Performance of disease-resistant grapevine varieties with reduction of fungicide sprayingAbstract:
The cultivation of wine grapes (Vitis vinifera) faces significant phytosanitary challenges, especially due to downy mildew (Plasmopara viticola), which is the main fungal disease in vineyards. The conventional practice for managing this disease involves intensive fungicide use, which poses health and environmental risks and significantly increases production costs. PIWI-resistant varieties emerge as promising alternatives, offering disease resistance and high enological quality. This study aimed to compare the response of ‘Bronner’ and ‘Helios’ varieties to downy mildew, anthracnose, and bunch rot and the traditional ‘Sauvignon Blanc’ variety, under reduction of fungicide application in the municipality of Videira, SC/Brazil, during the 2020/2021 and 2021/2022 cycles. Severity values were estimated for each disease using diagrammatic scales. Maximum incidence and severity were evaluated, and the area under the disease severity progress curve was calculated. The ‘Helios’ variety was more susceptible to anthracnose, while ‘Bronner’ was more affected by grape ripe rot. PIWI varieties were less affected by downy mildew compared to ‘Sauvignon Blanc’ variety. The reduction of fungicide spraying did not influence the performance of resistant varieties, but negatively affected the health of the traditional variety.Therefore, effective disease management requires a balanced and adaptive approach, considering the specific characteristics of each variety.
Index terms
Vitis vinifera; PIWI varieties; plant health; resilient management; viticulture
Resumo:
O cultivo de uvas finas (Vitis vinifera) enfrenta desafios fitossanitários significativos, especialmente devido ao míldio da videira (Plasmoparaviticola), que é a principal doença fúngica em vinhedos. A prática convencional para o manejo desta doença envolve o uso intensivo de fungicidas, o que representa riscos à saúde e ao meio ambiente e aumenta, significativamente, os custos de produção.As variedades resistentes PIWI surgem como alternativas promissoras, oferecendo resistência a doenças e alta qualidade enológica. O objetivo deste estudo foicomparar a resposta das variedades PIWI Bronner e Helios em relação ao míldio, à antracnose e a podridões com a variedade vinífera tradicional ‘Sauvignon Blanc’,manejadas com redução de pulverizações de fungicidas em Videira- SC, durante as safras de2020/2021 e 2021/2022. Valores de severidade para cada doença foram estimados com o uso de escalas diagramáticas. A incidência e a severidade máxima foram avaliadas e a área abaixo da curva de progresso da doença foi calculada. ‘Helios’ mostrou-se mais suscetível antracnose, enquanto a Bronner foi mais afetada pela podridão da uva madura.As variedades PIWI foram menos afetadas pelo míldio em comparação com a Sauvignon Blanc. A redução de pulverizações de fungicidas não prejudicou o desempenho das variedades resistentes, mas afetou, negativamente, a sanidade da variedade tradicional.Portanto, o manejo eficaz das doenças requer uma abordagem equilibrada e adaptável, considerando as características específicas de cada variedade.
Termos para indexação
Vitis vinifera; variedades PIWI; fitossanidade; manejo resiliente; viticultura
Introduction
Currently, the production of fine grapes (Vitis vinifera) is limited due to difficulties in phytosanitary management, as the grapevine is affected by diseases during all production stages, compromising yield, quality, and the physiological mechanisms of plants (ARMIJO et al., 2016).
The species plasticity allows it to be cultivated in different environments, facilitating the spread of pathogenic agents, such as downy mildew [Plasmopara viticola (Berk. and Curt) Berl., and Toni], considered the main fungal disease of grapevines worldwide, as reviewed by Koledenkova et al. (2022).
Traditional viticulture relies on the intensive use of fungicides (EISENMANN et al., 2023), which increases production costs and poses health risks to farmers and consumers, in addition to negative impacts on the environment. In this context, the use of resistant varieties known as PIWI (“Pilzwiderstandsfähige”), is a promising strategy for managing downy mildew in vineyards and reducing the use of pesticides.
These varieties are obtained through marker-assisted selection that combines high oenological quality and disease resistance (EIBACH et al., 2007).
Up to the present moment, 33 QTLs known as Rpv (resistance to Plasmopara viticola) have been identified, which confer quantitative resistance to grapevine downy mildew (SCHUMACHER et al. 2024).
