Generation Mean Analysis of Gene Action for Photosystem II Fluorescence Parameters in Two Bread Wheat Crosses

Chlorophyll fluorescence parameters are sensitive indicators of photosystem II (PSII) functionality and overall photosynthetic performance; however, their genetic architecture in wheat remains poorly understood. This study aimed to elucidate the gene action governing chlorophyll fluorescence traits in two bread wheat (Triticum aestivum L.) crosses: N-92-9 × Ehsan and Kohdasht × Ehsan. Six generations (P1, P2, F1, F2, BC1, and BC2) were evaluated under a randomized complete block design (RCBD) with three replications. Sixteen OJIP-based fluorescence parameters were recorded, including Fo, Fm, Fv, Fv/Fm, ABS/RC, TRo/RC, ETo/RC, REo/RC, φ(Po), ψ(Eo), ABS/CSo, DIo/CSo, TRo/CSo, ETo/CSo, ABS/CSm, and DIo/CSm. Significant generation effects were detected for 14 of the 16 parameters in N-92-9 × Ehsan and for 12 parameters in Kohdasht × Ehsan. These statistical patterns and the subsequent generation mean analyses indicated cross- and trait-dependent contributions of additive, dominance, and epistatic effects. The ratio |F|/√(D×H) was less than unity for the majority of traits in both crosses, indicating an asymmetrical distribution of dominant and recessive alleles between the parents and confirming the importance of dominance in controlling these traits. Broad-sense heritability ranged from moderate to high, reaching 0.991 for Fv/Fm in N-92-9 × Ehsan and 0.697 for ABS/CSm in Kohdasht × Ehsan. Dominance gene effects were predominant for most traits in both crosses, suggesting that hybrid breeding strategies would be more effective for improving these traits. An exception was TRo/CSo in Kohdasht × Ehsan, where additive effects were more prominent, making it amenable to improvement through selection-based methods. These findings provide a cross-specific quantitative-genetic assessment of gene action for PSII fluorescence parameters and illustrate the potential value of combining generation mean analysis with marker-based approaches when integrating photosynthetic efficiency into wheat breeding programs.