Optimization of in vitro pollen germination and viability testing of some Australian selections of date palm (Phoenix dactylifera L.) and their xenic and metaxenic effects on the tissue culture–derived female cultivar “Barhee”

Information regarding efficient pollen viability testing methods and the most favourable pollen storage conditions for internationally important date palm cultivars is limited. No such information has been reported on Australian male selections. The in vitro pollen germination of three elite Australian male selections, “Big pod”, “Campbell” and “Tanunda”, was estimated using a modified Brewbaker and Kwack (BK) medium with combinations of various chemicals. 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 used in a medium at pH 5.4. The viability of pollen of these three genotypes following storage in a refrigerator at 4°C was tested every 3 mo for 12 mo. Significant pollen viability was maintained after 9 mo of storage and the highest germinability (60.3%) was observed for the genotype “Tanunda”. Six tests for determining viability, including TTC (2,3,5-triphenyltetrazolium chloride), IKI (iodine potassium iodide), lactophenol cotton blue (LPCB), acetocarmine, fluorescein diacetate (FDA) and Alexander’s differential stain were evaluated and correlations between these pollen viability tests and in vitro germination were determined. A highly positive correlation between in vitro germination and the FDA viability test was observed. The metaxenic effect induced by pollinating the cultivar “Barhee” with three sources of pollen was investigated by assessing changes in the levels of malic acid, citric acid, fructose, glucose, sucrose, l-proline and myo-inositol during fruit development. The pollen source had a significant influence on the concentrations of these chemicals (metaxenic effect). Pollen of the genotype “Tanunda” significantly increased fruit size, fresh weight and seed size in comparison with other pollen sources.