Rapid sex-typing of asparagus for male hybrid seed production using n-propyl N-(3,4-dichlorophenyl)carbamate (NPC)

Precocious flowering can be induced in asparagus (Asparagus officinalis L.) seedlings with N-phenylcarbamate herbicides, such as n-propyl N-(3,4-dichlorophenyl) carbamate (NPC); however, only ≃50% of the treated seeds produce flowering plants because these compounds inhibit germination and seedling emergence. We have improved the treatment method by determining the environmental conditions, timing, dose, and duration needed to maximize the percentage of germination, emergence, and flowering. Imbibing seeds in water for 5 days, and then treating germinated seeds with 0.4 mm NPC for 5 days after radicle emergence, with seedling aeration in the light, resulted in the production of flowering seedlings from >90% of the treated seeds. For freshly harvested seeds, in which germination rates are more variable than aged seeds, individual seedlings must be transferred to NPC within 1 day after radicle emergence to produce a high percentage of flowering plants. For seven male asparagus cultivars, chemical induction of flowering in seedlings with NPC produced a sex ratio similar to that of field-grown plants, demonstrating that NPC induces flowering without altering floral differentiation or sex expression. This method can be used for rapidly and accurately identifying the percentage of females in 'male' cultivars.