THE EFFECTIVENESS OF RHIZOBACTERIA AS BIOPROTECTANTS TO MITIGATE FUSARIUM WILT DISEASE AND AS BIOSTIMULANTS TO IMPROVE THE GROWTH OF CHILI ( Capsicum annuum )

The aims of this study were to examine the potential of Rhizobacteria as bioprotectants and biostimulants on chili. The potential as bioprotectants was tested by the ability of these Rhizobacteria to inhibit the growth of the pathogenic fungus Fusarium oxysporum f.sp. capsici in vitro. Moreover, as biostimulants was tested by the ability of these rhizobacteria to produce IAA compounds and their ability to increase the plant growth parameter of chili. Four rhizobacteria were challenged for antagonistic activity against F. oxysporum f.sp . capsici. Chili seeds in this experiment were soaked in four different Rhizobacteria suspension for 15 minutes. For control, seeds were soaked with sterile water instead of Rhizobacteria suspension. Results of this experiment showed that four isolates of Rhizobacteria showed strong inhibitory activity against F. oxysporum f.sp. capsici on PDA medium. Percentage of inhibitory activity varied from 77,33% to 89,79%. The application of four isolates recorded significantly increased the plant growth parameters of chili. The plant height, number of leaves, leaf area, root length, shoot dry mass, root dry mass, and chlorophyll content on treated plants significantly higher than those of untreated control plants according to the Duncan’s multiple range test (P<0.05%). These results indicate that the tested Rhizobacteria can be used as bioprotectants because they can inhibit the growth of F. oxysporum f.sp. capsici and simultaneously as a biostimulant for the ability to produce IAA compounds and stimulate the growth of chili.


INTRODUCTION
Chili is an important and popular commodity in Indonesia which has a high economic value.This spice is one of the most widely used for household consumption, industry, and in food processing (Ismawati, 2016).However, the average productivity of chili in Indonesia is The purpose of this study was to examine the potential of Rhizobacteria as bioprotectants by challenging their ability to inhibit the growth of F. oxysporum f.sp.
capsici in vitro and to examine the potential of rhizobacteria as biostimulants by testing their ability to produce IAA compounds and mediated the growth of chili.

Biostimulant
The potential test of rhizobacteria as biostimulants was conducted by testing the ability of rhizobacteria to produce IAA