In Brazil, some resistant varieties containing Rpv1, Rpv3, Rpv10, and Rpv12 resistance alleles have already been introduced and are being evaluated in the state of Santa Catarina. The potential of PIWI varieties, including ‘Bronner’ (Rpv10 + Rpv3.3) and ‘Helios’ (Rpv3.1) has already been confirmed through adaptation tests, both from production and oenological perspectives (BRIGHENTI et al., 2019).
According to Zanghelini et al. (2019), these varieties enable the production of wine grapes with reduction of fungicide application due to greater ease of disease control.
However, since resistance is incomplete, the total exclusion of fungicides should be avoided. The effective control of downy mildew in a conventional system is achieved only through complementation with chemical control, especially in regions with climate favorable to the pathogen (CLIPPINGER et al., 2024; EISENMANN et al., 2023).
In vineyards in southern Brazil, soil and climate conditions also favor the occurrence of rot and anthracnose, diseases that can cause serious damage to winegrowers (DIAS et al., 2022).
Therefore, reducing fungicide application in vineyards of PIWI varieties may favor the development of secondary diseases if these are not included in application programs (DIAS et al., 2022; ALTIERI et al., 2023; WINGERTER et al., 2021).
Considering the above, the aim of this study was to compare the response of ‘Bronner’ and ‘Helios’ PIWI varieties with the traditional ‘Sauvignon Blanc’ wine variety in relation to downy mildew, anthracnose, and bunch rot, managed with reduction of fungicide application.
Material and Methods
Study location
The experiment was carried out at the Epagri Experimental Station of Videira, SC/ Brazil (27°01’S 51°08’W, altitude 840 m) during the 2020/2021 and 2021/2022 harvests.
According to Köppen, the region’s climate is classified as humid mesothermal with mild summer (Cfb), and the soil is dystrophic red nitisol (ALVARES et al., 2013; SANTOS et al., 2013).
Climate monitoring was conducted based on the average monthly temperature, relative humidity, and monthly precipitation during the 2020/21 and 2021/22 cycles, obtained from the Santa Catarina environmental variables database (Epagri/CIRAM).
The vineyard was established in 2015 with the white ‘Bronner’ (Rpv10 + Rpv3.3), ‘Helios’ (Rpv3.1), and ‘Sauvignon Blanc’ varieties grafted onto the Paulsen 1103 rootstock.
Vineyards were spaced at 3.0 m x 1.2 m (between rows and between plants) and managed using the espalier training system with double-spurred cordon pruning.
Additionally, a vineyard with traditional grapevine varieties, located adjacent to the experimental area and managed according to commercial vineyards, was used solely as a reference to obtain the number of fungicide applications used at the grower’s level.
Phytosanitary experiment management
For the two cycles evaluated, 15 fungicide applications were performed, one of which corresponded to the winter treatment (dormant phase) with a lime sulfur mixture at 4º Bé, and the remaining 14 corresponded to fungicides applied throughout each vegetative cycle.
This approach aimed to systematically intervene at times of greater susceptibility to each disease, to better explore the genetic resistance of PIWI varieties, while simultaneously reducing fungicide applications, as presented by Eisenmann et al. (2023).
An adjuvant based on 20% ethoxylated non-phenol (0.3 g L-1) was used in all fungicide applications. Products were selected based on the most restricted spectrum of action possible for the biological control target, while the solution volume applied respected the respective manufacturer’s recommendation (AGROFIT, 2024).
The phytosanitary anthracnose management involved four weekly applications: three of dithianone 75% (1.25 g L-1) and one of metiram 55% + pyraclostrobin 5% (2.00 g L-1), starting from the beginning of sprouting.
For downy mildew, one application was performed at the beginning of flowering (25% of open inflorescences) using cymoxanil 6% + mancozeb 70% (2.50 g L-1), and at full flowering (75% of open inflorescences) with metalaxyl 4% + mancozeb 64% (3.00 g L-1).
Additionally, two more alternating applications of each of these fungicides were carried out after harvest, with regular interval of 20 days.
The rot spraying program included the use of cyproconazole 10% (0.2 mL L-1) and procymidone 50% (2.00 g L-1) focusing on grape ripe rot (Colletotrichum sp.) and Botrytis bunch rot (Botrytis cinerea), respectively.
