First Report of Root-Lesion Nematode, Pratylenchus thornei, Infecting Wheat (Triticum aestivum) in Ethiopia

Abstract

Wheat (Triticum aestivum) is one of the most widely cultivated strategic crops to ensure food security in Ethiopia. In 2024, soil and root samples were collected from 300 wheat fields across 28 localities in 10 districts during a survey of Ethiopia’s major wheat-growing regions. Root-lesion nematodes were detected in 268 fields across 25 localities in 8 districts. One representative isolate from each positive locality was maintained, resulting in 25 isolates. Infected plants showed stunting and characteristic visible root lesions. The highest nematode density (1,200 ± 100 individuals/100 ml) was recovered from root and soil samples from Wudegetna Gefersa, East Sodo district, Gurage zone, Central Ethiopia Regional State (8°18′49.63″N, 38°58′12″E), using the modified Baermann tray method (Whitehead and Hemming 1965). These were identified as Pratylenchus thornei based on morphological characters following Castillo and Vovlas (2007), including a low, flattened lip region with two to three annuli, a well-developed stylet, and a conoid tail with a blunt terminus. The following morphometrics (mean ± SD) were recorded for adult females (n = 10): L = 692 ± 24.0 μm, stylet = 16.0 ± 0.43 μm, V = 75.1 ± 2.0%, and tail length = 33 ± 3.8 μm. Specimens were deposited in the Nematology Research Unit Collection, Ghent University, Belgium (UGnem-361–362). Species identity of 14 isolates was confirmed by sequencing the D2–D3 expansion segments of the 28S rRNA gene (PZ224314 to PZ224316; PZ228485 to PZ228495), the ITS rDNA region (PZ253353 to PZ253354; PZ270527) of 3 isolates, and the mitochondrial COI gene (PZ253376 to PZ253391) of 16 isolates, following Janssen et al. (2017). The obtained sequences were identical to the reference sequences of P. thornei in GenBank and clustered with other P. thornei sequences in maximum-supported clades. One representative P. thornei isolate from the field population with the highest nematode density (Wudegetna Gefersa) was confirmed by species-specific PCR targeting the 28S and ITS rDNA regions, established as a pure carrot-disc culture, and used for the pathogenicity experiment. Pathogenicity was confirmed under growth chamber conditions (18 to 23°C with 8 h dark and 16 h light) using a local wheat cultivar ‘Boru’ grown in sterilized soil–sand mixture, following Toktay et al. (2012) with minor modifications at test Pi = 100 individuals per pot (yellow stubby Cone-tainers [RLC4 type, 1.5 × 5.5 in.; Stuewe & Sons; n = 20]). After 10 weeks of growing, the nematodes were extracted using zonal centrifugation from both the roots and the soil (Hendrickx 1995). The Pf obtained was 427 ± 134.6 per pot (RF = 4.27), and typical brownish root lesions were observed. Recovered nematodes were morphologically and molecularly identical to P. thornei, fulfilling Koch’s postulates. Although ITS2 soil metabarcoding previously indicated the presence of P. thornei from soils associated with a soilborne pathogen complex of faba bean in the Amhara and Oromia regional states of Ethiopia (Yilma et al. 2025), the present study constitutes the first confirmed report of P. thornei infecting wheat in the Central Ethiopia Regional State based on morphological, molecular, and pathogenicity evidence. Given the well-documented yield losses caused by P. thornei in wheat worldwide, this finding underscores a significant threat to Ethiopian wheat production and the need to step up targeted surveillance, assess the damage, screen for resistance, and initiate effective management strategies.