Effects of ethylene biosynthesis in carrot root slices on 6-methoxymellein accumulation and resistance to Botrytis cinerea

The role of ethylene biosynthesis in the resistance response of carrot ( Daucus carota L., cv. Chantenay red-cored) slices to infection by Botrytis cinerea Pers. ex Pers. was investigated using aminoethoxyvinylglycine (AVG) and inhibitor of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (EC 4.4.1.-), and norbornadiene, an inhibitor of ethylene binding. Carrot slices became susceptible to a normally non-invasive level (10⁵ ml^-1) of spores of B. cinerea after treatment with AVG. ACC partially reversed the susceptibility induced by AVG. The ability of a crude pectic enzyme preparation from B. cinerea to induce resistance to a normally invasive level of B. cinerea spores (10⁶ ml^-1) was prevented by AVG. Accumulation of the carrot phyto-alexin 6-methoxymellein (6-MM) was prevented by norbornadiene, but it had no effect on the resistance response. An event associated with ethylene biosynthesis other than 6-MM accumulation appears to be responsible for the resistance of carrot slices to infection by B. cinerea.     

Colonization ability as an indicator of enhanced biocontrol capacity—An example using two Bacillus amyloliquefaciens strains and Botrytis cinerea infection of tomatoes

An understanding of biocontrol activities is important when developing microorganism‐based alternatives to conventional fungicides. From our bacterial collection, we selected two strains (BBC023 and BBC047) for their outstanding antagonistic capacity against fungal phytopathogens and growth‐promoting abilities towards Arabidopsis thaliana. According to physiological and molecular characterizations, both strains were classified as Bacillus amyloliquefaciens and were tested against Botrytis cinerea in vitro and in a tomato. Both strains secrete lipopeptide‐like compounds that contribute to their in vitro antagonism. SEM‐images showed altered B. cinerea mycelial structures that were consistent with previous reports of the direct action of lipopeptides against fungal hyphae. The strains were applied to the roots (R), leaves (foliar ‐ F) or root/leaves (R/F) on tomato plants. All treatments significantly reduced the severity of B. cinerea infection (measured as a control index). However, only root applications (R and R/F) led to growth promotion in the tomato plants. We detected the production of indole acetic acid (IAA) and 2,3‐butanediol as growth promotion traits in the two strains. For both strains, the R/F treatment showed the highest control index, suggesting a synergic effect of direct antagonism against B. cinerea and resistance induction in the plant. In addition, in vitro antagonism of BBC023 and BBC047 against B. cinerea was similar; whereas in the F application, strain BBC047 significantly improved plant resistance and maintained a higher population density over time on tomato leaves, compared to BBC023. BBC047 was also able to produce a complex and robust biofilm in Msgg medium compared with that of BBC023. We linked the reduced biocontrol of BBC023 on leaves with its limited ability to generate robust biofilms and colonize the phylloplane. At last, we highlight the potential of the native Bacillus strains as promising alternatives for the development of bioproducts for sustainable agriculture.     

Influence of prey quality on the fitness of two phenotypes of Harmonia axyridis adults

The performance of Harmonia axyridis Pallas (Coleoptera: Coccinellidae) adults of the aulica and nigra phenotypes fed on Aphis fabae Scopoli and Myzus persicae (Sulzer) was compared by measuring their voracity, daily biomass consumption, daily weight gain, efficiency of food utilisation, and reproductive capacity. Our results demonstrated differences in the suitability of A. fabae and M. persicae for the two phenotypes of the predator. This suggests that either differences occur in the nutritive requirements of the predators, or in the nutritive value of the two prey species. Both A. fabae and M. persicae supported the growth and oviposition of the aulica and nigra phenotypes. Although nigra females consumed fewer M. persicae, they achieved the same daily weight gain as aulica females. The predator phenotypes consumed the same amount of A. fabae, but the daily weight gain of aulica females was higher than that of nigra. The two predator phenotypes had the same feeding efficiency when consuming M. persicae or A. fabae. The reproductive capacity of nigra females was higher, when this phenotype consumed A. fabae rather than M. persicae.     

The Influence of o-hydroxyethylorutin on Botrytis cinerea Oxidant–Antioxidant Activity

The objective of this study was to evaluate the effects of o‐hydroxyethylorutin on Botrytis cinerea mycelium growth and metabolism. Hydrogen peroxide concentration, superoxide dismutase, catalase and peroxidase activities were compared in the pathogens’ mycelium grown on control and o‐hydroxyethylorutin containing medium. Transfer of B. cinerea mycelium to medium supplemented with 5 mm o‐hydroxyethylorutin resulted in a large decrease in catalase activity. No changes in mycelium growth, hydrogen peroxide concentration and superoxide dismutase activity were observed. Guaiacol and ascorbate peroxidases were not detected in mycelia. The data are consistent with previous findings that o‐hydroxyethylorutin treatment of tomato plants restricts the development of B. cinerea infection due to the induction of higher active oxygen species (AOS) generation in plants by this compound. Being poor in catalase, the pathogen may not be able to cope with increasing AOS formation. The results indicate that catalase is an infective agent of B. cinerea.     

