Abstract:

To clarify the thresholds of early frost damage for sunflower organs under different sowing dates in the Hetao irrigation district, this study used 'HZ2399' (the main local sunflower cultivar in the Hetao irrigation district) as experimental material and employed an MSX−2F artificial frost simulation chamber. During 2022 and 2023, artificial frost simulation tests with six temperature gradients (2℃ intervals) were conducted on seeds, disks, stems and leaves of sunflowers at three sowing dates: May 20^th (S1), May 31^st (S2) and June 10^th (S3). The study investigated the temperature ranges of the supercooling points and freezing points of each organ and analyzed the correlation between their freezing injury rates and the low temperatures. The results showed that: (1) the supercooling points of sunflower stems and leaves at sowing date S1 were −6.93±0.25℃ and −4.80±0.93℃, respectively, which were significantly lower (P<0.05) than those at sowing date S3 (−5.48±0.20℃ and −3.68±0.66℃). Overall, the supercooling points for different sowing dates followed the order with S1<S2<S3. Within the same sowing date, the supercooling points of the organs followed the order with disk<stem<leaf. (2) The critical temperature for irreversible freezing was generally 0.74–2.51℃ higher than the supercooling point. When the minimum air temperature did not reach the supercooling point, the crop freezing injury rate continued to increase with the prolongation of freezing duration. (3) The cold resistance of sunflowers in the Hetao irrigation district was in the order S1>S2>S3 from highest to lowest. For the same sowing date, the cold resistance of sunflower organs was ranked as disk>stem>leaf from highest to lowest.

Key words: Sunflower, Supercooling point, Frost simulation test, Meteorological disaster, Cold resistance