Tissue-dependent nature of plant susceptibility: a comparative pathogenicity study of the systemic phytopathogen Ralstonia pseudosolanacearum in eggplant and tomato seedlings through root and leaf

Ralstonia pseudosolanacearum causes a lethal bacterial wilt disease in many plant species, posing significant economic challenges. Although tomato has been a primary model host for investigating the pathogenicity and systemic infection of this bacterium, this manuscript presents a comparative pathogenicity study between two closely related solanaceous hosts, tomato and eggplant, revealing differential host responses to the same pathogen, specifically through leaves and roots. Interestingly, eggplant seedlings exhibited a significantly higher susceptibility to cotyledon leaf inoculation than tomato seedlings. In the case of tomato, a few seedlings escaped wilting (called escapees), which was usual at a high pathogen load, unlike the case of eggplant seedlings where escapees could not be observed even at a 100-fold lower pathogen concentration. The greater susceptibility of eggplant was further demonstrated by performing both single- and double-leaf inoculations in the seedlings. Surprisingly, root inoculations resulted in a significantly lower mortality for eggplant than for tomato seedlings. The contrasting susceptibility between the two hosts regarding root and leaf regions indicates the tissue-dependent nature of susceptibility. The study underscores the value of employing multiple host species to uncover new insights into pathogen behaviour and host-pathogen interactions.