First Report and Koch's Postulates Confirmation of Nectria spp. Causing Twig Dieback in Pomegranate Orchards

Abstract

First report and Koch’s postulates confirmation of Nectria spp. causing twig dieback in pomegranate orchards were investigated to establish causal association and characterize the pathogen responsible for the emerging disease. Field surveys were conducted in pomegranate-growing regions, and symptomatic twigs exhibiting dieback, bark cracking, vascular discoloration, and progressive branch drying were collected. Fungal isolation was performed from infected tissues, and pure cultures were obtained for morphological characterization based on colony growth, pigmentation, and perithecial structures. Molecular identification using ITS rDNA sequencing confirmed the presence of Nectria spp. associated with the disease symptoms. Pathogenicity tests were conducted under controlled conditions by inoculating healthy pomegranate twigs, resulting in reproduction of typical dieback symptoms consistent with field observations. Re-isolation of the pathogen from inoculated tissues satisfied Koch’s postulates, confirming its role as the causal agent. Results indicated that Nectria infection leads to progressive vascular disruption, reduced nutrient transport, and eventual twig mortality. Environmental stress conditions and pruning wounds were observed to favor pathogen entry and disease development. The study documents a new occurrence of Nectria-associated twig dieback in pomegranate orchards and highlights its potential threat to orchard productivity. These findings emphasize the need for timely identification, sanitation practices, and integrated disease management strategies to mitigate losses in pomegranate cultivation systems.