Grafting to Manage Soilborne Diseases in Heirloom Tomato Production

Abstract

<jats:p>Organic heirloom tomato production is limited in the southeastern United States by foliar and soilborne diseases, thermal stress, and weathered soil structure. Heirloom cultivars command a premium market, but tolerance to disease and abiotic stress is often poor. Organic growers need research that supports the advantages of market niches afforded by heirloom tomatoes through the development of integrated systems to manage pests and reduce risks of associated crop losses or low yields. Two major soilborne diseases common in the southeast, bacterial wilt (caused by <jats:italic>Ralstonia solanacearum</jats:italic>) and fusarium wilt (caused by <jats:italic>Fusarium oxysporum</jats:italic> f.sp. <jats:italic>lycopersici</jats:italic>), were effectively managed using susceptible heirloom scions grafted onto resistant rootstock. In naturally infested soil, bacterial wilt incidence for nongrafted ‘German Johnson’ was 79% and 75% in 2005 and 2006, respectively. ‘German Johnson’ showed no symptoms of bacterial wilt in either year when grafted onto the resistant genotypes CRA 66 or Hawaii 7996. Fusarium wilt incidence was 46% and 50%, respectively, in nongrafted and self-grafted ‘German Johnson’ controls. When ‘Maxifort’ rootstock was grafted with ‘German Johnson’, no symptoms of fusarium wilt were seen, and plants with ‘Robusta’ rootstock had an intermediate level of disease (29%). An evaluation of commercially available rootstock was carried out in three separate experiments in diverse organic production systems to determine yield impacts with low disease pressure. ‘Maxifort’ rootstock significantly increased yield in one location (<jats:italic>P</jats:italic> = 0.05), but ‘Maxifort’ and ‘Robusta’ rootstock did not consistently impact yield at the other two locations. Grafting is an effective management tool for organic growers in the southeast United States to reduce risk of crop loss resulting from soilborne diseases and will be a valuable component in an integrated pest management program.</jats:p>

Grafting Tomato to Manage Bacterial Wilt Caused by Ralstonia solanacearum in the Southeastern United States

“…lycopersici, Sclerotium rolfsii, and rootknot nematodes (Meloidogyne spp. ), as demonstrated in recent field trials in North Carolina (33,34). However, the rootstocks utilized in those studies have no known or reported resistance to bacterial wilt.…”

“…In this study, a self-grafted treatment was not included due to limited field space. A previous study showed that self-grafting did not significantly affect the incidence of bacterial wilt (33).…”

“…Breeding lines CRA 66 and Hawaii 7996 were found to significantly reduce bacterial wilt incidence in naturally infested soils in North Carolina (33). Although these findings are important for the implementation of rootstock breeding programs in the United States, they do not provide information that is readily useable for growers who face this devastating disease.…”

“…Grafting has been utilized to manage bacterial wilt in tomato crops worldwide (11,24,25,30,39), and has been proposed recently in the United States for open-field and high-tunnel production (22,33). Breeding lines CRA 66 and Hawaii 7996 were found to significantly reduce bacterial wilt incidence in naturally infested soils in North Carolina (33).…”

Management of tomato diseases caused by Fusarium oxysporum

“…Rivard and Louws (2008) indicated that the technique would be a very useful component in organic production especially with heirloom varieties which lack resistance to Fol and other soilborne pathogens. They conducted field studies in the USA and observed 0% and 29% FW incidences in heirloom tomato plants grafted on 'Maxifort' and 'Robusta' rootstocks, respectively, compared to 100% incidence in the self-grafted controls.…”