Sublethal application of various sulfonylurea and imidazolinone herbicides favors outcrossing and hybrid seed production in oilseed rape

Abstract

Background: Acetolactate synthase (ALS)-inhibiting herbicides from the chemical families of sulfonylureas and imidazolinones are used worldwide. However, drift or sprayer contamination from some sulfonylurea herbicides causes a high level of male sterility in cruciferous species, especially oilseed rape (OSR). In this paper, we evaluated the gametocidal effects of 27 ALS-inhibiting herbicides that were sprayed on OSR plants at the bolting stage. Results: OSR anther development was very sensitive to sublethal exposure to most ALS-inhibiting herbicides. The application of 18 out of the 20 tested sulfonylureas (except ethametsulfuron and ethoxysulfuron), two imidazolinones (imazethapyr and imazamox), and one sulfonylamino-carbonyltriazolinone (flucarbazone-sodium) at suitable rates could induce male sterility. Eight of the herbicides, including chlorsulfuron (at application rates of 60-120 mg/ha), halosulfuronmethyl (300-600 mg/ha), sulfosulfuron (400-600 mg/ha), triflusulfuron-methyl (500-750 mg/ha), pyrazosulfuron-ethyl (150-225 mg/ha), nicosulfuron (200-300 mg/ha), imazethapyr (750-1125 mg/ha), and imazamox (400-800 mg/ha), could induce over 90% male sterility and over 60% relative outcrossed seed set in six cultivars with different origins. These eight chemicals could be used as new gametocides for hybrid seed production. This study also examined the possibility of external application of these gametocides on several unstable Polima cytoplasmic male sterile and thermosensitive genic male sterile lines. Although the outcrossed seed set of the treated lines was slightly reduced, the gametocide application significantly increased the seed purity of the resulting hybrid. Conclusion: The finding of the gametocidal effects of most sulfonylureas and imidazolinones are of great importance for developing new functions for ALS-inhibiting herbicides. The application of gametocides will also greatly promote the safe utilization of environment-sensitive male sterility in hybrid seed production. Unexpectedly, the application of three triazolopyrimidines (florasulam, flumetsulam, and penoxsulam) and one pyrimidinylthiobenzoate (bispyribac-sodium) did not cause male sterility, although these herbicides obviously inhibited the activity of ALS and plant growth. This result suggests that inhibition of ALS activity does not always lead to male sterility in plants, and these gametocides may also inhibit other biological functions vital for microspore development.

Imidazolinone Resistance in Oilseed Rape (Brassica napus L.): Current Status, Breeding, Molecular Markers and Prospects for Application in Hybrid Seed Purity Improvement

“…In this study, the gametocidal effect of herbicides was tested on both fertile lines and unstable male sterile Polima lines (SU only). It has been shown that imidazolinone group herbicides have a gametocidal effect and can induce more than 90% male sterility when 750-1125 mg/ha imazethapyr and 400-800 mg/ha imazamox are applied [46]. The effect of imidazolinone group herbicides on increasing the purity of hybrid seeds when hybridized with Polima male sterile lines was not evaluated in this study.…”

“…At least seven male sterility systems have been used to produce rape hybrids, but they all have a number of drawbacks. These include the following: inheritance of male sterility systems is linked with unfavorable traits, it is time-consuming for cytoplasmic male sterility systems to establish isogenic pairs and other sterility systems can be unstable [46][47][48][49][50][51][52][53][54][55].…”

“…Many different types of gametocides have been developed for oilseed rape, such as gibberellins, etrel/ethephon, methyl arsenate, benzotriazole, etc. [46,[56][57][58], but most of these gametocides have not found practical applications due to high cost, low efficacy, high toxicity, etc. [46].…”

“…[46,[56][57][58], but most of these gametocides have not found practical applications due to high cost, low efficacy, high toxicity, etc. [46]. Therefore, it is relevant to search for gametocides with high efficacy, low toxicity and low cost.…”

“…Therefore, it is relevant to search for gametocides with high efficacy, low toxicity and low cost. Yu et al 2020 reported their research on testing 27 different AHAS-inhibiting herbicides as gametocides, among which were herbicides of the imidazolinone group. In this study, the gametocidal effect of herbicides was tested on both fertile lines and unstable male sterile Polima lines (SU only).…”