Morphological and Histological Studies of Mozafati Date Fruits (Phoenix dactylifera L.) During Their Developmental Stages

Dates are the second most important crops in Iran after pistachios, which show different structural and textural adaptations to drought and high temperatures. Acquiring the necessary knowledge about various structural and physiological changes from flowering to fruit ripening plays a significant role in obtaining high-quality and marketable fruit. Date fruit is a berry characterized by exocarp, fleshy mesocarp and membrane endocarp around the seed. This berry is formed from a fertilized carpel present in the female flower, while the other two carpels do not grow and decay. The fruit development period is long and lasts about 7 months. The sweetness and texture of date fruit is closely related to the maturity stage of the fruit. During the growth period of date fruit, several changes in the color and chemical composition of the fruit are observed. Mozafati is one of the most important commercial varieties of dates in Iran especially in Bam city. In the present study, the morphology and histology of the date fruit (Phoenix dactylifera L.) of the Mozafati cultivar were investigated during the developmental stages.

Samples were collected from a commercial garden located in Bam city. Five adult 17-year-old date palms of Mozafati cultivar derived from offshoots grown in similar environmental conditions were used as female parents. The pollen used in this experiment is the same pollen that is normally used by local gardeners for pollination. Sample collection was done in five different developmental stages including Hababouk, Kimri, Khalal, Sarkhal and Rutab (4, 12, 19, 24 and 25 weeks after pollination, respectively). In this research, the local Iranian names such as Sarkhal and Rutb were used for the last two stages. The collected fruits, after cleaning and sorting, were packed and stored at 4ºC. The hand sections prepared from the fresh samples at each developmental stage were studied with an optical microscope after staining and then photographed.

An anatomical study of fruits in different stages of development revealed several general characteristics in their pericarp structure: 1) Pericarp differentiation starts in the early stages of development (immediately after pollination) and its development continues progressively and regularly. 2) The exocarp contains four differentiated layers in all developmental stages, from outside to inside, includes layers of the epidermis, hypodermis, skin parenchyma, and layer of stone cells. 3) The mesocarp (which is the largest region forming the pericarp) has a large number of layers consisting of parenchymal cells and is divided into two outer and inner regions, which are separated by a layer of parenchymal cells specialized to store tannins (idioblast). Vascular vessels with different sizes are distributed in the outer and inner mesocarp, which are less abundant in the inner parts. 4) The endocarp can be recognized as an unspecialized single-layered epidermis only in the early stages of development and eventually forms the seed coat together with the inner layers of the mesocarp.

Organized protection and defense mechanisms, including the presence of thick cuticle, stone layer, and specialized tannin layer (tannin idioblasts) in all stages of pericarp development, were among the interesting histological features of this cultivar, which showed its adaptive and evolutionary role in specific habitats