Mixoploidy in wild and cultivated species of Cruciferae capable of hybridizing with rapeseed Brassica napus

The number of chromosomes in cells of the root meristem of seedlings of wild and cultivated species of Cruciferae plants capable of hybridizing with rapeseed Brassica napus is studied. Only diploid metaphases are observed in seedlings of Brassica juncea, Diplotaxis tenuifolia, and Raphanus raphanistrum. In B. napus and B. cretica roughly 5% of the seedlings are mixoploid. Diploid cells are dominant in the mixoploids, though hypo-and hyperdiploids are also encountered. Nearly 20% of the seedlings of B. campestris and R. sativum are mixoploid, a significant fraction of which contains di-triploid chimeras. In B. nigra less than one-half of the seedlings are truly diploid, the majority of the plants being mixoploid. Seedlings containing preferentially tetraploid and triploid cells are dominant. The biological significance and possible causes of the newly discovered mixoploidy are discussed.