Meloidogyne incognita intensifies the severity of Fusarium wilt on watermelon caused by Fusarium oxysporum f. sp. niveum

Authors: HUA, GIA - University Of Georgia; Timper, Patricia - Patty; JI, PINGSHENG - University Of Georgia

Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/28/2018
Publication Date: 1/23/2019
Citation: Hua, G., Timper, P., Ji, P. 2019. Meloidogyne incognita intensifies the severity of Fusarium wilt on watermelon caused by Fusarium oxysporum f. sp. niveum. Canadian Journal of Plant Pathology. https://doi.org/10.1080/07060661.2018.1564939.
DOI: https://doi.org/10.1080/07060661.2018.1564939

Interpretive Summary: Fusarium wilt of watermelon, caused by the fungus Fusarium oxysporum f. sp. niveum (FON), is a devastating soilborne disease in watermelon production. Race 1 and race 2 of the pathogen are widely distributed in different watermelon producing regions. To investigate if root-knot nematodes break resistance of watermelon varieties with resistance to FON race 1 and race 2, greenhouse experiments were conducted on two watermelon varieties Calhoun Gray and Fascination that are resistant to race 1, and an undeveloped variety PI 296341-FR that is resistant to race 2. The treatments included seedlings of Calhoun Gray and Fascination inoculated with root-knot nematodes or FON race 1 alone, co-inoculated with both pathogens, and a non-inoculated control. PI 296341-FR was inoculated with FON race 2, with or without nematode inoculation. The presence of root-knot nematodes enhanced the susceptibility of all watermelon varieties to Fusarium wilt. Co-inoculation with nematodes led to an early development of wilt symptoms and increased disease severity. Whereas inoculation of the nematodes alone did not reduce plant growth, growth suppression was evident when seedlings were inoculated with both pathogens. The results indicate that root-knot nematodes could enhance susceptibility of resistant watermelon varieties to Fusarium wilt, and host resistance alone is not sufficient for managing this disease of watermelon in soils infested with root-knot nematodes.

Technical Abstract: Fusarium wilt of watermelon, caused by Fusarium oxysporum f. sp. niveum (FON), is a devastating soilborne disease in watermelon production. Race 1 and race 2 of the pathogen are widely distributed in different watermelon producing regions. To investigate if root-knot nematodes break resistance of watermelon genotypes with resistance to FON race 1 and race 2, greenhouse experiments were conducted on two watermelon cultivars Calhoun Gray and Fascination that are resistant to race 1, and an accession PI 296341-FR that is resistant to race 2. The treatments included seedlings of Calhoun Gray and Fascination inoculated with Meloidogyne incognita or FON race 1 alone, nematodes 5 days before FON, FON 5 days before nematodes, nematodes and FON simultaneously, and non-inoculated control. PI 296341-FR was inoculated with FON race 2, with or without M. incognita inoculation. The presence of M. incognita enhanced the susceptibility of all watermelon genotypes to Fusarium wilt. Co-inoculation with M. incognita led to an early development of wilt symptoms and increased disease severity. Galls were observed on roots of all nematode-inoculated plants, and sequential inoculation of FON followed by nematodes resulted in lower galling indices compared to other inoculation methods. Whereas inoculation of the nematodes alone did not reduce plant growth, growth suppression was evident when seedlings were inoculated with both pathogens. The results indicate that M. incognita could enhance susceptibility of resistant watermelon genotypes to respective FON races, and host resistance alone is not sufficient for managing Fusarium wilt on watermelon in soils infested with root-knot nematodes.