Environmental Factors Relating to Dormancy Breaking, Germination and Emergence of Seeds in Monochoria korsakowii Regel et Maack and M. vaginalis (Burm. f.) Kunth

Abstract

Effects of environmental factors on the germination, emergence and dormancy breaking of M. korsakowii and M. vaginalis were investigated. Seeds of the two species stored in an outdoor water tank exhibited 100% germination 60 days after the beginning of storage and showed a higher germination percentage than those stored indoors. There was no appreciable difference in the germination percentage of M. korsakowii between seeds stored in outdoor water tank, outdoor upland soil and upland soil at 5°C. However, the seeds of M. vaginalis stored in the outdoor water tank exhibited a far higher germination percentage than those stored under the two other conditions, suggesting that soil moisture is related to the maintenance of seed dormancy (Table 1).
The cardinal temperatures for the germination of seeds released from dormancy were determined by testing the germination percentage at various temperatures. The optimal temperature for germination ranged from 20 to 30°C for M. korsakowii and 25 to 35°C for M. vaginalis. There was no difference in the maximum temperature for both species, 40°C. Seeds of M. korsakowii did not germinate at 10°C, but germinated well at 15C, while those of M. vaginalis did not germinate at these low temperatures and showed only 4% germination even at 20°C (Fig. 1).
The duration of the period from sowing to emergence in the weeds sown from March to July became shorter along with the delay in the sowing time, but when the plants were sown from August to October, it increased. The duration of the period from sowing to emergence was influenced by the total effective temperature (Fig. 2).
Both M. korsakowii and M. vaginalis showed higher seed germination percentages in the light than in the dark (Fig. 3). However, the germination percentages of the former species were always higher than those of the latter species, particularly at lower temperatures. These two species exhibited a high germination percentage under flooded conditions (3 to 5cm in depth), and the germination percentage decreased as the water level decreased and was below the soil surface. Seeds of M. vaginalis were unable to germinate when the water level was maintained at -5cm (Table 2). When buried in soil under flooded conditions, the germination percentage also decreased when the depth of soil burial increased. M. korsakowii and M. vaginalis could emerge within a 3.0cm and 2.0cm depth under submerged conditions, respectively (Fig. 4). M. korsakowii required at least 23 days from flowering to produce viable seeds, while M. vaginalis required 27 days (Fig. 5).