Pseudomonas fluorescens for the Management of Root-knot Nematode Meloidogyne incognit a in Tomato

A field experiment was conducted in Coimbatore district to study the efficacy of the biocontrol agent Pseudomonas fluorescens for the management of root-knot nematode Meloidogyne incognita in tomato. Soil application of the native isolates Pft 20 @ 2.5 kg/ha significantly reduced the nematode infestation in all the bacterized plants both in soil and roots with the least number of adult females, number of egg masses, number of eggs per egg mass and gall index and besides increased the plant growth, total soluble sugars and lycopene content of the fruit.

Tomato (Lycopersicon esculentum Mill) is one of the important vegetable crops grown in India.It is cultivated in an area of about 4.5 lakh hectares and contributes to total production of 7.5 lakh tonnes and productivity of 16.3 MT/ ha.Root-knot nematodes (Meloidogyne spp.) are the major pathogens of tomato throughout the world, affecting both the quantity and quality of marketable yields.The yield loss due to the root-knot nematode in tomato is estimated to be up to 40 percent (Dasgupta, 1998).The plant growth promoting rhizobacterium, Pseudomonas fluorescens Migula is reported to be effective in suppressing M. incognita in many crops viz., tomato (Jonathan et al., 2000).Therefore an investigation was undertaken for the management of root knot nematode infesting tomato by the rhizobacterium, P. fluorescens.

Materials and Methods
Soil samples were collected from the rhizosphere of healthy tomato plants in Coimbatore district to isolate native strains of P. fluorescens by serial dilution agar plate technique.One ml each of 10 -5 and 10 -6 dilutions were pipetted out and poured into sterile Petri dishes.King's B medium (King et al., 1954) was poured in Petri dish, rotated and inoculated at room temperature (28 ±1°C) for 24 h.The colonies with raised surface showing fluorescent colour were individually purified and subcultured.
Effective P. fluorescens isolates were formulated in purified talc powder (sterilized at 10°5 C for 12 h) with calcium carbonate 15g (to adjust the pH to neutral) and carboxy methyl cellulose (CMC) 10g (adhesive) following the method described by Vidhyasekaran and Muthamilan (1995).At the time of application, the population of bacteria in talc formulation was 2.5 -3 x 10 8 cfu/g.
A field experiment was conducted in Madampatti village, Coimbatore District to test the bioefficacy of talc based formulations of promising P. fluorescens isolates against the natural infestation of M. incognita in tomato.The talc based formulation of the promising P. flourescens isolates Pft 18, Pft 20 and Pft 25 applied to the soil at two doses viz., 2.5 kg/plot and 3.0 kg/plot.The strain Pf 1 was obtained from the Department of Plant Pathology, Tamilnadu Agricultural University, Coimbatore, India.The effectiveness of these isolates was compared with Pf1 and the chemical carbofuran 3G applied @ 1 kg a.i / plot.An untreated control was also maintained.The plot size of 10 m 2 was maintained for all the treatments.The formulation was applied 30 days after planting of the tomato seedlings of cv.PKM-1.The initial nematode population in the field was 240 juveniles/200 cm 3 which was obtained by taking samples at different locations randomly and the samples were mixed well.A representative sample of volume 200cm 3 was processed as per Cobb (1918) and modified Baermann funnel technique (Schindler, 1961).The study was conducted with 10 treatments by using randomized design with ten treatments each replicated three times.
Observations on fruit yield at the time of harvest; fruit qualitative characters viz., total soluble sugar (TSS) and lycopene content were recorded.The plants were carefully uprooted and the observations on gall index, number of females per 5 g of root, number of egg masses per 5 g of root and number of eggs per egg mass were recorded.The soil and roots were processed as per Cobb (1918)  1961).The gall indices were graded on 0 to 5 scales (Taylor and Sasser, 1978).All the data were statistically analyzed and critical differences determined (Gomez and Gomez, 1984).

Results and Discussion
The results showed that Pft 20 treatment @ 2.5kg/ha on tomato recorded significant increase in the total soluble sugar and lycopene content.The maximum fruit yield of 3.5 tonnes/ha was recorded in Pft 20(2.5kg/ha)treated plants compared to the control (Table 1).P. fluorescens is capable of surviving and colonizing in rhizosphere of all field crops and they are reported to promote plant growth by secreting auxins, gibberellins and cytokinins.Reduction in the multiplication of M. incognita by P. fluorescens treatment is also reported in several crops (Jonathan et al., 2000).
A significant decrease in the nematode population with the least number of adult females, number of egg masses, number of eggs per egg mass, gall index and population in soil and roots was recorded in the Pft 20 treated plants (Table 2).Several mechanisms were attributed to the  (Oostendorp and Sikora, 1990).Although there was not much difference in the application of talc formulation of P. fluorescens at two different rates ie., 2.5 and 3.0 kg/ha, results reveal that the application at 2.5kg/ha would be more effective for managing the soil pathogens especially the nematodes.It is obvious from the above study that P. fluorescens could effectively be used as an alternative for chemicals for managing root knot nematodes in crops.

Table 1 . Efficacy of talc formulations of P. fluorescens isolates on TSS, lycopene and yield of tomato cv. PKM-1 infested with M. incognita under field conditions
and modified Baermann funnel technique(Schindler,