Analysis of summer epidemic progress of apple scab at different apple production systems in the Netherlands and hungary

The Microbial Diversity in Relation to Postharvest Quality and Decay: Organic vs. Conventional Pear Fruit

(1) Background: Organic food produced in environmentally friendly farming systems has become increasingly popular. (2) Methods: We used a DNA metabarcoding approach to investigate the differences in the microbial community between organic and conventional 'Huangguan' pear fruit; and (3) Results: Compared to a conventional orchard, the fruit firmness in the organic orchard had significantly lowered after 30 days of shelf-life storage at 25 °C, and the soluble solids content (SSC), titratable acid (TA), and decay index were higher. There were differences in the microbial diversity between organic and conventional orchards pears. After 30 days of storage, Fusarium and Starmerella became the main epiphytic fungi in organic fruits, while Meyerozyma was dominant in conventional fruits. Gluconobacter, Acetobacter, and Komagataeibacter were dominant epiphytic bacteria on pears from both organic and conventional orchards after a 30-day storage period. Bacteroides, Muribaculaceae, and Nesterenkonia were the main endophytic bacteria throughout storage. There was a negative correlation between fruit firmness and decay index. Moreover, the abundance of Acetobacter and Starmerella were positively correlated with fruit firmness, while Muribaculaceae was negatively correlated, implying that these three microorganisms may be associated with the postharvest decay of organic fruit; (4) Conclusions: The difference in postharvest quality and decay in organic and conventional fruits could potentially be attributed to the variation in the microbial community during storage.

Strong Genetic Differentiation between Generalist Populations of Venturia inaequalis and Populations from Partially Resistant Apple Cultivars Carrying Rvi3 or Rvi5

The ascomycete fungus Venturia inaequalis causes scab disease, a major problem in apple production. The utilization of resistant cultivars is hindered by emerging new pathogen races, which erode their resistance. Increasing our knowledge on the population genetic processes of the fungus can contribute to the development of resistance gene deployment strategies and more durable resistance. We investigated the effect of four scab race indicator cultivars, ‘Gala’ (no R-gene), ‘Golden Delicious’ (Rvi1), ‘Geneva’ (Rvi3, complex), and OR45t132 (Rvi5), on the V. inaequalis population genetic structure and diversity. Sixty-six monosporic fungal isolates from the four cultivars were genotyped with seven simple sequence repeat primers. Furthermore, the partial resistance of the indicators and the pathogenicity profile of the conidia from each host were assessed. The genetic diversity and structure of the investigated V. inaequalis subpopulations correspond to the partial resistance of the original hosts as well as the subpopulations’ pathogenicity profiles. Indicators carrying Rvi3 and Rvi5 had strongly diverged and specialized V. inaequalis populations on them and fewer symptoms on the field. In line with the complete breakdown of the Rvi1 gene, the population from ‘Golden Delicious’ did not segregate from the susceptible ‘Gala’, and virulence towards Rvi1 was present in all subpopulations.

Assessment of Lipopeptide Mixtures Produced by Bacillus subtilis as Biocontrol Products against Apple Scab (Venturia inaequalis)

Apple scab is an important disease conventionally controlled by chemical fungicides, which should be replaced by more environmentally friendly alternatives. One of these alternatives could be the use of lipopeptides produced by Bacillus subtilis. The objective of this work is to study the action of the three families of lipopeptides and different mixtures of them in vitro and in vivo against Venturia inaequalis. Firstly, the antifungal activity of mycosubtilin/surfactin and fengycin/surfactin mixtures was determined in vitro by measuring the median inhibitory concentration. Then, the best lipopeptide mixture ratio was produced using Design of Experiment (DoE) to optimize the composition of the culture medium. Finally, the lipopeptides mixtures efficiency against V. inaequalis was assessed in orchards as well as the evaluation of the persistence of lipopeptides on apple. In vitro tests show that the use of fengycin or mycosubtilin alone is as effective as a mixture, with the 50–50% fengycin/surfactin mixture being the most effective. Optimization of culture medium for the production of fengycin/surfactin mixture shows that the best composition is glycerol coupled with glutamic acid. Finally, lipopeptides showed in vivo antifungal efficiency against V. inaequalis regardless of the mixture used with a 70% reduction in the incidence of scab for both mixtures (fengycin/surfactin or mycosubtilin/surfactin). The reproducibility of the results over the two trial campaigns was significantly better with the mycosubtilin/surfactin mixture. The use of B. subtilis lipopeptides to control this disease is very promising.