Fungicides were applied during the most susceptible phases such as full flowering, beginning of bunch compaction, berry softening, and pre-harvest. At the last stage, two applications were performed, at a weekly interval, and with a mixture of folpet 50% (1.35 g L-1).
Disease incidence and severity assessments
The vineyard was weekly monitored from the beginning of bud break, and evaluations of each disease began with the onset of the respective symptoms.
Severity assessments of anthracnose, downy mildew, and bunch rot were carried out based on symptoms and signs according to the diagrammatic scales of Modesto et al. (2020), Buffara et al. (2014) and Hill et al. (2010), respectively. The incidence percentage was calculated based on the presence and absence of disease symptoms and signs in each evaluation.
Anthracnose (Elsinoe ampelina) was fortnightly evaluated from the beginning of sprouting until flowering.
Downy mildew (P.viticola) was fortnightly assessed from the onset of disease symptoms until the beginning of physiological leaf fall. Bunch rot (gray mold, ripe grape rot, and sour rot) evaluations were conducted at 10-day intervals, starting from the color change of berries, as described by Costella et al. (2024).
The experimental design was in randomized blocks with five replicates, each composed of ten plants. In each replicate, 25 leaves were used for downy mildew assessment, 30 branches for anthracnose, and 30 clusters for rot evaluations.
Data analysis
With data obtained in the field, the occurrence of diseases was determined by epidemiological variables: maximum incidence (Imax) and severity (Smax) and area under the disease progress curve for severity (AUDPC) (CAMPBELL; MADDEN, 1990).
The mean severity, incidence, and AUDPC were verified for normality using the Shapiro-Wilk test and homoscedasticity using the Bartlett test (p<0.05).
If the assumptions were not met, the means were transformed by √x+1. Data underwent analysis of variance (ANOVA) and if significance was detected, means were compared using the Tukey’s test (p<0.05).
AUDPC data for downy mildew, anthracnose, and rots were submitted to Permutational Multivariate Analysis of Variance (PERMANOVA) to verify differences among varieties concerning the overall phytosanitary aspect. A total of 1000 permutations were used to ensure the robustness of results (using the ‘vegan’ package).
Subsequently, a post hoc test was conducted for pairwise comparison (among varieties) using the ‘pairwiseAdonis’ package. The p-values were adjusted using the Holm- Bonferroni method.
Principal component analysis (PCA) (using the ‘FactoMineR’ package) was performed using the standardized AUDPC data for each assessed disease (using the ‘scale’ function).
The results were plotted in a ‘Biplot’ to visualize differences between the varieties under study and their relationships with the diseases in a reduced-dimensional space (using the ‘FactoExtra’ package). All analyses were conducted using the RStudio 4.3.2 statistical software (R CORE TEAM, 2024).
Results and Discussion
In the two cycles evaluated under spray reduction management, the occurrence of anthracnose, mildew, and rot could be observed.
No presence of powdery mildew or other pathologies was observed on branches, leaves, or berries during the experiment, and therefore, it was not possible to evaluate other diseases.
Differences were observed between varieties regarding incidence and severity parameters, both for the traditional variety (Sauvignon Blanc) and for PIWI varieties (Helios and Bronner). The climate influenced the occurrence of grapevine diseases, attributed to the relative air humidity, which exceeded 70%, and the accumulated precipitation, reaching 1123.84 mm and 1234.52 mm during the 2020/2021 and 2021/2022 cycles, respectively (Figure 1).
Generally, E. ampelina is a destructive pathogen worldwide, especially in humid regions.
The conidial germination occurs over a large temperature range under high humidity conditions between 2°C and 32°C, although the ideal development range is between 24°C and 26°C (LI et al., 2021).
This disease has been gaining increased global attention due to the current climate change scenario, which may favor the development of E. ampelina in various regions (MODESTO et al., 2020; LEEUWEN et al., 2024). In addition, the hemibiotrophic characteristic of this pathogen supports its survival in unfavorable situations and its rapid pathogenicity when environmental conditions are favorable (LI et al., 2021).
At the beginning of the cycle (October and November), mild temperatures around 20 ºC and air humidity above 70% favor anthracnose development (Figure 1).
