Grain gains

A new strain of rice keeps off weeds and trebles yeild

Published: Friday 31 October 1997

poor farmers in Africa can now treble their rice yields at no extra cost. This has been made possible by hybrid plants that are suitable to African conditions. The hybrid combines in a single plant the hardiness of a long-forgotten native African strain with the high-yielding qualities of widely grown Asian plants, say rice breeders at the West African Rice Development Association's (warda) laboratories in Bouake, Cte dIvoire.

The hybrid was made by combining two rice species -- Oryza sativa and Oryza glaberrima . To cross two types of rice that would not interbreed normally, the researchers used a technique called "anther culture". They took pollen-producing anthers from individual plants and grew them into tiny plantlets containing a single set of chromosomes.

Treating the plants with special mixtures of chemicals makes them generate twin sets of the same chromosomes in each cell, a condition called double haploidy. Once equipped with two sets of chromosomes, the plants are no longer infertile and can form both pollen and ovules. Each trial has produced crops that yield three tonnes per hectare where only one tonne is usually harvested. Improved husbandry can boost yields to five tonnes per ha.

Upland rice farmers in West Africa produce 40 per cent of the continent's rice. The remainder is grown on rainy or irrigated lowlands. But the leaves of the plant do not cast much shade, allowing weeds to grow and limiting yields. warda researcher David Johnson, working with colleagues Monty Jones and Michael Dingkuhn, solved the weed problem by crossing O, sativa with its obscure African cousin O, glaberrima . The Hybrids generated had an early spurt of foliage and droopy leaves, added to the high grain yields of the Asian parent. Also, the hybrid has the Asian strain's strong stem, which prevents the plant from collapsing. More importantly, as far as the farmers are concerned, the weed control comes at no extra cost.

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