Light Intensity Alters the Behavior of Monilinia spp. in vitro and the Disease Development on Stone Fruit-Pathogen Interaction

The development of brown rot caused by the necrotrophic fungi Monilinia spp. in stone fruit under field and postharvest conditions depends, among others, on environmental factors. The effect of temperature and humidity are well studied but there is little information on the role of light in disease development. Herein, we studied the effect of two lighting treatments and a control condition (darkness) on: (i) several growth parameters of two Monilinia spp. (M. laxa and M. fructicola) grown in vitro and (ii) the light effect in their capacity to rot the fruit (nectarines) when exposed to the different lighting treatments. We also assessed the effect of such abiotic factors in the development of the disease on inoculated nectarines during postharvest storage. Evaluations also included testing the effect of fruit bagging on disease development as well as on ethylene production. Under in vitro conditions, lighting treatments altered colony morphology and conidiation of M. laxa but this effect was less acute in M. fructicola. Such light-induced changes under in vitro development also altered the capacity of M. laxa and M. fructicola to infect nectarines, with M. laxa becoming less virulent. The performance of Monilinia spp. exposed to treatments was also determined in vivo by inoculating four bagged or unbagged nectarine cultivars, indicating an impaired disease progression. Incidence and lesion diameter of fruit exposed to the different lighting treatments during postharvest showed that the effect of the light was intrinsic to the nectarine cultivar but also Monilinia spp. dependent. While lighting treatments reduced M. laxa incidence, they enhanced M. fructicola development. Preharvest conditions such as fruit bagging also impaired the ethylene production of inoculated fruit, which was mainly altered by M. laxa and M. fructicola, while the bag and light effects were meaningless. Thus, we provide several indications of how lighting treatments significantly alter Monilinia spp. behavior both in vitro and during the interaction with stone fruit. This study highlights the importance of modulating the lighting environment as a potential strategy to minimize brown rot development on stone fruit and to extent the shelf-life period of fruit in postharvest, market, and consumer’s house.info:eu-repo/semantics/publishedVersio

Environmental fate and behaviour of the biocontrol agent Bacillus amyloliquefaciens CPA-8 after preharvest application to stone fruit

BACKGROUND:Bacillus amyloliquefaciensstrain CPA-8 has been described as an effective biocontrol agent to control brownrot in stone fruit for both preharvest and postharvest applications. However, no information about the environmental fate andbehaviour of this strain under field conditions is available.RESULTS: The dispersion of the CPA-8 application was evaluated using water-sensitive papers, and complete coverage wasobserved on the leaves of treated trees, while<1% of non-treated tree leaves had CPA-8. CPA-8 persisted on the fruit of treatedtrees during preharvest and postharvest conditions, while a significant decrease on leaves and weeds was observed 21 daysafter treatment. On non-treated trees, CPA-8 was detected on leaves until 180 days after treatment, and on weeds, the CPA-8population was dependent on the distance from the treated trees. A high persistence of CPA-8 was detected on inert materials,suchasclothesandgloveswornbyhandlersandplasticharvestingboxes.Morethan99%ofthesampleswithaCPA-8phenotypewere confirmed as CPA-8 using polymerase chain reaction (PCR).CONCLUSION: This work demonstrated a good distribution, persistence and adaptation of the CPA-8 strain to field andpostharvest conditions. Monitoring of dispersion and persistence is an excellent tool to determine the time of application andprovides valuable information for registering issues.© 2017 Society of Chemical Industryinfo:eu-repo/semantics/acceptedVersio

Depicting the battle between nectarine and Monilinia laxa: the fruit developmental stage dictates the effectiveness of the host defenses and the pathogen’s infection strategies

Infections by the fungus Monilinia laxa, the main cause of brown rot in Europe, result in considerable losses of stone fruit. Herein, we present a comprehensive transcriptomic approach to unravel strategies deployed by nectarine fruit and M. laxa during their interaction. We used M. laxa-inoculated immature and mature fruit, which was resistant and susceptible to brown rot, respectively, to perform a dual RNA-Seq analysis. In immature fruit, host responses, pathogen biomass, and pathogen transcriptional activity peaked at 14–24 h post inoculation (hpi), at which point M. laxa appeared to switch its transcriptional response to either quiescence or death. Mature fruit experienced an exponential increase in host and pathogen activity beginning at 6 hpi. Functional analyses in both host and pathogen highlighted differences in stage-dependent strategies. For example, in immature fruit, M. laxa unsuccessfully employed carbohydrate-active enzymes (CAZymes) for penetration, which the fruit was able to combat with tightly regulated hormone responses and an oxidative burst that challenged the pathogen’s survival at later time points. In contrast, in mature fruit, M. laxa was more dependent on proteolytic effectors than CAZymes, and was able to invest in filamentous growth early during the interaction. Hormone analyses of mature fruit infected with M. laxa indicated that, while jasmonic acid activity was likely useful for defense, high ethylene activity may have promoted susceptibility through the induction of ripening processes. Lastly, we identified M. laxa genes that were highly induced in both quiescent and active infections and may serve as targets for control of brown rot.info:eu-repo/semantics/publishedVersio

