Genetic parameters and graphical analysis of bread wheat diallel crosses under drought stress conditions

الملخص EN

The objective of the present investigation was to study the genetic system controlling heading date, maturity date number of spikes / plant, number of grains / spike, 1000-grain weight, straw and grain yield / plant in seven spring wheat genotypes (Triticum aestivum L.) under well-watered condition (irrigation every 7 days interval) and drought stress (irrigation every 13 days interval) at Ras Sudr Agricultural Experiment Station of Desert Research Center at South Sinai Governorate.

The seven parents were crossed in diallel system excluding reciprocals and evaluated with its F1,s in the two seasons 2001 / 2001 and 2002 /2003.

The estimated values of additive component (D) for most traits under the two irrigation intervals in the 1st and 2nd seasons and straw yield under severe stress condition in both seasons were significant.

Presence of dominance effects (H1 and H2) were substantiated by significant estimates of H1 for all traits recorded except heading date under the two irrigation treatments in the first season and number of spikes /plant under the two irrigation treatments in the second season.

Also, H2 estimated values which represent dominance variance adjusted for asymmetric gene distribution, were highly significant for all cases except heading date under the two irrigation intervals in both seasons, maturity date under control treatment in the first season and number of spikes / plant under the control in the 1st season and two irrigation treatments in the 2nd season, and were higher than those of D in most cases.

(H1 / D) 0.5 derivative values which measure the average degree of dominance overall loci were greater than unity for all traits recorded indicating that these traits are controlled mainly by over dominance genetic effects.

The ratio of additive genetic portion to the phenotypic variance computed as narrow sense heritability [H (n.

s.)] was relatively high for 1000-grain weight and heading date under the two water treatments in both seasons.

These results confirm that additive gene effects play major role in the genetic variation of these traits under tested conditions and that selection in early segregating generations could be effective for isolating good new recombinants suitable to the aimed environments.

Data of graphical analysis showed variation in the dominance or recessive positions for parents where Wr (covariance between the parents and their offspring in the rth array), Vr (variance of the rht array) graph showed that Sakha8 (P4) and Line-2 (P7) contained the highest frequency of recessive alleles for heading and maturity dates, grain yield / plant, number of grains / spike and straw yield / plant under the two water treatments in both seasons.