I didn't find any seedless watermelons among the offspring, so I'm interpreting that to mean that the conversion to tetraploid was not successful.
Last year was a bad gardening year for me. I intend to attempt the tetrapoid conversion this summer on both species.
I'm no expert on watermelons, but from what I know about many other fruits, it's usually triploids that are seedless, not tetraploids.
(Furthermore, even in the case of triploids there can be just a few seeds that sometimes form)
my understanding was that Joseph Lofthouse was demasculating the [hoped tetraploids] and pollinating with diploid pollen. thus he expected triploid fruit with seedless fruit. or am i wrong?
edit: Joseph Lofthouse, what ever happened to the perrenial part of this project minus the tetraploid part? That would still be way interesting, or did you need tetraploid watermelons to cross with the wild species?
Seedless watermelon cultivars were developed as a result of the discovery by Kihara (1951) that triploid watermelons are mostly seedless. Triploid hybrids are produced by crossing two inbred lines: a tetraploid female parent with a diploid male parent (the reciprocal cross is unsuccessful). Among the first successful cultivars (6 kg size) were ‘Tri-X-313’ from O. J. Eigsti (American SunMelon, part of Syngenta), ‘AC 5244’ from W. Barham (Barham Seeds, part of Seminis). Later, mini seedless (3 kg size) cultivars were developed. One of the first successful ones was ‘Petite Perfection’ from X. Zhang (Syngenta Seeds).
Tetraploids are produced by the application of colchicine or oryzalin, and can be maintained by self- or sib-pollination. They are used as maternal parents in crosses with diploids. The resulting triploid F1 hybrids, because of their odd chromosome number, are female and male sterile. Germinating pollen grains stimulate enlargement of the triploid ovaries. The fruit are not always entirely seedless, but may have small, empty seed coats and occasional hard seeds. Few tetraploids have been successful in producing triploid hybrids in the marketplace, either in the small or mini fruit sizes.
Because seedless cultivars are male sterile, growers must plant a pollenzier (diploid cultivar) in order to get a high rate of fruit set. Usually, one row of the diploid is planted to for every three or four rows of triploid in the production field. The diploid and triploid cultivars should be distinguishable, such as one having round fruit with narrow stripes (seedless) and the other elongate fruit with wide stripes (seeded), so that they can be separated at harvest. An adequate bee population (two active hives per hectare) is needed for successful fruit set and to minimize the percentage of cull fruit. A second method for pollenizer use is the plant the diploid in the triploid rows, with one diploid plant for every four triploid plants.
Seed production of triploid cultivars is expensive and seeds germinate poorly if conditions are less than optimum. Therefore, growers often use transplants rather than direct seeding the field. Some growers remove the seed coats before planting in order to improve germination. Production of triploid seeds and transplants, along with the need for pollenizers makes seedless cultivars significantly more expensive than seeded cultivars. However, they have become popular in North America, Europe and Japan.
Post by lochaberbreeder on May 25, 2019 19:30:16 GMT -5
Interesting. I've got some tetra seeds (Charleston 1, 2, and 3) but would love to get more, and possibly make my own. I'm aiming to produce my own variety by crossing a bunch. I've got thousands of colchicum seeds that I was thinking to grow and/or crush for potential chromosome doubling.
From my understanding, triploids are not wholly sterile. During meiosis, chromosomes go one way or another, since triploids have an odd number of them. Any mismatch results in almost certainly fatal aneuploidy. There's a very low chance that the third set wholly migrates one way or another, though, yielding sexually derived polyploids. This has been documented in hops, and I'm assuming it would be the same with watermelon. I was thinking of crossing triploids (maternal) with tetraploid pollen to attempt this.