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Unlocking the breeding potential of the wild rice species Oryza barthii

April 29, 2013
Oryza barthii is one of two wild species in Africa that share the same basic genome as the cultivated species O. sativa and O. glaberrima. It is in fact considered by most as the species from which African rice O. glaberrima was domesticated.
Like its descendent O. glaberrima, Oryza barthii has a number of features that make it interesting to breeders: it has long panicles, diverse grain sizes, a long flag leaf and long awns. Long panicles, grain size and weight are a prerequisite for high yield, while flag leaves and awns both offer protection against bird damage — the flag leaf shielding the panicles from the sight of a bird flying overhead, and the awns making the grain difficult to access.  
However, the domestication of O. barthii as O. glaberrima resulted in a reduction of the species’ diversity. “This is normal for any crop domestication,” says Mandè Semonupland rice breeder at AfricaRice . “What it means for me as a breeder is that O. barthii harbors a lot of diversity that is now not available in O. glaberrima. Generating interspecific progenies from crosses involving O. barthii and O. sativa provides an opportunity to develop new varieties with increased yield potential, good grain characteristics, insect pest and disease resistance, as well as improved grain quality, good taste and aroma.”
Some of the new interspecific lines have inherited resistance to bacterial blight and stem borer from their O. barthii parent. They are also very early maturing (less than 90 days after sowing). Oryza barthii however is a riverine species, never found in the uplands where O. glaberrima is frequently cultivated, and if grown in the uplands, it typically lodges (falls over) and sheds all its grains prior to harvest. However, taking the interspecific lines with O. barthii introgressions to the uplands seems to have allowed traits for upland adaptation to be expressed.
“We already have good lines available,” enthuses Semon, “combining short duration to avoid drought, high yield and aroma. The aroma was a surprise, as neither parent — the O. barthii nor the O. sativa — was aromatic.” One case of releasing previously hidden traits.
“Yield trials were carried out with 148 fixed lines at two locations contrasting in altitude and soil acidity,” says Semon. Selections from these were then evaluated in Ethiopia, Côte d’Ivoire, Liberia, Ghana, Chad, Niger, Benin, the Democratic Republic of Congo (DRC) and Nigeria. The 30 highest-yielding lines were then nominated for regional evaluation in Rice Breeding Task Force trials in Guinea, Mali, Nigeria, Togo and Uganda.
Nwambam Iruka is a member of the Nigerian non-governmental organisation Golden Farmers working in Abakaliki, Ebonyi State. He was given seeds of 35 interspecific lines with O. barthii introgressions to test.“At the time when AfricaRice brought the new varieties to us, local farmers had given up on upland rice, because of the decline in yield of the local variety, China best,” he says, yield loss that was blamed on declining soil quality. "Now, 2 years later, we have two promising lines that are giving us 3.8 tonnes per hectare in the rainfed uplands.” These yields are high for the upland ecosystem in West Africa, even given that they are helped by the farmers’ use of 300 kg of fertilizer per hectare  — the yield of existing varieties under this level of fertilization is only 2–2.5 t/ha.

One or more of the interspecific varieties with O. barthii introgressions are likely to be officially released in Nigeria in 2014 or 2015.

This artricle is adapted from a piece published in the AfricaRice Blog on Thursday 25th April 2013.

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