Accumulated precipitation, average temperature, and relative humidity during the months including the main vegetative periods of PIWI varieties in the 2020/21 and 2021/22 cycles. Videira/SC, Brazil.
Evaluations indicate low anthracnose severity levels on branches and leaves, with no symptoms detected on inflorescences and bunches (Figure 2).
Anthracnose severity curve of ‘Bronner’, ‘Helios’ and ‘Sauvignon Blanc’ varieties in the 2020/21 (A) and 2021/22 (B) cycles. Videira/SC, Brazil. Legend: ns: not significant.
This is related to the characteristic of E. ampelina to infect young and tender tissues, reinforcing its importance as a disease that occurs early in the cycle (DIAS et al., 2022).
This pathogen infects young grapevine tissues, causing brown spots that evolve into lesions with gray-white centers, which can turn into cankers under severe conditions (MODESTO et al., 2020).
On leaves, damage may be observed as “shot holes” while on berries, sunken lesions resembling “bird’s eye” can develop, causing cracking as clusters become mature (LI et al., 2021).
Despite the low severity of diseases, differences in behavior were observed among evaluated genotypes. No difference was observed among varieties during the first two evaluations that took place at the beginning of the 2020/2021 cycle and the first three evaluations of the 2021/2022 cycle, respectively. In both cycles, subsequent evaluations showed greater severity for the ‘Helios’ variety (Figure 2).
Studies conducted during the spring of 2018 and 2019 in vineyards in Midwestern state of Santa Catarina also reported low severity rates in PIWI varieties (DIAS et al., 2022). However, based on the current information, there is no known resistance gene for anthracnose in these varieties.
Therefore, the different anthracnose severity levels observed can be explained by the variation in tissue age and the background of tested genotypes (Li et al., 2021), along with the influence of the fungicide spraying protocol adopted in this study.
The ‘Helios’ variety exhibited greater sensitivity to anthracnose, as it showed higher incidence and higher maximum severity and AUDPC values. Conversely, ‘Bronner’ and ‘Sauvignon Blanc’ varieties demonstrated greater resistance and did not show significant differences from each other (Table 1).
Dias et al. (2022), in their anthracnose evaluations under similar climatic conditions, concluded that the ‘Bronner’ variety presented greater anthracnose damage compared to the ‘Helios’ variety.
The authors also used fungicides to maintain the disease at low levels. However, fungicides difenoconazole and methyl thiophanate, including dithianon, were applied at longer application intervals, which may have corroborated the different response obtained, compared to that of the present study.
Anthracnose assessments were concluded at the flowering stage due to the small increase in average temperature, which, associated with spraying, was unfavorable for the disease development.
This was evidenced by the dry appearance of lesions and the absence of new symptoms, which did not justify further evaluations. Modesto et al. (2020) emphasize that the evaluation of this disease is only feasible at the beginning of bud break (especially in leaves and branches) and at the onset of fruit development (when symptoms are present).
Systematic fungicide applications during the early phenological stages of higher susceptibility can result in less damage to clusters and berries (LI et al., 2021).
Among the evaluated diseases, downy mildew showed the highest incidence, severity, and amplitude within the cycles during the experiment, which reinforces its relevance as the main grapevine disease (KOLEDENKOVA et al., 2022).
When the inoculum is associated with a susceptible cultivar and encounters favorable climatic conditions such as mild temperatures, high relative humidity, and rainfall, productivity losses can reach 100% (DE BEM et al., 2015).
According to Clippinger et al. (2024), the optimal temperature for P. viticola development ranges from 15°C to 25°C under high relative humidity (>70%), with accelerated mycelial development and sporulation at day or night temperatures close to 25°C.
In this context, the climatic conditions of the study area (Figure 1) increased the plant susceptibility to downy mildew at all vegetative and productive growth stages.
During the experiment, evaluations were limited to symptoms observed on leaves, as the disease was not present in inflorescences and grape bunches. The emergence of the first symptoms in each cycle under study occurred at different times and was associated with precipitation peaks (Figure 1).
In the 2020/2021 production cycle, the occurrence of the La Niña phenomenon reduced the rainfall frequency and intensity during the months of September, October, and November 2020 (Figure 1).
