This past week, the National Crop Variety Release Committee in Sudan approved the release of four Striga resistant varieties in the genetic backgrounds of popular, but Striga-susceptible, improved sorghum varieties “Tabat”, “Wad Ahmed” and “AG8”. These four experimental varieties released are ASARECA.T1” (T1BC3S4); “ASARECA.W2 Striga” W2BC3S4; “ASARECA.AG3” AG2BC3S4; and “ASARECA.AG4” (AG6BC3S4).
This is the first time where an African national program adopted and implemented marker-assisted back-crossing, through multi-institutional collaboration to generate improved cultivars against Striga, the bane of cereal farmers in sub-Saharan Africa.
The marker-assisted back-crossing program to develop these four varieties was initiated under a BMZ-supported project involving ICRISAT, the University of Hohenheim, and national program partners in Eritrea, Kenya, Mali and Sudan in 2004. All genotyping activities were carried out at the BecA facilities in Nairobi by MSc students from participating countries under supervision of ICRISAT scientists, Dr Rolf Folkertsma and later Dr Dan Kiambi.
The three-year project attempted to transfer and validate previously-mapped Striga-resistance QTLs from resistant donor parent N13 (from Nandyal, Andhra Pradesh, India), which had been identified by Bettina Haussmann and colleagues in an earlier BMZ-funded collaborative research project involving ICRISAT, the University of Hohenheim, KARI-Kenya and IER-Mali.
The backcross/QTL validation project advanced to the second backcross generation (BC2) in several locally-adapted, farmer-preferred, open-pollinated varieties for each target country. The resulting early-generation backcross progenies, although Striga resistant, were not agronomically superior enough for national trials and considered for release.
The national programs in Sudan, Eritrea and Kenya, led by Dr Abdalla Mohammed (a Purdue University-trained sorghum breeder with well-developed skills in phenotypic screening for Striga resistance) and with ICRISAT providing backstopping, then obtained funding through the regional agricultural science network (ASARECA Competitive Grant System for 2006) to fine-map the Striga-resistance QTLs and complete the task of recovering recurrent parent eliteness for materials in the genetic backgrounds of farmer-preferred improved sorghum varieties for Sudan, Eritrea and Kenya.
In Sudan, targeting different agro-climatic zones, a third popular drought-tolerant background (“AG8”) was added to that of recurrent parents “Tabat” and “Wad Ahmed,” and the crossing program advanced to the third backcross generation (BC3). The fine-mapping and marker-assisted backcrossing program was the subject of the PhD thesis research program of Ms Rasha Ahmed, of Sudan’s Agricultural Research Corporation. Rasha visited ICRISAT-Patancheru for the genotyping required to fine-map the Striga-resistance QTLs and for the SSR genotyping of three additional generations of the marker-assisted backcrossing program (up to BC4), where she received support and guidance from Drs Tom Hash and Santosh Deshpande.
Genotyping for the last generation of marker-assisted selection was completed in 2011 at the BecA facility of the ILRI-Nairobi campus under the guidance of Dr Santie de Villiers, before the product lines could reach the required state of agronomic eliteness combined with high and stable levels of host plant resistance to Striga hermonthica.
Standard variety trials were conducted in Striga-infested plots over three rainy seasons (2009-2011) at the Gezira Research Station (GRS), Damazine, Sinnar and Gedaref in Sudan. Results from these trials revealed that backcross-derived lines T1BC3S4, AG6BC3S4, AG2BC3S4 and W2BC3S4 were Striga resistant and agronomically superior, giving 180-298% increases in grain yield over their recurrent parents in the infested plots.
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