Assessing the Photosynthetic System Responses of Saffron Plant (Crocus sativus L.) to the Application of Haloxyfop R-methyl Herbicide with and without Adjuvants

Introduction: Saffron (Crocus sativus L.) is an important crop in Iran but is highly vulnerable to weeds due to its weak vegetative growth. Both annual and perennial weeds, are known as problematic weed in saffron fields. The primary weed control method in saffron fields is hand weeding, supplemented by other approaches, including chemical methods, due to the labor-intensive, costly, and time-consuming nature of manual weeding. The addition of adjuvants to herbicides can improve their efficiency in a cost-effective and environmentally sustainable approach. Haloxyfop-R-methyl, an ACCase inhibitor, effectively suppresses grass weed growth. Recent studies have indicated that incorporating adjuvants can enhance the performance of grass-selective herbicides that inhibit acetyl-CoA carboxylase. However, limited research has investigated the efficacy of herbicides combined with adjuvants in saffron cultivation. Previous findings have shown that ACCase inhibitors can reduce photosynthetic activity. Therefore, this study was conducted to assess the response of the saffron photosynthetic system to haloxyfop-R-methyl application, both with and without adjuvants.
 
Materials and Methods: A field experiment was conducted in a four-year-old saffron field in Sarayan (2023) to evaluate how different concentrations of haloxyfop-R-methyl affect saffron’s photosynthetic system. The factorial experiment, arranged in a randomized complete block design, tested four herbicide rates (0, 54, 81, 108 g ai ha⁻¹) and three adjuvants (none, Sitogate oil, and corn oil at 0.5% v/v). Chlorophyll fluorescence was measured 2, 4, 6, 8, and 10 days after herbicide application. Visual injury of saffron leaves was evaluated 7, 10, 13, 16, 19, 22, and 25 days after application. Chlorophyll a, chlorophyll b, and carotenoid contents were determined 25 days after treatment. Data were statistically analyzed using SAS software version 9.4, and mean comparisons were performed using the FLSD test at the 5% significance level. Graphs were prepared using Microsoft Excel.
Results and Discussion: The experimental results indicated that the concentration of haloxyfop-R-methyl herbicide, the type of adjuvant, and their interaction had no significant effect on chlorophyll fluorescence. Among the combined treatments, a significant difference was observed only on the tenth day after application at the 5% significance level. The absence of significant effects from the herbicide treatments suggests that saffron (Crocus sativus L.) possesses high tolerance to haloxyfop-R-methyl. This observation is consistent with the herbicide’s mode of action as an acetyl-CoA carboxylase (ACCase) inhibitor, which primarily targets grassy weeds without directly interfering with photosynthesis. Similar results were reported by Abbaspoor and Streibig (2005), who found that ACCase inhibitors such as clodinafop-propargyl caused minimal and delayed impacts on quantum efficiency in barley and oat. Therefore, haloxyfop-R-methyl can be considered physiologically safe for saffron under the tested conditions. Visual assessments showed no visible injury or only minor damage to saffron leaves at 7, 10, 13, 16, 19, 22, and 25 days after herbicide application, with differences remaining statistically insignificant. These findings confirm that haloxyfop-R-methyl is safe for use in saffron and that the inclusion of adjuvants such as corn oil or Sitogate does not alter the crop’s tolerance. The results are consistent with those of Dear et al. (2003), who emphasized the reliability of visual injury assessments for evaluating herbicide selectivity. The absence of phytotoxic symptoms up to 25 days after spraying indicates that haloxyfop-R-methyl can be used safely in established saffron fields for controlling grass weeds. According to Table 8, increasing the herbicide concentration led to higher pigment content. The highest chlorophyll a (10.11 mg/g FW) and chlorophyll b (7.37 mg/g FW) values were obtained at the full recommended rate, representing increases of 63.2% and 50.6% compared with the untreated control. Carotenoid content also increased by 67% at the full rate, although it did not differ significantly from the 75% treatment. These increases likely reflect improved weed control, resulting in greater light capture and nutrient availability for saffron. Effective weed management reduces interspecific competition and enhances photosynthetic performance, leading to higher pigment accumulation (Christensen et al., 2003).
 
Conclusion: Overall, haloxyfop-R-methyl, at 50%, 75%, and 100% of the recommended rate, either alone or in combination with Sitogit or corn oil, produced no adverse effects on Fv/Fm or visual injury. Instead, the treatments enhanced chlorophyll and carotenoid contents due to improved weed control. The strong agreement among fluorescence, visual assessment, and pigment data demonstrates the robustness of these physiological indicators in evaluating herbicide safety for saffron. These results clearly demonstrate saffron’s tolerance to haloxyfop-R-methyl and confirm the herbicide’s selectivity and safety for the crop. The findings also support the use of chlorophyll fluorescence and pigment analyses as rapid, non-destructive, and cost-effective tools for assessing crop–herbicide interactions (Abbaspoor & Streibig, 2005). Incorporating haloxyfop-R-methyl into saffron’s weed management strategy can therefore improve grass weed control without compromising crop health. Future research should investigate long-term effects on corm growth and saffron yield under various environmental conditions to confirm the consistency of these results.