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The studies on "Biocontrol of bacterial wilt in tomato using arbuscular mycorrhizal
fungi" were carried out at the Oept. of Plant Pathology, College of Horticulture,
Vellanikkara during the period 2000 - 2002. The main objectives of the study were to
identify suitable native AMF from high and low wilt incidence areas of Thrissur and
Palakkad districts, screen them against Ralstonia solanacearum in pot culture under sterile
and wilt sick conditions, to determine the optimum inoculation time and inoculum density of
:\\1f and to test ~h,- ,,;;;cicncy 0: Aj,\1f in thc wilt sick field.
The soil samples collected from Thrissur and Palakkad district were analyzed for
their nutrient status, pH, Ralstonia population and total AMF spore count. The Vellanikkara
soils were acidic with low ,K, Ca and Mg and high P content when compared to
Ozhalapathy and Eruthiampathy soils. The Ralstonia population were generally higher in
Vellanikkara soils. On the other hand, Ozhalapathy soils had higher AMF spore count. The
Glomus sp. was found to be the most predominant AMF in the soils of high wilt
(Vellanikkara, Thrissur district) and low wilt incidence (Ozhalapathy and Eruthiampathy,
Palakkad district).
The screening of the predominant native AMF cultures against R. solanacearum
were carried out individually and in combinations under sterile conditions along with the
TNAU commercial culture [or comparison. The treatments with the native AMF
combinations 1'i2., GIOIllIlS sp. (OT) + Glomus sp. (ER), Glomus sp. (OT) + Glomus sp.
(VM) and Glomus sp (OM) - Glomus sp. (VBT) recorded the least percent wilt incidence
with the native A0.1F combination Glomus sp. (OM) + Glomus sp. (VBT) recording the
maximum number of days of plant survival (11 days). The dry weight and root length were
also higher for these three native AM F combinations.
The determination of the optimum inoculation time (at the time of sowing, at 15 days
before transplanting and at the time of transplanting) in combination with the inoculum
density (@ 25 g kg 1 soil, 50 g kg 1 soil and 75 g kg -I soil) were carried out using different

species of AMF in pot culture using wilt sick soil. The inoculation time at 15 days before
transplanting 75 g kg -I soil was found to be optimum. This was evaluated further, under pot
culture and field experiment studies using the native AMF combinations selected from the
screening experiment.
The selected native AMF combinations from the screening experiment were tried at
15 days before transplanting @ 75 g kg -I soil in pot culture using wilt sick soil in
comparison with the TNAU commercial culture to select the best two combinations for the
field experiment. The native AMF combinations recorded the least percent wilt incidence
and maximum number of days of plant survival when compared to the TNAU commercial
culture. The AMF combinations Glomus sp. (OM) + Glomus sp. (VBT) and Glomus sp.
(OT) + Glomus sp. (VM) were found to be the best.
A field experiment to test the efficacy of the selected native AMF culture
combinations were carried out using the tomato varieties Pusa Ruby (susceptible) and
Mukthi (moderately resistant). The native AMF combination Glomus sp. (OT) + Glomus sp.
(VM) recorded maximum number of days of plant survival (32 and 50 days respectively) in
both the tomato varieties. However, it could not prevent wilt incidence in the case of Pusa
Ruby variety, which recorded 100 percent wilt, and Mukthi variety 97 .. 9 % wilt incidence.
The same native AMF combinations Glomus sp. (OT) + Glomus sp. (VM) also recorded
maximum fruit number in Mukthi whereas Pusa Ruby did not produce fruits as they did not
survive even upto flowering.
The present study clearly indicated that the native AMF combination Glomus sp.
(OT) + Glomus sp. (VM) was the best in pot culture studies using wilt sick soil and could
delay the disease incidence in the susceptible Pusa Ruby variety of tomato upto 82 days after
transplanting. However, under field conditions it could delay the disease incidence in the
susceptible variety Pusa Ruby only upto 32 days and in the moderately resistant variety
Mukthi upto 50 days. So more extensive studies are needed to develop a suitable native
AMF to control the bacterial wilt in tomato which is effective under field conditions.