8th INTERNATIONAL WHEAT CONFERENCE

ReLeASe STem RuST ReSISTANT VARIeTIeS foR
CommeRCIAL PRoduCTIoN IN keNyA
Njau P. N 1 .; Wanyera R 1 .; Singh D 2 ., and Gethi. M 1
1 Kenya Agricultural Research Institute (KARI)- Njoro. P. O. Njoro, Kenya
2 CIMMYT Nairobi, Kenya
E-mail Address of presenting author: Peter N. Njau, E-mail: njaupnn@yahoo.com
Stem or black rust, caused by Puccinia graminis, has historically caused severe losses to
wheat (Triticum aestivum) production worldwide. Its control for over 30 years through
the use of genetic resistance is a remarkable success story. However, in 1998 high susceptibility
of CIMMYT germplasm was noted in Uganda, and an increase in stem rust
incidence and severity was observed in Kenya in 2003. The causal race, commonly known
as Ug99 and designated as TTKS based on the North American nomenclature, carries
virulence for several genes commonly present in wheat germplasm. All Kenyan germplasm
are susceptible or partially susceptible to Ug99. The objective of this study was to
identify new sources of resistance to stem rust race, Ug99 and replace the existing commercial
varieties with resistant ones. This was to be achieved through, i)identification
of resistant lines from various CIMMYT advanced lines during international nursery
screening, ii) observing the lines in at least two sites in non-replicated trials, iii) evaluating
superior lines in multilocational trials and iv) releasing the best lines as varieties
to farmers. Good progress has been made in identifying diverse sources of resistance
to Ug99 and its variants in international germplasm including minor genes based adult
plant resistance (APR) having reputation of durability. A high proportion of lines (44%)
showed good to moderate levels of resistance in at least two seasons of evaluation under
high disease pressure in Kenya. The main sources for resistance were postulated as Sr2,
Sr24 and Sr38 in combination. Under national multi-location trial in late 2007 and 2008.
Lines R1101, R1107, R1111, R1115, R1116, R1117 and R1120 yielded more than 2 tons
per ha compared to the best check, Njoro BW2, which yielded less than 2 tons per ha.
From the preliminary results, three lines (R1112, R1115 and R1130) were promoted to
National Performance trial (NPT) and tested at 7 diverse agro-ecological wheat growing
sites distributed over predominant wheat growing areas of Kenya. These lines out performed
the check varieties in almost all the sites. In addition, they were early maturing
and produced high quality grains. The three lines have been released as varieties for commercial
production in Kenya.
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