Understanding vine response to Mediterranean summer stress for the development of rationale adaptation strategies: the kaolin case
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2021-11-05
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As previsões climáticas até ao final do presente século apontam para alterações globais nos ecossistemas vitivinícolas e nos respetivos contextos económicos e sociais. Nesse sentido, espera-se que a influência combinada de diversos fatores ambientais em regiões com clima tipicamente mediterrânico (luz e temperatura elevadas e baixa disponibilidade hídrica) possa prejudicar os mecanismos intrínsecos de resistência da videira, diminuindo consequentemente a respetiva produtividade e qualidade das uvas. Embora a videira seja considerada uma espécie geneticamente resistente a esses stresses abióticos, tais mecanismos poderão ser insuficientes para evitar consequências nefastas no normal desenvolvimento vegetativo e reprodutivo. Assim, a adequada interação entre múltiplos fatores ambientais e vitícolas (p.ex. clima, casta, porta-enxerto e práticas culturais) representa um desafio efetivo e emergente para a sustentabilidade da viticultura Mediterrânea. A aplicação foliar de caulino é uma estratégia de curto prazo amplamente conhecida e aplicada em várias culturas frutícolas porque incrementa a reflexão das radiações ultravioleta, visível e infravermelha, reduzindo a temperatura foliar e a consequente suscetibilidade ao escaldão de folhas e frutos. Contudo, no caso específico da videira, variáveis como a casta, estado hídrico, práticas culturais, fenologia e condições edafoclimáticas podem determinar a sua maior ou menor eficácia. Face ao exposto, nesta tese estudou-se o efeito do caulino (5%) nas castas Touriga-Franca (TF) e Touriga-Nacional (TN) implantadas em duas Regiões Demarcadas portuguesas (Douro e Alentejo) durante dois anos consecutivos(2017 e 2018; 2017 foi mais quente e seco que 2018 devido à ocorrência de duas ondas de calor e baixos níveis de precipitação). Várias metodologias de cariz fisiológico, bioquímico e molecular foram usadas para monitorizar as respostas das videiras durante o período estival, especialmente nas fases do pintor e próximo da vindima. Com o intuito de avaliar as funções foto / termoprotetoras do caulino, estudou-se detalhadamente as relações entre a aplicação desta argila e a acumulação de pigmentos fotossintéticos, o metabolismo de carotenóides, a regulação do ciclo das xantofilas e o possível envolvimento nos processos de quenching não fotoquímico (NPQ). Ao nível do fruto, foram igualmente avaliados vários atributos de qualidade, bem como o conteúdo hormonal e atividade anti-radicalar desde o pintor até à plena maturação. Os resultados demonstraram que os efeitos benéficos do caulino foram maioritariamente observados em 2017. Sucintamente, foi evidente uma melhoria da eficiência intrínseca do uso da água (23% no Douro e 13% no Alentejo), das taxas de assimilação de CO2 (PN; 72% no Douro e 25% no Alentejo) e do teor em açúcares solúveis, assim como uma menor acumulação de alguns reguladores de crescimento, nomeadamente de ácido abscísico (ABA) e de ácido salicílico (SA) à vindima. Relativamente aos pigmentos fotossintéticos, os efeitos do caulino variaram consoante a região: no Douro, ao longo do verão de 2017, as folhas tratadas com caulino apresentaram menor teor em clorofila e carotenoides e maior decréscimo de NPQ à vindima. Em contrapartida, no Alentejo as plantas TN tratadas com caulino apresentaram um aumento significativo do teor de clorofila enquanto na TF não se registaram alterações significativas, indicando que supostamente a aplicação de caulino nesta casta, nas condições ambientais prevalecentes, não foi tão necessária. Quanto aos carotenoides individuais, os respetivos teores aumentaram nas folhas tratadas de ambas as castas e locais, com uma concomitante regulação positiva da expressão dos genes da violaxantina de-epoxidase (VvVDE1) e da zeaxantina epoxidase (VvZEP1), indicando uma regulação otimizada do ciclo das xantofilas. Simultaneamente, o estado de de-epoxidação (DPS) e os valores de NPQ foram menores nas folhas tratadas, sugerindo uma modulação indireta das xantofilas nos processos de dissipação de energia durante o verão. Em 2017, à vindima, apenas nos bagos da TF das duas parcelas experimentais, constatou-se também que o efeito do caulino contribuiu para o aumento dos níveis de ABA e SA, assim como para uma ligeira melhoria na respetiva conservação da acidez. Embora a acumulação de antocianinas nos bagos não tenha sido consistente, no tratamento com caulino registámos maiores teores de flavonóides, orto-difenóis e taninos em 2017. Em contrapartida, em 2018, os bagos de TF e TN tratadas com caulino apresentaram menor acumulação de ABA e SA. Também se observou uma redução geral do teor de açúcares solúveis, sem comprometer os níveis de ácido málico e tartárico, bem como a produção de espécies reativas de oxigénio (ROS), durante o amadurecimento. Resumidamente, o trabalho desenvolvido no âmbito desta tese realçou a complexidade de estudar as respostas da videira ao stresse estival e respetivas associações com características varietais, variabilidade climática e eficácia do caulino. Dado que a ação deste protetor aparentou ser mais robusta em anos mais quentes e secos, esta estratégia reúne boas indicações para ser considerada uma prática sustentável para minimizar os impactos do stresse estival em videiras cultivadas em regiões de clima tipicamente mediterrânico fortemente ameaçadas pelas alterações climáticas.
