Fusarium Wilt on Watermelons

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu and Emmalea Ernest, Extension Associate – Vegetable Crops; emmalea@udel.edu

Production changes over the past decade have resulted in increasing levels of watermelon Fusarium wilt in Delaware and Maryland. Fusarium wilt is easily recognized by the characteristics of wilting of one vine or the whole plant (Figure 1 A and B) and the red to brown discoloration of the vascular systems (Figure 2).

Figure 1. Single vine runner wilted mid-season (A) and wilted plants at harvest (B).

Figure 2. Vascular discoloration within the cut watermelon stem (Image from A. P. Keinath, Clemson Univ.).

The fungus that causes Fusarium wilt, Fusarium oxysporum f.sp. niveum, was successfully managed for many years through a combination of cultivar resistance in seeded cultivars, rotation, and fumigation. However, the cultivation of seedless cultivars, which have lacked resistance in the past, and the loss of the use of methyl bromide as a fumigant have resulted in an increase in Fusarium wilt. In addition, the pathogen population has shifted to a more virulent type. The good news is that many watermelon breeding programs are working to develop seedless cultivars with resistance to the virulent races present here in Delaware and Maryland. A study conducted at the University of Delaware’s Research and Education Center in 2009 evaluated several seedless cultivars which had been reported to have resistance to race 1. Some cultivars performed well (Table 1) including Abbott & Cobb lines ACR6277TSS, ACX4674T, Seedway’s Sweet Delight and Seminis’ Olympia. We have confirmed that race 2 is present in the field which may have caused the poor results we observed on other lines that also had some resistance. Through a grant from the Delaware Department of Agriculture Specialty Crops Block Grant, we will continue our evaluations in 2010. Stay tuned for an announcement of a field day opportunity to see our results.

Table 1.Watermelon Cultivars Evaluated for Resistance to Fusarium Wilt in 2009

*  Percent of plants that were wilted or dead.

**Mean values in each column and year followed by the same letter are not significantly different at P = 0.05 based on Fisher’s protected least significant different test.