Effect of harvest time, cold stratification and sulfuric acid on seed germination of three varieties of olive (Olea europaea L.)

Background and Objectives: Olive (Olea europaea L.) seed face two problems (physiological and mechanical dormancy) for germination. Various treatments such as mechanical scraping, chemical scraping and cold stratification (wet cooling) are used to accelerate seed germination. Concentrated sulfuric acid is used to relieve mechanical dormancy and to eliminate physiological dormancy, wet cold stratification is used. In the present study, in order to eliminate seed dormancy, accelerate germination and obtain suitable seedlings to produce rootstocks compatible with climatic conditions of Rudbar city, seeds of Arbequina, Balidi and Mari cultivars were used and cold stratification and sulfuric acid were applied. Also, the effect of seed harvest time on germination rate was investigated.
Materials and Methods: Seeds were harvested from fruits of olive trees cultivars Arbequina, Mari and Balidi at Rudbar Olive Research Station. The first time of harvest was the stage of full ripening of seeds with change of olive color from green to yellow (early October) and the second time of harvest was the stage of full ripening of fruit with change of color to purple and blackening (late November). The pots were filled with rotten animal manure and river sand. Three seeds were planted in each pot. The cultivation bed and seeds were disinfected with carbendazim disinfectant at a rate of two per thousand. All treatment levels (36 levels) had 4 replications. Experiment as factorial and in the form of completely randomized design with four replications was performed. Factors included varieties at three levels (Arbequina, Balidi and Mari), harvest time at two levels (full seed ripening and full fruit ripening), cold stratification with the temperature of 6-7°C at three levels (0, 500 and 1000 h), and 97% concentrated sulfuric acid treatment at two times (0 and 9 h). Therefore, the present experiment had 36 treatment levels. For each cultivar, 240 pots in 12 levels (6 levels in the first stage of harvest and 6 levels in the second stage of harvest) and 20 pots in each level were used. Totally, 2160 seeds were used for 720 pots for three cultivars. Germination rate, germination average, germination percentage, germination vigor and vegetative growth indices such as shoot growth and seedling dry weight were measured. The data were analyzed using SPSS software and their mean was compared using LSD test at 5% probability level and EXCEL software was used to draw the graph.
Results: Analysis of variance of the data showed that there was statistically significant difference (p≤0.01) between treatments and measured traits in various cultivars. There was no significant difference between cold priming and acid priming and sprouted seed number and plantlet vigour index. The results showed that the combined treatment of Mari cultivar seed with 9 h of sulfuric acid treatment and 1000 h of cold stratification treatment induced the highest germination vigority. The combined application of cold priming and sulfuric acid in the second stage of harvest (after full fruit ripening) reduced the number of days to germination but increased the germination percentage, germination rate, germination average and seedling vigor index in all cultivars. In all three cultivars, the highest plantlet dry weight was obtained from the 500 h cold priming.
Conclusion: The production of more and stronger olive seedlings is important for the development of olive gardens in the olive-growing provinces of the country economically, ecologically and to prevent soil erosion, especially in sloping lands. In this study, an effective solution to increase the germination index of olive seeds was presented. Among the different olive cultivars used, Mari cultivar showed more and better response to priming, which was more evident in the second harvest.