Contrasting adaptive responses to cope with drought stress and recovery in Cenchrus ciliaris L. and their implications for tissue lignification.

Cenchrus ciliaris L. is a widely used species for cattle feed in arid and semi-arid regions due to good forage value and known tolerance to drought conditions. Here, we provide insights to adaptive responses of two contrasting genotypes of C. ciliaris (drought-tolerant "RN51" and drought-sensitive "RN1") to face drought stress and recovery conditions and the implications for tissue lignification. Drought stress caused a reversible decrease in the leaf water relationship and damage to photosystem II, leading to an increased generation of reactive oxygen species and lipid peroxidation. Plants of RN51 exhibited a pronounced increase of antioxidant enzymatic activities. Unlike the drought-sensitive genotype, RN51 exhibited further development of lignified tissues and bulliform cells and had the greatest thickness of the adaxial epidermis. Drought stress led to the rapid activation of the expression of lignin biosynthesis pathway-related enzymes. The transcript level of the caffeoyl-CoA O-methyltransferase gene decreased in RN1, whereas cinnamoyl-CoA reductase transcripts were increased in RN51. After rewatering, the tolerant genotype recovered more rapidly than RN1. Even though the two genotypes survived when they were exposed to drought stress, RN1 showed the highest reduction in growth parameters, and this reduction was sustained during rewatering. The results indicated that the capacity to regulate lipid peroxidation and mitigate oxidative damage could be one of the mechanisms included in tolerance to drought stress. In addition, the development of foliar characteristics, like thickness of the adaxial epidermis, well-developed bulliform cells, and intensive lignified tissues, are considered anatomical adaptive strategies for drought tolerance in C. ciliaris.

Genotypic variation in response to salinity in a new sexual germplasm of Cenchrus ciliaris L.

As part of a breeding program for new salt-tolerant sexual genotypes of Cenchrus ciliaris L., here we evaluated the salt-stress response of two new sexual hybrids, obtained by controlled crosses, at seedling and germination stages. A seedling hydroponic experiment with 300 mM NaCl was performed and physiological variables and growth components were evaluated. While salt-treated sexual material did not show a decrease in productivity with respect to control plants, a differential response in some physiological characteristics was observed. Sexual hybrid 1-9-1 did not suffer oxidative damage and its proline content did not differ from that of control treatment. By contrast, sexual hybrid 1-7-11 suffered oxidative damage and accumulated proline, maintaining its growth under saline stress. At the germination stage, sexual hybrid 1-9-1 presented the highest Germination Rate Index at the maximum NaCl concentration assayed, suggesting an ecological advantage in this genotype. These new sexual resources are promising maternal parental with differential response to salt and could be incorporated in a breeding program of C. ciliaris in the search of new genotypes tolerant to salinity.