In vitro Compatibility between Botanicals and Pesticides against Xanthomonas axonopodis pv. punicae

Bacterial blight caused by Xanthomonas axonopodis pv. punicae is a major concern. Since then several workers have reported the occurrence of blight and resultant losses from different states of the country viz., Tamil Nadu (Rangaswami, 1962), Himachal Pradesh (Sohi et al., 1964), Haryana (Kanwar, 1976), Karnataka (Chand and Kishun, 1991), Maharashtra (Kamble, 1990) and Punjab (Rani and Verma, 2001). Stem infection is also observed in severely infected orchards with girdling and cracking symptoms. Spots on fruits are variably dark brown in colour, irregular, slightly raised with oily appearance, which splits open with L or Y-shaped cracks under severe stages of disease (Bora and Kataki, 2014). Use of chemicals is not only the solution for management of any disease, while its use leads to pollution and hazard to the ecosystem.


Introduction
Bacterial blight caused by Xanthomonas axonopodis pv. punicae is a major concern. Since then several workers have reported the occurrence of blight and resultant losses from different states of the country viz., Tamil Nadu (Rangaswami, 1962), Himachal Pradesh (Sohi et al., 1964), Haryana (Kanwar, 1976), Karnataka (Chand and Kishun, 1991), Maharashtra (Kamble, 1990) and Punjab (Rani and Verma, 2001). Stem infection is also observed in severely infected orchards with girdling and cracking symptoms. Spots on fruits are variably dark brown in colour, irregular, slightly raised with oily appearance, which splits open with L or Y-shaped cracks under severe stages of disease (Bora and Kataki, 2014). Use of chemicals is not only the solution for management of any disease, while its use leads to pollution and hazard to the ecosystem.
Apart from the fact that pomegranate is largely exported to European and American markets, they have rigid grading standards vice-versa., residual toxicity level for various pesticides, hence, the use of antibiotics/ bactericides is discouraged. Thus, there is a need to develop alternative and eco-friendly measures for controlling the disease. Greater emphasis has been placed towards development of biological pesticides, which includes botanicals.

Materials and Methods
All the botanicals and their combinations were tested under laboratory condition by agar well diffusion method to know the compatibility between botanicals and pesticides. Compatibility of botanicals with different bactericides, fungicides and insecticides commonly used in pomegranate were tested under laboratory condition by agar well diffusion method (Table 1).
The compatibility of these botanicals was confirmed by Agar well diffusion method (Holder and Boyse, 1994). The culture of X. axonopodis pv. punicae was added to nutrient medium and poured in to the Petri plate and allowed solidify. The agar plates were punched aseptically with 6-mm sterilized cork borer to prepare wells. The wells were filled with 100 µl of botanical extracts. All plates were incubated (30°C) for 48h. After incubation, the diameters of any clear zones around the wells were measured in milli meter. Sterile water filled in agar well considered as negative control.
However, in case of insecticides, all three insecticides are compatible with P. juliflora (1:5) at their three different concentrations tested.   Among them dimethoate 30% EC at 0.5, 1 and 2 ml/lit in combination with P. juliflora (1:5) showed highest inhibition zone of 22.67, 23.67 and 26.67 mm respectively. Followed by P. juliflora (1:5) + chlorpyrifos 20% EC with 22.00, 22.33 and 26.67 mm at 1.5, 2 and 3 ml/lit respectively and P. juliflora (1:5) + dichlorovas 76% EC (20.00, 22.33 and 25.33 mm at 0.25%, 0.5% and 1.0% respectively) and there was no inhibition of bacterial growth when insecticides tested alone at their three different concentrations. Hulloli et al., (1998) recorded neem products can act as synergistically with antibiotics (Streptocyline and kanamycin)/fungicides (ridomylmancozeb) and reduced their hazardous effects. The MIC (minimal inhibitory concentration) of certain mixture was effective at lower concentrations than the MIC of individual chemicals indicating that neem formulations have synergistic activity when combined with antibiotics and fungicides. It is thus clear that addition of neem products to chemicals not only reduced their MIC but also eliminated the hazards of the development of the drug mutants. Kumbhar et al., (2001) evaluated the combined formulation of Capsicum annuum (green chilli), Zingiber officinale and Allium sativum with 5 per cent cyclohexane exhibited better potential than individual formulation and crude extracts against A. niger, A. flavus and F. oxysporum under in vitro.  (18.67, 20.67 and 23.00 mm at 1.5, 2 and 3 ml/lit respectively) and G. indica (1:5) + dichlorovas 76% EC (17.67, 20.00 and 21.33 mm at 0.25%, 0.5% and 1.0% respectively) and there was no inhibition of bacterial growth when insecticides tested alone at their three different concentrations. Meena et al., (2017) reported efficacy of antibiotic, fungicide and botanical were examined individually as well as in combinations for two consecutive years. Combined application of tetracycline @ 250 ppm + copper hydroxide @1000 ppm along with garlic clove extract @ 20 per cent effectively suppressed the disease and recorded the minimum of 16.20 PDI with 76.72 per cent reduction over control than the individual treatments. Application of garlic cloves extract along with tetracycline @ 250 ppm and copper hydroxide @1000 ppm had synergistic effect on the suppression of the bacterial pathogen associated with pomegranate. Similar response were also recorded during 2014 with the foliar application of tetracycline + copper hydroxide + garlic cloves extract, which had a minimum of 13.40 PDI with 79.51 per cent disease reduction over control. It was comparatively superior over the standard check namely, streptocycline + copper oxychloride. However, individual application of tetracycline @ 250 ppm or copper hydroxide @1000 ppm or, garlic cloves extract were least effective in the suppression of pomegranate bacterial blight. Therefore, it can be hypothesized that combine application of these chemicals with different mode of action have very good response in managing plant disease due to their synergistic effect. Besides, it also reduced the chance of multidrug resistance development within pathogen's population.