The pink stem borer (PSB) is the main and most important insect attacks
maize (Zea mays L.) in Egypt. Little is know about combining ability for antibiosis and
tolerance to this insect. Therefore, the objectives of this work were: to estimate
combining ability effects; to determine mode of gene action; to measure heterotic
effects for antibiosis traits [ percentage of resistance to infested plants (RIP %) , dead
hearts ( RDH%) ], to determine tolerance traits measured as [ yield of infested (YI),
yield of non-infested (YN) plants and estimates of percentage of yield loss (YL%) ].
And finally to find out the phenotypic and genotypic correlation among tolerance and
antibiotical traits. A half-diallel crosses of 8 inbreds were evaluated for the above traits under two
conditions, I.e. artificial infestation with PSB and non-infestation. Both additive and
non-additive types of genetic variation were operative in the genetic control of the five
studied traits. However, the non-additive genetic variance were found to represent the
major part of the total genetic variance in the inheritance of RIP%, RDH%,YI and YN
traits while, the additive genetic variance effect played an important role in the
inheritance of YL% trait. It seems that over-dominance was prevailing than partial
dominance gene action in the conditioning of all studied traits. Average heterotic
effects relative to mid-parent were 68.6, 46.8, 380.8, 318.4 and -11.8% for RIP%,
RDH%, YI, YN and YL% traits, respectively. Meanwhile, heterotic effects relative to
better-parent gave 36.7,15.1,289.0,235.9 and -36.6% for RIP%, RDH%, YI, YN and
YL% traits, respectively. The inbred lines Gem-1002, L-121 and B-73 are elite and
good combiners for resistance to PSB, yielding ability and decreased yield loss. The
single crosses SK-7266 x SK-9203 and B-73 x S K-8118 showed positive and
significant SCA effects for resistance to PCB attack and high yielding ability
simultaneously. Thus, both hybrids could be used directly by farmers in areas and/or
planting date which showed heavy attack with PSB or in future breeding programs as
a source of a new antibiotical resistant inbred lines. Phenotypic correlation between each of the two antibiosis traits and the
tolerance traits (YI and YN ) was found to be positive and highly significant. While, it
was negative and significant with YL % trait. Correlation coefficients between line p < /em>er
se and their gi effects of any of the two antibiotic traits were positive and highly
significant. Furthermore, additive genetic (GCA effects of line) linkage between YI and
each of the tow antibiosis traits was found to be significantly positive.