The foreseen climate change points to shifts in agricultural patterns worldwide, which may impact ecosystems directly and the economic and cultural contexts of the wine industry. Moreover, the combined effects of environmental threats (light, temperature and water availability) at different levels are expected to impair natural grapevine mechanisms, decreasing yield and the quality of grapes. Though grapevines present several mechanisms to sustain growth and development upon prevailing stress factors, it might not be enough to counterpart the increasing magnitude of summer stress impacts in Mediterranean areas. Hence, the interaction between several factors (e.g. climate, grapevine varietal stress responses, and management practices) represent a serious challenge for sustainable Mediterranean viticulture, promoting the development of adaptive strategies to cope with environmental stresses. The foliar application of kaolin particle film is a well-known short-term strategy applied in many fruit crops that increases the reflection of ultraviolet, photosynthetically active and infrared radiation, reducing leaf temperature and preventing leaf and fruit sunburn damage. However, kaolin’s effectiveness in improving grapevine resilience when subjected to severe environmental conditions can significantly change according to the variety, water status, management practices, phenology, and edaphoclimatic conditions. Hence, this thesis focused on the comprehensive study of kaolin foliar application (5%) to Touriga-Franca (TF) and Touriga-Nacional (TN) grapevine varieties located in two Portuguese Demarcated Regions (Douro and Alentejo) to study its effects on several defence mechanisms and related metabolites at the leaf and fruit level during two consecutive growing seasons (2017 and 2018). This study aims to evaluate kaolin application effects on the physiological performance of vines, photochemistry processes, hormonal balance, and expression of leaf stress related genes at both veraison and harvest stages. Besides, to get a closer insight regarding kaolin photoprotective functions, we focused on the relations between kaolin treatment and photosynthetic pigments accumulation, carotenoids metabolism, xanthophyll cycle regulation, and its putative role on the non-photochemical quenching (NPQ) processes during 2017. Several quality traits and secondary metabolites were evaluated at the fruit level, as well as the hormonal content and antiradical activity throughout ripening. Data show that 2017 was warmer and drier than 2018 due to the occurrence of two heatwave events and low rainfall levels, which can modulate kaolin efficiency in alleviating summer stress impacts. Indeed, kaolin effects were mainly observed in the first year of study, enhancing the intrinsic water use efficiency of vines (23 % in Douro and 13 % in Alentejo), net CO2 assimilation rates (PN; 72 % in Douro and 25 % in Alentejo), and soluble sugars content, while decreasing the accumulation of plant growth regulators, namely abscisic (ABA) and salicylic (SA) acids at the ripening stage. Regarding pigments accumulation and high light responses, kaolin effects differed among locations. In the Douro vineyard, TF and TN treated leaves displayed lower chlorophyll and carotenoids content throughout the 2017 summer season and reduced NPQ at ripening, suggesting a long-term response to summer stress. Reversely, TN kaolin treated vines from the Alentejo vineyard showed a significant increase of chlorophyll content compared to untreated ones, while no changes were found in TF, which might indicate a lower need for particle-film technology in this variety under the prevailing environmental conditions. Moreover, individual carotenoids were mainly higher in treated leaves, with a concomitant up-regulation of the violaxanthin de-epoxidase (VvVDE1) and zeaxanthin epoxidase (VvZEP1) gene expression in both varieties and locations, indicating optimised regulation of the xanthophyll cycle. Simultaneously, the de-epoxidation state (DPS) and NPQ values were lower in treated leaves, suggesting that there might be other components influencing NPQ levels beyond zeaxanthin, with an indirect role in long-lasting NPQ processes. Under the severe summer conditions of 2017, kaolin application increased ABA and SA levels in TF berries at harvest in both vineyards, with slight effects on berry acidity conservation, while no significant differences were observed in TN. Conversely, TF and TN kaolin treated berries showed lower SA and ABA accumulation in 2018. Though kaolin treatment had no consistent effect on anthocyanins accumulation, flavonoids, ortho-diphenols, and tannins increased in the berries from kaolin treated grapevines in 2017, along with lower sugar content without compromising malic and tartaric acid levels, as well as reactive oxygen species (ROS) accumulation throughout berry ripening. In summary, the work developed in the scope of this thesis revealed the complexity of understanding plant stress responses under field conditions and their interactions with varietal and climate features and kaolin effectiveness, which seems stronger under harsh environmental conditions. Nonetheless, kaolin application can be considered a promising practice to minimise summer stress impacts in grapevines grown in Mediterranean-type climate regions.
