Dominique Roussel

Systemic and Local Responses Associated with UV- and Pathogen-Induced Resistance to Botrytis cinerea in Stored Carrot

ABSTRACT The induction of resistance to Botrytis cinerea in carrot roots by UV radiation, a possible means for controlling storage diseases, was compared with systemic resistance induced by inoculation with the pathogen. UV radiation did not have any systemic effect, and disease resistance was induced only in tissues directly exposed to the radiation. Although UV radiation induced a local accumulation of 6-methoxymellein (6-MM), inoculation with B. cinerea caused 6-MM to accumulate systemically, away from the inoculation site. Because of amounts near or higher than the ED(50) (50% effective dose) for inhibiting B. cinerea found in both UV-treated and preinoculated roots at the time of challenge, 6-MM could be involved in both types of resistance. Freshly harvested carrots had a number of constitutive chitinases and beta-1,3-glucanases, which were not affected by UV radiation or inoculation. When challenged with B. cinerea, the induction of a 24-kDa chitinase was enhanced in UV-treated and preinoculated roots. Again, UV radiation had only a local effect in priming this chitinase response. Although UV- and pathogen-induced resistance in carrot may involve the same defenses, the responses are probably mediated differently, because UV radiation has an essentially local effect.

Potential link between fruit yield, quality parameters and phytohormonal changes in preharvest UV-C treated strawberry

Preharvest ultraviolet-C (UV-C) treatment of strawberry is a very new approach, and little information is available on the effect of this treatment on plant growth regulators. In this study, the effect of preharvest UV-C irradiations at three different doses on strawberry yield, fruit quality parameters and endogenous phytohormones was investigated simultaneously. The overall marketable yield of strawberry was not affected by the preharvest UV-C treatments, although more aborted and misshapen fruits were found in UV-C treated groups than in the untreated control. The fruits in the high dose group were firmer and had approximately 20% higher sucrose content and 15% higher ascorbic acid content than the control, while fruits from the middle and low dose groups showed no significant changes in these parameters. The lower abscisic acid (ABA) content found in the fruits in the high UV-C group may be associated with those quality changes. The citric acid content decreased only in the low dose group (reduction of 5.8%), with a concomitant 37% reduction in jasmonic acid (JA) content, compared to the control. The antioxidant status of fruits that received preharvest UV-C treatment was considered enhanced based on their oxygen radical absorbance capacity (ORAC) and malondialdehyde (MDA) content. In terms of aroma, three volatile alcohols differed significantly among the various treatments with obvious activation of alcohol acyltransferase (AAT) activity. The observed synchronous influence on physiological indexes and related phytohormones suggests that preharvest UV-C might affect fruit quality via the action of plant hormones.

Pre-harvest UV-C irradiation triggers VOCs accumulation with alteration of antioxidant enzymes and phytohormones in strawberry leaves

Recent studies have highlighted the biological and physiological effects of pre-harvest ultraviolet (UV)-C treatment on growing plants. However, little is known about the involvement of volatile organic compounds (VOCs) and their response to this treatment. In this study, strawberry plants were exposed to three different doses of UV-C radiation for seven weeks (a low dose: 9.6kJm-2; a medium dose: 15kJm-2; and a high-dose: 29.4kJm-2). Changes in VOC profiles were investigated and an attempt was made to identify factors that may be involved in the regulation of these alterations. Principle compounds analysis revealed that VOC profiles of UV-C treated samples were significantly altered with 26 VOCs being the major contributors to segregation. Among them, 18 fatty acid-derived VOCs accumulated in plants that received high and medium dose of UV-C treatments with higher lipoxygenase and alcohol dehydrogenase activities. In treated samples, the activity of the antioxidant enzymes catalase and peroxidase was inhibited, resulting in a reduced antioxidant capacity and higher lipid peroxidation. Simultaneously, jasmonic acid level was 74% higher in the high-dose group while abscisic acid content was more than 12% lower in both the medium and high-dose UV-C treated samples. These results indicated that pre-harvest UV-C treatment stimulated the biosynthesis of fatty acid-derived VOCs in strawberry leaf tissue by upregulating the activity of enzymes of the LOX biosynthetic pathway and downregulating antioxidant enzyme activities. It is further suggested that the mechanisms underlying fatty acid-derived VOCs biosynthesis in UV-C treated strawberry leaves are associated with UV-C-induced changes in phytohormone profiles.

Preharvest Ultraviolet C Irradiation Increased the Level of Polyphenol Accumulation and Flavonoid Pathway Gene Expression in Strawberry Fruit

Preharvest ultraviolet C (UV-C) irradiation is an innovative approach for increasing the bioactive phytochemical content of strawberries to increase the disease resistance and nutritional value. This study investigated the changes in individual flavonoids in strawberry developed with three different cumulative doses of preharvest UV-C treatment (low, 9.6 kJ m-2; middle, 15 kJ m-2; and high , 29.4 kJ m-2). Significant accumulation (p < 0.05) of phenolics (25-75% increase), namely, cyanidin 3-glucoside, pelargonidin 3-glucoside/rutinoside, glucoside and glucuronide of quercetin and kaempferol, and ellagic acid, was found in the fruit subjected to low and middle supplemental doses of UV-C radiation. The expression of the flavonoid pathway structural genes, i.e., FaCHS1, FaCHI, FaFHT, FaDFR, FaFLS, and FaFGT, was upregulated in the low- and middle-dose groups, while the early stage genes were not affected by the high dose. FaMYB1 was also relatively enhanced in the low- and middle-dose groups, while FaASR was upregulated in only the low-dose group. Hormetic preharvest UV-C dose ranges for enhancing the polyphenol content of strawberries were established for the first time.

Development of a Cabbage Harvester

From 1999 to 2003, Agriculture and Agri-Food Canada engineers, in collaboration with Univerco Hydraulique, developed a mechanical cabbage harvester. It is a single row machine mounted on a farm tractor. The picker was the main challenge in the project; it pulls up the cabbages using two belts and lifts the cabbages up to a rotating blade that cuts the stalks very cleanly. The height is fairly uniform from one cabbage to the next and can be adjusted to keep more or fewer leaves with the cabbage. The roots fall to the ground and two lateral belts carry the cabbages and their leaves up to an inclined conveyor which carries the cabbages up to a horizontal conveyor belt installed on the other side of the tractor. Five workers located on a trailer pulled by a second tractor pick up the cabbages and carefully place them in storage bins. For the 2003 harvest season, tests were performed on two commercial farms; a team of 8 workers harvested at an average rate of 3277 cabbages per hour. The cabbages were slightly more damaged by mechanical harvesting than by hand harvesting. But when the mechanical harvester was compared to hand harvesting with a harvesting aid, the harvesting aid caused more damages to the cabbages. Long term storage experiments were performed on six different sites and showed that mechanically harvested cabbages could be stored satisfactorily for up to 4 months and even up to 6 months in some cases. The machine is now commercially available.