A Novel Pear Scab (Venturia nashicola) Resistance Gene, Rvn3, from Interspecific Hybrid Pear (Pyrus pyrifolia × P. communis)

Asian pear scab is a fungal disease caused by Venturia nashicola. The identification of genes conferring scab resistance could facilitate the breeding of disease-resistant cultivars. Therefore, the present study aimed to identify a scab-resistance gene using an interspecific hybrid population ((Pyrus pyrifolia × P. communis) × P. pyrifolia). Artificial inoculation of V. nashicola was carried out for two years. The segregation ratio (1:1) of resistant to susceptible individuals indicated that resistance to V. nashicola was inherited from P. communis and controlled by a single dominant gene. Based on two years phenotypic data with the Kruskal–Wallis test and interval mapping, 12 common markers were significantly associated with scab resistance. A novel scab resistance gene, Rvn3, was mapped in linkage group 6 of the interspecific hybrid pear, and co-linearity between Rvn3 and one of the apple scab resistance genes, Rvi14, was confirmed. Notably, an insertion in pseudo-chromosome 6 of the interspecific hybrid cultivar showed homology with apple scab resistance genes. Hence, the newly discovered Rvn3 was considered an ortholog of the apple scab resistance gene. Since the mapping population used in the present study is a pseudo-BC1 population, pyramiding of multiple resistance genes to pseudo-BC1 could facilitate the breeding of pear cultivars with durable resistance.

Molecular Screening of Some Apple Progenies for Detection Vf Gene Using Marker Assisted Selection

Apple scab, caused by Venturia inaequalis is one of the most damaging pathogens that affects apple species. Cross combinations were made between Auriu de Bistrița cv. (female genitor) - a valuable local variety in terms of fruit quality but only tolerant to scab, and Florina cv. (male genitor) used as a donor of Vf resistance gene. It was first detected in Malus floribunda Clone 821, which was later transferred to commercial varieties by different breeding programs. To confirm the presence of Vf gene, progenies resulting from the mentioned combination were tested with MAS (Marker Assited Selection), using two dominant primers pairs (AM19, U1400), and another one codominant (AL07) used to distinguish homozygous and heterozygous genotypes. After the crossing combination, a number of twenty-six hybrids were obtained, of which 50% (13 hybrids) were clasified as resistant (heterozygous), respectively 50% (13 hybrids) as susceptible (recessive homozygotes), so the Mendelian ratio was confirmed.

Successful intergeneric transfer of a major apple scab resistance gene (Rvi6) from apple to pear and precise comparison of the downstream molecular mechanisms of this resistance in both species

Background Scab is the most important fungal disease of apple and pear. Apple (Malus x domestica Borkh.) and European pear (Pyrus communis L.) are genetically related but they are hosts of two different fungal species: Venturia inaequalis for apple and V. pyrina for European pear. The apple/V. inaequalis pathosystem is quite well known, whereas knowledge about the pear/V. pyrina pathosystem is still limited. The aim of our study was to analyse the mode of action of a major resistance gene of apple (Rvi6) in transgenic apple and pear plants interacting with the two scab species (V. inaequalis and V. pyrina), in order to determine the degree of functional transferability between the two pathosystems. Results Transgenic pear clones constitutively expressing the Rvi6 gene from apple were compared to a scab transgenic apple clone carrying the same construct. After inoculation in greenhouse with V. pyrina, strong defense reactions and very limited sporulation were observed on all transgenic pear clones tested. Microscopic observations revealed frequent aborted conidiophores in the Rvi6 transgenic pear / V. pyrina interaction. The macro- and microscopic observations were very comparable to the Rvi6 apple / V. inaequalis interaction. However, this resistance in pear proved variable according to the strain of V. pyrina, and one of the strains tested overcame the resistance of most of the transgenic pear clones. Comparative transcriptomic analyses of apple and pear resistant interactions with V. inaequalis and V. pyrina, respectively, revealed different cascades of molecular mechanisms downstream of the pathogen recognition by Rvi6 in the two species. Signal transduction was triggered in both species with calcium (and G-proteins in pear) and interconnected hormonal signaling (jasmonic acid in pear, auxins in apple and brassinosteroids in both species), without involvement of salicylic acid. This led to the induction of defense responses such as a remodeling of primary and secondary cell wall, lipids biosynthesis (galactolipids in apple and cutin and cuticular waxes in pear), systemic acquired resistance signal generation (in apple) or perception in distal tissues (in pear), and the biosynthesis of phenylpropanoids (flavonoids in apple but also lignin in pear). Conclusion This study is the first example of a successful intergeneric transfer of a resistance gene among Rosaceae, with a resistance gene functioning towards another species of pathogen.

