Physiologic and Molecular Basis of Dry Land Adaptability in Echinochloa Species

Abstract

Echinochloa species is distributed around the world and regarded as one of the most problematic weeds because of its high competitiveness against crop and ecological adaptability. In Korea, two Echinochloa species, E. oryzicola (2n=4X) and E. crus-galli (2n=6X), are known to inhabit crop lands. Interestingly, each Echinochloa species inhabits a different habitat: E. oryzicola inhabits flooded paddy fields, while E. crus-galli mainly inhabits upland area, particularly E. crus-galli var. praticola. It is assumed that the different habitats of the two Echinochloa species may be related to the difference in their adaptability to osmotic stress. Therefore, this study was conducted to investigate the adaptability of Echinochloa species, such as E. colona, E. crus-galli, E. oryzicola and E. oryzoides collected from different habitats, to osmotic stress induced by polyethylene glycol (PEG) and NaCl, which were used to mimic osmotic stress conditions. Plant response to each osmotic stress was investigated at various growth stages of the Echinochloa species including germination (petri-dish assay), seedling emergence (growth pouch assay), and early juvenile plant growth (pot assay). In this study, seed germination test revealed that E. colona was the most tolerant to osmotic stress, maintaining high germination rate even at high PEG and NaCl concentration, while E. oryzicola (USA) was the most sensitive. Seedling emergence test revealed that E. colona and E. crus-galli var. praticola (only PEG) had higher root/shoot (R/S) ratio than E. oryzicola and E. oryzoides, in high PEG and NaCl concentration, suggesting that greater R/S ratio of Echinochloa is related to its adaptation to dry upland condition. Juvenile plant growth test revealed that the tolerant species maintained their growth ability and plant homeostasis in osmotic stress conditions. For instance, fresh weight, plant temperature and chlorophyll fluorescence of the most sensitive species, E. oryzoides changed much more than those of the most tolerant species, E. colona. At the molecular level, tolerant species and sensitive species showed difference in the expression profiles of genes related to drought tolerance mechanism such as enzymes included in ABA synthesis pathway and salt overly sensitive (SOS) pathway. In conclusion, our results demonstrate that the different adaptability of Echinochloa to osmotic stress enables Echinochloa species widely distribute at various crop lands with different water regimes.