Screening Vitis Genotypes for Responses to Botrytis cinerea and Evaluation of Antioxidant Enzymes, Reactive Oxygen Species and Jasmonic Acid in Resistant and Susceptible Hosts

Biochemical and genetic characterization of Botrytis cinerea laboratory mutants resistant to propamidine

BACKGROUND

Botrytis cinerea, the causal agent of gray mold, is one of the top 10 fungal pathogens in the world. Propamidine, an aromatic diamidine compound, exhibited both protective and therapeutic effects against B. cinerea. However, the resistance risk and mechanism of B. cinerea to propamidine are unclear.

RESULTS

Twelve high and stable resistant mutants were obtained from B. cinerea B05.10 by fungicide induction. Compared with the parental strain, the biological fitness of the mutants, including growth rate, spore germination, pathogenicity, and oxalic acid decreased significantly. There was no cross-resistance among propamidine and other commonly used fungicides, while the efficacy of propamidine against the resistance mutants declined. In addition, the cell membrane permeability, substance metabolism, and defense enzyme activities of the resistant mutants were significantly increased compared with the wild strain. Whole-genome sequencing of all resistant mutants found that there were 32 SNPs and nine InDels. Importantly, nine common single-point mutant genes in the exon region were found in all 12 resistant mutants, and these genes were related to multiple pathways in vivo, indicating that many factors contributed to the formation of propamidine resistance.

CONCLUSION

These data suggested the resistance risk of B. cinerea to propamidine was low to moderate and the mechanism of propamidine was different from that of the existing fungicides. These results will increase understanding of the resistance mechanism of propamidine and provide a critical basis for the rational design of pesticide molecules based on targets. © 2022 Society of Chemical Industry.

Constitutive Defense Mechanisms Have a Major Role in the Resistance of Woodland Strawberry Leaves Against Botrytis cinerea

The necrotrophic fungus Botrytis cinerea is a major threat to strawberry cultivation worldwide. By screening different Fragaria vesca genotypes for susceptibility to B. cinerea, we identified two genotypes with different resistance levels, a susceptible genotype F. vesca ssp. vesca Tenno 3 (T3) and a moderately resistant genotype F. vesca ssp. vesca Kreuzkogel 1 (K1). These two genotypes were used to identify the molecular basis for the increased resistance of K1 compared to T3. Fungal DNA quantification and microscopic observation of fungal growth in woodland strawberry leaves confirmed that the growth of B. cinerea was restricted during early stages of infection in K1 compared to T3. Gene expression analysis in both genotypes upon B. cinerea inoculation suggested that the restricted growth of B. cinerea was rather due to the constitutive resistance mechanisms of K1 instead of the induction of defense responses. Furthermore, we observed that the amount of total phenolics, total flavonoids, glucose, galactose, citric acid and ascorbic acid correlated positively with higher resistance, while H₂O₂ and sucrose correlated negatively. Therefore, we propose that K1 leaves are more resistant against B. cinerea compared to T3 leaves, prior to B. cinerea inoculation, due to a lower amount of innate H₂O₂, which is attributed to a higher level of antioxidants and antioxidant enzymes in K1. To conclude, this study provides important insights into the resistance mechanisms against B. cinerea, which highly depend on the innate antioxidative profile and specialized metabolites of woodland strawberry leaves.

Comparative transcriptomic analysis highlights contrasting levels of resistance of Vitis vinifera and Vitis amurensis to Botrytis cinerea

Botrytis cinerea is a major grapevine (Vitis spp.) pathogen, but some genotypes differ in their degree of resistance. For example, the Vitis vinifera cultivar Red Globe (RG) is highly susceptible, but V. amurensis Rupr Shuangyou (SY) is highly resistant. Here, we used RNA sequencing analysis to characterize the transcriptome responses of these two genotypes to B. cinerea inoculation at an early infection stage. Approximately a quarter of the genes in RG presented significant changes in transcript levels during infection, the number of which was greater than that in the SY leaves. The genes differentially expressed between infected leaves of SY and RG included those associated with cell surface structure, oxidation, cell death and C/N metabolism. We found evidence that an imbalance in the levels of reactive oxygen species (ROS) and redox homeostasis probably contributed to the susceptibility of RG to B. cinerea. SY leaves had strong antioxidant capacities and improved ROS homeostasis following infection. Regulatory network prediction suggested that WRKY and MYB transcription factors are associated with the abscisic acid pathway. Weighted gene correlation network analysis highlighted preinfection features of SY that might contribute to its increased resistance. Moreover, overexpression of VaWRKY10 in Arabidopsis thaliana and V. vinifera Thompson Seedless enhanced resistance to B. cinerea. Collectively, our study provides a high-resolution view of the transcriptional changes of grapevine in response to B. cinerea infection and novel insights into the underlying resistance mechanisms.