Bacterial Endophyte Community Dynamics in Apple (Malus domestica Borkh.) Germplasm and Their Evaluation for Scab Management Strategies

The large genetic evolution due to the sexual reproduction-mediated gene assortments and propensities has made Venturia inaequalis (causing apple scab) unique with respect to its management strategies. The resistance in apple germplasm against the scab, being controlled for by more than fifteen genes, has limited gene alteration-based investigations. Therefore, a biological approach of bacterial endophyte community dynamics was envisioned across the apple germplasm in context to the fungistatic behavior against V. inaequalis. A total of 155 colonies of bacterial endophytes were isolated from various plant parts of the apple, comprising 19 varieties, and after screening for antifungal behavior followed by morphological, ARDRA, and sequence analysis, a total of 71 isolates were selected for this study. The alpha diversity indices were seen to fluctuate greatly among the isolation samples in context to microflora with antifungal behavior. As all the isolates were screened for the presence of various metabolites and some relevant genes that directly or indirectly influence the fungistatic behavior of the isolated microflora, a huge variation among the isolated microflora was observed. The outstanding isolates showing highest percentage growth inhibition of V. inaequalis were exploited to raise a bio-formulation, which was tested against the scab prevalence in eight apple varieties under controlled growth conditions. The formulation at all the concentrations caused considerable reductions in both the disease severity and disease incidence in all the tested apple varieties. Red Delicious being most important cultivar of the northwestern Himalayas was further investigated for its biochemical behavior in formulation and the investigation revealed different levels of enzyme production, chlorophyll, and sugars against the non-inoculated control.

Meta-Learning for Few-Shot Plant Disease Detection

Plant diseases can harm crop growth, and the crop production has a deep impact on food. Although the existing works adopt Convolutional Neural Networks (CNNs) to detect plant diseases such as Apple Scab and Squash Powdery mildew, those methods have limitations as they rely on a large amount of manually labeled data. Collecting enough labeled data is not often the case in practice because: plant pathogens are variable and farm environments make collecting data difficulty. Methods based on deep learning suffer from low accuracy and confidence when facing few-shot samples. In this paper, we propose local feature matching conditional neural adaptive processes (LFM-CNAPS) based on meta-learning that aims at detecting plant diseases of unseen categories with only a few annotated examples, and visualize input regions that are ‘important’ for predictions. To train our network, we contribute Miniplantdisease-Dataset that contains 26 plant species and 60 plant diseases. Comprehensive experiments demonstrate that our proposed LFM-CNAPS method outperforms the existing methods.

Calcium and Silicon Fertiliser Influence on Fungicide Efficacy Against Guignardia Leaf Blotch and Apple Scab Management

