Structural modifications and development of galls in tobacco (Nicotiana tabacum) induced by the false root-knot nematode, Nacobbus celatus

Tobacco ( Nicotiana tabacum ) is cultivated in more than 120 countries, with an annual production of 6.2 million tons. Due to its high nicotine content, the Virginia variety is highly demanded in international markets and domestic industrial production. Among the pathogens affecting this crop, plant-parasitic nematodes are particularly problematic. The genus Nacobbus , known as the false root-knot nematode, is associated with tobacco cultivation, but its interaction with different varieties remains poorly documented. This study analyzed the histopathology of Virginia tobacco (cultivar K394) roots from a production area in northwestern Argentina, naturally infected by N. celatus . Healthy and parasitized (galled) roots were fixed, processed, and examined using conventional light microscopy techniques. The galls contained female nematodes that induced feeding sites (syncytia) in the central cylinder, consisting of numerous hypertrophic cells with dense cytoplasm. The establishment of the parasite and syncytium development caused significant alterations in vascular tissues, cambium, and cortical parenchyma. Additionally, non-functional syncytia associated with fungal hyphae and filiform nematodes were observed. This study provides the first detailed histopathological description of this association, offering new insights into the infection process and highlighting aspects of the nematode's life cycle and interactions with other organisms, such as fungi, which may contribute to increased host damage.