COMBINING ABiLITY OF RESISTANCE TO LATE WILT DISEASE AND GRAIN YIELD AND THEIR RELATIONSHIPES UNDER ARTIFiCiAL AND NATURAL INFECTIONS IN MAIZE

Late wilt (Cephalosporium maydis) is one of the most serious diseases of
ma’ze in egypt. It causes a noticeable reduction ¡n plant yield. A half dtaIle crosses
mating design among eight yellow inbred lines of maize were used in 2002 growing
season. The eight parental inbred lines and their 28F1’s were evaluated in two trials at
Sakha Agricultural Research Station. . ne first oe was conducted ¡n season 2003
under natural infection, while, the second trial was performed during two growing
season 2003 and 2004 ¡n a disease nursery under artifìcia infection, The genetic
an&ysis of crosses was done according to Griffing (1956) method 4, model 1.
Mean squares of general combining abi’ity (GCA) were significant for all
studied traits under artificial and natural infections. While, the mean squares due to
specific combining abilty (SCA) were significant for resistance to late wilt disease,
drain yield? p’ant and ear length under artificial infection but for grain yield/plant only
under natural infection. The ratios between GCA and SCA mean squares exceeded
the unity for al studied traits. These results indicate that the additive gene effects
payed a major role than the non additive gene effects in the inheritance of all studied
traits under artíflcial and natural infections.
The parental inbred line Sk9203 considered as a good combiner for percentage
of resistance to late wilt disease, grain yield? p’ant, ear length and number of kern&s/
row under aiifìcial infection and grain yield? plant under natural infection. While,
inbred hne LI 21 showed significant desirable GCA effects for grain yield/p’ant and ear
length under artificial infecon and percentage of resistance to late wilt disease and
grain yeId/ plant under nawra infection. In the same time SC Sk7266 x Sk9203
exhibited highiy signifìc€ìnt and desirable SCA effects for grain yield? plant under
artificia’ and natural infections.
Mean , over all the crosses, was higher compared to per se mean over all the
inbred lines for percentage of resistance to late wilt disease and grain yield? plant
under artificial and natural infections. Also, mean over ail the inbred lines and mean
over all the crosses were reduction under artificial infection compared to its under
natural infection for resistance to late wilt disease ar.d grain yield? plant.
The correlation coefficient (r) , between perse means of the inbred lines and
those of their averages from 7F1’s to other 7 inbred lines was significant for
percentage of resistance o late wilt disease under artificial and natural infections,
indicating that resistance to late wilt disease was transmitted from inbreds to hybrids.
Correlation coefficient between percentage of resistance to late wilt dtsease under
artificial and natural infections was insignificant. While, highly significant and positive
correlation coefficient was observed between grain yield? plant under artificial and
natural infections with late wilt disease. Therefore, grain yield? plant under artificial
infection with late wilt disease could be used as an estimation of grain yield? plant
under natural infection.