Bioprotectant
The test results of the ability of rhizobacteria to inhibit the growth of F. oxysporum f.sp.capsici in vitro showed that rhizobacteria were able to inhibit the growth of F. oxysporum f.sp.capsici fungal colonies with the percentage of inhibition ranging from 77.33% to 89.79% (Table 1).The area of fungal colonies in the TR78 treatment amounted to 285.77 mm2 with a percentage inhibition of 77.33% when compared to the control.While the colony area in the SW04 treatment amounted to 267.82 mm 2 with a percentage inhibition of 78.76%, the colony area in the KC29 treatment amounted to 188.21 mm 2 with a percentage inhibition of 85.07%, and the colony area in the KC66 treatment amounted to 128.79 mm 2 with the highest percentage inhibition of 89.79% when compared to the control.when compared to the control.
The rhizobacterial treatments of P.
agglomerans TR78, S. maltophilia KC29 and K. pneumoniae KC66 were able to reduce the root length while K. pneumoniae SW04 was able to increase the root length of chili plants (Figure 3).The rhizobacterial treatments of P. agglomerans TR78, S.
low.According to the Central Bureau of Statistics (2022), in 2021 national chili production in Indonesia decreased by 8.09% compared to the production in 2020.The national chili production decreased to 1.39 million tons in 2021 while in 2020 the national chili production was 1.5 million tons.One of the factors that lower chili production in Indonesia is because of fusarium wilt disease invasion.Wilt disease on chili commonly caused by the fungal infection Fusarium oxysporum f. sp capsici.The use of synthetic fungicides to control F. oxysporum f.sp.capsici has been widely practiced and proven less effective in controlling this fungus.Besides, an excessive amount of applied synthetic fungicides lead to severe environmental pollution.One of the efforts that become a moral responsibility for us to reduce the use of synthetic fungicides is plant growth because they produce substances that have biological activity as growth promoters.
compounds and testing their ability to increase the growth of chili plants.The test of the ability of rhizobacteria to produce IAA was conducted by colorimetric method based on Wahyudi et al. (2011).Rhizobacteria were grown for 48 hours in Nutrient Broth medium added with 1 mM Ltryptophan.The rhizobacterial culture was centrifuged at 1610 x g for 30 min, then the supernatant was separated from the bacterial sediment and filtered with Millipore filter paper (0.45 mm).Furthermore, IAA content in the filtrate was detected using Salkowski reagent (1 ml 0.5 M FeCl3 and 49 ml 35% HClO4).A total of 1 ml of rhizobacterial filtrate was put into a 2 ml eppendorf tube and then 1 ml of Salkowski reagent was added.The eppendorf tube containing the solution was incubated in a dark room at room temperature for 30 minutes.A change in the color of the solution in the eppendorf tube to pink indicates that the rhizobacteria produce IAA.Test the ability of rhizobacteria in increasing the growth of chili plants was carried out by invigorating chili seeds with 2% suspension of each rhizobacteria.The 2% concentration was obtained from 2 ml of culture in PPDC media (5 g potato extract, 5 g peptone, 10 g dextrose, 1000 ml Coconut water) per 100 ml of water.The design used in this study was a randomized group design (RAK) with 5 treatments and 5 replicates.The treatments were control (KTRL); seed invigoration with P. agglomerans TR78 suspension (PAGS); seed invigoration with K. pneumoniae KC66 suspension (KLPE); seed invigoration with K. pneumoniae SW04 suspension (KLPN); seed invigoration with S. maltophilia KC29 suspension (STMA).Each replicate consisted of 10 plants.Seeds were then planted in pots that had been filled with planting media.Growth parameters observed were plant height, number of leaves, root dry weight, crown dry weight, root length, leaf area, and leaf chlorophyll content.Measurement of leaf chlorophyll INTERNATIONAL JOURNAL OF BIOSCIENCES AND BIOTECHNOLOGY • Vol. 10 No. 1 • September 2022 eISSN: 2655-9994 pISSN: 2303-3371 https://doi.org/10.24843/IJBB.2022.v10.i01.p0429 content (SPAD unit) was determined with Chlorophyllmeter SPAD-502.

Figure 1 .
Figure 1.Test the ability of rhizobacteria in inhibiting the growth of fungus F. oxysporum f.sp.capsici in vitro A. KTL0 treatment; B. TR78 treatment; C. KC29 treatment; D. KC66 treatment; and E. SW04 treatment
maltophilia KC29 and K. pneumoniae KC66 reduced root length by 17.72%, 12.30%, and 8.48% respectively when compared to the control while K. pneumoniae SW04 increased root length by 2.53% when compared to the control.The rhizobacterial treatment was able to reduce and increase the root length presumably due to differences in the concentration of IAA compounds produced by the rhizobacteria.Loper and Schroth (1986) reported the same research results that rhizobacteria are able to reduce root length and increase root length depending on the level of concentration of IAA compounds produced by rhizobacteria, the higher the IAA produced by rhizobacteria, the higher the reduction power of primary root length, where the percentage of reduction power of primary root length of sugar beet plants in the rhizobacterial treatment of P. fluorescens E8 which is high in concentration.fluorescens E8 which

Table 1 .
The results of the rhizobacterial ability test in inhibiting the growth of the fungus F.
* Values in the same column followed by the same letter are not significantly different (p>0.05) according to Duncan's Multiple Range Test at the 5% level.Fungal colonies of F. oxysporum f.sp.capsici in the control treatment grew normally with a colony growth rate of 180.14 mm2/day (Figure1and Table1).

Table 2 .
Table 2).The results of the rhizobacterial ability test in increasing the growth parameters of chili Effectiveness of Rhizobacteria as Bioprotectants to Mitigate Fusarium Wilt Disease and as Biostimulants oo Improve the Growth of Chili (Capsicum annuum) The