Role of chemicals in alleviating salinity and light related seed dormancy in sub-tropical grasses

Abstract

This study is based on the assumptions that annual grasses express more complex seed dormancy than perennials, while dormancy regulating chemicals (DRCs) help in recovering seeds from dormancy. The role of six such chemicals, viz. plant hormones − Kinetin, Fusicoccin; organic osmotica − Proline, Betaine; nitrogenous compounds − Nitrate, Thiourea, in alleviating effects of salinity and light on seed germination of three subtropical grasses (perennials: Phragmites karka, Dichanthium annulatum; and annual: Eragrostis ciliaris) was hence investigated. All seeds of P. karka and D. annulatum germinated in non-saline condition while in E. ciliaris, 60% seeds germinated in absence of salts, 10% were dead and 30% were dormant. Salinity reduced germination of the test species to following levels (% of non-saline control) under highest NaCl concentration used: P. karka (30% at 500mM), D. annulatum (25% at 400mM) and E. ciliaris (10% at 125mM). The application of all DRCs alleviated conditional dormancy associated with salinity more in P. karka than D. annulatum but negligibly in the case of E. ciliaris. Absence of light inhibited seed germination of P. karka (partially) and E. ciliaris (completely) but under these conditions the application of DRCs increased germination of P. karka only. Nitrate was generally more effective than other DRCs in increasing seed germination both in salinity as well as in complete darkness. Seed germination was synergistically inhibited by salinity under dark conditions compared to their individual effects and was completely alleviated in P. karka and D. annulatum seeds by DRCs. In conclusion, the annual grass (E. ciliaris) used both innate and induced type of seed dormancy along with absolute light demand for successful seedling establishment while perennials (P. karka and D. annulatum) depended on enforced dormancy. Moreover, seed dormancy could be alleviated by DRCs in perennial grasses but not in the annual species.