The Effect of Low Temperature on Physiological, Biochemical and Flowering Functions of Olive Tree in Relation to Genotype

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. Three more genes involved in hydroxytyrosol biosynthesis upregulated their expression levels as a response to cold stress. The numerous plant phenology aspects measured reinforced the conclusion that both cultivars responded to the stress applied. The results of the present study may contribute to better understanding olive tree adaptive responses to low temperature events, an abiotic stress condition that is often present in an open plantation, thus assisting farmers on breeding and cultivar selection.

Cold Stress, Freezing Adaptation, Varietal Susceptibility of Olea europaea L.: A Review

“…At a sub-optimal temperature (10/20 °C) it undergoes a rapid decrease in production; at chilling-temperature or critical temperature (from 7.5 to 12.5 °C) are strongly slow down the metabolic processes such as respiration and photosynthesis; at freezing temperatures (temperatures average below −10 °C) irreparable damage to organs and tissues and the death of the entire plant can occur. In ecological and agronomic contexts, it is very useful to know the critical temperature and freezing temperature that play a decisive role in tree phenology and adaptation ( Figure 2 ) [ 16 , 31 , 33 , 39 , 40 ]. In spite of a high ecological plasticity of the species, there are few observations on the vegetative-productive behavior of a cultivar transferred from warm to cooler zones.…”

“…Furthermore, the reproductive organs, flower buds, flowers and fruit are seriously damaged [ 29 , 53 , 54 , 55 ]. The exposure of plants to low temperatures (below 10 °C) induces changes in the function of the photosynthetic apparatus, causing photoinhibition phenomena [ 56 ] changes in respiration and enzymatic activity [ 33 , 40 ] and alteration in the plasma membrane potential (V m ) [ 39 ]. Low temperatures also cause dehydration symptoms in shoots and leaves due to an imbalance between water absorbed by roots and transpiration [ 57 , 58 ].…”

“…The response of the cultivars to soil chilling may be used as an indicator of their frost resistance [ 60 ]. The acquisition of chilling tolerance in olive is poorly understood as only a few studies have been published [ 33 , 40 , 62 ]. Rejŝková et al [ 62 ] investigated, under in vitro conditions, the changes in the soluble carbohydrate fraction in shoot segments (cv Picual) exposed chilling temperatures (4 °C).…”

“…The authors observed an increase of total endogenous carbohydrate content; in particular, changes were observed in the proportions of mannitol and raffinose family oligosaccharides (RFO), while the sucrose proportion did not change. Recently, Mougiou et al [ 40 ] analyzed the response of Koroneiki and Mastoidis cvs subjected to mild cold stress (LT 0 ± 2 °C). The cold stress treatments conducted for a few days did not affect nor physiological (photosynthetic rate, stomatal conductance and intercellular CO 2 ), biochemical parameters (antioxidant enzymes activity) neither plants phenology.…”

“…The cold stress treatments conducted for a few days did not affect nor physiological (photosynthetic rate, stomatal conductance and intercellular CO 2 ), biochemical parameters (antioxidant enzymes activity) neither plants phenology. Koroneiki and Mastoidis cvs were classified as tolerant to mild cold stress [ 40 ]. This behavior was confirmed by analysis of genes involved in hydroxytyrosol biosynthesis (olive polyphenol oxidase, OePPO; tyrosine decarboxylase, OeTDC; alcohol dehydrogenase, OeALDH; and copper-amine oxidase OeCuAO).…”