Investigating the germination response of two Echinochloa species to temperature and photoperiod with emphasis on invasiveness

This experiment، conducted to examine the effects of temperature and photoperiod on seed germination of watergrass (Echinochlo aoryzoides) as a new-introduced and barnyardgrass (E. crus-galli) as a common weed species in rice fields of Guilan province. This study was consisted of two separate experiments. At the first study، germination responses of two species to different temperatures (10، 15، 20، 25، 30، 35، 40 and 45°C) were evaluated and the cardinal temperatures were estimated. For the second study، the photoperiod effects (0/24، 4/20، 8/16، 10/14، 12/12، 14/10، 16/8، 20/4، and 24/0 hours light/dark) under two constant temperatures of 25 and 30 °C were intended. The results indicated that، for the both species، the highest final germination، maximum germination rate، and nil germination were observed in 25 to 30، 30 and 40 °C، respectively. At low temperatures، greater germination was recorded for barnyardgrass compared to watergrass. The minimum، optimum and maximum germination temperatures were 9. 6، 31، and 45. 5°C for barnyardgrass، and 10. 5، 31. 4، and 45. 6°C for watergrass، respectively. Despite the occurrence of some germination in complete darkness، increased light exposure promoted the germination. Short photoperiods promoted germination more in barnyardgrass rather than watergrass. Increasing temperature from 25 to 30°C، caused partial reduction in light requirement for germination، especially in barnyardgrass. Overall، it seems that the new-introduced species compared with the common species needs higher temperatures and is more tolerant to different photoperiods for germination. These characteristics can be enumerated as competitive advantages for this species، especially under the early season higher mean temperature scenarios.