Date Palm

The date palm is one of the oldest cultivated trees in the world, with evidence of domestication dating back >5,000 years. The discovery of dates in the tombs of pharaohs and in neolithic sites dating from 7,000 to 8,000 years ago demonstrates the historical significance of the species to human nutrition. Date palm trees are critical to agriculture in many hot and arid regions, and dates are the most important agricultural product of many countries in the Arabian Gulf. Total global production of dates in 2007 was 6.9 million tons ( ).

However, date palm biotechnology faces many challenges, including long generation times, the inability to simply distinguish between the many varieties of date palm and the inability to distinguish female from male trees at an early stage. There are >2,000 date varieties with differences in color, flavor, shape, size and ripening time and the genetic component of gender determination is not well understood. Specifically, date palms take 5–8 years after planting to flower, the earliest point at which male and female trees can be distinguished. Especially because date palm orchards, which primarily comprise fruit-bearing female trees, can be rapidly ravished by disease, the ability to quickly replant orchards from seeds or seedlings known to be female would be of great benefit. There are no easily distinguishable sex chromosomes in date palm, despite some cytological evidence that they exist. As biochemical studies have yielded little insight into how to identify the genders of immature plants, the identification of DNA sequences or sequence polymorphisms that are gender specific offers a promising alternative to efficiently determine date palm gender.

In large part owing to its long generation time, there are few genetic resources for date palm. The most extensive is a backcrossing program initiated in California in the 1940s, which required >30 years to generate. To our knowledge, there is no publicly available physical or genetic map for the genome of any date palm, and at the outset of this project only ~100 kbp of nuclear date palm DNA sequences were found in GenBank ( 

, March 1, 2009). To provide date palm researchers with the additional resources needed for comprehensive efforts to study and improve this important crop, we used massively parallel sequencing to assemble a draft genome sequence of date palm. Our analysis of nine varieties reveals polymorphisms that should provide an invaluable resource for the date palm community to identify ways to predict plant gender, maintain genetic diversity and improve traits such as fruit quality and ripening time.