Phylogenetics and histology provide insight into damping-off infections of ‘Poblano’ pepper seedlings caused by Fusarium wilt in greenhouses

The ‘Poblano’ pepper crop is economically important in Mexico and throughout the world as it is used as a hot spice in food. The cultivated area of the ‘Poblano’ pepper crop is decreasing yearly for many reasons, among them a wilt disease commonly associated with Fusarium spp. This disease is a problem of field and greenhouse production plants. Moreover, it is not clear whether the pathogens that cause wilt in mature plants are the same as those involved in the damping-off symptoms and death of pepper seedlings in greenhouses. For this reason, the aim of the present study was to identify the causal agent of damping-off in pepper during seedling production, establish its relationship with the causal agent of wilting in mature plants, and determine whether histological damage in seedlings occurs. Isolates were recovered from the crown rot and stem base of 4-month-old infected ‘Poblano’ mature pepper plants and were identified using morphological and phylogenetic approaches. Fusarium oxysporum and F. solani were isolated from the crown rot and base stem, respectively. A pathogenicity test showed that both species caused damping-off in pepper seedlings. Histological studies with inoculated seedlings of both isolates showed several changes in the external cortex, epidermal cells, endodermis, Casparian strips, cell size, and xylem wall. Casparian strip rupture resulted in permeability loss and regulatory activity to maintain the cellular equilibrium inside the vascular bundles. Hence, according to these findings, producers should avoid seedling contamination by infected mature plants because the aggressiveness of Fusarium isolates can cause rapid seedling mortality.