Comparative Studies on the Effect of Adjuvants with Urea to Reduce the Overwintering Inoculum of Venturia inaequalis

A 2-year study on the use of organic and conventional adjuvants alone, or mixed with urea, was conducted for management of overwintering inoculum of the apple scab pathogen, Venturia inaequalis. Select adjuvants (LI 700, Bond Max, Latron B-1956, and Organic Wet Betty [OWB]) have the potential to hasten urea-driven leaf litter decomposition and reduce V. inaequalis overwintering inoculum comparable to urea, and that one organic surfactant could perform the same level of leaf decomposition as urea. Combinations of adjuvants with urea significantly improved leaf litter degradation compared with urea alone, concomitant with reducing the number of pseudothecia present and pseudothecium fertility. We demonstrate that the combination of urea with Bond Max or OWB reduced pseudothecia fertility and ascospore production to less than 5% in the remaining pseudothecia, a significantly greater reduction than with urea alone. These results suggest that conventional growers combine urea with Bond Max or OWB to more effectively reduce overwintering inoculum, and that the adjuvant OWB can provide organic growers with comparable performance to urea used in conventional orchards for improved sanitation.

Integrated Control of Apple Scab and Powdery Mildew in an Organic Apple Orchard by Combining Potassium Carbonates with Wettable Sulfur, Pruning, and Cultivar Susceptibility

In a 4-year study in a whole-field sanitized organic apple orchard, the effectiveness of nine fungicide treatments, including potassium mono- and bicarbonate and their combinations with wettable sulfur, were evaluated for scab and powdery mildew control on two cultivars with different susceptibility to scab and powdery mildew, under two pruning treatments. The whole-field sanitation practice was performed by removal of infected fallen leaves. Treatment effects on phytotoxicity and yield were also determined. Pruning significantly reduced leaf scab incidence but only on the more scab-susceptible Idared. Pruning significantly reduced mildew incidence in most years and on both cultivars but the more mildew-susceptible Jonathan showed significantly higher mildew incidence than Idared. Among products approved for organic production, the best scab control was achieved with a potassium mono- or bicarbonate treatment combined with wettable sulfur, except for Jonathan in 2011 on leaf and in 2014 on both leaf and fruit, and for Idared in 2013 on fruit. The best mildew control was also achieved with potassium mono- or bicarbonate treatments combined with wettable sulfur, with exceptions on shoots of Idared in 2011 and 2013 and on fruit of Idared in 2012. Leaf phytotoxicity was significantly higher in all potassium carbonate treatments compared with untreated plots, except for Idared in 2012, while fruit russet in these treatments did not differ significantly from the untreated plots. However, phytotoxicity values of all carbonate treatments were significantly lower than the lime sulfur treatment in most years on both cultivars. Yield of the potassium mono- or bicarbonate treatments combined with wettable sulfur was significantly higher than the untreated plots in the pruned treatments for both cultivars in all years. The integrated control approach designed for organic disease management against the two pathogens is discussed.

Plant Diseases and Management Approaches in Organic Farming Systems

Organic agriculture has expanded worldwide. Numerous papers were published in the past 20 years comparing plant diseases in organic and conventional crops. Root diseases are generally less severe owing to greater soil health, whereas some foliar diseases can be problematic in organic agriculture. The soil microbial community and nitrogen availability play an important role in disease development and yield. Recently, the focus has shifted to optimizing organic crop production by improving plant nutrition, weed control, and plant health. Crop-loss assessment relating productivity to all yield-forming and -reducing factors would benefit organic production and sustainability evaluation.

