In vitro evaluation of antibiotics against Enterobacter cloacae causing leaf rot of onion

Introduction

Onion (Allium cepa L.) is one of the oldest bulb crops belongs to Amaryllidaceae family. The genus Allium comprises over 700 species which can be found throughout the tropical, temperate and sub-temperate regions of the world (Fritsch and Friesen, 2002) [2] . There are five important species of Allium of which the onion (Allium cepa) is the major cultivated species grown all over the world. According to Vavilov (1951) [7] the primary center of origin lies in central Asia. Onion has manifold use such as spice, vegetable, salad-dressing etc., (Vohra et al., 1974) [4] . Among vegetables, onion often called as "queen of kitchen" it is one of the oldest known and an important crop. India (288.00 lakh tons) is the largest producer of onion. In India Maharashtra is the leading producing state. In Karnataka the area under onion is 2.32 lakh hectares, with production of 38.91 lakh tons, (Anon., 2024) [1] . Onion has high value both in domestic use and export purpose, but growing of onion has some constraints such as insect pests and diseases. The pests are thrips, whiteflies, beetles etc. Now a day's bacterial leaf rot is becoming an important disease in northern part of Karnataka from past 8-10 years. There is a need to develop ecofriendly management practice for mitigating the plant diseases. Hence, commercially available bio-agents and botanicals were evaluated against the disease under in vitro.

Materials and Methods

Evaluation of different Antibiotics

Antibiotics were screened under in vitro against the growth of bacterium causing leaf rot of onion at different concentrations by agar well diffusion method. The list of chemicals which were evaluated with three replications in each treatment is mentioned in Table 1. The bacterium was multiplied by inoculating the fresh culture into 50 ml of nutrient broth taken in a 100 ml Elsmere's flask. The flask which is inoculated with the pathogen was kept in a shaker incubator at 30 0 C for 48 hours. The suspension of the bacterial culture was then poured into to the lukewarm nutrient agar medium (1000 ml) i.e. 5ml / litre in a conical flask. The medium was seeded with bacteria was poured into the sterilized Petri plates and plates were allowed to solidify. The chemicals and antibiotics were prepared at different concentrations as mentioned in the list.

International Journal of Advanced Biochemistry Research 2025; SP-9(10): 724-728

The Agar well diffusions measuring 10 mm in diameter were made after solidification of the seeded medium in the Petri plates and then poured with the respective chemical solution into the wells. The inoculated plates were incubated at 28 ± 2 o C for 24h and observed for the production of inhibition zone around agar well diffusions. The results obtained by the experiment were analyzed statistically.

Results

The antibiotics / chemicals were screened against the growth of Enterobacter cloacae, by agar well diffusion method. Among the different antibiotics, streptocycline (31.33, 33.50 and 35.33 mm) and plantamycin (26.00, 26.83 and 28.33 mm) were shown highest inhibition at 300, 400 and 500 ppm concentrations, respectively. It was followed by 2bromo-2 nitropropane-1, 3-diol (23.17, 25.83 and 31.67 mm) at different concentrations, respectively. Among the fungicides copper hydroxide (16.17, 18.83 and 22.17 mm) and copper oxy chloride (15.83, 17.50 and 20.83 mm) recorded highest inhibition at 1500, 2000 and 2500ppm, respectively. Whereas kasugamycin (Omycin) was not shown any inhibition zone at all the concentrations tested. Wheras in water control no inhibition was observed (Table 2 and Plate 1).

Discussion

In vitro evaluation of chemicals or antibiotics against the growth of Enterobacter cloacae

A total of seven chemicals were evaluated for their efficacy against growth of Enterobacter cloacae by agar well diffusion method and the mean inhibition diameter was recorded. Among the different antibiotics, streptocycline (33.39 mm) and plantamycin (27.06 mm) were shown the highest average inhibition at 300, 400 and 500 ppm concentrations respectively. This was followed by 2-bromo-2 nitropropane-1, 3-diol (26.89 mm respectively). Among the fungicides, copper hydroxide (19.06 mm) and copper oxy chloride (18.05 mm) recorded highest inhibition at 1500, 2000 and 2500 ppm respectively. However, kasugamycin showed no inhibition zone in all the concentrations tested (Figure 3). Similar kinds of investigations were also reported on banana by Thammaiah et al. (2005) [5] through in vitro screening of chemicals against Erwinia chrysanthemi by the modern paper disc method with seven treatments. The result showed that the combination of streprocycline at 1000 ppm + copper oxy chloride at 2000 ppm, recorded the maximum inhibition (24.00 mm) followed by copper oxy chloride at 4000 ppm (23.33 mm). Nagrale et al., (2013) [6] studied the effectiveness of different chemicals against E. chrysanthemi pv. paradisiaca under in vitro conditions. The maximum inhibition zone was noticed for streptocycline (200 ppm) + copper oxychloride (0.1%), tetracycline (200 ppm) and streptocyline (200 ppm) viz., which is followed by agrimycin (200 ppm), bordeaux mixture (0.1%) gentamycin (200 ppm), captan (0.2%) and copper oxychloride (0.25%).

Conclusion

Among the different antibiotics evaluated against the E. cloacae, streptocycline (33.39 mm) shown highest mean zone of inhibition. Among the fungicides, copper hydroxide (19.06 mm) recorded highest mean zone of inhibition. The results on evaluation of chemicals, botanicals and bio agents against leaf rot disease revealed that, among the treatments, T1 (Streptocycline at 500 ppm + Copper oxy chloride (0.3%) was found most effective. In which the percent reduction of disease in terms of percent disease incidence (77.83%) and number of lesions per branch (76.24%).

Acknowledgement

AcknowledgmentsThe authors gratefully acknowledge the Dept. Plant Pathology for providing guidance during my research period and helping in publishing the research paper.

References

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