Biotic and Abiotic Stress Management in Grapevine: Recent Advances and Major Breakthroughs

1. Introduction

Grapevine (Vitis vinifera L.) is one of the most cultivated fruit plants worldwide, with an estimation of 260 million hl of wine produced in 2022 [1]. Most V. vinifera cultivars used for wine and table grape production are highly susceptible to diseases and extreme weather conditions. It is commonly acknowledged that alternative solutions are required to lessen the reliance on chemical controls in fighting pests and diseases. In fact, the European Union has published a directive with guidelines that stress the need for massive pesticide reduction leading to more sustainable practices in viticulture (Directive 2009/128/EC). Plants have developed defense strategies that allow them to activate an immune response upon an initial pathogen infection. This “memory” phenomenon, known as immune priming, is characterized by the activation of defense-related genes at lower levels. This allows for a more vigorous and rapid response after pathogen stimuli. A better knowledge of these processes can help build more sustainable practices to control grapevine pathogens.

Climate change is also posing a significant threat to viticulture, with higher temperatures and water deficit decreasing either the wine quality or the production yield in most wine-growing regions. Assessing the magnitude of the potential risk for vines will assist the development of rationale and sustainable adaptation strategies for winegrowers, even with the use of photovoltaic panels to produce either grapes or renewable energy [2]. Through the development of different grapevine stress assessment methodologies, it might be possible to increase the quality, profitability, efficiency, and sustainability of the wine industry in a changing climate. Hence, adaptation strategies should be explored to sustain grapevine yield and quality towards a sustainable viticulture.

Present and future research efforts in this area are crucial to better understand grapevine biotic and abiotic stress responses and develop adaptation strategies to ensure the longevity of the wine industry.

This Agronomy Special Issue “Biotic and Abiotic Stress Management in Grapevine: Recent Advances and Major Breakthroughs” addressed the cutting-edge technological and knowledge advances on grapevine stress adaptation aiming at understanding plant dynamics and mechanisms to tackle both biotic and abiotic challenges. Overall, it comprises five articles from 24 authors [3,4,5,6,7] that mainly summarize technical advances to rate Plasmopara viticola infection by RBG images and convolutional neural networks (SCNNs), to access water stress by hyperspectral measurements, that present new regenerative viticulture approaches, based on beneficial microorganisms, either improving grapevine fitness and physiology or potentiating grapevine resilience towards grapevine trunk diseases. Phenological responses and phenology–climate relations were also exploited and projected shifts for years 2050 and 2070 under the RCP45 and RCP8.5 emission scenarios were pointed out [4].

2. Phenological Changes upon Abiotic Stress

The grapevine vegetative–productive cycle is modulated by several factors, two of the most important ones being temperature and water availability [8,9]. Temperature severely influences the grapevine’s main physiological processes, development, quality, and productivity. Although a 10 °C base temperature is required for the onset of the grapevine’s vegetative cycle, it is also known that if the high-temperature threshold peaks at critical points of development, negative impacts occur, namely on photosynthesis, berry size, sugar accumulation and ripening [10]. Moreover, rising temperatures lead to increased heat stress and consequently drought stress [11]. The study by Ramos and Yuste, 2023, analyzes the phenological response of the cultivars Verdejo, Viura and Sauvignon Blanc, cultivated in Rueda Designation of Origin (DO), Spain, under the present climate conditions within the period of 2008–2021, and their potential shifts were projected under climate change scenarios. Budbreak, flowering, véraison and harvest were analyzed as phenological markers, and the influence of temperature (maximum and minimum) and water availability averaged for different periods between phenological events were evaluated. These data were analyzed and used to project potential phenological changes for 2050 and 2070 under two Representative Concentration Pathway (RCP) scenarios: RCP4.5 and RCP8.5. Overall, the authors were able to show that an advance (in days) of all phenological dates is predicted, with particular impact in véraison (13–14 days in RCP4.5 and 16–19 days in RCP8.5 scenarios in 2050) and ripening (20 days earlier in RCP4.5 and 25 in RCP8.5) stages. Verdejo is predicted to suffer a slightly higher advance than Sauvignon Blanc.

These results point out the need for establishing new management strategies to maintain production sustainability, not only because ripening will occur earlier under warmer conditions, mainly during August (which could have effects on grape composition and yield), but also as water stress may be more persistent in the periods between flowering and véraison and between véraison and harvest, which could even increase under warming climate [5].

