Iranian Journal of Seed Research

Osmotic stress is the most important of the abiotic stresses that lead to limitation of growth and yield in rapeseed. This study was conducted to examine the effect of cycocel seed priming on osmotic stress tolerance in germination and early growth stages of rapeseed, as a factorial experiment based on completely randomized design at Agriculture College of Shiraz University in 2012. The treatments included seed priming in three cycocel concentrations: 0 (without priming as control), 2.5 and 3.5 g L-1 and osmotic stress in five levels: 0 (as control), -0.3, -0.6, -0.9 and -1.2 MPa using polyethylene glycol. The results showed that osmotic stress was significantly reduced germination percentage (15.1%), germination rate (15.3%), radicle length (29.5%), plumule length (31.6%), radicle fresh weight (22.4%), plumule fresh weight (37.6%) and vigor index (39.9%). Furthermore, osmotic stress leads to increase radicle to plumule fresh weight and radicle to plumule length ratio as 6.8 and 24.3 percent, respectively. Seed priming with cycocel reduced the adverse effects of osmotic stress on measured parameters. Although, there was no positive effect on germination percentage and rate under osmotic and nonosmotic conditions for cycocel in both concentrations, but cycocel at 3.5 g L-1 appeared to have a greater positive effect than 2.5 g L-1. Considering positive impact of cycocel seed priming on the reduction adverse effects of osmotic stress further research on cycocel seed priming and osmotic stress tolerance is recommended under field conditions.

Objective: This experiment aims to evaluate relative fitness and seed germination indices of tribenuron-methyl sensitive and resistant wild mustard (Sinapis arvensis L.) biotypes under different temperature conditions and gibberellic acid concentrations.
Method: This experiment was conducted in 2023 at the laboratory of the University of Mohaghegh Ardabili. It was performed as a three-factorial arrangement in a completely randomized design (CRD) with three replications. The first factor consisted of two levels (seeds of tribenuron-methyl sensitive and resistant biotypes), the second factor included four levels of gibberellic acid concentration (500, 1000, 1500, and 2000 mg L^-1), and the third factor comprised two temperature regimes: 20/15 °C and 15/10 °C (day/night). The measured parameters included germination percentage, germination rate and uniformity, seed water uptake, and seedling vigor index.
Results: The sensitive biotype of wild mustard exhibited a higher final germination percentage, and germination uniformity. The interactions of temperature × biotype and temperature × gibberellic acid concentration were significant on seed water uptake. Furthermore, the rate of water absorption by seeds was higher under the 10/15 °C temperature regime compared to the 20/15 °C (day/night) regime. The sensitive biotype showed a 1.8-fold higher germination rate and a 38% increase in seedling vigor compared to the resistant biotype.
Conclusions: These findings not only contribute to a deeper understanding of the mechanisms underlying herbicide resistance but also demonstrate that while resistance provides a selective advantage, it may entail a physiological cost in the long term. This fitness cost can be leveraged for sustainable weed management. Specifically, farmers could potentially delay wheat sowing—provided it does not compromise wheat yield—to create suboptimal temperature conditions that suppress the germination of resistant wild mustard biotypes. Furthermore, the slower water uptake observed in the resistant biotype suggests that strategic irrigation management could be employed to further inhibit its germination. Additionally, since the germination of resistant wild mustard is slower at lower temperatures, soil temperature monitoring can be utilized to predict the optimal timing for implementing mechanical control measures or post-emergence herbicide applications.

Highlights

• A simultaneous study of the effects of temperature and gibberellic acid on the germination and growth of herbicide-sensitive and herbicide-resistant wild mustard biotypes.
• Evaluation of the fitness cost in herbicide-resistant biotypes.
• Differential effects of growth-affecting factors on the phenotype of two wild mustard biotypes.