Polyploid Breeding

Most flowering plants are diploid, carrying two sets of chromosomes (2n); polyploids are plants that carry more than two sets, and polyploidy is a major evolutionary force in both wild and cultivated plants. Polyploid plants often show increased hybrid vigour, greater heterozygosity, and improved tolerance to biotic and abiotic stress, along with a buffering effect against deleterious mutations; because meiosis in polyploids is more error-prone, fertility is often reduced, an effect that is actually exploited deliberately to produce seedless varieties. When a plant's own chromosome number is simply doubled within the same species, the result is called autopolyploidy — a triploid condition in sugar beet, apple and pear, for instance, increases vigour and fruit size, root size, leaf and flower size, and seed and sugar content, and has also been used to produce seedless tomato, apple, watermelon and orange; chromosome doubling for this purpose is commonly induced using the chemical colchicine. When chromosome sets are combined from two diffe …