Effect of light on nectarine-Monilinia spp. interaction and analysis of fungal and fruit responses during M. laxa infection

La podridura marró és una important malaltia de la fruita de pinyol causada per diferents espècies de Monilinia. Aquest patogen pot infectar la fruita durant el seu creixement, però les principals pèrdues de fruita es produeixen durant el període de postcollita. El primer objectiu d'aquesta tesi va consistir en avaluar l'efecte de tractaments d'il·luminació durant el període d’emmagatzematge de postcollita en fruita embossada (fruita que s’havia embossat durant el període de creixement a camp) i fruita sense embossar, inoculades artificialment amb dues espècies de Monilinia (M. laxa i M. fructicola). A més, l'efecte d'aquests tractaments d'il·luminació també es va avaluar en el comportament de Monilinia spp. en nectarines, i en la qualitat global de nectarines embossades i sense embossar. El segon objectiu principal d’aquesta tesi va incloure un estudi d'interacció hoste-patogen, el qual va consistir en un anàlisi dual de seqüenciació d'ARN en dos estadis de desenvolupament de la nectarina que mostraven una susceptibilitat diferent a M. laxa. L’objectiu era destacar les estratègies globals desplegades tant pel fruit com pel patogen durant la seva interacció. També es va avaluar el paper d'alguns metabòlits secundaris (en concret, el metabolisme dels terpenoides i els compostos orgànics volàtils (COVs)) en teixits de nectarina que presentaven una susceptibilitat diferent a M. laxa mitjançant anàlisis d'expressió gènica i anàlisi del perfil de COVs, respectivament.La podredumbre parda es una enfermedad importante en fruta de hueso que está causada por Monilinia spp. Este patógeno puede infectar a la fruta durante todo su crecimiento, aunque las principales pérdidas ocurren durante el periodo de postcosecha. El primer objetivo de esta tesis fue evaluar el efecto de tratamientos de iluminación durante el almacenamiento de postcosecha de nectarinas embolsadas y no embolsadas en precosecha, y artificialmente inoculadas con dos especies de Monilinia (M. laxa y M. fructicola). Además, el efecto de estos tratamientos también se evaluó sobre el comportamiento de Monilinia spp. en nectarinas y sobre la calidad global de nectarinas embolsadas y no embolsadas. El segundo objetivo principal incluía un estudio de interacción huésped-patógeno, el cual consistió en un análisis dual de secuenciación masiva del ARN en dos estadios del desarrollo de la nectarina con diferente susceptibilidad a M. laxa. También se evaluó el papel de algunos metabolitos secundarios (por ejemplo, los terpenoides y los compuestos orgánicos volátiles (COVs)) en tejidos de fruta con una susceptibilidad diferente a M. laxa, mediante análisis de expresión génica y análisis de los perfiles de COVs, respectivamente.Brown rot is a significant disease in stone fruit caused by Monilinia spp. This pathogen can infect fruit during its growth, but the main fruit losses occur at the postharvest period. The first objective of this thesis was to evaluate the effect of lighting treatments along the postharvest storage on bagged (fruit that was bagged during preharvest) and unbagged fruit, which were artificially inoculated with two Monilinia species (M. laxa and M. fructicola). Besides, the effect of these lighting treatments was also evaluated on the behavior of Monilinia spp. on nectarines, and on the global quality of bagged and unbagged nectarines. The second main objective of this thesis covered the host-pathogen interaction, which consisted of a dual RNA-Sequencing analysis of two nectarine developmental stages that showed different susceptibility to M. laxa. The objective was to decipher the global strategies deployed by both the fruit and the pathogen during their interaction. A focus on the role of some secondary metabolites (i.e., terpenoid metabolism and volatile organic compounds (VOCs)) was also assessed in fruit tissues that presented different susceptibility to M. laxa through gene expression analyses and VOCs profile analyses, respectively

Emission of volatile organic compounds during nectarine-Monilinia laxa interaction and its relationship with fruit susceptibility to brown rot

