Investigation of Growth Regulators Profile in Reproductive Organs of Tissue Culture-Derived and Offshoot-Derived ‘Barhee’ Date Palm

Document Type : Full Paper

Authors

• Maryam Boroujerdnia ¹
• Seyyed Samih Marashi ²
• Seyyed Nasser Mousavi ³

¹ Date Palm and Tropical Fruit Research Center, Horticultural Science Research Institute, Agricultural Research Education and Extension Organization, Ahwaz, Iran

² Date Palm and Tropical Fruits Research Center, Horticultural Sciences Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Ahwaz, Iran

³ Date Palm and Tropical Fruit Research Center, Horticultural Science Research Institute, Agricultural Research Education and Extension Organization, Ahwaz, Iran.

Abstract

Keywords

• Abscisic acid
• Fruit set
• Parthenocarpic fruit
• Pollination

Main Subjects

• Fruit Science

Extended Abstract

Introduction

Date palm (Phoenix dactylifera L.) is an important fruit crop in arid and semi-arid regions of the world. Today, the development of tissue culture propagation methods has enabled date palm to be rapidly propagated on a large scale. One of the main weaknesses of this method is the possibility of the appearance of abnormal phenotypes such as delayed flowering, low levels of fruiting and the formation of parthenocarpic fruits. There is a difference in the amount of abnormalities among date palm cultivars. The low levels of natural fruiting due to the high production of parthenocarpic fruits or high fruit drop in some cultivars of tissue culture date palm compared to the trees obtained from offshoot date palm, especially in the Barhee cultivar, leads to inappropriate yields and economic losses to gardeners. Growth regulators play an important role in fruit formation during the stages of flowering, pollination and fertilization. Therefore, this study was conducted to compare the hormonal levels of the flowers and fruits in date trees derived from tissue culture and offshoot and their relationship with the amount of fruiting in two groups of trees.

Materials and Methods

This study was conducted in order to investigate the changes in the growth regulators related to fruit setting in the pollination season on both tissue culture-derived and offshoot-derived date palms cv. Barhee, in ate Palm and Tropical Fruit Research Center of Ahvaz city. At the beginning of spring, palm trees were selected from each group of tissue culture and offshoot trees and sampling of flowers and fruits was done in the three stages including spath appearance, ripe spath and 2 weeks after pollination in three replications. In the pollination stage, three spathes in each palm (1-2 days before natural opening) were pollinated with Ghanami cultivar pollen. The plant hormones: auxin (IAA and IBA), gibberellin (GA₁, GA₃, GA₄, GA₉), cytokinin (Zeatin and Kinetin), abscisic acid and jasmonic acid were measured in the flower or fruit samples collected from tissue culture and offshoot trees. Five weeks after pollination, fruit set percentage, parthenocarpic 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 percentage and more parthenocarpic fruits and fruit drop percentages as compared to off shoot derived plants. Also, the fruit yield in the tissue culture derived plants was lower than off shoot derived plants.  The levels of gibberellin, auxin, and cytokinin hormones in the off shoot derived plants were higher than tissue culture plants in most of the measured stages. The tissue culture plants had a higher amount of abscisic acid and jasmonic acid than offshoot plants. By using multiple linear regression analysis and superior model selection, the amount of abscisic acid and jasmonic acid of flower and fruit had a negative relationship with the amount of fruit set. The fruit setting was positively correlated with the amount of kinetin, indole acetic acid, GA₃, GA₄ and GA₉ of flowers and fruits, while had a negative correlation with the amount of abscisic acid and jasmonic acid . Therefore, higher parthenocarpic percentage in tissue culture-derived date palms compared to offshoot-derived date may be due to the difference in hormone levels or different ratios of hormones in them. The failure of normal fruiting in the tissue culture derived plants was probably due to many interrelated events that lead to a slow growth of pollen tube at early stages of fruit growth and which may possibly be accentuated by the relatively high ABA contents during this period.

Conclusion

According to the results of this research, one of the causes of unfavorable fruiting in tissue culture-derived date palms is the change in the internal hormone profile of the flowers and fruits compared to the offshoot-derived trees. Changes in the levels of internal hormones accompany with a decrease in the growth of the pollen tube lead to lack of fertilization or incomplete fertilization and as a result, the formation of parthenocarpic fruits and finally, a decrease in fruiting and fruit growth.