sustainability Article The Effect of Low Temperature on Physiological, Biochemical and Flowering Functions of Olive Tree in Relation to Genotype 1, 2, 3 3 Niki Mougiou y , Boushra Baalbaki y, Georgios Doupis , Nektarios Kavroulakis , Stylianos Poulios 1, Konstantinos E. Vlachonasios 1 and Georgios C. Koubouris 3,* 1 Department of Botany, School of Biology, Faculty of Sciences, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece;
[email protected] (N.M.);
[email protected] (S.P.);
[email protected] (K.E.V.) 2 Department of Sustainable Agriculture, Mediterranean Agronomic Institute of Chania (CIHEAM), Alsyllio Agrokepiou, P.O. Box 85, 73100 Chania, Greece;
[email protected] 3 Institute for Olive Tree, Subtropical Crops and Viticulture, ELGO DEMETER, Agrokipio, 73100 Chania, Greece;
[email protected] (G.D.);
[email protected] (N.K.) * Correspondence:
[email protected]; Tel.: +30-28210-83434 These authors contributed equally to this work. y Received: 11 October 2020; Accepted: 30 November 2020; Published: 2 December 2020 Abstract: Olive tree growth and reproduction are severely affected by temperature extremes, compromising fruit yield. In that aspect, the olive varieties “Koroneiki” and “Mastoidis” were employed in a mild cold stress experiment, imitating night frost incidents to assess their biochemical, physiological and reproductive functions in relation to genotype. The physiological performance of the stressed plants was not significantly altered, suggesting that both cultivars were well adapted to mild cold night stress. The biochemical response of the plants, regarding antioxidant enzymes, H2O2 and TBARS accumulation, confirmed that both cultivars could cope with the stress applied. The mRNA levels of the PPO gene, which participates in hydroxytyrosol biosynthesis and plant defense, were elevated after 24-h stress at 0 ◦C, in both cultivars with “Mastoidis” plants exhibiting higher levels for a longer period.