| dc.description.abstract | The maj or obj ecti ves of this study were to determine
genetic variability for parameters of resistance to
Partellus and other desired agronomic traits, construct and
test appropriate selection procedures, and estimate
heritabilities, predict both direct and correlated responses
to selection. The study involved a white grained parental
population named ICZ3 from which 163 S2 lines and 150 ~
testcrosses were obtained and evaluated according to the study
objectives so far stated.
Genetic variability and predicted responses to S2 and S2
testcross selection methods were studied in the ICZ3
population. Evaluation of progress after one cycle of
selection for grain yield, parameters of resistance to ~hilo
partellus and agronomic traits were investigated.
The results of determining the genetic variability for
each of the three parameters of resistance (leaf feeding, dead
heart and stem tunnelling) and grain yield in each progeny
type revealed high levels of variability for effective
selection to be practised. Using a 9 - point rating scale for
leaf feeding, populations derived from S2 and testcross
progenies s'howed a difference of 5.00-6.33 and 5.00- 6.17,
3.14%-3.29% and 2.56%-3.14% for dectd heart, 27.97%-28.52% and
19.46%-23.92% for stem tunnelling and 5.65-11.10 and 7.85-8.60
t/ha for grain yield for S2 and testcross progenies,
respectively. After one cycle of selection the S2 and
testcross progenies exhibited a reduction In leaf damage
rating of 0.01-0.11 and 0.05-0.08 per cycle corresponding to
a decrease of 0.40%-4.38% and 1.99%-3.19% per cycle relative
to the source population (Co) respectively. Stem tunnel length
decreased by 0.15%- 1.81 % per cycle in S2 progenies and
0.13%-1.76% per cycle in the test cross hybrids corresponding
to 1.15% - 13.92% and 1.00% - 13.54% per cycle relative to Co.
Grain yield increased by 5.29% to 24.23% per cycle and plant
height by 4% per cycle of selection.
Genetic variances and heritability estimates were
moderate to high for the S2 progenies with the heritability
estimates being higher for the agronomic traits compared to
the resistance parameters.
Predicted direct response for grain yield, parameters of
resistance and rank summation index were generally higher in
the S2 selections as opposed to the test crosses. Generally
more gain/cycle of selection was achieved through single trait
selections than by index selection.
Predicted correlated response in grain yield assuming
selection was done for the parameters of resistance were
smaller than predicted direct responses to selection for grain
yield.
In all cases, there was poor correspondence between
predicted and observed gains to selection.
A breeding procedure involving recurrent selection for
parameters of resistance (leaf feeding, dead heart and stem
tunnelling) and selection indices should aid in combining C.
Partellus resistance with desirable agronomic traits. | en |
