الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The present study was undettaken in an attempt to; identifY the more simplest and useful criteria for screening genotypes for drought tolerance under field conditions, find out plant attributes for selecting cultivars suited for drought conditions in order to reach a better judgment on the validity of using these traits in breading for drought tolerance in maize crop, and identifY’ the parental-lines with good general combining ability and high specific combinations which express high heterotic effects that would be of great impmtance to hybrid production for drought stress under field conditions.
The experimental work was canied out at TI1e Faculty of Ag1iculture, Ai:n Shams University, Fanus at Shoubra El-Kheinla and Shalakan, Kalnobia Gavernorate, Egypt during four successive growing seasons lasted in 1994 using half diallel. Crosses among I 0 maize inbred
lines
Our results demonstrate that a genotypes with a short grain filliug pe1iod, high number of leaves, long ear leaf and roots, high number of rows/ear and heavy grains will be more desirable for this conditions while the genotype with a short grain filliug period and maturity period, taller plants, thick ears, heavy stalks, high number ofleaves, rolled leaves and light grains will be more tolerant and suitable for drought conditions. Genotypes that are; early in tasseling with high number ofleaves /,plant, long ear leaf, high ear position, low number of grain rows and, high number of grains I row could be more suitable for normal and I or drought· conditions,
Mean squares due to genotypes for all accepted characters under nmmal and/or drought conditions were highly significant and large
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m gnitude suggesting, the existence of large genetic variation wb..ich resulted fiotn the crossing among parents with wide divergent ecogeogrophic origins. Mean values and heterosis for all selected characters wtder normal condition revealed that the best crosses were cross 42 for filling period, cross 2 for total number ofleaves/plant, cross
28 for leaf length, cross 45 for leaf angle and root length, cross 7 for number of rows/ear, cross 5 for seed index, crosses 2, I I and 14 for grain yield/plant. llte results for mean·perfonnance and heterosis wtder. drought conditions indicated that the best crosses for the accepted characters were
I 6, 17 and 50 for maturity date, 39 for filling period, 33 for number of leaves/plant, crosses 6 and 32 for leaf rolling, 27 for plant height, 15 for ear circumference, I 0 for seed index ’and stalk weight and I I for grain yield/plant.
Mean squares due to inigation conditions were highly significant for all accepted characters except ear leaflength and number of rows/ear. TI1e significance ofinigation indicates that the crosses perfotmance varied li”om normal to drought conditions. Also, mean square of genotypes by irrigation conditions interaction was h.ighly significant and it seems that these traits are greatly influenced by inigation conditions.
Pattitioning genetic variance into general (GCA) and specific (SCA) combining ability variance Wider normal and/or drought conditions indicated that both GCA and SCA mean squares were h.ighly significant under all conditions suggesting that both additive and non-additive genetic effects were involved in the inheritance of all characters. However, SCA/ GCA ratio revealed that the magnitude of SCA variance was greater than that of SCA variance for all traits. Highly significant interactions between inigation treatments and both types of combining ability effects. were detected for all characters. The magnitude of the interactions for GCA by inigation were generally h.igher than those for SCA for all traits. This finding indicated that additive and additive by additive types of gene action
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appeared to be more affected by irrigation treatments than non-additive genetic type.
Narrow sense heritability for accepted characters w1der nmmal conditions showed high value for filling period, moderate values for total number ofleaves/plant, ear leaflength, ear leaf angle, number of rows/ear and seed index, and low value for total roots length. While narrow sense he1itability for accepted characters ooder drought conditions showed high
values for days to matwity and filling period, moderate values for total number of leaves/plant, leaf rolling, ear circumference, seed index and’
stalk weight, and low value for plant height.
It is generally concluded that;
1-In breeding program designed to develop germplasm for abiotic stress, careful consideration should . be given to select material ooder the environment for which the product is intended. With reference to moisture stress, it has been suggested that direct selection in a moisture deficit environment should be most useful.
2- It would be recommended that additional experiments are required to study the genetic behavior of maize tolerance to drought and its effect on both various.stages and different organs of maize piant.
3- Estimates of genetic behavior are influenced by the amooot of genotypic variance present for a trait in the population being studied. Thus the number and genetic diversity of parents used to from a population will have a direct bearing on the amount of genetic va1iation present. A population derived from crosses between many divergent parents is expected to express more genetic variance than a population derived fi·om a few related parents.