The foreseen climate change points to shifts in agricultural patterns worldwide, which may impact ecosystems directly and the economic and cultural contexts of the wine industry. Moreover, the combined effects of environmental threats (light, temperature and water availability) at different levels are expected to impair natural grapevine mechanisms, decreasing yield and the quality of grapes. Though grapevines present several mechanisms to sustain growth and development upon prevailing stress factors, it might not be enough to counterpart the increasing magnitude of summer stress impacts in Mediterranean areas. Hence, the interaction between several factors (e.g. climate, grapevine varietal stress responses, and management practices) represent a serious challenge for sustainable Mediterranean viticulture, promoting the development of adaptive strategies to cope with environmental stresses. The foliar application of kaolin particle film is a well-known short-term strategy applied in many fruit crops that increases the reflection of ultraviolet, photosynthetically active and infrared radiation, reducing leaf temperature and preventing leaf and fruit sunburn damage. However, kaolin’s effectiveness in improving grapevine resilience when subjected to severe environmental conditions can significantly change according to the variety, water status, management practices, phenology, and edaphoclimatic conditions. Hence, this thesis focused on the comprehensive study of kaolin foliar application (5%) to Touriga-Franca (TF) and Touriga-Nacional (TN) grapevine varieties located in two Portuguese Demarcated Regions (Douro and Alentejo) to study its effects on several defence mechanisms and related metabolites at the leaf and fruit level during two consecutive growing seasons (2017 and 2018). This study aims to evaluate kaolin application effects on the physiological performance of vines, photochemistry processes, hormonal balance, and expression of leaf stress related genes at both veraison and harvest stages. Besides, to get a closer insight regarding kaolin photoprotective functions, we focused on the relations between kaolin treatment and photosynthetic pigments accumulation, carotenoids metabolism, xanthophyll cycle regulation, and its putative role on the non-photochemical quenching (NPQ) processes during 2017. Several quality traits and secondary metabolites were evaluated at the fruit level, as well as the hormonal content and antiradical activity throughout ripening. Data show that 2017 was warmer and drier than 2018 due to the occurrence of two heatwave events and low rainfall levels, which can modulate kaolin efficiency in alleviating summer stress impacts. Indeed, kaolin effects were mainly observed in the first year of study, enhancing the intrinsic water use efficiency of vines (23 % in Douro and 13 % in Alentejo), net CO2 assimilation rates (PN; 72 % in Douro and 25 % in Alentejo), and soluble sugars content, while decreasing the accumulation of plant growth regulators, namely abscisic (ABA) and salicylic (SA) acids at the ripening stage. Regarding pigments accumulation and high light responses, kaolin effects differed among locations. In the Douro vineyard, TF and TN treated leaves displayed lower chlorophyll and carotenoids content throughout the 2017 summer season and reduced NPQ at ripening, suggesting a long-term response to summer stress. Reversely, TN kaolin treated vines from the Alentejo vineyard showed a significant increase of chlorophyll content compared to untreated ones, while no changes were found in TF, which might indicate a lower need for particle-film technology in this variety under the prevailing environmental conditions. Moreover, individual carotenoids were mainly higher in treated leaves, with a concomitant up-regulation of the violaxanthin de-epoxidase (VvVDE1) and zeaxanthin epoxidase (VvZEP1) gene expression in both varieties and locations, indicating optimised regulation of the xanthophyll cycle. Simultaneously, the de-epoxidation state (DPS) and NPQ values were lower in treated leaves, suggesting that there might be other components influencing NPQ levels beyond zeaxanthin, with an indirect role in long-lasting NPQ processes. Under the severe summer conditions of 2017, kaolin application increased ABA and SA levels in TF berries at harvest in both vineyards, with slight effects on berry acidity conservation, while no significant differences were observed in TN. Conversely, TF and TN kaolin treated berries showed lower SA and ABA accumulation in 2018. Though kaolin treatment had no consistent effect on anthocyanins accumulation, flavonoids, ortho-diphenols, and tannins increased in the berries from kaolin treated grapevines in 2017, along with lower sugar content without compromising malic and tartaric acid levels, as well as reactive oxygen species (ROS) accumulation throughout berry ripening. In summary, the work developed in the scope of this thesis revealed the complexity of understanding plant stress responses under field conditions and their interactions with varietal and climate features and kaolin effectiveness, which seems stronger under harsh environmental conditions. Nonetheless, kaolin application can be considered a promising practice to minimise summer stress impacts in grapevines grown in Mediterranean-type climate regions.
Descrição
Tese de Doutoramento em Cadeias de Produção Agrícola – Da mesa ao campo
Palavras-chave
fisiologia da videira , fitohormonas