Dose Response of Meloidogyne incognita Infected Cherry Tomatoes to Application of Pasteuria penetrans

Abstract

Pasteuria penetrans, an obligate parasite of Meloidogyne incognita was applied to field soil infested with M. incognita to measure the suppressive affect of P. penetrans on M. incognita numbers during three consecutive plantings of cherry tomato. The field soil, initially infested with 225 J2/20 g soil, was mixed with or without a P. penetrans powder formulation to obtain 0, 10⁴, 3×10⁴, 10⁵, 3×10⁵ and 10⁶ spores/g soil. The treated soil in 11 cm pots were then used for three consecutive cherry tomato plantings that were transplanted as seedlings and maintained in a greenhouse 63, 62 and 60 days respectively for the three plantings and harvested. There was a dose response for number of juveniles (J2)/20 g soil, root gall index, number of spores/J2, % J2 with spores, spores produced/root system, and total plant weights. At the first harvest only soil receiving 10⁶ spores/g soil suppressed J2 numbers significantly but the dose response increased with each harvest. At the third harvest, J2 numbers and the root gall index were significantly reduced in all treatments inoculated with P. penetrans with a 90% reduction in J2 numbers at the 10⁶ spore level. The results suggest 1) the suppressive affect of P. penetrans on M. incognita is dependent on the density of spores in soil, 2) at low spore densities, the suppressive affect is primarily due to reducing egg mass production and not on nematode mobility and/or root penetration, 3) at high spore densities, J2 mobility and/or root penetration as well as egg mass production are reduced, and 4) soil spore densities that result in close to 100% of J2 with spores attached are necessary for maximum beneficial affect.