Induced chromosome doubling in microspores and regenerated haploid plants of Brassica napus

The spontaneous diploidization rates in oilseed rape (Brassica napus L.) via in vitro androgenesis are too low for practical applications. In contrast, artificial doubling of chromosomes of the microspore has proven to be more successful and allows homozygous plants to be obtained in a short time. Here, we present the efficiency of diploidization of B. napus haploids using three different chromosome doubling methods. Using the in vitro approach in microspores, the rate of chromosome doubling in 24 populations of androgenic plants ranged from 15.8% to 94.0%. An alternative in vivo method for the induction of chromosome doubling involves colchicine treatment of young haploid plants, and this yielded doubling rates ranging from 47.5% to 86.4% in 10 different plant populations. Another in vivo method of chromosome doubling is colchicine treatment of the excised young axillary shoots of haploid plants at the early flowering stage. The high efficiency of this method was confirmed in haploid plant populations from 11 genetically distinct donors in which the frequency of occurrence of diploids ranged from 53.3% to 100%. However, in this case, the time required for seed formation from doubled haploids increased by about 3–5 months. The availability of several methods of chromosome doubling at various stages of the androgenic process – from isolated microspores through to young plants and flowering plants – allows seeds to be obtained from nearly every selected individual haploid.