Abstract:

A large number of chemicals capable of selectively inhibiting pollen development have been identified as chemical hybridizing agents(CHA) for large-scale commercial production of hybrid seeds in various crops. Some commercial CHAs such as methyl arsenate (Gametocide No.1 and No.2) have been successfully used to produce commercial hybrid in oilseed rape in China. However, researchers of hybrid breeding are still attempt to develop novel efficient CHAs without environmental and toxic effects. In the present paper, the effect of a new CHA developed by the authors, named EXP, on inducing male sterility of oilseed rape and on the change of the content of pigments (chlorophyll and carotenoid) and soluble protein and the activity of peroxidase and esterase isozyme in treated plant was investigated. Plants of Brassica napus breeding line L82089, Brassica juncea breeding line L638 and Brassica campestris variety Qinyou No.4 were treated with various concentrations of EXP in peduncle-growing period with 1 mm-2 mm long flower bud. All the treatments with EXP were found to be quite effective in inducing pollen sterility. The percentage of sterility and hybrids between treatment and control were significantly different for all doses. The treatments with 12－15 mL of 0.05 μg/mL and 0.25 μg/mL EXP per plant on Brassica napus breeding line L82089 caused about 92% and 97% sterile plants respectively. The plants treated with 0.25 μg/mL EXP were sterile steadily with 6.6% selfing rate (Table 1 and Table 2). So the treatment with 12－15 mL of 0.25 μg/mL EXP could be recommended for producing hybrid in Brassica napus. The development of vegetable and reproductive organs was all suppressed due to the spray of EXP. The induced sterile plants were distinctly characterized by fading leaf, shorter plant height, serried bud, later flowering, fading petal, and shriveling anther with no pollen. The morphology between male sterile and fertile flowers was so different that the treated and untreated plants could be easily discriminated. The content of chlorophyll and carotenoid in the flower of induced sterile plant was decreased (Fig.1). In treated stamen, the activity of peroxidase and esterase isozyme was diminished and the content of soluble protein was very low (Fig.2). Simultaneously, the treatment with 5 mL of 0.05 μg/mL EXP could make breeding line L638 (Brassica juncea) and variety Qinyou No.4 (Brassica campestris) sterile, too. However, it was not suitable for producing hybrid because the period of male sterility of L638 was too short and the seedseting of Qinyou No.4 was poor (Table 3). The active ingredient of EXP belongs to sulfonylurea family that can inhibit acetolactate synthase (ALS, EC 4.1.3.18), the key enzyme that exist in the chloroplast of all green plants and catalyzes the common reaction to synthesize leucine, valine, and isoleucine. As a matter of fact, it have been found that other ALS-inhibiting chemicals could induce male sterility to a considerable level in oilseed rape and other Brassica family vegetables, too. A significance of this discovery may be the potential of a larger number of ALS-inhibitors to be used as the candidate of CHAs.

Key words: Oilseed rape, Chemical hybridizing agent, Sulfonylurea, Acetolactate synthase, Male sterility