D-Tagatose-Based Product Triggers Sweet Immunity and Resistance of Grapevine to Downy Mildew, but Not to Gray Mold Disease

Abstract

The use of natural bio-based compounds becomes an eco-friendly strategy to control plant diseases. Rare sugars would be promising compounds as inducers of plant “sweet immunity”. The present study aimed to investigate the induced resistance of grapevine leaves against Plasmopara viticola and Botrytis cinerea by a rare sugar-based product (IFP48) and its active ingredient D-tagatose (TAG), in order to elucidate molecular mechanism involved in defense-related metabolic regulations before and after pathogen challenge. Data showed that spraying leaves with IFP48 and TAG lead to a significant reduction of downy mildew, but not of gray mold disease. The induced protection against P. viticola relies on IFP48’s and to a lesser extent TAG’s ability to potentiate the activation of salicylic acid- and jasmonic acid/ethylene-responsive genes and stilbene phytoalexin accumulation. Most of defense responses remained upregulated in IFP48-treated plants after infection with P. viticola, but inconsistent following challenge with B. cinerea. The beneficial effects of IFP48 were associated with an enhanced accumulation of tagatose inside leaf tissues compared to TAG treatment. Meanwhile, the amounts of sugars, glucose, fructose, maltose, galactose and trehalose remained unchanged or decreased in IFP48-treated leaves after P. viticola infection, although only a few genes involved in sugar transport and metabolism showed transcriptional regulation. This suggests a contribution of sugar homeostasis to the IFP48-induced sweet immune response and priming plants for enhanced resistance to P. viticola, but not to B. cinerea.

The Amount of the Rare Sugar Tagatose on Tomato Leaves Decreases after Spray Application under Greenhouse Conditions

“…Tagatose is known to suppress late blight symptoms on tomato plants under greenhouse conditions [ 14 , 15 ] and to inhibit P. infestans growth in vitro [ 8 , 9 , 10 , 12 ]. A negligible amount of tagatose was found on H 2 O-treated plants in our experiments, and it was also previously detected on untreated cucumber leaves [ 11 ] and grapevine leaves [ 17 ], as well as in apples, pineapples, oranges, and raisins [ 5 ], suggesting that a small tagatose quantity could be produced by plant and/or microbial metabolism. Moreover, the amount of tagatose decreased after spray application on tomato leaves from 1 dpt to 7 dpt on TAG-treated and F_TAG-treated plants under commercial greenhouse conditions, in the absence of rain wash-off.…”

“…Due to its negligible effects on human health and the environment, tagatose has attracted the attention of the agricultural sector and showed promising efficacy in suppressing plant diseases caused by a wide range of phytopathogens, such as potato and tomato late blight ( Phytophthora infestans ), grapevine downy mildew ( Plasmopara viticola ), grapevine powdery mildew ( Erysiphe necator ) and cabbage downy mildew ( Hyaloperonospora parasitica ) [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ]. In particular, tagatose inhibited P. infestans growth in vitro [ 8 , 9 , 10 , 12 ] and reduces late blight symptoms on tomato plants under greenhouse conditions [ 14 , 15 ].…”

“…In particular, tagatose inhibited P. infestans growth in vitro [ 8 , 9 , 10 , 12 ] and reduces late blight symptoms on tomato plants under greenhouse conditions [ 14 , 15 ]. Tagatose inhibits sugar metabolism and mitochondrial processes of P. infestans [ 8 , 10 , 12 ], and it can activate grapevine resistance against downy mildew [ 16 , 17 ], suggesting multiple mechanisms of action against phytopathogens. In particular, tagatose causes severe mitochondrial alterations in P. infestans , with the consequent decrease in ATP content, accumulation of reactive oxygen species, and downregulation of genes involved in transport, sugar metabolism, signal transduction, and growth-related processes [ 8 , 10 ].…”

“…In particular, tagatose causes severe mitochondrial alterations in P. infestans , with the consequent decrease in ATP content, accumulation of reactive oxygen species, and downregulation of genes involved in transport, sugar metabolism, signal transduction, and growth-related processes [ 8 , 10 ]. In addition to testing pure tagatose on its own for disease control, efforts have been made to test its efficacy in mixtures with other compounds [ 16 , 17 ]. Herein, we refer to any chemical mixture that contains tagatose as a formulation.…”

Foliar Application of a Tagatose-Based Product Reduces Downy Mildew Symptoms through Induction of Grapevine Resistance and Anti-Oomycete Action

“…The B. cinerea glycoprotein (BcPG1) was also reported to upregulate the expression of phenylpropanoid pathway defense genes and enhance reactive oxygen species (ROS) production in grapevine [35,36]. Furthermore, cellodextrins exhibited protective effects on grapevine challenged with B. cinerea by inducing elevated levels of cytosolic calcium, oxidative burst, and defense-related gene expression [9].…”