Isa Keramatlou; Saeid Navabpour; Khalil Zainilnejad; Elahe Tavakol; Seyyed Mehdi Hosseini Mazinani
Abstract
Introduction
Low temperature is one of the major abiotic stresses which can cause a significant reduction in olive growth and productivity mainly at late autumn, winter and early spring. Although olive is moderately freezing tolerant, temperatures below a certain threshold -7oC can damage the plant, ...
Read More
Introduction
Low temperature is one of the major abiotic stresses which can cause a significant reduction in olive growth and productivity mainly at late autumn, winter and early spring. Although olive is moderately freezing tolerant, temperatures below a certain threshold -7oC can damage the plant, while at -12oC damage may be serious enough to threaten the life of the tree. Different cultivars of olives have diverse reactions to cold stress and so, the selection of cold resistant cultivars is the most effective method to avoid frost damages. First step to achieve this goal, is indentifying tolerant cultivar and genotypes in olive area growing. Due to extensive and high freezing damage in November 2016, the objective of the present study was to evaluate morphological characteristics and selection of single -tolerant cold trees.
Materials and Methods
The present study was carried out in some cold tolerant olives after freezing event in December 2016 in Eastern region of Golestan province of Iran. After freezing stress Healthy olive trees were identified in tow major olive cultivation regions and then were evaluated in four stages. Thus, this study included: 1- Meteorological data analysis, 2- Evaluation of freezing stress symptoms in olive orchards and identification of single tolerant trees, 3-stugy of single tolerant cold trees in 4 stages. For each genotype, studies on morphological traits (Tree age, location altitude, dip direction and its percentage, previous yield, tree height, canopy height, average of canopy diameter, canopy volume, canopy surface area, trunk perimeter, trunk diameter, trunk cross section area, length of internodes, growth habit, canopy density, canopy defoliation, barksplit ranging, flowering and fruit set) based on CFC / IOOC / 03 and Lodolini et al. (2016) results.
Results and Discussion
History of cold climate in the last two decades showed freezing event several times cause damage to olive orchards. The last freezing stress occurred with the entrance of the cold air to the Golestan province and a sudden drop in temperature to less than 0 degrees Celsius and stability of these conditions for 5-days in the late of November, 2016. The temperature drops below 0 ° C began on November 23 and lasts for 4-days. However, the main damage to the olive orchards is on November 25, when temperature is - 7 ° C. The minimum temperature recorded in the studied regions in November 25, Maravehtapeh, Gonbad, Kalaleh and Minoudasht are -14.2, -12.7, -12.3 and -8.5 ° C, respectively. Symptoms of freezing damage on olive tree can range from shoot tip burns and defoliation up to bark split on branches or trunk. After 4 stages visiting olive orchards, Finally, from 218 primary individual trees, 58 trees were introduced for further evaluation. Location altitude (meters above sea level) of the idividual trees are 81-411 in the CTO-17 and CTO-5 genotypes, respectively. Generally, 93% of all trees identified in sloping land orchards, and the Percentage variation for this trait is 48. 99. Fruit production of selected olives before freezing event in 2016 showed except of 13 trees, 44 of olives was of 2-60 kg/tree. Tree height was 2-6.82 in CTO-35 and CTO-17 genotypes, respectively. However, average of canopy diameter in all genotypes was 2.68. Also, trunk diameter (TD) and trunk cross section area (TCSA) was maximum in CTO-29 and minimum in CTO-9. But the average of this trait was 17.13 cm. Variation between genotype in internode length changed between 1.05 in CTO-20 and 16.2 in the CTO-49. Reduction of internode spaces and shoot growth, even though the total node number is normal resistance of the olive tree to cold is reduced. Leaf defoliation is one of the most important symptoms of freezing event. The study of selected trees showed that 48 trees (83%) did not showed symptoms of leaf loss, and only 10 trees showed less than 50% leaf loss. Except for the CTO-54 genotype, which showed symptoms of bark spliting on one-year shoots, no evidence of bark spliting observed in other selected olives.
Conclusions
Although olive is the most cold-hardy of the subtropical fruit trees, some varieties can withstand low temperatures better than the other. Although temperatures at which olive trees can be damaged vary, depending on climatic conditions, temperatures at or below -7°C are often critical. The most important symptoms were leaf defoliation, bark split, and limb dieback. Finally, because of different influence of environmental factor in different regions, evaluation of location, yield and morphological traits showed some of cold tolerant olive in different region had a similar behavior, thus by supplementary molecular studies, it can be hoped that among recognized trees, cold resistant cultivars with acceptable yields were introduced.
