Impacts and Mitigation Strategies of Abiotic and Biotic Stresses in Olive Orchards in the Era of Climate Change

Introduction

Plants are subject to biotic and abiotic stress factors that are often unfavorable to their growth and development processes, reducing their productivity and the quality of their products, which can lead to considerable economic losses. Hence, major abiotic stress factors, including drought, salinity, low and high temperatures and waterlogging, pose risks to global agricultural production and food supply. Similarly, epidemics of biotic stress factors such as diseases and herbivore attacks represent major and growing threat to primary productivity, global food security and biodiversity loss in many sensitive regions of the planet.

The olive is the most representative tree of the Mediterranean region, and is of considerable economic, social and ecological importance. The proliferation of olive groves with the development of human civilization can be explained by the many uses of olive trees, both domestic and wild, as a source of food, wood and livestock feed. Olive-growing covers some 10.3 million hectares worldwide, over 95% of which is in the Mediterranean basin, mainly in Spain (25%), Tunisia (12%), Italy (11%), Morocco (11%), Turkey (9%) and Greece (8%) (FAOSTAT, 2021). Recent decades have seen an expansion of olive-growing areas and an increase in world production, both attributed to greater public awareness of the nutritional benefits of olive oil and table olives. Therefore, rising global demand is putting considerable pressure on arable land to increase production, and pushing olive growers to improve their productivity in the face of new constraints linked to climate change.

According to the latest contribution by Working Group II to the IPCC's Sixth Assessment Report, all regions of the planet are already suffering the effects of climate change, and humanity is expecting even more drastic and powerful effects in the near future (IPCC, 2022). Depending on future trends in GHG concentrations, which are themselves sensitive to social and technical developments, the observed warming trends are likely to persist and intensify throughout the 21st century (IPCC, 2021; Zittis et al., 2019). According to several studies (Cramer et al., 2018; Lelieveld et al., 2012; Waha et al., 2017), these significant changes in the environment and climate could have a negative impact on a number of industries and socio-economic activities, including water resource management and agriculture, human health, energy demand and production, transport, ecosystems, biodiversity, forest fires, and many others.

The Mediterranean region is particularly vulnerable to climate change, with an increased frequency of severe weather events (Zittis et al., 2022). Droughts, heat waves and intense rainfall are just some of the phenomena that pose a major and additional challenge for agriculture in this part of the world. The impact of these occurrences can be observed through changes in atmospheric CO₂ concentration, temperature and water resource availability, which affect plant growth and productivity, the ability to conduct agricultural operations and the geographical distribution of crops (Brito et al., 2019). Hence, the combined impact of prolonged periods of drought and higher temperatures will have a significant impact on the main Mediterranean crops, such as olives, as well as on the viability of olive orchards (Fraga et al., 2020). Furthermore, elements that affect the months preceding the flowering season, such as weather conditions, management practices or diseases, are reflected in the annual production of flowers and pollen (Ribeiro et al., 2008). In the past, environmentally induced alterations were often poorly understood and went unnoticed, particularly in the case of plants such as olive, which can thrive for years with little or no maintenance. However, growers are now aware of the importance of abiotic factors in determining high yields and good quality. In addition, abiotic stresses can affect the level of resistance to parasitic and non-parasitic diseases (Graniti et al., 2011).