Consequently, the first symptoms were observed at the end of January 2021, following 376.60 mm of rainfall (Figure 3A). In the subsequent harvest, the disease manifested earlier, in November 2021, after 238.40 mm of rainfall in the preceding month (October) (Figure 3B).
Downy mildew severity curve of ‘Bronner,’ ‘Helios’ and ‘Sauvignon Blanc’ varieties in the 2020/21 (A) and 2021/22 (B) cycles. Videira/SC, Brazil. Legend: ns: not significant. Different letters in same evaluation date indicate statistical difference according to the Tukey’s test (p < 0.05).
For the 2020/2021 harvest, there was no difference in the downy mildew severity among varieties in the first evaluation (01/25/21). In the subsequent evaluations, the ‘Sauvignon Blanc’ variety showed greater disease intensity, with no difference observed between the PIWI varieties (Figure 3A).
These results were corroborated in the following cycle (2021/2022), in which, although the disease occurred earlier, no difference was found among varieties in the first two evaluations (03/11/21 and 18/11/2021).
The three varieties differed only in the evaluation carried out on 01/28/22, with the ‘Helios’ variety showing less severity. In the remainder of the period, the ‘Sauvignon Blanc’ variety showed greater disease intensity, resulting in early defoliation (Figure 3B).
It is important to highlight that although downy mildew damage to clusters was not recorded, early defoliation can alter the phenological behavior of plants, interfere with the accumulation of reserves, and reduce the productivity and quality of fruits in the following harvest (ARMIJO et al., 2016; EISENMANN et al., 2023). Vezzulli et al. (2018) observed consistent resistance to downy mildew in the leaves of ‘Bronner’ (Rpv10 + Rpv3.3), ‘Solaris’ (Rpv10 + Rpv3.3), ‘Prior’ (Rpv3.1 + Rpv3.3), and ‘Muscaris’ (Rpv10) varieties over three consecutive harvests.
In the two evaluated cycles, AUDPC and maximum severity were significantly higher in the ‘Sauvignon Blanc’ variety, while PIWI varieties exhibited similar behavior between them for these variables. High maximum incidence values were also observed.
Although these values were lower in the ‘Bronner’ variety during the 2020/2021 cycle, there was no difference among varieties in the following cycle (Table 2). Although the evident lower virulence of P. viticola, a pattern in the pathogen behavior was observed in PIWI varieties regardless of genotype, with a resistance allele (Rpv3.1; Helios) or the pyramidization of Rpv10 + Rpv3.3 genes (Bronner).
Continuous increase in mildew severity curves was observed throughout the cycle until the onset of physiological leaf drop (Figure 3), resulting in high disease incidence rate (I.Max) (Table 2).
This can be explained by the local effect associated with the variability in the pathogen-host interaction process, which translates into differences in the genetic composition of the pathogen (P. viticola), potentially indicating greater selection pressure effect for genotypes with higher virulence degree (ZANGHELINI et al., 2019; WINGERTER et al., 2021; PAINEAU et al., 2022).
Regarding the additive effect of gene pyramiding, different results were found by Zanghelini et al. (2019) when evaluating some PIWI varieties in southern Brazil, submitted to a minimal chemical intervention regime. This study observed indications of the initial adaptation of the pathogen to resistant grapevine genotypes, showing that a single resistance locus was not sufficient to control the disease, and that combining two or more Rpv alleles significantly increased resistance.
This finding is supported by the observation that, at the end of the cycle and under field conditions favorable to the pathogen, disease symptoms and pathogen signs are visible even in genotypes containing pyramided resistance alleles (SANCHEZ-MORA et al., 2017; ZANGHELINI et al., 2019).
This confirms the hypothesis that the resistance of PIWI varieties to downy mildew is quantitative (SCHUMACHER et al., 2024), and in certain environments, the disease incidence will occur but with less severity compared to susceptible varieties (Table 2).
Plasmopara viticola is a heterothallic pathogen, indicating that the emergence of virulent races is closely related to their evolutionary potential (WONG et al., 2001).
Pathogens with a mixed reproduction system (both sexual and asexual), as observed in the state of Santa Catarina, and with cross-fertilization, show high evolutionary potential. Therefore, they are more likely to overcome resistance (BITENCOURT et al., 2021). Given the notable adaptive nature of this pathogen, spraying reduction programs to be adopted in resistant varieties must be meticulous and consider not only the evolutionary aspects of the pathogen but also the periods of greatest susceptibility of plants (KOLEDENKOVA et al., 2022; SCHUMACHER et al., 2024).
