Document Type : Original Article
Abstract
Six populations of three bread wheat (Triticum aestivum L.) crosses namely 1) Giza 168 x Sids 6, 2) ACSAD 925 x Gemmeiza 10 and 3) ACSAD 935 x Line 1 were grown during 2009/2010, 2010/2011 and 2011/2012 at the Experimental Farm, Fac. Agric., Zagazig Univ., Egypt. The six populations were evaluated in two adjacent experiments, one with 30 ppm cadmium (Cd), and the other without, to assess some breeding parameters for Cd stress tolerance, flag leaf area, leaf chlorophyll content, proline content, and grain yield/plant. Results indicated that, F1 exceeded the better parent for low Cd concentration in all crosses; flag leaf area and grain yield/plant in most studied crosses under both conditions. Positive and significant heterobeltiosis was detected for proline content in 3rd cross under control and leaf chlorophyll content in 1st and 2nd crosses under Cd stress. The lowest amount of Cd has been accumulated by Giza 168 and Sids 6 and their BC1 and Gemmeiza 10 and their BC1, which were bellow or equal the critical concentration, 0.2 mg/ kgsuggested by CAC (2010). Cd sensitivity index revealed that F2 population in 1st cross; Gemmeiza 10 and their BC2 in 2nd cross as well as ACSAD 935 and Line 1 and their F1, F2, BC1 and BC2 in 3rd cross expressed as tolerant to Cd stress. Genetic system and gene expression differed greatly from the control to Cd stress treatment in most cases. Where, scaling tests (A, B and C) provide evidence for the suitability of a simple additive - dominance genetic model for explaining the genetic system controlling flag leaf area in 1st cross; proline content in 3rd cross; Cd concentration in 2nd and 3rd crosses and leaf chlorophyll content in the three crosses under control, as well as leaf chlorophyll content in 2nd cross; proline content in 3rd cross and Cd concentration in 1st and 2nd crosses under Cd stress. Otherwise, the complex genetic model was responsible for the inheritance of proline content in 1st and 2 nd crosses and grain yield/plant in all crosses under both conditions, and flag leaf area in all crosses; leaf chlorophyll content in 1st and 3rd crosses and Cd concentration in 3rd one under Cd stress. Additive gene effect (d) was significant for leaf chlorophyll content in all crosses; Cd concentration in 2nd and 3rd crosses; flag leaf area in 1st cross and proline content in 3rd one under the control, and Cd concentration in 1st and 2nd crosses under Cd stress condition. Both additive (d), dominance (h) and their interaction types, additive × additive (i) and dominance × dominance (l) were involved in the genetics of flag leaf area and grain yield/plant in 2nd and 3rd crosses under control as well as flag leaf area in 2nd and 3rd crosses under Cd stress condition. Additive (d), dominance (h), additive x additive (i), additive x dominance (j) and dominance x dominance (l) were highly significant for proline content in 1st and 2nd crosses and grain yield/plant in all crosses under Cd stress. Additive (D) and dominance (H) genetic variances were significant for flag leaf area, leaf chlorophyll content and Cd concentration in all crosses under both conditions, and proline content under Cd stress one, with the predominant of additive component, resulting in (H/D)1/2 < 1. Dominance genetic variance played a major role in controlling grain yield/plant in all crosses, with (H/D)1/2 ›1 under both conditions. Heritability in narrow sense was high (> 50%) for flag leaf area, leaf chlorophyll content, proline content and Cd concentration in most cases and ranged from low to moderate for grain yield/plant under both conditions. Expected response from selection was high for praline content and Cd concentration, while it varied from low to moderate for the remaining characters under both conditions.
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