Abstract
Ascorbate oxidase (AO) is an enzyme involved in catalyzing the oxidation of apoplastic ascorbic acid (AA) to dehydroascorbic acid (DHA). In this research, the potential of AO spraying to induce systemic resistance was demonstrated in the interaction between sugar beet root and cyst nematode Heterodera schachtii and the mechanism was elucidated. Plant bioassays showed that roots of AO-sprayed plants were infested by a significantly lower number of females and cysts when compared with mock-sprayed control plants. Hormone measurements showed an elevated level of jasmonic acid (JA) salicylic acid (SA) and ethylene (ET) in the roots of AO-sprayed plants, with a dynamic temporal pattern of activation. Experiments with chemical inhibitors showed that AO-induced systemic resistance is partially dependent on the JA, ET and SA pathways. Biochemical analyses revealed a primed accumulation of hydrogen peroxide (H2O2), and phenylalanine ammonia lyase (PAL) activity in the roots of AO-sprayed plants upon infection by cyst nematodes. In conclusion, our data shows that AO works as an effective systemic defense priming agent in sugar beet against cyst nematode infection, through activation of multiple basal plant defense pathways.
Highlights
Sugar beet (Beta vulgaris L.) is the primary source of sugar in the temperate zone, and it accounts for 20% of the world’s total sugar production
Plants sprayed with 10 U/mL, and 20 U/mL of Ascorbate oxidase (AO) had significantly reduced number of cysts (38% and 60% reduction respectively) (Supplementary Figure S1A)
In this research we evaluated the use of another compound that induces plant resistance and defense priming in rice against root knot nematode (RKN) (Singh et al, 2020)—ascorbate oxidase (AO)—to protect sugar beet plants against beet cyst nematode (BCN) H. schachtii
Summary
Sugar beet (Beta vulgaris L.) is the primary source of sugar in the temperate zone, and it accounts for 20% of the world’s total sugar production. The EU is the world’s leading sugar beet producer with 16.84 million tons of sugar production in 2019 (FAOSTAT, 2019). While fungal diseases such as Cercospora leaf spot, rust, powdery mildew and Ramularia leaf spot are the most common aboveground diseases negatively affecting sugar beet yield (Heick et al, 2020; Rangel et al, 2020), belowground plant-parasitic-nematodes (PPN) contribute to damage in sugar beet production (Cooke, 1987, 1993). In addition to direct damage caused by BCN, penetration of nematodes in the roots cause an entry point for infection by other pathogens such as Rhizoctonia, viruses, and Cercospora spp. The root exudates provides a cue for infective second-stage juveniles (J2) to hatch which invade the roots in the elongation zone behind the root tips
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