PIWI varieties facilitate disease control.
However, they show different resistance levels throughout phenological development, with resistance increasing with maturation (SCHUMACHER et al., 2024) and decreasing after harvest. In this context, higher indication of pathogen adaptation can be observed in the downy mildew severity curve (Figure 3), with the increase in the disease mainly from February until the onset of physiological leaf drop, a period between late summer and early autumn, conducive to oospore formation (BITENCOURT et al., 2021).
Therefore, greater attention is needed in the management of these varieties in the field to maintain durable resistance level over the years, which is crucial as there are reports of the emergence of virulent races of P. viticola for Rpv3, Rpv10, and Rpv12 alleles (WINGERTER et al., 2021; PAINEAU et al., 2022).
These varieties exhibited minimal bunch rot severity in all cycles. The short interval between berry color change and harvest (40 days), in addition to fungicide applications during susceptibility phases, delayed the onset of symptoms to approximately 15 to 20 days before harvest. Consequently, severity levels remained low, with only three assessment points, as reported by Costella et al. (2024).
In the 2020/2021 cycle, there was no difference in the occurrence of grape sour rot, while in the subsequent cycle, the disease occurred only for the ‘Sauvignon Blanc’ variety.
The incidence of grape ripe rot for the 2020/2021 cycle was higher for the ‘Sauvignon Blanc’ variety, although the other variables did not differ among evaluated genotypes. In the subsequent cycle, the incidence was also higher for the ‘Sauvignon Blanc’ variety, while severity (S.Max and AUDPC) was intermediate.
The greatest development of the disease occurred for the ‘Bronner’ variety and the lowest rates for the ‘Helios’ variety. The ‘Sauvignon Blanc’ variety was also the most sensitive to Botrytis bunch rot in the two evaluated cycles, compared to PIWI varieties, which did not differ from each other (Table 3).
Rot contributes to losses in fruit production and quality, mainly nearing harvest. This disease can be caused by different agents, categorized into Botrytis bunch rot (Botrytis cinerea), grape ripe rot (Colletotrichum sp.), and grape sour rot (complex of microorganisms) (HALL et al., 2018; ALTIERI et al., 2023; HSIEH et al., 2023).
Generally, infection by Colletotrichum sp. or Botrytis cinerea conidia occurs during flowering and can develop immediate symptoms or remain latent until the berry nutritional composition becomes favorable for the occurrence of the respective diseases (ALTIERI et al., 2023; HSIEH et al., 2023).
Another infection strategy of Colletotrichum sp. and Botrytis cinerea involves the direct penetration of the mycelium on the berry surface. This process is enhanced as the ripening process advances or through mechanical damage or wounds caused by insects.
However, it can also occur independently through the development of a structure called appressorium (ARMIJO et al., 2016). For sour rot, a study by Hall et al. (2018) demonstrated that fruit flies (Drosophila spp.) can mediate the co-infection processes of various yeast strains responsible for converting sugars into ethanol and its oxidation into acetic acid by different bacteria.
After infection by Colletotrichum sp., spots ranging from brown to purple are observed, which quickly evolve into dark necrotic spots with concentric rings and acervuli production (HSIEH et al., 2023). Botrytis bunch rot (B. cinerea) occurs more easily than ripe grape rot under lower humidity conditions or when mechanical damage facilitates pathogen entry.
Consequently,symptoms of softening and light brown discoloration of berries are quickly observed, leading to pathogen sporulation, characterized by a grayish mold (ARMIJO et al., 2016; ALTIERI et al., 2023). Sour rot has symptoms similar to Botrytis bunch rot, distinguished by the odor of acetic acid (HALL et al., 2018).
In both cycles, the average air temperature above 20 ºC, combined with relative humidity above 70% and the advancement of maturation, favored the rot development (Figure 1).
Therefore, the strategy used in this work, based on the spraying of specific chemical fungicides for these pathogens, promoted positive responses.
