Abstract
Watermelon is an important commercial crop in the Southeastern United States and around the world. However, production is significantly limited by biotic factors including fusarium wilt caused by the hemibiotrophic fungus Fusarium oxysporum forma specialis niveum (Fon). Unfortunately, this disease has increased significantly in its presence over the last several decades as races have emerged which can overcome the available commercial resistance. Management strategies include rotation, improved crop resistance, and chemical control, but early and accurate diagnostics are required for appropriate management. Accurate diagnostics require molecular and genomic strategies due to the near identical genomic sequences of the various races. Bioassays exist for evaluating both the pathogenicity and virulence of an isolate but are limited by the time and resources required. Molecular strategies are still imperfect but greatly reduce the time to complete the diagnosis. This article presents the current state of the research surrounding races, both how races have been detected and diagnosed in the past and future prospects for improving the system of differentiation. Additionally, the available Fon genomes were analyzed using a strategy previously described in separate formae speciales avirulence gene association studies in Fusarium oxysporum races.
Highlights
As a single species, Fusarium oxysporum is rated the fifth most important fungal plant pathogen in the world [1]
Within the Fusarium oxysporum species complex (FOSC), there are over 106 known formae speciales which infect more than 100 different hosts causing vascular wilts [1,2]
It is reasonable to say that no currently available method can rapidly and accurately differentiate forma specialis niveum (Fon) races, but rather the previously designed markers likely amplify the regions that contribute to pathogenicity and may be of assistance to Fon diagnosis by identifying pathogenicity-related genes [24,36]
Summary
Fusarium oxysporum is rated the fifth most important fungal plant pathogen in the world [1]. Within the Fusarium oxysporum species complex (FOSC), there are over 106 known formae speciales which infect more than 100 different hosts causing vascular wilts [1,2]. They are soilborne, can survive for long periods, are often unaffected by chemical management, and can evolve to overcome host resistance quickly [3,4]. Additional problems exist when assigning a race based on the virulence that determines the level of pathogenicity; for example, an isolate which is highly virulent on Sugar Baby, mildly virulent on Charleston Grey and Calhoun Grey, and highly virulent on PI-296341-FR While this may result in a race 3 assignment, there are clearly other mechanisms that contribute to the disease reaction and host response that are still unknown. Diagnosis to the forma specialis level is clearly improved using molecular tools as there are multiple options which
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