Seasonal and Cross-Seasonal Timing of Fungicide Trunk Injections in Apple Trees to Optimize Management of Apple Scab

To optimize the number and timing of trunk injections for season-long control of apple scab (Venturia inaequalis), we evaluated 1 to 2 and 4 seasonal and cross-seasonal injections of potassium phosphites and synthetic fungicides and quantified residues in leaves and fruit. Phosphites accumulated in the canopy at the highest concentrations, aligned well in time with scab suppression, and gave better leaf scab control of 41.8 to 73.5% than propiconazole (16.9 to 51.5%) or cyprodinil + difenoconazole (5.4 to 17.4%). More injections of phosphites controlled leaf scab better than fewer (23.7% versus 48.2%), and more fungicide injections resulted in 21.9 to 51.1% better leaf scab control than fewer. Leaf scab control with phosphites was only 3.2 to 13.9% better with 4 cross-seasonal compared with 4 seasonal injections, while 1 to 2 seasonal compared with 1 to 2 cross-seasonal injections improved scab control only for 4.2 to 22.1%. On shoots, injected phosphites provided comparable or for 4.4 to 10.5% and 22.3 to 41.4% better scab control than spray standards. On fruit, injected phosphites slightly improved control compared with sprayed phosphites or the sprayed fungicide standard (33.4 to 40.8%). Two seasonal injections of phosphites controlled shoot scab 5.7% better than 9 spray applications. Five sprays of cyprodinil + difenoconazole controlled scab better than their injections. Fruit residues of phosphites reached 2.8 ppm and declined in all treatments except in 2 seasonal injections and phosphite sprays. Cyprodinil and difenoconazole fruit residues reached 0.02 and 0.07 ppm and declined sharply toward the end of the season. These were far below the United States, Codex, and EU MRL-s of 1, 0.8, and 0.5 ppm for difenoconazole, and 1.7, 2, and 1 ppm for cyprodinil, respectively.

Lagged association between powdery mildew leaf severity, airborne inoculum, weather, and crop losses in strawberry

Knowledge about epidemiology and the impact of disease on yield is fundamental for establishing effective management strategies. The purpose of this study was to investigate the relationship between foliar strawberry mildew severity, Podosphaera aphanis airborne inoculum concentration, weather, and subsequent crop losses for day-neutral strawberry. The experiment was conducted at three, five, and four sites in 2006, 2007, and 2008, respectively, for a total of 12 epidemics. At each site, data were collected on 25 plants at 2-day intervals from the end of May to early October for a total of 60 to 62 samplings annually. First, seasonal crop losses were statistically described; then, a lagged regression model was developed to describe crop losses from the parameters that were significantly associated with losses. There was a strong positive linear relationship between seasonal crop losses and the area under the leaf disease progress curve (R(2) = 0.90) and daily mean airborne conidia concentration (R(2) = 0.86), and a negative linear relationship between crop losses and time to 5% loss (R(2) = 0.76) and time to 5% leaf area diseased (R(2) = 0.61). Among the 53 monitoring- and weather-based variables analyzed, percent leaf area diseased, log10-transformed airborne inoculum concentration, and weather variables related to temperature were significantly associated with crop losses. However, polynomial distributed lag regression models built with weather variables were not accurate in predicting losses, with the exception of a model based on a combined temperature and humidity variable, which provided accurate prediction of the data used to construct the model but not of independent data. Overall, the model based on log10-transformed airborne inoculum concentration did not provide accurate crop loss predictions. The model built using percent leaf area diseased with a time lag of 8 days (n = 4) and a polynomial degree of 2 provided a good description of the crop-loss data used to construct the model (r = 0.99 and 0.90) and of independent data (r = 0.92). For the 12 epidemics studied, 5% crop loss was reached when an average of 17% leaf area diseased was observed since the beginning of symptom development. These results indicate that information on foliar powdery mildew must be considered when making strawberry powdery mildew management decisions.

