Introduction
Date is one of the important crops in arid and semi-arid regions in the world. Today, plant tissue culture technology, as an important commercial method, provides the possibility of rapid reproduction of trees needed for the development of groves. Despite this, one of the main weaknesses of this method is the possibility of abnormal phenotypes such as delay in flowering, low levels of fruit set and formation of parthenocarp fruits. There is a difference between tissue culture date varieties in terms of the amount of abnormalities. In young tissue culture palm trees of Berhi cultivar, the amount of parthenocarp fruits reaches 59-86% and the yield of the date palm is greatly reduced. Therefore, identifying the causes of these abnormalities in tissue culture palms is very important.
 
Materials and Methods
This study was conducted in order to investigate the changes in nutrient elements related to fruit set in the pollination season on tissue culture derived date palms and derived from offshoot cv. Barhee in Date Palm and Tropical Fruit Research Center of Ahvaz city (year 2022). At the beginning of spring season, palm trees were selected from each group of tissue culture and offshoot trees 10- years -old. Sampling of flowers and fruits were done in the three stages of spath appearance, ripe spath and 2 weeks after pollination from three spathes. In the pollination stage, three spathes in each palm (1-2 days before natural opening) were pollinated with the same male pollen. Nitrogen, zinc, iron, magnesium, manganese, boron and potassium elements were measured in the flower or fruit samples collected from tissue culture and offshoot trees. In 5th week after pollination, fruit set percentage,  parthenocarp fruits percentage and flower and fruit drop percentage were recorded.
Results and Discussion
The results showed that tissue culture derived plants had less fruit set and more seedless fruits and drop as compared to off shoot derived plants. Also, the fruit yield in the tissue culture plants was lower than off shoot derived plants. The levels of magnesium, manganese, boron, zinc and potassium in off shoot derived plants were higher than tissue culture plants in most of the measured stages.  By using multiple linear regression analysis and superior model selection, the amount of calcium and iron of flower and fruit had a negative relationship with the amount of fruit set and the amount of nitrogen, phosphorus, magnesium, manganese and boron had a positive relationship with it.
 
Conclusion
The lack of nutritional elements in tissue culture plants in comparison to offshoot derived plants in different stages, especially pollination and fruit formation, may cause disturbances in the synthesis of carbohydrates, protein, and organic matter, so the growth and development of the plant and ultimately the amount reduce fruit yield. Therefore, optimal feeding of trees and foliar spraying with key elements such as boron, zinc, manganese and magnesium at different stages can be one of the effective ways to improve fruiting and achieve maximum yield and increase the quality of the fruit of these trees.