Assessment of ploidy level on stress tolerance of Cenchrus species based on leaf photosynthetic characteristics

Many species of the genus Cenchrus, with different ploidy are important components of world grasslands. In the present investigation, influence of ploidy on leaf water potential (Ψ_leaf) and photosynthetic characteristics under water-stress condition was studied in 2-month-old plants of eight Cenchrus species representing three ploidy and two life spans. Stress was imposed for 2, 4, 6, and 8 days by withholding watering. Decrease in water potential, chlorophyll content, photosynthetic rate (P _N), stomatal conductance for CO₂ (g _s), and carboxylation efficiency (P _N/C _i) occurred in all species. Nevertheless, perennial and diploid C. setigerus maintained the highest P _N/C _i at maximum stress indicating its higher assimilation potential. Photosynthetic water use efficiency (P _N/E) in general decreased with increase of water stress; however, at low stress, reverse trend was observed in diploid C. prieurri, C. setigerus, and tetraploid C. glaucus. Results indicate that relative reduction in photosynthetic characteristics was more in annual diploid than perennial diploid and tetraploid. Stress tolerance in terms of plant height, rolling and wilting of leaves also indicated better adaptability of tetra and hexaploid species over diploid. Moreover, recovery of different physiological traits was more pronounced in perennial tetraploid and hexaploid over annual diploid, thus making them suited more to drought conditions. Analysis of variance results showed direct correlation (r = 0.675) of ploidy with gas exchange parameters indicating better impact of this on physiological performance of different species of Cenchrus under water stress. This is the first report where influence of ploidy levels on photosynthetic characteristics and overall responses to moisture stress is studied in a tropical grass species.