  Citation: Iovane, M.; Cirillo, A.; Izzo, L.G.; Di Vaio, C.; Aronne, G. High Temperature and Humidity Affect Pollen Viability and Longevity in Olea europaea L. Agronomy 2022, 12, 1. https://doi.org/10.3390/ agronomy12010001 Academic Editor: Rina Kamenetsky Goldstein Received: 17 November 2021 Accepted: 17 December 2021 Published: 21 December 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). agronomy Article High Temperature and Humidity Affect Pollen Viability and Longevity in Olea europaea L. Maurizio Iovane , Aurora Cirillo *, Luigi Gennaro Izzo * , Claudio Di Vaio and Giovanna Aronne Department of Agricultural Sciences, University of Naples Federico II, Via Università 100, 80055 Portici, Italy; maurizio.iovane@unina.it (M.I.); claudio.divaio@unina.it (C.D.V.); giovanna.aronne@unina.it (G.A.) * Correspondence: aurora.cirillo@unina.it (A.C.); luigigennaro.izzo@unina.it (L.G.I.) Abstract: Olea europaea L. is a crop typical of the Mediterranean area that has an important role in economy, society, and culture of this region. Climate change is expected to have significant impact on this crop, which is typically adapted to certain pedo-climatic characteristics of restricted geographic areas. In this scenario, the aim of this study was to evaluate the time-course response of pollen viability to different combinations of temperature and humidity. The study was performed comparing flowering time and pollen functionality of O. europaea from twelve cultivars growing at the same site belonging to the Campania olive collection in Italy. Pollen was incubated at 12 ◦ C, 22 ◦ C, and 36 ◦ C in combination with 50% RH or 100% RH treatments for 5 days. The results highlighted that a drastic loss of pollen viability occurs when pollen is subjected to a combination of high humidity and high temperature, whereas 50% RH had less impact on pollen thermotolerance, because most cultivars preserved a high pollen viability over time. In the ongoing climate change scenario, it is critical to assess the effect of increasing temperatures on sensitive reproductive traits such as pollen viability to predict possible reduction in crop yield. Moreover, the results highlighted that the effect of temperature increase on pollen thermotolerance should be evaluated in combination with other environmental factors such as humidity conditions. The screening of olive cultivars based on pollen thermotolerance is critical in the ongoing climate change scenario, especially considering that the economic value of this species relies on successful fertilization and embryo development, and also that production cycle of Olea europaea can be longer than a hundred years. Keywords: climate change; germplasm; olive; pollen viability; pollen functionality 1. Introduction Climate change will severely impact the Mediterranean Basin with an expected rise in temperatures in the range of 2–5 ◦ C[1–3]. Besides substantial warming, it has been estimated that climate change will result in a significant decrease in precipitation in this region [3,4], which might cause serious economic and ecological changes, influencing plant growth, the attack of pests and weeds, and ultimately, crop yield [5]. The olive (Olea europaea L.) is one of the most characteristic crops of the Mediterranean Basin, having a remarkable economic, social, and cultural impact. This species is widely spread and well adapted to the environmental conditions of the Mediterranean Basin. However, the predicted increase in ambient temperature due to global warming may affect plant physiology, phenology, and reproductive biology of this crop, ultimately reducing its yield [6,7]. The Mediterranean region is characterized by a changeable climate, especially in spring season, when daily temperatures can vary considerably. Moreover, it has been shown that inter-annual climate variations can affect flowering time and pollen production [8]. Indeed, previous studies have shown that the flowering time of O. europaea is highly dependent on yearly spring temperatures, which are rising steadily over time due to global warming [9,10]. In this scenario, the olive phenology may provide useful indications to evaluate the influence of climate change on plant growth for the whole Mediterranean Agronomy 2022, 12, 1. https://doi.org/10.3390/agronomy12010001 https://www.mdpi.com/journal/agronomy