Isolation of Entomopathogenic Nematodes (EPNs) from Different Agroecosystems along the Syrian Coast and Evaluation of Abiotic Factors Affecting Their Natural Occurrence and Persistence

Abstract

This study aimed to determine the occurrence of entomopathogenic nematodes (EPNs) in different vegetation types along the Syrian coastal region as well as the appropriate time of the year for soil sampling to obtain EPN isolates from each vegetation type. In addition, it aimed to evaluate the influence of vegetation type, some applied agricultural practices, and some soil characteristics on the occurrence and persistence of EPNs during three growing seasons; spring, summer, and autumn. Ninety composite soil samples were collected from March 2021 to March 2022, including seven vegetation types, from 30 locations. To assess the persistence of EPNs, 84 soil samples were collected from 14 locations in 2022, consisted of most previous fields (according to the results of the examination of 90 samples), positive soil samples, and others showing previous negative results with different land uses. The occurrence was related to vegetation types and was assessed for the first sampling collection (90 samples) as the recovery frequency and abundance (%). The persistence of EPNs in the same experimental fields related to seasons and soil type was assessed for the second sampling collection (84 samples). CO-inertia analysis was applied to evaluate the response of EPNs to various abiotic factors, seasons, and different agricultural practices. Nine EPN isolates were obtained from 90 soil samples; six isolates belonged to Heterorhabditis, two isolates belonged to Steinernema, and one was a free-living nematode (Rhabditidae). At different proportions, EPNs were detected in four of the seven surveyed vegetation types (citrus, banana, olive, and tobacco), but no significant differences were reported. EPNs were found in all of the study seasons (spring, summer, and autumn), but with more frequency in summer. Some abiotic factors, such as soil texture, adding organic fertilizer, irrigation method, and the absence of chemical pesticides, apparently supported some isolates persistence. The results also showed that the appropriate time (i.e., the time of the year for sampling) varied according to vegetation type; it was spring for olive orchards, summer for banana fields, spring, summer, autumn for citrus orchards, and the end of summer and beginning of autumn for tobacco.

Keywords:

Entomopathogenic nematodes, occurrence, persistence, Syria, vegetation type, soil characteristics, seasonality, Heterorhabditis, Steinernema.