| dc.description.abstract | Striga hermonthica is a parasitic weed which compensates for its lack of an elaborate root system by invading the roots of a host plant sucking away nourishment intended for the host. The weed is a major constraint to maize production in Western Kenya, where it mostly invades small scale farms and depending on the severity, damage caused by the weed can range from 10% to
100%.The number of weeds was higher in Kibos than Alupe. After twelve weeks of growth 4410weeds had germinated in Kibos while 1771 weeds had germinated in Alupe. This can be attributed to differences in the soil parameters assessed in the two benchmark sites. Increase in soil nitrogen content is known to discourage germination of the weed since nitrogen can limit the production of a Striga germination stimulant called strigolactone and this was the case in Alupe which had
0.15% nitrogen content in the soil compared to Kibos which had 0.08% nitrogen content in the soil. The levels of organic carbon was significantly higher in Alupe compared to Kibos with Alupe having 1.36% organic carbon content in the soil when Kibos had 0.75% organic carbon content in the soil. On the other hand, the levels of phosphorus, manganese, magnesium, calcium, and zinc were significantly higher in Kibos compared Alupe. Sandy soils are known to encourage the growth of the weed while clay soils are known to discourage the growth of the weed by lowering the temperature and diluting the germination stimulant and this was the case in Alupe which had clay soils while Kibos had sandy soils.
The different cropping systems and maize varieties planted influenced the emergence of the weed. Maize intercropped with Desmodium uncinatum had the least number of the weed while maize rotated with soybeans had the highest number of the weed. WH 403 was the most susceptible maize variety to the weed having the highest number of the weed while IR OPV and IR Hybrid had the least numbers of the weed. All the fungal isolates tested against the weed caused infection and consequently death of the weed. Fusarium incarnatum had the highest infection rate of 92% while F. oxysporum had the least infection rate of 76%. To the contrary, F. oxysporum caused the highest mortality of 60% with Gibberella intricans causing the least mortality of only 36%.
Maize intercropped with Desmodium uncinatum was the best cropping system in managing the weed while IR hybrid and IR OPV were the best maize varieties in managing the weed. Nitrogen was the most important nutrient with direct effects on the weed. Fusarium oxysporum was the most aggressive fungus against the weed portraying its potential for exploitation as a biocontrol agent against the weed.
Measures recommended for the control of this weed such as the use of chemical fertilizers and herbicides are very expensive and therefore out of reach for farmers. This study aimed at testing different cropping systems and use of different maize varieties as possible options for control of the weed and evaluating fungal isolates pathogenic to the weed for their efficacy as possible biocontrol agents against the weed.
Striga hermonthica seeds were inoculated in plots of maize intercropped with Desmodium uncinatum, maize intercropped with groundnuts, pure maize and maize rotated with soybeans in CIMMYT experimental stations in Kibos (Kisumu County) and in Alupe (Busia County). The maize varieties planted were: Open pollinated maize variety coated with imazapyr herbicide (IR OPV), a hybrid variety bred from two parents coated with imazapyr herbicide (IR Hybrid), Striga resistant hybrid and a commercial maize variety susceptible to Striga (WH 403). Similar experiments were set up in Kibos and Alupe. Emerged S. hermonthica were counted in the two experimental blocks. Soil samples collected from the two blocks were analyzed for their physical chemical and biological properties and their means compared using ANOVA tests. Fungi were isolated from diseased S. hermonthica and their virulence efficacy against the weed tested in the greenhouse. | en |
