Freezing injury is one of the most important limiting factors in commercial pomegranate production. The objectives of this study were to compare cold hardiness of seven Iranian pomegranate cultivars at three stages: November, January, and March, and to investigate the relationship between freezing tolerance and soluble carbohydrate and proline changes of shoots during acclimation and deacclimation. LT50 values, estimated by both electrolyte leakage measurement (EL LT50) and tetrazolium stain test (TST LT50), allowed us to discriminate between the cultivars in terms of freezing tolerance. Acclimation and deacclimation did not occur simultaneously in different cultivars, having a key role in cold tolerance of cultivars, especially in fall and late winter. Post Sefid Bafgh cultivar showed high cold tolerance early in fall, but it was susceptible to cold during winter. ‘Naderi’, ‘Yusef Khani’, ‘Malas Saveh’, and ‘Robab Neyriz’ had the highest midwinter cold hardiness; ‘Mahabadi’ showed an intermediate hardiness, whereas ‘Post Sefid Bafgh’ and ‘Shishe Kap’ were found to be cold-susceptible in this period. Freezing tolerance estimated by TST corresponded to those measured by the EL method in all cultivars, but in November and January, higher variation in freezing tolerance was observed among the cultivars through TST compared with EL measurement. However, LT50 values, estimated by EL measurement, were lower than those estimated through TST in November and March. Soluble carbohydrate concentrations of stem samples increased during cold acclimation from November to January; then it decreased in March. Proline had a narrow range of variation among the cultivars in November, but an increase in the amount of proline was observed during the period of hardening. In general, stronger correlations were observed between LT50 values and the amounts of soluble carbohydrates compared with proline, particularly from fall to midwinter.

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The objective of this study was to investigate the shelf life of arils and the changes in their biochemical compounds in nineteen Iranian pomegranate cultivars during storage. Fruits were harvested when commercially mature and the arils were removed, packaged and stored at 5 ± 1°C, at 85-90% relative humidity in a cold room. Samples of the stored arils were examined for biochemical features in temporal checkpoints throughout a storage period that lasted for 35 days. By using the onset of decay as an index, the shelf life of arils varied among cultivars, ranging from 7 days to approximately 21 days. Considering the quality attributes of ready-to-eat arils at the beginning of the experiment, substantial variations were observed among the cultivars with regard to their titratable acidity (0.50-8.47%), total soluble solids (13-18.66°Brix), DPPH radical scavenging activity (63-87.44%), Gallic-acid-equivalent (2.64-6.95 mg/ml) and ascorbic acid (12.21-75.09 mg/l). In general, the decay of arils gradually increased during storage, but several cultivars-which exhibited a very slow process of decaycontained the highest content of titratable acidity, Gallicacid-equivalent and total soluble solids (since the signs of decay appeared on around the twenty-first day of storage). In addition, titratable acidity increased slightly by the end of storage, whereas the ascorbic acid content, total soluble solids and Gallic-acid-equivalent were cultivar-dependent and did not show consistent patterns of change during storage.

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Chilling and heat requirements can affect agroclimatic distribution, growing season, and the marketing period of pomegranate (Punica granatum L.) cultivars in commercial production. This study was carried out to determine the chilling and heat requirements of 20 Iranian pomegranate cultivars/accessions, and to also examine the correlation of these features with tree and fruit characteristics, as well as geographic and climatic parameters of the original environment the plant materials came from. One-year-old stem cuttings from mature trees were used for measurements of chilling and heat requirements. The results showed a range of variation in chilling requirement among cultivars from 233 to 633 hours and heat requirement from 4096 to 7928 growing degree hour (GDH). Based on chill hours accumulated, cultivars including Bihaste Ravar, Bihaste Sangan Khash, and Anar Siah were categorized as very low chill (233–266 hours), whereas cultivars Poost Nazok Torosh Abarkuh, Malas Yazdi, Jangali Poost Ghermez Roodbar, Rabab Poost Ghermez Neyriz, and Makhmal Malas Shahreza were grouped as low chill (600–633 hours). Variation in seed hardness from 15 to 78 N was also recorded. Chilling requirement showed a moderate correlation with stomatal density, seed hardness, and wind speed (r = 0.42, 0.44, and −0.39, respectively), whereas stomatal density showed correlations of r = −0.34 and −0.57 with altitude and wind speed, respectively. We suggest taking chilling and heat requirements into account when selecting individual’s cultivars and/or accessions suitable for cultivation in different agroclimatic regions.