Management of fungal diseases within urban landscapes relies heavily on repeat fungicide sprays. Environmental concerns have led to a need to eliminate or reduce fungicide use. Foliar sprays of calcium- (Ca) and silicon- (Si) based fertilisers have been shown to reduce symptom severity of several fungal pathogens. The aim of our research was to evaluate the influence of Ca chloride, Ca metasolate, tetra ethyl silicate, and potassium silicate fertilisers, applied independently and in combination with a synthetic fungicide (penconazole) at full and half strength, on apple scab (Venturia inaequalis) and Guignardia leaf blotch (Guignardia aesculi) symptom severity, as well as leaf chlorophyll content, fruit yield, and crown volume. Trials used container-grown Aesculus hippocastanum and field-grown Malus domestica cv. ‘Golden Delicious’. Applications of Ca, Si, and penconazole sprays alone significantly reduced scab and leaf blotch severity compared to water-sprayed controls; however, a significant difference between the type of Ca and Si fertilisers was recorded. A combined mix of a Ca or Si fertiliser with a full or half dose of penconazole was more effective at reducing symptom severity of both foliar pathogens than a full or half dose of penconazole alone. Data analysed with Limpel’s formula indicated positive synergistic effects between Ca and Si and penconazole in some, but not all, cases. The integration of Ca and Si foliar sprays as an alternative to, or additive with, penconazole for scab and leaf blotch management appears feasible based on results of our studies and may have applicability against other fungal pathogens.

Disease Detection in Apple Leaves Using Deep Convolutional Neural Network

The automatic detection of diseases in plants is necessary, as it reduces the tedious work of monitoring large farms and it will detect the disease at an early stage of its occurrence to minimize further degradation of plants. Besides the decline of plant health, a country’s economy is highly affected by this scenario due to lower production. The current approach to identify diseases by an expert is slow and non-optimal for large farms. Our proposed model is an ensemble of pre-trained DenseNet121, EfficientNetB7, and EfficientNet NoisyStudent, which aims to classify leaves of apple trees into one of the following categories: healthy, apple scab, apple cedar rust, and multiple diseases, using its images. Various Image Augmentation techniques are included in this research to increase the dataset size, and subsequentially, the model’s accuracy increases. Our proposed model achieves an accuracy of 96.25% on the validation dataset. The proposed model can identify leaves with multiple diseases with 90% accuracy. Our proposed model achieved a good performance on different metrics and can be deployed in the agricultural domain to identify plant health accurately and timely.

Optimizing the integration of a biopesticide (Bacillus subtilis QST 713) with a single-site fungicide (benzovindiflupyr) to reduce reliance on synthetic multi-site fungicides (captan and mancozeb) for management of apple scab.

Apple scab is one of the most economically important diseases of apple in temperate production regions. In the absence of durable host resistance in commercially preferred cultivars, considerable applications of fungicides are needed to manage this disease. With the sequential development of resistance to nearly all classes of single-site fungicides in the apple scab pathogen Venturia inaequalis, synthetic multi-site fungicides, such as mancozeb and captan, often comprise the core of chemical management programs for apple scab. While these fungicides have demonstrable benefits for both disease and fungicide resistance management, the sustainability movement within agriculture aims to reduce reliance on such fungicides due to their broader environmental impacts. In this study, we establish a framework to enhance the feasibility of chemical management programs that do not rely on use of synthetic multi-site protectant fungicides to manage apple scab. Specifically, we wish to evaluate chemical programs that integrate the biopesticide, Bacillus subtilis QST 713 (Serenade Opti), in rotation with benzovindiflupyr (Aprovia), a single-site fungicide belonging to the class of succinate dehydrogenase inhibitors (SDHI), to circumvent the need for applications of synthetic multi-site fungicides. During implementation of these programs, disease incidence data were taken at biweekly intervals. Irrespective of the seasonal challenges presented in the two years of this study, when Bacillus subtilis QST 713 was used in place of captan and mancozeb mixtures, we did not observe any significant differences (P > 0.05) in development of apple scab symptoms between any of the management programs for the vertical axis or super spindle orchards in either year. This potential for substituting synthetic multi-site fungicides with biopesticides is best realized when the programs are used with a decision support system in a super-spindle planting system, where trees have reduced canopy densities. This two-year study shows the potential to achieve adequate disease control using the integration of SDHI fungicides and biological controls without the use of synthetic multi-site fungicides.