Analysis of nonlinear relationships in dual epidemics, and its application to the management of grapevine downy and powdery mildews

Dual epidemics are defined as epidemics developing on two or several plant organs in the course of a cropping season. Agricultural pathosystems where such epidemics develop are often very important, because the harvestable part is one of the organs affected. These epidemics also are often difficult to manage, because the linkage between epidemiological components occurring on different organs is poorly understood, and because prediction of the risk toward the harvestable organs is difficult. In the case of downy mildew (DM) and powdery mildew (PM) of grapevine, nonlinear modeling and logistic regression indicated nonlinearity in the foliage-cluster relationships. Nonlinear modeling enabled the parameterization of a transmission coefficient that numerically links the two components, leaves and clusters, in DM and PM epidemics. Logistic regression analysis yielded a series of probabilistic models that enabled predicting preset levels of cluster infection risks based on DM and PM severities on the foliage at successive crop stages. The usefulness of this framework for tactical decision-making for disease control is discussed.

Effect of Production System and Pruning on Temporal Development of Cercospora depazeoides and on Berry Yield in Black Elderberry Orchards

In a 2-year study, the temporal development of Cercospora leaf spot (Cercospora depazeoides) and berry yield were evaluated in two production systems (integrated and organic) and in two winter pruning treatments (trees pruned to four and eight scaffolds) in two black elderberry (Sambucus nigra) orchards in Hungary. Under organic production, leaf spot onset occurred 2 to 4 weeks earlier (mid- and late July) in both years and both orchards compared with the integrated program. Disease then continuously progressed until the final assessment date (late September) in both years, reaching a maximum final disease incidence of 15.9% in the integrated system and of 38.2% in the organic system. In general, disease progress after late August was greater on trees pruned to eight scaffolds than on trees pruned to four scaffolds in both production systems. Both final disease incidence and area under the disease progress curves (AUDPC) were significantly lower (P < 0.001) in the integrated treatments compared with organic ones. Across all treatments, both disease measures were significantly (P < 0.05) lower on trees pruned to four scaffolds compared with trees pruned to eight scaffolds. However, when the effect of pruning on final disease incidence and AUDPC was analyzed separately for integrated and organic systems, pruning caused uniformly significant differences in disease development only for the organic system. Berry yield was significantly higher (P < 0.05) in the integrated system compared with the organic system, but pruning showed no significant effect on yield. Overall, pruning to four scaffolds resulted in consistently lower disease development in organic production compared to integrated. Thus, winter pruning may be useful as a Cercospora leaf spot management practice in organic elderberry orchards.

Action Thresholds for Summer Fungicide Sprays and Sequential Classification of Apple Scab Incidence

The objectives of this study were to establish scab incidence thresholds at which summer fungicide sprays should be initiated and to develop sequential sampling for classification plans to facilitate decision making. The relationship between proportion of scabbed leaves per shoot and percent scabbed fruits at harvest was established based on data collected in both experimental and commercial orchards. Action threshold at which fungicide spray program should be initiated in order to maintain fruit scab at harvest below 2% was established at 0.006 scabbed leaves per shoot; hence incidence thresholds of 0.005 and 0.01 scabbed leaves per shoot were evaluated. Sequential sampling for classification procedures (SSCP), using the Wald's sequential probability ratio test (SPRT), were developed based on a beta-binomial distribution and using parameter estimates of the binary power law. Monte Carlo simulations were used to establish the probability of classifying mean scab incidence as less than the action thresholds (pth = 0.005 and pth = 0.01). Operating characteristic (OC) and average sample number (ASN) curves were established for eight combinations of stop lines and error levels (α and β). Based on the results of the Monte Carlo simulations, four sets of stop lines (two for each pth threshold) were selected for further evaluation. Bootstrap simulations of 50 data sets indicated that both the OC and ASN curves for each of the four pairs of stop lines were similar to OC and ASN values determined by Monte Carlo simulation. When validated with data not used to construct the models, the SSCPs provided the appropriate classification in 98 and 95% of the simulations for the pth = 0.005 and pth = 0.01 (α = 0.05 and β = 0.10), respectively. The sequential sampling plans developed in this study should allow for rapid and accurate classification of the incidence of apple scab on leaves, and aid in sampling for summer scab management decision making.

