A trial to enhance cold tolerance of passion fruit (Passiflora edulis) crop in Lebanon through foliar application of the natural osmoprotectant glycine betaine

Passion fruit (Passiflora edulis) cultivation is gaining growing interest by Lebanese farmers who are trying to diversify their income from agriculture. However, production volumes are low facing the high local demand due mainly to the plant preferences for tropical climate conditions which restricted the spread of this cultivation and limited it to coastal zones. The experiment aimed to expand passion fruit cultivation into new areas by enhancing its cold stress. It was carried out on seedlings of 2 purple cultivars: 'Black Knight' (BK) and 'Perfecta' (PR) that were grown in 3 Lebanese regions: Louaize (LO), Ajaltoun (AJ) and Hrajel (HJ) with increasingly cold weather conditions. The goal was to investigate the effect of foliar application of the natural osmoprotectant glycine betaine (GB) on cold tolerance of plants. Thus, plant performance was evaluated among plants treated by 2 different concentrations of GB (GB1: 20mM and GB2: 40mM) and compared to control (GB0: 0mM). Separated and combined effects of the factors: cultivar, GB concentration and Location was studied on various parameters (plant height, number of shoots, leaf number, internodal length, stem diameter and leaf area). Results of Repeated Measures ANOVA showed that average plant height and leaf number were mainly affected by the factor Location recording the highest values in LO compared to AJ and HJ especially regarding the treatment GB2. On the other hand, the combined effect of the factors Location and GB concentration was significant on average stem diameter, leaf area and number of shoots; At LO, the treatment GB2 has increased leaf area and internodal length of PR and the number of shoots of BK. GB applied with a concentration 40mM improved plant growth mainly in LO and had a non-significant effect in colder conditions (AJ and HJ) showing no significant effect on cold tolerance of passion fruit plants.