Photosynthesis, Leaf Anatomy, and Morphology of Progeny from Hybrids between C3 and C3/C4Panicum Species

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Abstract
Species in the Laxa group of Panicum have C3 or C3/C4 photosynthesis based on leaf anatomical and CO2 exchange characteristics. Hybrids were previously made between C3/C4 and C3 species in this group (RH Brown et al. 1985 Plant Physiol 77: 653-658). In this paper, CO2 exchange, morphological, and leaf anatomical characteristics of F2 or F5 progeny from colchicine-induced amphiploids of C3/C4 .times. C3 hybrids (Panicum milioides Nees ex Trin. [C3/C4] .times. Panicum laxum Mez [C3] and Panicum spathellosum Doell [C3/C4] .times. Panicum boliviense Hack. [C3]) were studied. There were no differences found in morphology or physiology between the amphiploids and the F1 hybrids from which they were produced. In the segregating progeny, CO2 compensation concentration and photorespiration values typical of C3, but not of C3/C4 plants, were recovered. Progeny were found from both crosses which possessed O2 inhibition of apparent photosynthesis typical of the parents, and in the case of the P. milioides .times. P. laxum cross, leaf anatomy and overall plant morphology typical of the parents were observed in some progeny. The progeny were found to possess recombinations of various traits associated with reduced photorespiration, so that no correlation existed among O2 inhibition of apparent photosynthesis, CO2 compensation concentration, and leaf anatomical traits. One plant was especially noteworthy in possessing leaf anatomy typical of C3/C4 plants, but with CO2 exchange characteristics of C3 plants.