Influence of environmental factors on seed germination and emergence of Iresine diffusa

Iresine diffusa has become more abundant under no-till soyabean in Argentina. The influence of temperature, light, cold-wet storage, osmotic potential, dry storage and depth of seed burial on germination and emergence of I.diffusa was examined in a growth chamber experiment. Iresine diffusa seeds germinated at the highest proportion (>0.80) in all fluctuating day/night temperatures tested. Conversely, under a constant temperature regime, maximum germination rates occurred at 15 (0.78) and 20 degrees C (0.82), and minimum germination rates occurred at 10 (0.19) and 30 degrees C (0.36). Seed germination was not influenced by light exposure. However, germination decreased after 12 (0.76) and 16 (0.65) weeks in cold-wet storage. To reduce germination significantly, -0.4MPa of osmotic potential (induced by PEG-6000) or 120mmolL(-1) of salt (NaCl) concentration was required. Seeds of I.diffusa showed high viability (0.85) after 720days of dry storage. Low emergence was recorded for seeds buried at 2cm, and seedling emergence was completely inhibited when seeds were buried at 5 and 10cm. Iresine diffusa seeds had high viability and were capable of emerging in a broad range of environmental conditions. The thermal germination conditions, shallow soil depths and high moisture conditions in germination phase for I.diffusa are congruent with the conditions in Argentina no-tillage soyabean. Thus, no-tillage could provide better conditions for germination than conventional tillage systems. However, due to the fact that I.diffusa can reproduce by rhizomes, further research should be conducted to understand the relative importance of the vegetative reproductive strategy in relation to the presence and persistence of this weed in fields.