3. Hyperspectral Imaging to Assess Heat Stress in Vineyards

Water stress is intimately connected to heat stress. The study by Cogato et al. (2021) aimed at verifying if evaporative cooling systems may minimize the effects of heat stress and if spectral sensors may be used as a strategy to measure the physiological responses to heat and water stress. Ultimately, the authors aimed at identifying a non-destructive (hyperspectral imaging) approach to assess heat stress in vineyards. To evaluate the physiological and spectral responses of Vitis vinifera L. cv. Sauvignon Blanc to individual (heat only) and combined (heat + water) stress, four different cooling and irrigation strategies were tested: SI—standard drip irrigation; SI+—extra drip irrigation; SPRI—extra sprinkler irrigation; and SDI—sustained deficit irrigation (accounting for 50% of SI). The authors were able to show that the cooling systems evaluated in the present study were efficacious, particularly SI+ and SPRI, thus highlighting that the implementation of vineyard irrigation strategies is important to ensure sustainable and profitable production. Additionally, it was shown that the hyperspectral data were consistent with physiological data, identifying SI+ and SPRI as effective cooling strategies to cope with heat stress. Altogether, it was proposed that for field measurement of physiological parameters, spectral assessments either from proximal or remote instrumentation would represent an effective and rapid tool to monitor heat stress and water stresses [4].

4. Downy Mildew Can Be Efficiently Detected through Convolutional Neural Networks and Automated Imaging Systems

When accounting for biotic stresses, downy mildew is one of the most devastating grapevine diseases, leading to heavy production losses [12]. Disease management strategies include the preventive application of fungicides and its reinforcement when weather conditions are favorable for pathogen infection. Breeding programs between the American and/or Asian tolerant to resistant Vitis spp. and the European susceptible Vitis vinifera are one of the most promising strategies to control this disease, with several crossing-hybrids presenting P. viticola resistance being commercialized nowadays. For these programs, assessment of phenotypic traits, namely the categorical classes describing disease severity, is still based on visual observation, involving the evaluation of several thousand inoculated leaf discs from mapping crosses and breeding lines every year and being prone to human errors. The study by Zendler et al. (2021) proposes a new tool for automated high throughput scoring of disease severity on inoculated leaf discs, using as a proof-of-concept leaf discs inoculated with Plasmopara viticola ((Berk. & Curt.) Berl. & De Toni). A convolutional neural network (SCNN) was combined with an automated imaging system and trained for efficient detection and classification of leaf disc segments showing P. viticola sporangiophores. This scoring pipeline removes the subjective manual scoring, ensuring unbiased results throughout all experiments. Additionally, authors state that this pipeline can be adjusted to new pathogen–plant systems with a minimal set of training images, becoming a highly valuable phenotyping tool [3].

5. Microbial Antagonists to Tackle Grapevine Trunk Diseases

Grapevine trunk diseases (GTDs) also cause significant yield losses worldwide, limiting the lifespan of vineyards. In the last few years, using biological control agents (BCAs) for pruning wound protection has become a promising management strategy for the control GTDs. The study by Langa-Lomba et al. (2023) exploited the potential of several native fungal and bacterial microorganisms as microbial antagonists against two of the most important pathogens associated with the “Botryosphaeria dieback” disease in grapevines. The authors tested the antifungal activity of a grapevine native Trichoderma harzianum isolate and a Bacillus velezensis strain against the Botryosphaeriaceae species. Significant differences in the control of vascular necrosis lengths with different BCA-based products (including native microorganisms and those under experimental development) were found both for N. parvum- and D. seriata-infected plants. While treatments with T. harzianum and T. atroviride only resulted in significant reductions in necrosis caused by N. parvum, a remarkable protective effect from Bacillus velezensis BUZ-14 was detected against the two etiological agents. The use of BCA may thus be a promising approach for pruning wound protection against Botryosphaeriaceae fungi [7].

6. Mycorrhizal Fungi as a Tool to Improve Plant Fitness

When considering the biotic interaction of grapevine with microorganisms, within below ground-living microbes, arbuscular mycorrhizal fungi (AMF) should be given emphasis. AMF colonizes about 80% of terrestrial plants, and it was already shown to colonize grapevines. It establishes a symbiotic relationship at the root level leading to an increase of plant biomass and photosynthetic activity, along with alleviation of damage caused by biotic and abiotic stress [13]. The study by Luca et al. (2023) reinforces the capability of AMF (particularly Rhizophagus irregularis and Funneliformis mosseae species) to balance growth and defense responses of Vitis vinifera cv Glera plants grafter in two different rootstocks (1103P and SO4) in field conditions. The authors were able to show the positive impact of the symbiosis in vineyards, through the evaluation of the expression of genes associated with nitrogen (N) uptake and metabolism, photosynthetic performances, and stilbenes accumulation. All the analyzed parameters were higher in AMF inoculated plants. This study highlights the potential of exploiting AMF benefits in vineyards as a strategy to improve plant fitness [6].

7. Conclusions

This Special Issue combines heterogeneous approaches to tackle biotic and abiotic stress in grapevines, aiming for more sustainable agricultural practices. Novel stress management strategies must be put in place so that the grapevine industry maintains its relevance as one of the most important economic activities. We are confident that the future of the industry will join the efforts of fundamental research with the more recent phenotyping and robotic solutions.