Abstract
Two field experiments were carried out to study the efficacy of different biological control agents in controlling certain plant-parasitic nematode species including Meloidogyne javanica, Tylenchorhynchus mediterraneus, Hoplolaimus seinhorsti, Longidorus latocephalus, and Xiphinema elongatum on guava and fig trees under the tropical field conditions of Jazan region, south-west Saudi Arabia during two successive seasons from Feb. 15, 2016 to Jan. 15, 2017. The evaluated bio-agents were used in different integrated management combinations of certain fungal species (Trichoderma harzianum, Verticillium chlamydosporium, and Purpureocillium lilacinum), the bacterium Pasteuria penetrans, some organic amendments (cow manure, compost, and chicken manure), urea 46% as a nitrogenous fertilizer, and the nematicide carbofuran 10G for comparison. Results showed that all the tested treatments gradually decreased (P0.05) the population densities of plant-parasitic nematodes on guava and fig trees over the study period. The highest reduction of nematode densities occurred at the end of the experiment. Carbofuran 10G was the most effective treatment in suppressing the nematode densities on guava and fig trees. The most effective management combinations, next to carbofuran 10G, in suppressing the nematode densities in the rhizosphere of guava trees were P. lilacinum + P. penetrans + urea 46%, P. lilacinum + P. penetrans + chicken manure, and T. harzianum + P. penetrans + chicken manure (66.54-69.22% nematode reductions). Correspondent combinations in the rhizosphere of fig trees were P. lilacinum + P. penetrans + cow manure, T. harzianum + P. penetrans + cow manure, P. lilacinum + P. penetrans + urea 46%, and V. chlamydosporium + P. penetrans + urea 46% (54.68-57.17% nematode reductions). On the other hand, nematode population densities continued to increase (P0.05) in the rhizosphere of guava and fig trees in the absence of nematode management combinations. All the tested treatments significantly increased (P0.05) the number of fruits/tree on guava and fig trees. Treatments which included the combinations of fungal and bacterial parasites along with chicken manure gave the highest numbers of fruits/tree, followed by the treatment with the nematicide carbofuran 10G. Regression analysis showed a significant negative linear relationship between the number of nematodes/kg soil and the number of guava and fig fruits/tree.