GUANGZHOU, China, Sept 12 (Reuters) - Oilseed plant jatropha does not offer an easy answer to biofuels problems as some countries hope, because it can be toxic and yields are unreliable, experts and industry officials warned on Wednesday.

The woody plant can grow on barren, marginal land, and so is increasingly popular in countries such as China that are keen to boost biofuels output but nervous about food security.

But its nuts and leaves are toxic, requiring careful handling by farmers and at crushing plants, said experts at an oils and fats conference.

In addition, it is a labour-intensive crop as each fruit ripens at a different time and needs to be harvested separately. Its productivity is also low and has yet to be stabilised.

M. R. Chandran, adviser to the Roundtable on Sustainable Palm Oil, told Reuters it would take five years of intensive research before jatropha could achieve productivity that would make its cultivation economically viable. The oil yield of the plant, originating in Africa and still largely a wild species, is less than 2 tonnes per hectare with large swings from year to year.

An engineer specialising in oil and fat processing plants, including for biodiesel production, said special facilities were needed for crushing jatropha nuts as they could produce a toxic vapour.

The engineer, who declined to be named, said his company hoped to seal a deal with a private investor to build one of the world's first large-scale jatropha-based biodiesel plants in China's southern province of Yunnan before the end of this year.