Salt Effects on Germination, Emergence, and Seedling Mortality of Onion

Abstract

Good stands of furrow irrigated onion (Allium cepa L.) are difficult to obtain in saline areas of the Southwest. This study examined salt effects on seed germination, emergence, and seedling mortality of five onion cultivars in a series of greenhouse experiments at diurnal temperatures of 15 to 25 °C. Germination exceeded 80% within 10 d at solution salinity of 20 dS m−1 or less. Cultivar effects on germination appeared initially, but diminished after approximately 1 wk. Seedling emergence from potted and subirrigated loamy sand declined significantly when salinity of irrigation water exceeded 4.9 dS m−1. This decline was apparently caused by hypocotyl mortality when the cotyledon came into contact with the salts accumulated at the soil surface, but not by reduced seed germination. Soluble salts accumulated mostly within the top 5 mm of the soil and the accumulation below 5 mm was minimal. The removal of the salted surface layer improved seedling emergence. Leaching of the surface‐accumulated salts into the seedling root zone 3 wk after seeding resulted in seedling mortality of significant magnitude; 12 and 20% in seedlings previously subirrigated with solutions of 2.8 and 4.9 dS m−1, respectively. A significant increase in seedling mortality was also observed when seedlings were sprayed twice after emergence with saline solutions of 28 and 39 dS m−1. The ability of cotyledons and seedlings to tolerate salinity, rather than the ability of seed to germinate in highly saline solutions, may be a limiting factor for obtaining good stands in furrow‐irrigated onion in saline areas.

Salinity and specific ion effects on onion establishment in relation to disposal of desalting concentrates

“…5). This fi nding is in agreement with the work of Wannamaker and Piker [8], reporting a signifi cant reduction in seedling growth when grown with 2.0 dS m -1 of a NaCl solution in hydroponic culture. The current fi nding is also in agreement with an earlier work of Bernstein and Ayers [2], indicating a signifi cant reduction in bulb weight at soil salinity as low (EC e ) of as 1.2 dS m -1 in the saturation extract.…”

“…High soil salinity is known to reduce seed germination and/ or increase hypocotyl damage [20]. A previous study with 'BR-1' has shown that seed germination is significantly reduced when salinity of the incubating solution approaches 20 dS m -1 , but it does eventually germinate even at 30 dS m -1 [8]. Since salinity of the surface 1 cm of Harkey 3 and the loamy sand was 6 and 11 dS m -1 (or 12 and 22 dS m -1 in soil solution) respectively, the seed placed at 0.5 cm deep might have germinated without diffi culty.…”

“…1, the soil salinity at the seeding depth of 0.5 cm seemed to have been in the range of 16 to 18 dS m¯1 in the saturation extract (30 and 35 dS m¯1 in the soil solution). This range of soil salinity is high enough to reduce both seed germination and hypocotyl development [8]. When the second seeding method was used, the seed was placed at 2.5 cm below the soil surface where soil salinity was probably less than 5 dS m -1 in the Downloaded by [University of Lethbridge] at 07:46 12 June 2016 saturation extract (Fig.…”

“…Likewise to many other vegetable crops, seedling emergence and growth of onions can be reduced as soluble salts accumulate in crop bed. According to a greenhouse study, onion seed can germinate in saline solutions with an electrical conductivity (EC) as high as 27 dS m -1 , but seedling emergence under subirrigation can be reduced at irrigation water EC of 4.9 dS m -1 in loamy sand initially free of salts [8]. The use of sprinklers can reduce salt accumulation in crop beds, but soil surface crusting can impair seedling emergence of onions which have hooked hypocotyl.…”

Effects of salinity stress on seed germination and seedling growth of tomato

“…Exposure of tomato seeds to high salt concentration did not only inhibit germination but also decreased germination rate. The delay in germination in the higher salinity level had been also reported in tomato (Miyamoto, 1989), jojoba (Kayani et al, 1990) and sugar beet (Ghoulam et al, 2002). Sharma et al (2005) reported that salinity levels below 4 dSm -1 resulted in a delay of 1-2 days in rice.…”