Fruit volatile organic compounds (VOCs) can be emitted by stone fruit in response to biotic stress. One of the main fungal diseases of stone fruit is brown rot, caused by species of Monilinia spp. Hence, we aimed to reveal the most relevant VOCs that participate either in resistance or susceptibility to Monilinia laxa in nectarines. To this aim, we analyzed the VOCs emitted by two developmental stages (immature, one month before harvest; mature, commercial harvest) of two nectarine cultivars, with different susceptibility to M. laxa. Furthermore, we also determined the VOCs profile of M. laxa grown in in vitro culture media based on peach juice. Results elucidated 34 VOCs whose production pattern was different among samples (control and inoculated of both stages and cultivars), being 13 VOCs also emitted by M. laxa culture. A hierarchical analysis and a multivariate analysis exhibited the variations in the VOCs profile of all samples according to their susceptibility to M. laxa, and the suitability of the model to predict the M. laxa disease (91.94% of the total variation). In general, results highlighted i) a group of VOCs, positively correlated with M. laxa disease, that were emitted by visual M. laxa symptomatic tissues (e.g., aldehyde (E,E)− 2,6-nonadienal) and also by M. laxa itself (e.g., terpenoids alpha-muurolene and (E)-beta-ionone), and ii) a group of VOCs, negatively correlated with brown rot disease, that were emitted by tissues with no visual M. laxa symptoms (e.g., ketone butyrolactone and aldehyde (E)− 2-decenal) and also by M. laxa itself (e.g., aldehyde decanal), suggesting an antifungal role of these compounds. Therefore, this study provides putative potential VOCs that not only will help to improve the knowledge of brown rot development on nectarines, but also provides target volatiles that may serve as potential brown rot control compoundsinfo:eu-repo/semantics/acceptedVersio

Impact of fruit bagging and postharvest storage conditions on quality and decay of organic nectarines

Abiotic factors such as light influence the physicochemical properties of fruit and may alter the response of the fruit to the environment. The aim of this study was to investigate the effect of two postharvest storage conditions on the overall quality and natural fungal disease incidence (fruit decay) of organic nectarines. Experiments were conducted with four organically grown nectarine cultivars (two early-mid season and two late-season) that were unbagged or bagged during preharvest. After harvest, they were stored for 7–9 days in darkness or under a treatment with lighting. Quality parameters (weight, diameter, firmness, soluble solids content, titratable acidity, and single index of absorbance difference), ethylene production, and fruit decay (% incidence of decay) were evaluated. Preharvest bagging reduced fruit decay in the late-season cultivars, for which storage under darkness reduced fungal decay (up to 100%) more than storage under lighting treatment (47% reduction). Bagging altered the initial fruit quality, but values were within official recommendations. Storage conditions reduced differences attributed to bagging, especially under storage with lighting. This work highlighted the importance of modulating the light, both in the field by fruit bagging and during postharvest, to reduce fruit decay and improve fruit quality. These results may serve as a tool for both farmers and postharvest chain managers.info:eu-repo/semantics/acceptedVersio

Transcriptional profiling of the terpenoid biosynthesis pathway and in vitro tests reveal putative roles of linalool and farnesal in nectarine resistance against brown rot

The most devastating fungal disease of peaches and nectarines is brown rot, caused by Monilinia spp. Among the many plant responses against biotic stress, plant terpenoids play essential protective functions, including antioxidant activities and inhibition of pathogen growth. Herein, we aimed to characterize the expression of terpenoid biosynthetic genes in fruit tissues that presented different susceptibility to brown rot. For that, we performed artificial inoculations with Monilinia laxa at two developmental stages (immature and mature fruit) of two nectarine cultivars (‘Venus’ –mid-early season cultivar - and ‘Albared’ –late season cultivar-) and in vitro tests of the key compounds observed in the transcriptional results. All fruit were susceptible to M. laxa except for immature ‘Venus’ nectarines. In response to the pathogen, the mevalonic acid (MVA) pathway of the ‘Venus’ cultivar was highly induced in both stages rather than the methylerythritol phosphate (MEP) pathway, being the expression of some MEP-related biosynthetic genes [e.g., PROTEIN FARNESYLTRANSFERASE (PpPFT), and 3S-LINALOOL SYNTHASE (PpLIS)] different between stages. In ‘Albared’, both stages presented similar responses to M. laxa for both pathways. Comparisons between cultivars showed that HYDROXYMETHYLGLUTARYL-CoA REDUCTASE (PpHMGR1) expression levels were common in susceptible tissues. Within all the terpenoid biosynthetic pathway, linalool- and farnesal-related pathways stood out for being upregulated only in resistant tissues, which suggest their role in mediating the resistance to M. laxa. The in vitro antifungal activity of linalool and farnesol (precursor of farnesal) revealed fungicidal and fungistatic activities against M. laxa, respectively, depending on the concentration tested. Understanding the different responses between resistant and susceptible tissues could be further considered for breeding or developing new strategies to control brown rot in stone fruitinfo:eu-repo/semantics/acceptedVersio