Abstract
The composition and allelopathy to Phytophthora nicotianae (the causal agent of tobacco black shank disease) of root exudates from a resistant tobacco (Nicotiana tabacum L.) cultivar Gexin 3, a susceptible cultivar Xiaohuangjin 1025 and their reciprocal grafts were investigated. Grafting with disease-resistant rootstock could improve resistance to black shank; this is closely related to the allelopathy of root exudates. The root exudates from the resistant cultivar inhibited the growth of P. nicotianae, while those from the susceptible cultivar promoted the growth; the grafting varieties had intermediate properties. The root exudate composition differed among cultivars. Gexin 3 was rich in esters and fatty acids, while Xiaohuangjin 1025 contained more hydrocarbons and phenolic acids. The composition of root exudates of grafted cultivars as well as their allelopathy to P. nicotianae were altered, and tended to be close to the composition of cultivar used as rootstock. Eugenol, 4-tert-butylphenol, mono (2-ethylhexyl) phthalate, 4-hydroxybenzoic acid, 2,6-di-tert-butylphenol, dipropyl phthalate, and methyl myristate were identified as the main compounds contributing to inhibitory properties of root exudates. Sorbitol was suggested to play a role in disease induction. Overall, rootstock–scion interaction affected the composition of tobacco root exudates, which may be attributed to the different disease resistance among grafted plants, rootstock and scion.
Highlights
Tobacco black shank, caused by the oomycete pathogen Phytophthora nicotianae, is a destructive disease with worldwide distribution
The current study found that a resistant tobacco cultivar used as the rootstock or scion improved the disease resistance of the susceptible cultivar, and the difference in exudate composition might contribute to that
Grafting on disease-resistant rootstock can effectively improve the resistance of tobacco to black shank, which is closely related to the allelopathy of root exudates
Summary
Tobacco black shank, caused by the oomycete pathogen Phytophthora nicotianae, is a destructive disease with worldwide distribution. Because of the wide range of crop hosts, the diversity of disease transmission, and the formation of oospores and other dormant bodies which can survive in the soil for long periods, as well as the low resistance of major cultivated tobacco (Nicotiana tabacum) varieties, there are no effective prevention and control measures at present [1,2]. The widespread use of these agents has many negative effects such as environmental pollution, fungicide residues in crops, and increased pathogen resistance [3]. Grafting with disease-resistant rootstock is considered to be an effective way to control plant soil-borne diseases, and has been widely applied in the production of fruits, vegetables, cotton, and other economic crops [4,5,6,7]. There have only been a Plants 2020, 9, 1652; doi:10.3390/plants9121652 www.mdpi.com/journal/plants
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