Quantitative relationships between different injury factors and development of brown rot caused by Monilinia fructigena in integrated and organic apple orchards

In a 4-year study, the incidence of various types of injuries (caused by insects, birds, growth cracks, mechanical wounding, and other, unidentified factors) was assessed in relation to brown rot development (caused by Monilinia fructigena) on fruit of three apple cultivars (Prima, Jonathan, and Mutsu) in integrated and organic blocks of two apple orchards in Hungary. In addition, populations of male codling moths (Cydia pomonella) were monitored with pheromone traps season-long in both management systems. On average, injury incidence on fruit at harvest was 6.1 and 19.2% in the integrated and organic treatments, respectively. Insect injury, which was caused primarily by C. pomonella, had the highest incidence among the five injury types, accounting for 79.4% of the total injury by harvest in the organic blocks and 36.6% in the integrated blocks. Levels of all other injury types remained close to zero during most of the season, but the incidence of bird injury and growth cracks increased markedly in the final 3 to 5 weeks before harvest in both production systems. Brown rot developed more slowly and reached a lower incidence in the integrated (6.4% final incidence on average) compared with the organic blocks (20.1% average incidence). In addition, the disease developed later but attained higher levels as the cultivar ripening season increased from early-maturing Prima to late-maturing Mutsu. Overall, 94.3 to 98.7% of all injured fruit were also infected by M. fructigena, whereas the incidence of brown-rotted fruit without visible injury was very low (0.8 to 1.6%). Correlation coefficients (on a per plot basis) and association indices (on a per-fruit basis) were calculated between brown rot and the various injury types for two selected assessment dates 4 weeks preharvest and at harvest. At both dates, the strongest significant (P < 0.05) relationships were observed between brown rot and insect injury and between brown rot and the cumulative number of trapped C. pomonella. At the harvest assessment, two additional significant correlations were between brown rot and bird injury and between brown rot and growth cracks. In every case, correlation coefficients were larger in organic than in integrated blocks. Although it is well established that brown rot in pome fruits is closely associated with fruit injuries, this is the first study to provide season-long progress data on different injury types and quantitative analyses of their relative importance at different times in the growing season and across two distinct management systems.

Temporal dynamics of brown rot in different apple management systems and importance of dropped fruit for disease development

ABSTRACT Epidemic development of brown rot, caused by Monilinia fructigena, was monitored in integrated and organic apple orchards at two locations in eastern Hungary between 2002 and 2005 on three cultivars with early, midseason, and late ripening periods. Disease incidence and severity measures were affected significantly (P < 0.05) by management system (organic versus integrated) and cultivar, but there was no significant management system-cultivar interaction. Epidemics started 2 to 4 weeks earlier in organic orchards and on the early cv. Prima compared with integrated orchards and the late cv. Mutsu. Disease intensity increased markedly in the final 3 to 5 weeks before harvest and was considerably lower in integrated than in organic orchards. Final brown rot incidence on fruit in the tree was correlated with incidence on dropped fruit on the orchard floor (r > 0.75, P < 0.05), whereby the lag period from the appearance of the first symptomatic fruit on the ground to the occurrence of the first symptomatic fruit in the tree ranged from 2 weeks to 2 months, depending on the cultivar. The inflection point of the disease progress curve was attained first by fruit on the ground, followed successively by fruit in the lower, middle, and upper thirds of the tree canopy. This may indicate that dropped fruit that became infected early provided a source of inoculum for subsequent epidemics by serving as a bridge between sporulation from overwintered fruit mummies in the spring and the first fruit with sporulating lesions in the tree in midsummer. Removal of dropped fruit from the orchard floor resulted in a significantly lower disease incidence on fruit in the tree on all cultivars; thus, drop-removal may be useful as a brown rot management practice in apple orchards.