The two-spotted spider mite (Tetranychus urticae Koch) is an important pest of many horticultural crops. A study was conducted to evaluate the effect of three fluorescent Pseudomonas isolates obtained from rhizospheric soil of tomato (Solanum lycopersicon) in Agadir, Morocco: Q110B, Q036B and Q172B, as potential biological control agents for T. urticae. Both acaricide and repellent activities were assessed on homogenous adult mites. The acaricidal activity test evaluated five concentrations of bacterial suspensions: 0 (control), 10 2 , 10 4 , 10 6 , 10 8 , and 10 10 cfu ⋅ ml -1 , while only the 10 10 cfu • ml −1 concentration of each bacterium was used for the repellent bioassay. The mortality rate and repellentindex were recorded 24, 48 and 72 h after application. Results indicated that the survival rate of T. urticae was reduced (p ≤ 0.01) by all three bacterial isolates compared to control. Within the 24-72 h time period the mortality rates ranged from 8 to 87%, 16 to 99%, and 13 to 89%, for Q110B, Q036B and Q172B isolates, respectively. The isolate Q036B (LC 50 = 0.598 cfu ⋅ ml -1 ) provided higher mortality rates than Q172B and Q110B with LC 50 values of 90,846 and 169,585 cfu ⋅ ml -1 , respectively. Repellent activity was also the highest with Pseudomonas Q036B having a 71% repellence index at 48 h after application. Regarding the mechanism of action, all three isolates produced hydrogen cyanide, and exhibited protease and cellulose activities, although only Q036B and Q172B had potential chitinase action. Identification analysis showed that the isolates were either Pseudomonas putida (Q172B) or P. fluorescens (Q110B and Q036B). Our results indicate that the P. fluorescens isolate Q036B is a promising candidate for biological control of T. urticae, and has potential to contribute to an integrated pest management program to control this important pest. Then the fruits produced will be qualified as safe for consumers and the environment. The present work was customized to give support for policy decision makers as an agroecological potential meeting needs of industries and ecological balance.
In agroecosystems, soil biodiversity is increasingly becoming more recognized as providing benefits to both plants and human health. It performs a wide variety of ecological services beyond the recycling of nutrients to plant growth and manage pests and diseases below the economic injury level. This study investigated the effects of three Pseudomonas isolates (Q172B, Q110B and Q036B), isolated from untreated tomato rhizospheric soil, as a biological control agent of Bemisia tabaci which is a key pest of tomato crops. The study was conducted under laboratory and glasshouse conditions and the water treatment was used as a control. Adult mortality rates were assessed during three days at 24h interval and larva mortality rates were evaluated during six days after treatment at 48h interval. Results indicate that Q036B isolate has a faster effect on B. tabaci adult and larvae. Under laboratory conditions, all three Pseudomonas isolates (Q110B, Q036B and Q172B) have a significant effect on B. tabaci adult mortality compared to control. The earliest and the most important mortality rate of 76% was recorded by Q036B. Two isolates Q036B and Q110B caused a significant mortality on B. tabaci larvae; with highest mortality effect (79%) was observed for Q036B compared to control. However, Q172B has no mortality effects on B. tabaci larvae under laboratory conditions. In glasshouse conditions, only Q036B provided high mortality rates of 91% at 168h after treatment. The results of this study indicate that the Pseudomonas isolate Q036B significantly suppresses B. tabaci in tomato plant and could substitute the excessive use of chemicals. Current research indicates that soil biodiversity could be promising to preserve agro-ecological sustainability.
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