

Seedling Root lengths
Seedling root lengths of both varieties were significantly (P<0.05) increased by biostimulants. Biostimulants resulted in 27.65% higher root longer rooth lengths compared to control ( Table 1). Variety of Sunren F1 produced 64.44% longer roots than Tuktuk (Table 1). There was no effects of interaction between Biostimulant and TSS variety on seedling root lengths. Rhizobacteria promote better root development directly through production of phytohormones and indirectly by inhibiting pathogen infection with synthesis of different substances (Benizri et al., 2001).

Leaf Chlorophyll Content
There was significant (P<0.05) effect of interaction between types of biostimulant and variety on leaf chlorophyll content. Biostimulants significantly increased leaf chlorophyll both on variety of Sunren F1 and Tuktuk although the effects on Sunren F1 higher than on Tuktuk. Leaf chlorophylls were increased by 58%, 48% and 60% due to biostimulants A, B and C application respectively compared to without biostimulant ( Table 2). The total chlorophyll content was also reported to be significantly stimulated by P. agglomeranset Proteamaculansen on tomato leaves (Moustaine et al., 2017) in comparison with other treatments.

Leaf and Bulb Fresh Weights and Bulb Number
per Pot Biostimulant significantly increased (P<0.05) leaf and bulb fresh weights (FW) and bulb number per pot (Table  1). These parameters were 38.05%, 48.09% and 38,43% respectively higher than control. The effects of biostimulant were not different among types of biostimulant.
Variety of Sunren F1 produced significantly higher values of those variables than Tuktuk (Table 1). Better root growth caused by the effects of biostimulant enhanced the absorbtion of soil nutrients and moisture surrounding roots and finally increased plant growth. As it well known biostimulant is defined as formula that contains living microorganisms which have potential to colonize plant roots and enhance plant growth due to increasing the availability and the acquisition of soil nutrients (Packialakshmi and Aliya, 2014). Biostimulant or Plant growth promoting rhizobacteria (PGPR) is basic components of biofertilzer. Strains of PGPR such as Burkkholderia, Azospirillium, Enterobacter, Azotobacter, Erwinia, Rhizobium and Flavobacterium have proved that function (Rodriguez and Fraga, 1999). The biostimulants increased the availability of soil nutrients (N, P, Zn and Fe) as well as production of phytohormones which were categorized as phytosimulators) (Naveed et al., 2008). Representatives of Bacillus and Pseudomonas were reported as bioinoculants with high potential on cereals (Talic et al., 2006).Better plant growth, due to biostimulant application resulted in increased leaf number and leaf fresh weights. Enhancement of leaf growth and other shoot parts contributed to increasing photosynthates and finally enhancing the growth of shallot bulbs compared to without biostimulants. Variety of Sunren F1 may be genetically better than Tuktuk so its growth and yield performance were higher (Table 1).

Bulb Diameter
Biostimulants significantly (P<0.05) increased diameter of shallot bulbs. Bulb diameter was 27.92% bigger due to biostimulant application compared to without biostimulant. Sunren F1 variety had 64.83% bigger bulb diameter compared to Tuktuk (Table 1). Cell division, cell elongation, cell formation, and the formation of new tissue required carbohydrates. Carbohydrate synthesis was heavily influenced by the ability of plants to perfo rm photosynthesis (Husen, 2007), although Sumiyati et al. (2016) did not find any differences in bulb diameter of shallots due to PGPR application.

IV. CONCLUSION
Biostimulants significantly (P<0.05) increased germination percentage, root length, leaf and bulb fresh weights and bulb number of TSS per pot. Biostimulants increased root length, bulb fresh weights, bulb number, leaf chlorophyll content and bulb diameter. by 27.65%, 45.09%, 38.43%, 55.33% and 27.92% respectively. There was no different effect between types of biostimulant. Variety Sunren F1 performed higher values than Tuktuk in all parameters. There was significant interaction effect between types of biostimulant and variety only on leaf chlorophyll content.