Effect of calcium on cell-wall degrading enzymes of Botrytis cinerea

Effective anti-Botrytis strategies leading to reduce pesticides on strawberries are examined to provide the protection that is harmless to humans, higher animals and plants. Calcium treatments significantly inhibited the spore germination and mycelial growth of B. cinerea. The intracellular polygalacturonase and CMCase showed low activities in B. cinerea cultivated by medium containing calcium. On the other hand, calcium-stimulated β-glucosidases production occurred. Our findings suggest that the calcium treatments keep CMCase activity low and cause low activities of cell-wall degrading enzymes of B. cinerea in the late stage of growth.     

Biological control of onion neck rot (Botrytis aclada): Protection of wounds made by leaf topping

The efficacy of fungal antagonists in protecting onions from neck rot caused by Botrytis aclada was investigated. Leaf wounds made by topping of onions during harvest, which are considered as important entrance sites for B. aclada, were treated with conidial suspensions (5 × 10⁷ conidia ml^‐1) of antagonists. In field experiments with artificial inoculation with conidia of B. aclada, applications of Trichoderma viride during harvest reduced the incidence of neck rot, assessed after three months’ storage of the onions at 9° C, from 35% to 24% in 1989 and from 28% to 18% in 1990, when onions initially had been stored under favourable conditions for fungal development. Comparable results were obtained with T. hamatum and Gliocladium roseum. A bioassay based on wound treatment of detached onion leaves was developed to select further antagonists. From 40 candidate antagonists tested, 20 strains gave similar or better control than the strain of T. viride applied in the field experiments. Effective antagonists could be found amongst strains of Trichoderma spp. Gliocladium spp. and Penicillium spp. as well as amongst fungi such as Aureobasidium pullulans and yeasts isolated from green leaves of onion or rye.     

Aphid–ant mutualism: how honeydew sugars influence the behaviour of ant scouts

Honeydew is the keystone on which ant–aphid mutualism is built. The present study investigates how each sugar identified in Aphis fabae Scopoli honeydew acts upon the feeding and the laying of a recruitment trail by scouts of the aphid‐tending ant Lasius niger Linnaeus, and thus may enhance collective exploitation by the ant mutualists. The feeding preferences shown by L. niger for honeydew sugars are: melezitose = sucrose = raffinose > glucose = fructose > maltose = trehalose = melibiose = xylose. Although feeding is a prerequisite to the launching of trail recruitment, the reverse is not necessarily true: not all ingested sugar solutions elicit a trail‐laying behaviour among fed scouts. Trail mark laying is only triggered by raffinose, sucrose or melezitose, with the latter sugar being specific to honeydew. By comparing gustatory and recruitment responses of ant foragers to sugar food sources, the present study clarifies the role of honeydew composition both as a source of energy and as a mediator in ant–aphid interactions. Lasius niger feeding preferences can be related to the physiological suitability of each sugar (i.e. their detection by gustatory receptors as well as their ability to be digested and converted into energy). Regarding recruitment, the aphid‐synthesized oligosaccharide (melezitose) could be used by ant scouts as a cue indicative of a long‐lasting productive resource that is worthy of collective exploitation and defence against competitors or aphid predators.     

TOR inhibition primes immunity and pathogen resistance in tomato in a salicylic acid-dependent manner

All organisms need to sense and process information about the availability of nutrients, energy status, and environmental cues to determine the best time for growth and development. The conserved target of rapamycin (TOR) protein kinase has a central role in sensing and perceiving nutritional information. TOR connects environmental information about nutrient availability to developmental and metabolic processes to maintain cellular homeostasis. Under favourable energy conditions, TOR is activated and promotes anabolic processes such as cell division, while suppressing catabolic processes. Conversely, when nutrients are limited or environmental stresses are present, TOR is inactivated, and catabolic processes are promoted. Given the central role of TOR in regulating metabolism, several previous works have examined whether TOR is wired to plant defence. To date, the mechanisms by which TOR influences plant defence are not entirely clear. Here, we addressed this question by testing the effect of inhibiting TOR on immunity and pathogen resistance in tomato. Examining which hormonal defence pathways are influenced by TOR, we show that tomato immune responses and disease resistance to several pathogens increase on TOR inhibition, and that TOR inhibition-mediated resistance probably requires a functional salicylic acid, but not jasmonic acid, pathway. Our results support the notion that TOR is a master regulator of the development–defence switch in plants.     

Potential of bioinsecticidal Bacillus thuringiensis inoculum to suppress gray mold in tomato based on induced systemic resistance

The potential of the active ingredient of a commercial bioinsecticide, XenTari^® (Bacillus thuringiensis [BT] serovar aizawai strain ABTS‐1857), to suppress gray mold in tomato plants was elucidated. First, a suspension of the active ingredient of XenTari^® and a liquid culture of the bacterial strain as BT inocula were sprayed onto detached leaves or drenched into pots of tomato seedlings, and then, propagules of the gray mold fungus, Botrytis cinerea, were inoculated onto the leaves. The gray mold disease was significantly suppressed when rhizospheres were drenched with either inoculum, but not when inocula were sprayed onto detached leaves of seedlings. Both BT inocula were verified not to directly inhibit the mycelial growth of B. cinerea based on in vitro culture plate assays. Additionally, real‐time RT‐PCR analysis verified that the active ingredient increased the expression levels of defence‐related genes, such as PR‐1(P6) and P4, in the leaves of tomato seedlings. These results suggest that the active ingredient has the potential to suppress gray mold disease in tomato, not through direct antagonistic interactions with B. cinerea, but rather through systemic activation of the plant defence system by increased expression of several defence‐related genes.