Diagnosis and pathogenicity of Fusarium oxysporum and Rhizoctonia solani associated with root rot and damping-off of eggplant seedlings in Najaf Governorate

Abstract

Root rot and damping-off caused by soil-borne fungi are among the most destructive diseases of eggplant, causing poor seedling establishment and heavy economic losses. This study was conducted to isolate and identify the causal fungus of root rot and damping-off of eggplant (Solanum melongena L.) seedlings in the growing areas of Najaf Governorate, recovering and molecularly identifying Fusarium oxysporum, and to compare its pathogenicity with that of a previously registered reference isolate of Rhizoctonia solani in the laboratory and in potting soil. A field survey covering the areas of Al-Hira, Al-Haidariyah and Bahr Al-Najaf showed the spread of the disease at all sites, with infection rates ranging from 29% to 62% (Al-Haidariyah recording the highest). The pathogenic fungi were isolated and purified from the surveyed fields. Isolation and morphological identification yielded three isolates belonging to Fusarium spp. (F.1, F.2 and F.3), all isolated from eggplant plants infected with root rot and damping-off, while two isolates belonging to Rhizoctonia solani (R.1 and R.2) were obtained from the culture collection of the Plant Protection Department. The isolated fungi differed in some morphological characters such as colour, mycelial density and growth rate, as well as in their pathogenicity. Pathogenicity testing on water-agar (WA) medium and in sterilized potting soil showed that isolates R.2 and F.2 were the most pathogenic; R. solani R.2 was the most virulent, recording 100% seed rot in Petri dishes and 88.50% disease severity in pots, while F. oxysporum F.2 recorded 72.50% disease severity in pots. Molecular diagnosis using PCR and sequencing of the ITS region showed that isolate F.2 belonged to F. oxysporum with 100% identity to global isolates, and it was deposited in GenBank under accession number PZ531662.1, whereas isolate R.2 matched reference isolates of R. solani registered in GenBank (e.g., PP767138.1)