However, given the wide genetic diversity of the etiological agents, future management strategies should integrate approaches based on the development of resistant varieties, adoption of protected cultivation, and different control agents associated with the rotation of chemical fungicide modes of action (ALTIERI et al., 2023; HSIEH et al., 2023; HALL et al., 2018).
In Figure 4, it is possible to observe the PCA scatter plot illustrating the relationship between grape varieties and the diseases under study.
Biplot graph containing the projection of the principal component analysis (PCA) to assess the relationship between grape varieties and anthracnose, downy mildew, and rots during the 2020/2021 and 2021/2022 growing season, along with results of the pairwise comparison test (PERMANOVA). Legend: * Indicates significant difference at 5% error probability in the pairwise comparison (PERMANOVA) of the mean AUDPC values for the different cultivars, with p-values adjusted by the Holm-Bonferroni method.
Dim1 (PC1) and Dim2 (PC2) explain 50.1% and 26.7% of data variation, respectively, together accounting for 76.8% of the total variability. The dispersion of treatments shows that the variables were separated into three groups, each corresponding to a variety analyzed, which agrees with results previously presented by the means test.
According to PCA, there is a closer relationship between the two PIWI varieties and, consequently, a less close relationship with the traditional variety. The pairwise posthoc comparison test did not indicate differences between the two PIWI varieties (p=0.675), although both differed from the traditional variety (p=0.003).
PCA shows greater association of downy mildew, Botrytis bunch rot, and grape sour rot with the ‘Sauvignon Blanc’ variety. Although there is a less close relationship of downy mildew with the ‘Bronner’ and ‘Helios’ varieties, there was greater association of anthracnose with ‘Helios’ and a closer relationship of ripe grape rot with the ‘Bronner’ variety (Figure 4).
In the absence of resistance genes, the control of anthracnose and rots may be insufficient if only the additive and protective effects of fungicides used to control downy mildew are considered (HALL et al., 2018; WINGERTER et al., 2021; ALTIERI et al., 2023; HSIEH et al., 2023).
Therefore, the strategy adopted in this study yielded satisfactory results given the edaphoclimatic conditions under which the experiment was conducted (Figure 1). The results of this study reinforce that reducing fungicide applications is compatible with the use of resistant varieties, especially regarding downy mildew (WINGERTER et al., 2021).
During the same study period, a vineyard with traditional V. vinifera varieties managed according to commercial standards required an average of 34 fungicide applications per cycle to maintain health. Based on this information, the phytosanitary management adopted in this research corresponds to reduction of 55.88% compared to traditional fungicide applications.
Although this reduction did not result in high disease severity in PIWI varieties, it is important to highlight that for the adoption of similar strategies on a commercial scale, phenotypic particularities must be considered.
However, breeding programs have not yet developed varieties resistant to anthracnose or rot, which means that the existing PIWI varieties may be susceptible to pathogens that cause these diseases.
If not controlled, these diseases could become more significant in the future, especially considering the current climate change scenario (DIAS et al., 2022; HSIEH et al., 2023; LEEUWEN et al., 2024).
Furthermore, integrating different forms of phytosanitary control is essential to promote the resilience of genetic resistance mechanisms and mitigate possible losses (KOLEDENKOVA et al., 2022; HSIEH et al., 2023; CLIPPINGER et al., 2024).
Conclusion
The resistance of PIWI varieties to diseases enabled a reduction of over 50% in the number of fungicide applications compared to traditional grapevine varieties.
There is a difference in the behavior of tested genotypes regarding the evaluated diseases, with the ‘Helios’ variety showing higher susceptibility to anthracnose and ‘Bronner’ to grape ripe rot, while PIWI varieties were more resistant to downy mildew.
However, the spray reduction management allowed some pathogen sporulation level to occur at the end of the cycle. Grape sour rot and Botrytis bunch rot caused less damage to PIWI varieties than to the ‘Sauvignon Blanc’ variety, indicating that the reduced spraying used in this work does not meet the minimum phytosanitary requirements for traditional wine varieties.
Acknowledgments
To the Foundation for Research and Innovation of the State of Santa Catarina – FAPESC (Fapesc) and the Secretariat of Agriculture and Livestock of Santa Catarina (SAR-SC) for financial support.
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Edited by
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Scientific Editor
Alexandre Pio Viana
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Associate Editor
Gerson Adriano Silva