Towards Sensor-Based Phenotyping of Physical Barriers of Grapes to Improve Resilience to Botrytis Bunch Rot

Botrytis bunch rot is one of the economically most important fungal diseases in viticulture (aside from powdery mildew and downy mildew). So far, no active defense mechanisms and resistance loci against the necrotrophic pathogen are known. Since long, breeders are mostly selecting phenotypically for loose grape bunches, which is recently the most evident trait to decrease the infection risk of Botrytis bunch rot. This study focused on plant phenomics of multiple traits by applying fast sensor technologies to measure berry impedance (Z _REL ), berry texture, and 3D bunch architecture. As references, microscopic determined cuticle thickness (MS _CT ) and infestation of grapes with Botrytis bunch rot were used. Z _REL hereby is correlated to grape bunch density OIV204 (r = -0.6), cuticle thickness of berries (r = 0.61), mean berry diameter (r = -0.63), and Botrytis bunch rot (r = -0.7). However, no correlation between Z _REL and berry maturity or berry texture was observed. In comparison to the category of traditional varieties (mostly susceptible), elite breeding lines show an impressive increased Z _REL value (+317) and a 1-μm thicker berry cuticle. Quantitative trait loci (QTLs) on LGs 2, 6, 11, 15, and 16 were identified for Z _REL and berry texture explaining a phenotypic variance of between 3 and 10.9%. These QTLs providing a starting point for the development of molecular markers. Modeling of Z _REL and berry texture to predict Botrytis bunch rot resilience revealed McFadden R ² = 0.99. Taken together, this study shows that in addition to loose grape bunch architecture, berry diameter, Z _REL , and berry texture values are probably additional parameters that could be used to identify and select Botrytis-resilient wine grape varieties. Furthermore, grapevine breeding will benefit from these reliable methodologies permitting high-throughput screening for additional resilience traits of mechanical and physical barriers to Botrytis bunch rot. The findings might also be applicable to table grapes and other fruit crops like tomato or blueberry.

Chitosan induces jasmonic acid production leading to resistance of ripened fruit against Botrytis cinerea infection

Chitosan can function a key role in plant resistant against Botrytis cinerea infection, while its mechanism is unclear in ripened fruits. In this study, we investigated the chitosan effect on two type of ripened fruits including strawberry and grapes (Kyoho and Shine-Muscat) when were infected with B. cinerea. Results showed that chitosan inhibited B. cinerea growth, increased phenolic compounds and cell wall composition, modulated oxidative stress and induced jasmonic acid (JA) production in ripened fruits. Data-independent acquisition (DIA) showed that 224 and 171 proteins were upregulated 1.5-fold by chitosan in Kyoho and Shine-Muscat grape, respectively. Topless-related protein 3 (TPR3) were identified and interacted with histone deacetylase 19 (HDAC19) and negatively regulated by JA and chitosan. Meanwhile, overexpression of VvTPR3 and VvHDAC19 reduced the stability of cell wall against B. cinerea in strawberry. Taken together, chitosan induces defense related genes and protect the fruit quality against Botrytis infection through JA signaling.

Histochemical and Microscopic Studies Predict that Grapevine Genotype "Ju mei gui" is Highly Resistant against Botrytis cinerea

The necrotrophic fungus Botrytis cinerea causes devastating pre- and post-harvest yield losses in grapevine (Vitis vinifera L.). Although B. cinerea has been well-studied in different plant species, there is limited information related to the resistance and susceptibility mechanisms of Vitis genotypes against B. cinerea infection. In the present study, leaves and berries of twenty four grape genotypes were evaluated against B. cinerea infection. According to the results, one genotype (Ju mei gui) was highly resistant (HR), one genotype (Kyoho) was resistant (R), eight genotypes were susceptible (S), and fourteen genotypes were highly susceptible (HS) against infection of B. cinerea in leaves. Whereas in the case of B. cinerea infection in grape berry, three genotypes were found to be highly resistant, three resistant, eleven genotypes susceptible, and seven were highly susceptible. To further explore the mechanism of disease resistance in grapevine, we evaluated "Ju mei gui" and "Summer black" in terms of B. cinerea progression, reactive oxygen species reactions, jasmonic acid contents, and the activities of antioxidant enzymes in leaf and fruit. We surmise that the resistance of "Ju mei gui" is due to seized fungal growth, minor reactive oxygen species (ROS) production, elevated antioxidant enzyme activity, and more jasmonic acid (JA) contents. This study provides insights into the resistance and susceptibility mechanism of Vitis genotypes against B. cinerea. This will help for the selection of appropriate germplasm to explore the molecular basis of disease resistance mechanisms in grapevine.