Abstract
BackgroundFusarium oxysporum f. sp. niveum (FON) causes Fusarium wilt in watermelon. Several disease-resistant watermelon varieties have been developed to combat Fusarium wilt. However, the key metabolites that mount defense responses in these watermelon varieties are unknown. Herein, we analyzed hormones, melatonin, phenolic acids, and amino acid profiles in the leaf tissue of FON zero (0)-resistant (PI-296341, Calhoun Grey, and Charleston Grey) and -susceptible (Sugar Baby) watermelon varieties before and after infection.ResultsWe found that jasmonic acid-isoleucine (JA-Ile) and methyl jasmonate (MeJA) were selectively accumulated in one or more studied resistant varieties upon infection. However, indole-3-acetic acid (IAA) was only observed in the FON 0 inoculated plants of all varieties on the 16th day of post-inoculation. The melatonin content of PI-296341 decreased upon infection. Conversely, melatonin was only detected in the FON 0 inoculated plants of Sugar Baby and Charleston Grey varieties. On the 16th day of post-inoculation, the lysine content in resistant varieties was significantly reduced, whereas it was found to be elevated in the susceptible variety.ConclusionsTaken together, Me-JA, JA-Ile, melatonin, and lysine may have crucial roles in developing defense responses against the FON 0 pathogen, and IAA can be a biomarker of FON 0 infection in watermelon plants.
Highlights
Fusarium oxysporum f. sp. niveum (FON) causes Fusarium wilt in watermelon
On the 16th day of postinfection, Sugar Baby FON 0-inoculated plants formed a discrete cluster from its respective control group plants, and from untreated and inoculated a group of plants of other varieties (Figs. 1c, S2)
Results of the present study showed that anabolism of most of the studied free amino acids increased at the late phase of post-inoculation in both fusarium wilt-susceptible and -resistant varieties (Table 1, Fig. 4); this indicates that free amino acids, predominantly histidine, citrulline, valine, and phenylalanine are involved in watermelon plant defense response
Summary
Niveum (FON) causes Fusarium wilt in watermelon. Several disease-resistant watermelon varieties have been developed to combat Fusarium wilt. Fusarium wilt in watermelon is caused by the fungus Fusarium oxysporum F. sp. Kasote et al BMC Plant Biology (2020) 20:481 race, mainly found to cause wilt on cultivars with no wilt-resistance genes, such as Sugar Baby [5]. Race 1 is a medium aggressive race, which causes slight to moderate wilt on most of the varieties that are classified as resistant to Fusarium wilt, for instance, Charleston Gray [5, 6]. Race 2 is found to be highly aggressive, which can overcome the wilt-resistance in all commercial watermelon varieties [5]. In addition to race 2, a most virulent race 3 has been found in Florida, and Maryland, for which no watermelon resistant variety is commercially available [6, 9]
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