Thursday, April 25, 2013

Unlocking the potential of wild Oryza barthii

Oryza barthii is one of two wild species in Africa to share the same basic genome as the cultivated species (O. sativa and O. glaberrima), in fact O. barthii is considered by most as the species from which African rice (O. glaberrima) was domesticated.

Like its descendent, it has a number of features that make it interesting to the canny breeder: it has long panicles, diverse grain sizes, long flag leaf and long awns. Long panicles, grain size and weight might be considered 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.  

Moreover, 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 Semon AfricaRice upland rice breeder. “What it means for me as a breeder is that O. barthii harbors a lot of diversity that is not available in O. glaberrima.”

“I chose to use O. barthii in part because it has long slender grains that are heavier than those of O. glaberrima,” says Semon. “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. Moreover, they are very early maturing (less than 90 days after sowing). Oryza barthii is a riverine species, never found in the uplands (where O. glaberrima is frequently cultivated).

If O. barthii itself is 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, where they never would in the wild.

“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 NGO Golden Farmers working in Abakaliki, Ebonyi State. Because of his links with the National Cereals Research Institute (NCRI), Iruka 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. The yield loss was blamed on declining soil quality.

“Now, 2 years later, we have two promising lines that are giving us 3.8 t 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 (200 kg of compound NPK and 100 kg of urea) — the yield of existing varieties under this level of fertilization is 2–2.5 t/ha.

“Ebonyi is one of six states involved in the evaluation process,” explains Semon. “The protocol we have in place is closely linked with the varietal release process, and so we hope to see one or more of the interspecific varieties with O. barthii introgressions officially released in Nigeria in 2014 or 2015.”

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