F. Faretra

Sexual Behaviour and Mating System of Botryotinia fuckeliana, Teleomorph of Botrytis cinerea

Summary: Analysis of 213 field isolates of Botrytis cinerea and 240 ascospore isolates of its sexual form Botryotinia fuckeliana indicated that sexual compatibility of this fungus is controlled by a single mating type gene with two alleles. Most isolates were heterothallic, that is, they were self-sterile and able to produce ascospore progeny when crossed with reference strains carrying the mating type gene MAT1-1 or MAT1-2. About 16% of the field isolates and 6% of the ascospore progeny were homothallic, that is, self fertile and compatible with both MAT1-1 and MAT1-2 strains. Both mating types are widespread in nature. The close association of MAT1-1 and MAT1-2 field isolates on various hosts in several regions of Italy shows that sexual reproduction and meiotic recombination might be an important source of genetic variation in this pathogenic fungus.

Characterization and genetic analysis of field isolates ofBotryotinia fuckeliana (Botrytis cinerea) resistant to dichlofluanid

Field isolates ofBotryotinia fuckeliana were collected from naturally infected plants. Their responses to the multisite fungicide dichlofluanid in mycelium growth test fell into three phenotypic classes, characterized by the following EC50 (and MIC) values inμg ml−1: sensitivity, 1–3 (6–10); low resistance, 3–10 (> 100); high resistance, 10–30 (> 100). The corresponding values obtained for these classes in a spore germination test were respectively: ≅ 0.05 (0.2), 0.05–0.1 (0.5), 0.5–1 (0.9–1.5). Resistant isolates were crossed with two sensitive and two resistant strains of appropriate mating type to determine the genetic basis of resistance. Distribution of resistance phenotypes in ascospore progeny indicated that a gene, namedDic1, was probably responsible for the low or high resistance of 14 mutants selectively collected from experimental plots of greenhouse-grown gerbera sprayed several times with dichlofluanid or tolyfluanid. A second gene, namedDic2, was probably responsible for the low resistance displayed by two isolates (from grapevine and from carnation) maintained in the laboratory collection. As a result of the investigation, the use of dichlofluanid in integrated management programmes against grey mould is discussed.

Global Transcriptome Analysis and Identification of Differentially Expressed Genes in Strawberry after Preharvest Application of Benzothiadiazole and Chitosan

The use of resistance inducers is a novel strategy to elicit defense responses in strawberry fruit to protect against preharvest and postharvest decay. However, the mechanisms behind the specific resistance inducers are not completely understood. Here, global transcriptional changes in strawberry fruit were investigated using RNA-Seq technology. Preharvest, benzothiadiazole (BTH) and chitosan were applied to the plant canopy, and the fruit were harvested at 6, 12, and 24 h post-treatment. Overall, 5,062 and 5,210 differentially expressed genes (fold change ≥ 2) were identified in these fruits under the BTH and chitosan treatments, respectively, as compared to the control expression. About 80% of these genes were differentially expressed by both elicitors. Comprehensive functional enrichment analysis highlighted different gene modulation over time for transcripts associated with photosynthesis and heat-shock proteins, according to elicitor. Up-regulation of genes associated with reprogramming of protein metabolism was observed in fruit treated with both elicitors, which led to increased storage proteins. Several genes associated with the plant immune system, hormone metabolism, systemic acquired resistance, and biotic and abiotic stresses were differentially expressed in treated versus untreated plants. The RNA-Seq output was confirmed using RT-qPCR for 12 selected genes. This study demonstrates that these two elicitors affect cell networks associated with plant defenses in different ways, and suggests a role for chloroplasts as the primary target in this modulation of the plant defense responses, which actively communicate these signals through changes in redox status. The genes identified in this study represent markers to better elucidate plant/pathogen/resistance-inducer interactions, and to plan novel sustainable disease management strategies.

Genetics of Botrytis cinerea

Botrytis cinerea displays an extraordinary variability in phenotypic traits, making it a model for studying sources of variation in filamentous fungi and in particular in plant pathogens. The whole genome sequence was recently made available and is sustaining an impressive progress of knowledge. The present review aims at giving an updated picture on the genetic features of this fungal pathogen and, in particular, on mechanisms underlying its broad variation and adaptation capability, i.e. mating system and sexual behavior and other sources of variation (chromosome number, mycoviruses, transposons, vegetative compatibility, etc.), as well as on tools available for its genetic manipulation.

Genetics of Fungicide Resistance

Acquired resistance to fungicides in fungal plant pathogens is a challenge in modern crop protection. Fungi are indeed very able to adapt to changing environmental conditions, such as the introduction of a new fungicide in the agricultural practice. Several genetic mechanisms may underlay fungicide resistance and influence the chance and time of its appearance and spreading in fungal populations. Resistance may be caused by mutations in major genes (monogenic or oligogenic resistance) or in minor genes (polygenic resistance) which may occur in nuclear genes as well as in cytoplasmic genes. They are immediately expressed in haploid fungi, while they may be dominant or recessive in diploid fungi. Allelic variants may cause different levels of resistance and/or different negative pleiotropic effects on the fitness of resistant mutants. The sexual process, where occurring, plays an important role in releasing new recombinant genotypes in fungal populations. Heterokaryosis provides multinucleate fungi with a further mechanism of adaptation. Resistant mutants can be obtained from samples representative of field population of a pathogen or under laboratory conditions through selection of spontaneous mutations or following chemical or physical mutagenesis. Nowadays, molecular tools, such as gene cloning, sequencing, site-directed mutagenesis and gene replacement, make genetic studies on fungicide resistance amenable even in asexual fungi for which classical genetic analysis of meiotic progeny is not feasible.