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Universidade de Trás-os-Montes e Alto Douro (UTAD) 2019

Strategies to improve olive orchards sustainability under a changing environment

Brito, Cátia Vanessa Queijo

Titre : Strategies to improve olive orchards sustainability under a changing environment

Auteur : Brito, Cátia Vanessa Queijo

Université de soutenance : Universidade de Trás-os-Montes e Alto Douro (UTAD)

Grade : Doctor of Philosophy (PhD) 2019

Résumé
One of the major challenges for agriculture are the environmental conditions. In the Mediterranean Region, where olive is an emblematic crop, is commonly notice a severe summer stress that includes drought, heat and high irradiance levels, a scenario tendentially worsened by climate change. In addition, as the demand for olive oil is increasing all over the world, urge the necessity to increase the sustainability and competitiveness of the traditional rainfed olive orchards that highly contribute to the economy of remote regions and for the autochthone ecosystems preservation. Among the constituents of summer stress, drought is perhaps the most critical, as is highly exacerbated by the others. A better understanding of how olive tree responds to drought help to design and select agronomic practices to improve the crop profitability. In this regard, nighttime physiological responses has been less discussed. Under drought, olive tree increases both nighttime stomatal open in the first hours of night and the proportion of nighttime water loss in relation to whole-day losses. Although some potential benefits to plants can be associated to this response, as the reduction in nighttime respiration and the improvement in minerals uptake, a continuous nighttime water loss might be detrimental under severe drought conditions. Along with the understanding of olive tree response to stress conditions, it is important to act in the short-term, by evaluating and selecting strategies that contribute to alleviate and/or to improve olive tree adaptability (stress resistance and recovery capacity) to summer stress. The application of exogenous products on leaf surface can be considered in this sense. The use of kaolin (KL) and salicylic acid (SA) as summer stress mitigating agents was evaluated in this thesis. KL forms a white protective particle film which increases the reflection of excess radiation, reducing the heat load, and SA is a signaling phytohormone with diverse regulatory roles in stress response. The influence of these products was primarily evaluated in young potted plants subjected to repeated cycles of drought-rewatering, to properly assess the drought resistance and the recovery capacity. In the case of SA, three different concentrations were tested (10, 100 and 1000 µM) since concentration highly determine its effectiveness and no manufacture recommended dosage is available, as for KL (5% w/v). To confirm the pots experiment results under realistic field conditions, and to evaluate the influence on yield and harvests quality, rainfed olive trees were sprayed with KL and the most effective SA concentration, 100 µM, for two consecutive growing seasons. Pulling up together the results of both experiments, a better understanding about KL and SA induced responses was achieved. KL particle film induced shade-related leaf characteristics and contributed to improve plant water status, reduced the stress-induced stomatal and nonstomatal limitations to photosynthesis, improved plant mineral status and reduced the necessity to invest in secondary metabolism during stress and in extra repair damages under stress recovery.

Mots clés  : Ácido salicílico balanço hídrico noturno caulino oliveira stresse estival seca

Présentation

Page publiée le 13 avril 2020