Occurrence of plant parasitic nematodes in commercial pineapple fields and effect of biocontrol agents on Meloidogyne species in Kenya
Kiriga, Agnes Waringa
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Plant-parasitic nematodes, in particular Meloidogyne spp., cause significant yield reduction in commercial pineapple (Ananas comosus) worldwide. In Kenya limited studies have been conducted on nematodes in pineapple although the main commercial producer in Kenya has sole mandate to use Telone II (1, 3-Dichloropropene) indicating the seriousness of the problem. The current study was conducted to provide an update on the occurrence of plant-parasitic nematodes in commercial pineapple farms and to evaluate the effect of selected biocontrol agents on Meloidogyne species. Sampling was done in Delmonte and Kakuzi farms in Kiambu and Murang’a Counties respectively. Soil and root samples were collected from different stages of the crop. The top 5 cm of the soil was removed and 25 root and soil sub-samples were collected from randomly selected locations in each pineapple field. After extraction using modified Baermann technique, the recovered vermiform nematodes were counted and identified to genus level using morphological features including molecular techniques for the Meloidogyne species. The remaining soils were baited for Meloidogyne with pineapple plants cv. Smooth cayene to obtain nematode inoculum for the biocontrol experiments. Greenhouse experiments on rooted pineapple crowns were conducted to evaluate the efficacy of three isolates of Trichoderma spp. Trichoderma asperellum M2RT4, T. atroviride F5S21, Trichoderma sp. MK4 and two isolates of Purpureocillium lilacinum KLF2 and MR2 against Meloidogyne spp. in pot experiment. Data on the occurrence of PPNs was analyzed using two-way analysis of variance (ANOVA) while one on effect of biocontrol agents against Meloidogyne spp. was analyzed using one-way ANOVA. All the means were separated using Tukey-HSD at P ≤ 0.05. There was widespread distribution of plant parasitic nematodes and the most frequently occurring were Meloidogyne spp., Helicotylenchus spp. and Tylenchus spp. both in soil and root samples. More nematodes were recovered from older fields, 24 and 36 months after planting, 4380 and 3260 nematodes per 100mls soil respectively than in younger fields, fallow and 3 months old, (2919 and 1687 nematodes per 100 mls soil respectively). All the three Trichoderma isolates successfully colonized pineapple roots endophytically. The application of two isolates of Trichoderma (T. asperellum M2RT4 and Trichoderma sp. MK4) individually and the two isolates of P. lilacinum significantly reduced nematode egg and egg mass production reducing root galling damage by up to 60.8% and increased the plant root mass growth compared to the untreated control. T. asperellum M2RT4 most effectively reduced galls, egg mass and eggs, by 81.8, 78.5 and 88.4%, respectively. Treatment with T. asperellum M2RT4 increased root fresh weight by 91.5%, Trichoderma sp. MK4 by 63.8%, T. atroviride F5S21 by 50.0%, P. lilacinum KLF2 by 43.8% and MR2 by 32.3%. Trichoderma atroviride F5S21 application, however, had no significant effect on nematode multiplication or root damage compared to the control. Results indicate that both Trichoderma spp. and P. lilacinum isolates directly and indirectly affected nematode reproduction (eggs counts and egg masses) and host response (host growth and root galling), demonstrating their control potential against M. javanica on pineapple. The results provide alternative options for managing Meloidogyne spp. that are more environmentally sensitive and can be combined with other management methods towards more sustainable pineapple production systems.