Cucurbit rootstocks resistant to fusarium oxysporumf.sp. niveum remain resistant when co-infected by <i>Meloidogyne incognita in the field

Authors: KEINATH, ANTHONY - Clemson University; Wechter, William - Pat; Rutter, William; AGUDELO, PAULA - Clemson University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2019
Publication Date: 4/8/2019
Citation: Keinath, A.P., Wechter, W.P., Rutter, W.B., Agudelo, P.A. 2019. Cucurbit rootstocks resistant to fusarium oxysporumf.sp. niveum remain resistant when co-infected by <i>Meloidogyne incognita in the field. Plant Disease. 103(6):1383-1390. https://doi.org/10.1094/PDIS-10-18-1869-RE.
DOI: https://doi.org/10.1094/PDIS-10-18-1869-RE

Interpretive Summary: The two main disease and pest of watermelon crops in the southern United States are Fusarium wilt and southern root-knot nematode. To control for certain pathogens, susceptible watermelons can be grafted to resistant rootstocks. Interspecific hybrid squash rootstocks used to graft watermelon are resistant to Fusarium wilt of watermelon, but susceptible to the southern root-knot nematode. A new citron rootstock ‘Carolina Strongback’ is resistant to both Fusarium wilt and southern root-knot nematode. The objective of this study was to determine if an interaction between Fusarium wilt and southern root-knot nematode occurred on grafted triploid watermelon. It was found that while watermelons grafted to the squash rootstock were resistant to Fusarium wilt, they were quite susceptible to southern root-knot nematode. The citron rootstock ‘Carolina Strongback’ was resistant to both pathogens and maintained a high production level of harvested fruit. When interspecific hybrid squash rootstocks are used to graft watermelon, root-knot nematode must be managed because of the risk of yield loss. Management likely will require application of fumigant or granular nematicides. Carolina Strongback would be the preferred rootstock for growers to use in fields infested with both Fusarium wilt and root-knot nematodes, a situation found in most southern U.S. watermelon growing areas. Using a rootstock like Carolina Strongback that is resistant to both pathogens would eliminate the need for pesticide treatments for either pathogen.

Technical Abstract: Interspecific hybrid squash (Cucurbita maxima × C. moschata) rootstocks used to graft watermelon (Citrullus lanatus var. lanatus) are resistant to Fusarium oxysporum f. sp. niveum, the fungus that causes Fusarium wilt of watermelon, but susceptible to Meloidogyne incognita, the southern root-knot nematode. A new citron (Citrullus amarus) rootstock ‘Carolina Strongback’ is resistant to F. oxysporum f. sp. niveum and M. incognita. The objective of this study was to determine if an interaction between M. incognita and F. oxysporum f. sp. niveum race 2 occurred on grafted or nongrafted triploid watermelon susceptible to F. oxysporum f. sp. niveum race 2. In 2016 and 2018, plants of non-grafted ‘Fascination’ and Fascination grafted onto Carolina Strongback and interspecific hybrid squash ‘Carnivor’ were inoculated or not inoculated with M. incognita before transplanting into field plots infested or not infested with F. oxysporum f. sp. niveum race 2. Incidence of Fusarium wilt and area under the disease progress curve did not differ when hosts were inoculated with F. oxysporum f. sp. niveum alone or with F. oxysporum f. sp. niveum and M. incognita together. Fusarium wilt was greater on nongrafted watermelon (78% mean incidence) than on both grafted rootstocks and lower on Carnivor (1% incidence) than on Carolina Strongback (12% incidence) (P = 0.01). Plants not inoculated with F. oxysporum f. sp. niveum did not wilt. At the end of the season, Carnivor had a greater percentage of the root system galled than the other two hosts, whereas galling did not differ on Fascination and Carolina Strongback. F. oxysporum f. sp. niveum reduced marketable weight of nongrafted Fascination with and without co-inoculation with M. incognita. M. incognita reduced marketable weight of grafted Carnivor compared to noninoculated, nongrafted Fascination. In conclusion, cucurbit rootstocks that are susceptible and resistant to M. incognita retain resistance to F. oxysporum f. sp. niveum when they are co-infected with M. incognita.