Hairy fleabane germination in response to temperature, osmotic potential, pH, salinity levels, and seed dormancy periods

Abstract

Hairy fleabane (Erigeron bonariensis L. Cronq.) is an invasive weed in lowdisturbance annual, perennial, and noncrop systems in the San Joaquin Valley (SJV), California. It is often observed emerging year-round in diverse environmental conditions in the SJV. However, very little information is available on the reasons for this. The study aimed to assess the effect of temperature, water potential, salinity, pH level, and dormancy periods on hairy fleabane's germination. Tests were conducted at different day/night temperatures (5:0, 10:5, 15:10, 20:15, 25:20, and 30:25 ˚C), water potential (0 to -5.56 MPa), salinity (0-25 dS m -1 ), and pH (5-9). Germination tests were also performed on seeds the day they were collected from mature plants, and 7, 14, and 21 d later. Tests were conducted in growth chambers set to 20 ˚C or under ambient laboratory conditions at 22 ˚C. About 1% of the seeds germinated at 5 ˚C but maximum germination occurred at 25:20 ˚C. About 9% of the seeds germinated at -0.51 MPa and the estimated value for 50% germination reduction was -0.2 MPa. Seed germination had high tolerance to salinity, as 42% of the seeds germinated at 15 dS m -1 . Germination did not differ across pH levels. About 50% of the seeds germinated the day they were collected, indicating that this species had a very short seed dormancy requirement. These findings could explain why hairy fleabane is observed emerging year-round in the SJV, particularly in irrigated cropping systems. INTRODUCTIONHairy fleabane (Erigeron bonariensis L. Cronq.) is considered to be a native plant of the more temperate parts of South America (Michael, 1977). In the United States, it is now a common annual weed in cropped and noncropped areas of California (Shrestha et al., 2016), and other west coast and southern states (USDA-NRCS, 2021). Thébaud and Abbott (1995) considered this species as a summer annual weed, and it is classified as a summer annual weed in California