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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