The Effect of Bacillus cereus and Bacillus subtilis on Pathogenicity of Meloidogyne javanica in Three Rootstocks of Peach under Greenhouse Condition

Plant-parasitic nematodes, especially root-knot nematodes, cause a lot of damage to most agricultural products and a lot of efforts are made to control them. Biological control is one of the most widely studied methods to reduce nematode damage. This study aimed to evaluate the effect of two bacteria including Bacillus cereusIPRI95 and B. subtilisVUPF52 on the infection of Meloidogyne javanica on three rootstocks under greenhouse conditions.

This study was performed as a factorial experiment in a completely randomized design with five replications. In this way, the soil of the pots was disinfected before planting the seedlings, and then the seedlings were planted. After the establishment of the rootstocks, a three-day liquid culture peach for each bacterial isolate was prepared with a concentration of 107 colony-forming units in milliliters (CFU / ml) and 15 ml of suspension from each bacterium to the soil around the seedlings were added in each treatment. Two days after treating the plants with bacteria in the pots, inoculation with 2000 eggs with larvae of nematodes per kilogram of soil, entered into 3 holes created around the seedlings and then covered with soil these holes. Experimental plants to pass at least three generations of nematodes, three months in suitable greenhouse conditions with a temperature of 20 to 25 degrees, relative humidity 60-80% and optical period (13 hours of light, 11 hours of darkness) maintenance and regular watering twice in the week was over. At the end of the experiment, plant growth indices include (length, fresh and dry weight of shoots, length, fresh and dry weight of roots) and nematode growth parameters including (number of galls, number of second larvae (j2), number of egg mass in plant roots and number Eggs per egg mass, as well as a reproductive factor (RF), were measured an statistically analyzed using SAS 9.4 software. A comparison of mean treatments in all cases was performed by LSD-protected test at 5%.

Nematode contamination in the absence of biocontrol agents significantly reduced the growth index at all levels compared to other treatments. So the peeling of peach bases with nematode reduces the stem length by 34% and 30% in GF677 and Shorabi local cultivars, respectively, compared to the control treatment. The results of comparing the means between treatments in GF677 showed that stem length in these plants treated with two bacterial strains increased significantly compared to the control. Root length also decreased by 14 and 50 percent in Helendri and GF677 cultivars, respectively, following infection with nematode compared to control treatment. However, following the treatment of peach roots with bacterial strains, we saw a significant increase in root length, so that the maximum root length in Helendri cultivar in treatment with B. subtillis strain and GF677 cultivar followed by treatment with B. cereus was obtained. Statistical analysis showed that the two bacterial isolates mentioned, in addition to affecting the growth factors of vegetative bases, also had a significant effect on nematode growth and development indicators and disease reduction. So that the number of eggs and egg mass decreased in all three cultivars. The mean number of galls per gram of root in GF677 treated with B. subtilis and B. cereus bacteria decreased by 48.4% and 40.68%, respectively, compared to the non-bacterial control. The results of this study also showed that the J2 population in treatments with nematodes alone compared with treatments with bacteria have a significant difference. The number of J2 larvae in the presence of B. subtilis bacteria decreased by 67.73, 52.52 and 12.6% in Helendri cultivars, GF677 and local cultivar Shorabi compared to the control. The use of biological bacteria affected all stages of nematode growth and development. However, the ability of bacteria to reduce nematode reproductive factors was significant in the nematode-sensitive cultivar (Gf). The findings of this study showed the controlling effect of biocontrol bacteria used on the propagation and damage of root-knot nematodes. So that by increasing plant growth indices, nematode damage was reduced. Although the bacteria used were effective on all three rootstocks, due to GF677 being more sensitive to root-knot nematodes than Helendri cultivars and the local cultivar Shorabi, the effect of bacterial agents on the rootstock was less than the other two rootstocks.