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Introgression
of resistance to Striga
hermonthica and Striga
asiatica from wild relatives and selections in maize (Zea
mays L.)
J.G. Gethi
The
genetic study of three population sets derived from Zea
mays L. x Zea diploperennis
L. (3 inbred lines), TZL Comp population (3 inbred lines) and low
stimulant producing pool (3 inbred lines) showing resistance to Striga
hermonthica and Striga
asiatica in Kenya was done to determine the gene action of the
resistance gene(s). These lines were crossed in a diallel design to
introgress these genes into seven locally-adapted lines, coded as MUG-1,
2, 3 and 4 (from KARI) and KEN-1, 2 and 3 (from CIMMYT). Two hundred and
twenty single-cross hybrids were evaluated in three locations in the
first season and 199 in the second season in S.
asiatica and S. hermonthica endemic areas of Coast Province and western Kenya.
Data collected included Striga
emergence at 6, 9 and 12 weeks, Striga
complex rating and yield depression. Other traits included germination
stimulant production, Striga vigor
rating and plant response to Striga
were recorded. Data from the first season indicate there was a large
variation in Striga emergence
in locally adapted and resistant/tolerant materials for both species.
The reaction of single cross hybrids to infestation was also varied.
Crosses involving some locally adapted and exotic inbred lines did not
show any firing symptoms indicating potential of identifying possible
hybrids. Some crosses however supported high Striga
plant population but showed little stress (tolerant). Hybrid vigor was
noted in locally adapted materials that could be used in other areas
without Striga infestation.
Some of the single cross hybrids yielded better than local commercial
and resistant checks by up to three times. Materials introduced from
West Africa were very sensitive to leaf diseases such as turcicum blight
and were later than locally adapted materials. Striga
supported by different crosses had varying degrees of vigor (number
of branches and height) with the local checks and locally adapted lines
showing the most vigor. The preliminary data indicate it is possible to
introgress the resistance/tolerance genes into locally adapted
genotypes. The combining ability information generated will be important
in determining how the resistant sources can be best utilized in the
development of resistant maize varieties. Data analysis is going on and
will be reported in due course.
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