KENYA AGRICULTURAL RESEARCH INSTITUTE
National Plant Breeding Research Center, P.O. Njoro, Kenya.
Evaluation of resistance of selected wheat cultivars to three isolates of Septoria tritici under field conditions.
P.F.Arama, J.E. Parlevliet, and C.H. Van Silfhout.
A field experiment in Wageningen, the Netherlands, evaluated the resistance in some wheat cultivars to three isolates of S. tritici collected from different locations in the Netherlands. The isolate IPO290 was virulent to all the cultivars with the exception of Clement and Milan. Clear 'isolate x cultivar' interactions were shown especially involving the less virulent isolates IPO001 and IPO323. Although the 'cultivar x isolate' interaction variance was highly significant, the variances due to main effects of cultivars and isolates were far greater.
Selection from the SAWYT for dryland variety development in Kenya.
M.G. Kinyua, H. Wanga, O. Abdalla, and J.K. Wanjama.
Breeding crops for tolerance to drought is increasingly important in Kenya, given the need to improve national food security by expansion of crop production into more marginal areas of the country. The 3rd Semi-Arid Wheat Yield Trial (3rd SAWYT) was planted at Katumani, in southern Kenya, in 1997. The trial consisted of 40 entries, with two replicates, planted in an alpha-lattice experimental design. Twelve selections, based on yield performance, were advanced to the Kenyan Preliminary Dryland Wheat Performance Trial. This trial was planted in a three replicate, random complete block at Katumani and Narkok. The commercial cultivars Duma, Pasa, and Kenya Chiriku were used as controls. Analysis of variance indicated significant differences for yield only at Narok. The preliminary data indicate that it may be possibile select elite wheat material from the SAWYT for release as commercial varieties for dryland areas of Kenya.
Response of commercial varieties to seed-dressing aphicides for preventing Russian wheat aphid damage in Kenya.
M. Macharia, P.M. Muthangya, and J.K. Wanjama.
Yield trials evaluated the effectiveness of seed-dressing aphicides at planting for control of RWA. Eleven Kenyan wheat varieties were tested. Four treatments were evaluated: Gaucho 350FS (imidacloprid) seed treatment, Carbofuran 350ST (furadan) seed treatment, a single foliar application of Brigade (bifenthrin), and an untreated check. Evaluation tests in two locations for 2 years demonstrated that RWA can be substantially avoided using seed treatment insecticides. Average increases in grain yield for the 11 varieties at Njoro for the Gaucho 350FS, Carbofuran 350ST, and Brigade treatments were 158.9 %, 127.9 %, and 113.6 %, respectively, compared with the untreated check. At Mau Narok, average yield gain was 175.2 %, 146.9 %, and 123.1 % for Gaucho 350FS, Carbofuran 350ST and Brigade treatments, respectively, compared with the untreated check. In conclusion, insecticide seed-dressings are effective in control of RWA in Kenya, and such treatments can prevent heavy production losses. Foliar spray treatment with Brigade was ineffective because of incomplete protection of the crop.
Bread wheat variety development by selection for complete resistance to yellow rust.
F. Kiriswa, D.L. Daniel, and F.M. Kirigwi.
Of the 11,000 bread wheat introductions screened in Kenya between 1984 to 1986, six genotypes were selected with with good agronomic performance and stable resistance to leaf, stem, and yellow rusts. These selections were crossed with three Kenyan commercial cultivars in a half diallel. Selection for near complete or complete resistance to yellow rust and good agronomic performance was performed at each generation of advancement. Twenty-one F7 genotypes representing 10 crosses were ultimately selected. These were entered into preliminary yield trials in 1992 and 1993. Seven entries were advanced to the National Performance Trials in 1994, 1995, and 1996. The genotypes K.7635, K.7638, and K.7642 are now being considered for release.
Occurrence of entomopathogenic fungi and aphilinid parasitoids infecting cereal aphids in Kenya.
J.K. Wanjama and P.F. Arama.
Entomopathogenic fungi were found infecting the rose grain aphid, Metopolophium dirhodum, on wheat grown at the National Plant Breeding Research Center, Njoro in 1997. The fungi were identified as Pandora neoaphidis (Remaudiere and Hennebert) Humber and Entomophthora planchoniana Cornu at the Small Grain Research Institute, South Africa. Three wheat- and barley-growing regions in Kenya were surveyed for aphid cadavers and mummies for isolation and characterization of entomopathogenic fungi. At Njoro and Timau, we evaluated the percent of aphids naturally infected by entomopathogenic fungi on a commercial cereal crop. The percentages of aphid mortality were between 5.6-9.7 % in Timau and 25.6-44.4 % in Njoro. In addition, samples of bird cherry oat aphid mummies collected from barley grown in a greenhouse at Njoro were sent to the Plant Protection Research Institute, South Africa. The pupae that emerged were of a hyperparasitoid, Aphidencertus africanus. This hyperparasitoid can cause up to 100 % mortality on R. padi in the greenhouse.
Seedborne fungal pathogens of wheat in Kenya.
Ruth Wanyera.
Seventy-eight seed samples of wheat from the National Plant
Breeding Research Centre-Njoro and farmers fields were analyzed
for health status in the laboratory. The study showed that the
seeds, abnormal seedlings and un germinated (dead) seeds had fungal
infections of (in decending order of importance) Phoma spp.,
Bipolaris spp., Fusarium spp., Micrododium oryzae,
Alternaria spp., Nigrospora spp., Acremonium
spp., and S. nodorum. Seed treatment with Raxil 025 OFS
(Tebconazole) showed no significant difference in germination
between the treated and untreated seed samples, but reduction
of most of the pathogens occurred in both abnormal seedlings and
ungerminated seeds. Seed treatment with Raxil 025FS reduced the
disease infection but did not improve germination. This study
assesses the impact of these diseases as seedborne pathogens for
wheat production in Kenya.
Bipolaris spp., Fusarium spp., Micrododium
oryzae, Alternaria spp., Nigrospora spp., Acremonium
spp., and S. nodorum. Seed treatment with Raxil 025
OFS (Tebconazole) showed no significant difference in germination
between the treated and untreated seed samples, but reduction
of most of the pathogens occurred in both abnormal seedlings and
ungerminated seeds. Seed treatment with Raxil 025FS reduced the
disease infection but did not improve germination. This study
assesses the impact of these diseases as seedborne pathogens for
wheat production in Kenya.