In Vitro Propagation, Reproductive Biology and Genetic Diversity of Date Palm (Phoenix dactylifera L.)

Abstract

Date palm (Phoenix dactylifera L.) is an important fruit crop in many arid areas and understanding the relatedness among genotypes is important for effective date palm improvement. Molecular markers were used to assess the molecular variation and genetic diversity of 54 and 12 date palm genotypes collected from Australia and Iraq, respectively. The accessions could be separated into geographic origin; specifically, Iraqi female cultivars, exotic female cultivars collected in Australia and male accessions collected in Australia, with a few exceptions. However, the Australian accessions did not group geographically in Australia; instead separate male and female groups differentiated. The amenability of date palm to micropropagation was examined to avoid the use of mutagenic growth regulators currently required for date palm breeding and cultivation. Embryogenic callus induction and proliferation was observed to be significantly higher when the woody plant nutrient culture medium (WPM) was supplemented with 5 mg/l Thidiazuron (TDZ). Shoot regeneration derived from callus was improved with the addition of 2 mg/l zeatin. Bud initiation and adventitious shoot formation were further improved by the addition of 0.5 mg/l GA3, 1.5 mg/l 2,4-D and 5 mg/l 2-ip. The in vitro pollen germination of three elite male selections was tested using modified Brebaker and Kwack (BK) medium. Germination was maximized when 75 mg/l H3BO4, 400 mg/l Ca (NO3)2.4H2O, 100 mg/l KNO3, 50 mg/l MgSO4.7H2O and 15% (w/v) sucrose were added to the medium at pH 5.4. The fluorescein diacetate (FDA) test was observed to be the most effective method for assessing pollen viability. The metaxenic effect induced by pollinating the cultivar female “Barhee” with various pollen sources was investigated. Pollen source had a significant influence on pollination efficiency and the cultivar “Tanunda” significantly increased fruit size, fresh weight and seed size in comparison with other pollen sources.