Thermoperiodism in cocklebur seed germination

Area of Science:

• Plant Physiology
• Seed Biology
• Environmental Science

Background:

• Nondormant cocklebur (Xanthium pensylvanicum Wallr.) seeds exhibit limited germination at constant temperatures below 25°C.
• Understanding factors influencing seed germination is vital for agricultural and ecological applications.

Purpose of the Study:

• To investigate the effect of diurnally alternating temperatures on the germination potential of nondormant cocklebur seeds.
• To determine the optimal temperature regimes and pretreatment conditions for maximizing cocklebur seed germination.

Main Methods:

• Seeds were exposed to diurnally alternating temperatures after varying periods of aerobic presoaking or anaerobic pretreatment.
• Germination percentages were recorded under different thermoperiodic regimes, including varying durations of high (23°C) and low (8°C) temperature phases.
• The influence of inserting high-temperature periods within the low-temperature phase was also examined.

Main Results:

• Alternating temperatures significantly increased germination potential compared to constant temperatures.
• Responsiveness to temperature fluctuations required prior aerobic or anaerobic pretreatment.
• Maximal germination was achieved with an 8-hour high-temperature (23°C) and 16-hour low-temperature (8°C) cycle.
• The duration of the low-temperature phase required for induction was dependent on the length of preceding anaerobiosis.
• Germination percentage correlated positively with the number of thermoperiodic cycles, and brief high-temperature interruptions could enhance germination.

Conclusions:

• Diurnally alternating temperatures are a critical factor for breaking germination dormancy in cocklebur seeds.
• Seed pretreatment, particularly anaerobic treatment, primes seeds for temperature-induced germination.
• The interplay between aerobic and anaerobic processes during temperature fluctuations influences germination success.