Evaluation of Botanicals against Phoma tropica Causing Leaf Spot Disease in Lablab purpureus

The aqueous phytoextracts of commonly available seventeen plant species were evaluated in vitro by poisoned food technique against their inhibitory effect on the mycelial growth and micro-sclerotial formation in Phoma tropica . The extract of Gando baval ( Prosopis juliflora L.) proved excellent in inhibiting mycelial growth and micro-sclerotial production. Extracts of nilgiri, turmeric, marigold. Pink barmasi, tulsi, ardusi, Jetropha, Bougainvillea, karanj, Lantana, onion, ginger, garlic, Dhatura and neem were found slightly inhibitory.

Indian bean is one of the important pulse cum vegetable crop of India. Leaf spot [Phoma tropica Schneider and Boerema] disease of Indian bean has become a major problem in recent past with a threat to successful and profitable cultivation in south Gujarat. The hazardous effects of chemicals used in plant disease management have diverted plant pathologists to find out the alternative methods of plant disease control which may cause little or no adverse effect on environment. Notable success of disease control through use of botanicals in the laboratory, glass house and field have been achieved during past several years. On the basis of this information, there is a possibility of development of biological control for plant diseases through botanical pesticides. Use of botanicals is an ecofriendly way to manage the disease so present work was carried out.

Materials and Methods
Healthy fresh plant parts i.e., leaves, bulbs or rhizomes were washed thoroughly with fresh water and finally rinsed with sterilized distilled water. Fifty gram of plant parts was cut into small pieces and homogenised with the help of a grinder by adding 50 ml sterilized distilled water. The phytoextracts were filtered through double-layered muslin cloth in 150 ml conical flasks and plugged with nonabsorbent cotton. These filtered extracts were autoclaved at 1.2 kg cm -2 pressure for 20 minutes. Autoclaved extract was individually added into previously sterilized PDA @ 10 per cent (i.e. 2 ml extract + 18 ml PDA plate -1 ) and mixed thoroughly at the time of pouring in the previously sterilized petriplates. The petriplates were inoculated aseptically after solidification by placing 5 mm diameter mycelial disc at the centre, cut aseptically with cork borer from 7 days old pure culture of P. *Corresponding author email: vijay.patilagri@gmail.com tropica. Three replications of each treatment were maintained. The plate without phytoextract served as control. The petriplates were incubated at 27 + 2°C temperature for 5 days.
The observation on radial mycelial growth was recorded by taking the average of two diameters of colony at right angles to one another for each Petriplate in each replication by subtracting 5 mm of the mycelial discs kept at the time of inoculation. The amount inhibition of growth was calculated by using the formula given by Vincent (1927) 100 (C-T) PI = C Where, PI = Per cent growth inhibition C = Average growth diameter of mycelial colony of control set (mm) T = Average growth diameter of mycelial colony of treated set (mm)

Results and Discussion
The results presented (Table 1.) revealed that the least average colony diameter was recorded in the leaf extracts of Gando baval (Prosopis juliflora L.). The next best in order of merit was leaf extracts of nilgiri (Eucalyptus citriodora Hook.) followed by turmeric which was on par with marigold. Pink barmasi was at par with tulsi. The remaining phyto extracts exhibited minimum growth inhibition over control.
Thus, leaf extract of Gando baval showed significantly maximum inhibitory effect. The next best were nilgiri followed by turmeric, marigold, pink barmasi and tulsi (38.78%) while extracts of ardusi, Jetropha, Bougainvillea, karanj, Lantana, kadvi mehandi, onion, ginger, garlic, Dhatura and neem also recorded inhibition of P. tropica to some extent. Ezhilan et al. (1993) recorded maximum inhibition of micro-sclerotial germination of Rhizoctonia solani, causal agent of sheath blight of rice with T. peruviana (31.7%) followed by P. juliflora (39.7%) and E. globulus (40.3 %). Both hot and cold water extracts of all the treatments significantly inhibited the mycelial growth of Macrophornia phaseolina and garlic proved to be the most effective remaining at par with carbendazim (Raza and Kurucheve 1998). Sindhan et al. (1999) studied the efficacy of different leaf extracts at 5, 10 and 20 % concentrations against Rhizoctonia solani and M. phaseolina and reported extracts of onion, ginger and garlic to be more inhibitory to the mycelial growth of pathogen at all the concentrations.
The effective phytoextracts viz., Gando baval, nilgiri, turmeric and marigold reported here suggests the possible alternative to over come the hazardous effect of chemicals which requires detail investigation for their active principle involved for inhibitory effect and testing at different concentrations in the field against Phoma tropica leaf spot disease in Indian bean (Lablab purpureus).