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No Evidence of Cytoplasmic Male-Sterility Systems Influencing Gas Exchange Rate of Sorghum Leaves

Dep. of Agronomy, Texas Tech Univ., Lubbock, TX 79409

^* Corresponding author.

The presence of an extranuclear genome in the chloroplast (ctDNA) suggests possible cytoplasmic inheritance of photosynthetic characteristics of leaves. Recent evidence indicated a strong maternal influence on photosynthetic rates (A) of grain sorghum [Sorghum bicolor (L.) Moench] hybrids. Since essentially all commercial grain sorghum hybrid seed production is accomplished using cytoplasmic male-sterility (CMS), we were concerned about the possible effects of CMS on photosynthetic rates of sorghum hybrids and about potential ntclear—cytoplasmic interactions. The purpose of this experiment was to evaluate the effect of different sources of CMS and potential nuclear—cytoplasmic interactions on photosynthetic rate (A) and stomatal conductance (g) of H₂O for sorghum leaves under field and greenhouse conditions. Five sources of male-sterility-inducing cytoplasm (A₁, A₂, A₃, A₄, and 9E) and a male-fertile line (B) were compared in a common nuclear background (TX398) to test the effect of source of cytoplasmic genotype on leaf gas exchange parameters. Additionally, eight commonly used sorghum lines with different nuclear backgrounds were used to determine nuclear—cytoplasmic interaction effects by comparing fertile with male-sterile counterparts. No significant differences were observed among lines with different sources of CMS in a common nuclear background (TX398) for A or g. Significant genetic variation in A and g was observed within the eight lines having different nuclear backgrounds. However, no significant differences were observed in any of the gas exchange parameters between fertile and sterile lines within each nuclear genome. The interaction of cytoplasm with genotype or environment was not significant. Results from this study suggest that the genetic expression of leaf gas exchange rates was not influenced by CMS, nor were there any differences among the sources of CMS.

Received for publication February 20, 1992.