Colchicine Alternatives for Chromosome Doubling in Maize Haploids for Doubled-Haploid Production

In vivo production of doubled-haploid (DH) lines in maize (Zea mays L.) routinely involves artificial chromosome doubling by colchicine treatment of seedlings. Because colchicine is a hazardous chemical, replacing it by less-toxic alternatives would be highly desirable. Our objectives were to (i) test the efficacy of various herbicides alone or in combination with other herbicides or phytohormones as chromosome doubling agents, (ii) evaluate the efficacy of application of these chemicals for different durations and methods of delivery to meristems, and (iii) compare colchicine treatment with the most promising alternative treatment under economic aspects. Several antimitotic herbicides with different modes of action and two phytohormones were tested in various combinations and concentrations in four experiments for survival rate (SR) of germinated seedlings, reproduction rate (RR) measured as the proportion of D-0 plants with seed set, and overall success rate (OSR) measured as the proportion of D-1 ears with seed set obtained from the germinated seedlings. Amiprophosmethyl (APM) and pronamid, applied with the seedling soaking method, outperformed all other alternative treatments tested and reached almost the same OSR as colchicine. Cost comparison between the best treatment, containing APM and pronamid, and the colchicine control showed that the total production cost per D-0 plant with seed set was about 10% higher than for colchicine as a result of slightly lower OSR. In conclusion, APM combined in an optimum dosage with pronamid is a promising alternative to colchicine in view of the lower toxicity and similar rate of chromosome doubling in maize.