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The golden future of rice?

Golden rice, a rice variety genetically engineered to produce beta-carotene, has been hailed by researchers as a new miracle rice that could solve vitamin A deficiency in afflicted countries. But will golden rice live up to its promise and be as valuable to farmers as varieties they have nurtured and cherished for thousands of years?

Reviewing the last fifty years, there is no doubt that rice breeding has already benefited thousands of farmers. In his keynote address to the CropLife International Annual Conference, held in Brussels in early June 2004, renowned rice breeder, Gurdev Khush, gave the example of a book written in the 1950s predicting widespread famine in the 1970s due to stagnant food production and increasing population. Through the efforts of scientists that laid the foundations of the Green Revolution, the apocalyptic predictions of 'Famine - 1975', written by William and Paul Paddock, were fortunately never realised. But, with world population still increasing and the added impact of climate change, widespread famine by 2075 could yet be a possibility unless plant breeders maintain their efforts to meet the challenges that lie ahead.

On the wild side

Rice variety trials at IRRI in the Philippines
Rice variety trials at IRRI in the Philippines

Notable achievements in rice breeding include improvement in grain quality and shorter maturation times. Newer varieties mature in half the time of old varieties (down from 180 to 95 days) allowing farmers to grow a second crop, such as a soil improving legume. Major strides have been also made against disease, including resistance to grassy stunt virus which once devastated harvests across South and Southeast Asia. During the early 70s, scientists at the International Rice Research Institute (IRRI) screened over 7,000 rice lines. From this comprehensive screening, only a single line from an Indian wild rice (Oryza nivara), showed any resistance to the virus. The particular population of O. nivara is no longer to be found in Uttar Pradesh and only exists as seeds in IRRI's genebank, but its genes for grassy stunt resistance are present in most rice varieties developed by IRRI and its partners. The technique used to obtain genes from wild rices, known as wide-crossing, has also been used to develop resistance against bacterial blight, blast and tungro diseases - all major rice diseases - as well as resistance to brown planthopper. This major pest of rice is the vector for grassy stunt virus but it also damages the crop by feeding.

Multiple resistance to pests and diseases is now common in many of IRRI's varieties. Twelve genes have so far been identified to provide protection against four major insects as well as against the four main diseases. Durability of resistance genes is an important consideration but the search for novel genes continues and has been greatly assisted by modern molecular biology techniques. In collaboration with the Africa Rice Center (WARDA), IRRI is currently working on O. glaberrima, in efforts to breed weed-competitive plants, which would be particularly valued by farmers practising direct seeding of rice fields. Future efforts by IRRI will also include trying to identify genes to provide tolerance of abiotic stresses, such as drought and saline or acid soils. IRRI's popular IR64 variety has already been crossed with a wild species, O. rufipogon, that is found in the acid soils of Vietnam. In collaboration with Vietnam's Cuu Long Delta Rice Research Institute, a new hybrid (AS996) was released for commercial cultivation in 2003 and is already grown on 10,000 ha of moderately acid soil. The variety has proved so popular with farmers in less favourable rice-growing areas that it has been recognized by an award from the Vietnam Union of Science and Technology Association.

Bigger and better?

Identifying genes for improved tolerance or better resistance is not the only way forward and IRRI scientists, led by Dr Gurdev Khush during his time as IRRI's principal rice breeder, have been working on redesigning the rice plant. Known as the 'New Plant Type', or NPT, these improved varieties are shorter, sturdier, and produce fewer tillers but with twice as many grains (200) per panicle as conventional types. However, grain filling is a major problem in NPT varieties and future developments to solve this may rely on genetic engineering techniques.

The world's first accurate map of the rice genome, produced by Chinese scientists, was announced in December 2002. It is the largest genomic map produced of any plant to date but its genetic similarity to other cereal crops will greatly speed identification of useful traits. In fact, scientists have admitted, it is possible to produce a non-GM vitamin-A rice by identifying and using natural genes already present in rice for producing beta-carotene. Genetic engineering of rice, as with any crop, is a contentious issue but it is likely that there will always be more than one route to producing new varieties of rice.

Date published: July 2004

 

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