Evaluating the efficacy of Aspergillus bio-agents against the citrus nematode Tylenchulus semipenetrans: Laboratory and greenhouse trials

The citrus nematode Tylenchulus semipenetrans is a major plant pathogen with significant economic losses. While chemical nematicides are effective, their high toxicity poses environmental risks. As a sustainable alternative, nematicidal fungi offer a promising approach to managing nematode populations. This study focused on isolating and evaluating the efficacy of two nematophagous fungi, Aspergillus terreus, and Aspergillus ustus, against T. semipenetrans under controlled conditions. Four concentrations of fungal spores (1 x 105, 1 x 106, 1 x 107, and 1 x 108 spores/ml) were tested. In vitro, assays demonstrated that all fungal isolates, whether applied individually or in combination, effectively inhibited egg hatching, with complete inhibition observed at concentrations of 1 x 108, 1 x 107, and 1 x 106 spores/ml. The mortality of second-stage juveniles (J2s) was directly proportional to both fungal concentration and exposure duration. Notably, the combined treatment achieved 100 % juvenile mortality after 168 h of incubation. The nematicidal activity of fungal culture filtrates peaked between days 20 and 23 of incubation, coinciding with the maximum fungal biomass, indicating a strong relationship between fungal growth kinetics and nematicidal properties. Under greenhouse conditions, the application of the combined treatment (1 x 108 spores/ml) significantly (P < 0.0001) reduced T. semipenetrans populations. The most substantial reduction (>94 %) was achieved with the combined treatment, followed by A. terreus (>90 %) at 1 x 108 spores/ml. Additionally, soil treatments with A. terreus, A. ustus, and their combination resulted in significant increases in root and shoot length, as well as in the dry biomass of both roots and shoots. These findings suggest that Aspergillus terreus and Aspergillus ustus could serve as effective strategies for managing T. semipenetrans infestations in citrus orchards.