Physiological responses and the expression of cellulose and lignin associated genes in Napier grass hybrids exposed to salt stress

Soil salinity can adversely affect crop quality and production. Napier grass hybrids with high cellulose and low lignin contents could be the most viable candidates for cost-effective bioethanol production. In this study, eight Napier grass hybrids with high ratios of cellulose to lignin contents were used as plant material to screen for salt tolerance. Among these, four hybrids were able to maintain chlorophyll content and leaf greenness. The crude fiber, cellulose and hemicellulose contents in the Napier Phetchaboon (NP) and Napier Yak Lampang (NL) hybrids increased under salt stress while lignin content did not change. Net photosynthetic rate and the amounts of total chlorophylls and total carotenoids of the NP hybrid were not affected by salt stress. Total fresh weight of the NL hybrid was reduced after 7 days of salt exposure while in the sensitive hybrid, this occurred after 1 day of exposure. Cellulose and lignin synthesis under salt stress is not directly correlated to cellulose (CesA2, CesA3 and CesA4) and lignin (PAL and CAD) associated genes. Of the hybrids tested under conditions of salt exposure, the NP and NL hybrids were the most salt-tolerant and most suitable for bioethanol production.