Sequencing of the oil palm, one of the world's most important crops, has pinpointed a gene that should boost yields and ease pressure on tropical rainforests, studies said on Wednesday.

Published in the scientific journal Nature, the genome highlights the role of an all-important gene called Shell, according to a probe led by the Malaysian Palm Oil Board (MPOB).

With 32 chromosomes and around 35,000 genes, the oil palm has an impressively long lineage, dating back to the origins of flowering plants during the Cretaceous period some 140-200 million years ago, says the investigation.

It comprises two species -- Elaeis guineensis, which originates from West Africa, and E. oleifera, from Central and South America, and has a higher content of unsaturated fatty acids and resistance to disease.

The oil palm is grown widely in the tropics, accounting for 45 percent of edible oil worldwide, but its image has been badly damaged by destruction of rain forest and peatland to create plantations.

Land clearance by illegal burning on the Indonesian island of Sumatra has been blamed for last month's smog scares in neighbouring Singapore and Malaysia, the region's worst pollution episode in more than a decade.

The Shell gene is responsible for the three known forms of oil palm shell: dura (thick); pisifera (shell-less) and tenera (thin), says the study.

Tenera, a highly desired hybrid of dura and pisifera, contains a normal version of Shell and one of two different mutations of the gene.

This combination results in 30-percent higher yield of palm oil per fruit than dura palms.

"Mutations in this gene... explain the single most important economic trait of the oil palm: how the thickness of its shell correlates to fruit size and oil yield," said Rajinder Singh of the MPOB's Advanced Biotechnology and Breeding Center.

"This discovery may help balance the competing interests of meeting increasing world-wide demand for edible oil and biofuels on the one hand, and of rainforest conservation on the other."

Oil palms have a notoriously long reproductive cycle, lasting up to a dozen years.

As a result, it can take growers six years to identify whether a plantlet is of the high-yielding type and deserves to be transferred to the plantation.

Being able to get a genetic marker at the seedling stage will speed the process and dampen demand for acreage, according to the researchers. Other traits in the genome point to characteristics for fruit ripening and use of cloned plants for planting.