Use of Trap Crops and Biocontrol Agents in Root Knot Nematode Management Under Greenhouse Tomato Production

Abstract

Root knot nematode (RKN) infestation in tomato results in a substantial reduction in yields. Management of the nematodes is constrained by their polyphagous nature, inaccurate diagnosis, and the fact that synthetic nematicides are expensive and not eco-friendly to the soil flora and fauna. This study aimed at determining 1.) the efficacy of different crops in trapping RKN under greenhouse tomato production, ii.) the timing of destruction of selected trap plants., and iii.) the efficacy of biocontrol agents in the control of RKN. Selected vegetable crops namely giant nightshade, African nightshade, cowpea, amaranthus, green grams, crotalaria and tomato seedlings were transplanted into 4000 cc of potting media infested with 2000 second stage juveniles (J2). The plants were carefully uprooted at 14, 19, 21, 28 and 35 days after transplanting (DAT) to determine the trapping of RKN based on the J2 populations per 4000cc of soil and galls. Seeds of lentils, cowpeas, green grams, cucumber, squash, maize, beans and tomato were soaked for three days and sown into 4000 cc potting media infested with 2000 J2. Eighteen days after establishment, the plants were uprooted and then the number of J2 per 4000cc of soil and galls were determined. Tomato was considered the control treatment in experiments to assess trap crops and the time of destruction of plants in managing RKN. Eight bio-controls namely Paecilomyces lilacinus (Mytech), Trichoderma asperellum (TRC900- ICIPE), Trichoderma asperellum (TRC901- ICIPE), Trichoderma asperellum (TRC902- ICIPE), Purpureocillium lilacinum (PLO3- ICIPE), Paecilomyces lilacinus (Bio-Nematon), Azadirachtin and neem limonoids (Achook) and Bacillus subtilis were separately drenched into cocopeat medium where tomato seedlings were raised in trays. The seedlings were then transplanted into 4000 cc potting media infested with 2000 J2 and maintained for eight weeks. Tomato seedlings treated with sterile distilled water were included as control. The efficacy of the biocontrols was assessed on shoot and root length, shoot fresh and dry weights, J2 and gall counts. The treatments were configured in a completely randomized design with five replications and repeated once. This study showed that cowpea had a significantly (p<0.05) lower J2 population 14 DAT whereas Amaranthus and crotalaria had a lower J2 population from 19 to 35 DAT. Black nightshade and cowpea had significantly (p<0.05) higher gall counts, 19 to 35 DAT. Overall, cowpea was an ideal trap crop owing to the potential of trapping J2 – lowest J2 population per 4000cc of soil- and high gall count. Both maize and beans were determined as poor hosts for RKN following the few gall counts despite the presence of J2 populations in the soil...