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Old 09-28-2018, 09:56 AM   #1 (permalink)
SoCal2warm
 
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Default How to breed (seedless) Bananas for Temperate climates

This post is about how to breed seedless bananas for temperate climates, a rough outline idea.

Select a cold-hardy banana (such as Musa basjoo or Darjeeling) and then select another "edible" (good tasting, but seeded) banana which is very early ripening (Dwarf Cavendish or Orinoco).
(Helen's hybrid might be a good one to try further hybridizing too)

Treat the apical bud with either Colchicine or Oryzalin to double the chromosome number, obtaining a tetraploid.


"Tetraploid plants were induced successfully from diploid bananas Musa acuminata ‘Kluai Leb Mu Nang’ and ‘Kluai Sa’ (2n = 2x = 22) with in vitro oryzalin treatment. Calluses from in vitro-grown shoot tips of both cultivars were treated with oryzalin at concentrations of 1.5 or 3 mg l−1 for 24, 48 and 72 h, respectively. The oryzalin treatments produced tetraploids at a frequency of 15.6% in ‘Kluai Leb Mu Nang’ and 16.7% in ‘Kluai Sa’ as detected by flow cytometry. Chromosome counting showed that the tetraploid plant chromosome number was (2n = 4x = 44). The selected tetraploid plants were transplanted in the field and variations in the morphological characteristic of leaf shape and fruit bunch compared to normal diploid plants were found under the same growing condition even after 3 years of cultivation."

In vitro induction of tetraploid plants from callus cultures of diploid bananas (Musa acuminata , AA group), Kluai Leb Mu Nang, Kluai Sa


Here's another relevant article as well: Effectiveness of Colchicine and Oryzalin at Inducing Polyploidy in Watsonia lepida N.E. Brown


When a normal diploid is bred with a tetraploid, the result is a seedless triploid variety.


"Most bananas purchased at your local supermarket came from sterile triploid hybrids."
https://www2.palomar.edu/users/warmstrong/hybrids1.htm


I have another idea also.
Take a regular seedless banana (3n), double its chromosome set number to 6 (hexaploid), then breed it with another banana.
Once the chromosome set number has been doubled from 3 to 6 it should then produce seed because 6 is an even number (and the chromosomes can be evenly split during meosis).
Hybridizing a 6n (hexaploid) with a seeded 2n (diploid) should give a 4n (tetraploid) banana (also seeded), which could then in turn be hybridized again with a 2n seeded banana to give a seedless 3n triploid.
I believe it could also be possible to use seedless (3n) banana pollen to fertilize a hexaploid (6n) flower, also resulting in tetraploid (4n). I'm not exactly sure about bananas but this type of phenomena can work in citrus. There are some issues with trying to breed triploids but in general some normal (1n) haploid gametes are able to form from the meosis of triploids, and the majority of offspring able to form from triploids will be the same as if they came from a normal diploid parent (though the rate of fertility is normally substantially lower). Basically 3 is unable to split evenly into two, so some 1n gametes are able to escape from the division intact. Maybe someone with more knowledge than I will be able to give some input about whether seedless bananas have fertile pollen.


Edit: A quick search reveals triploid bananas can produce fertile pollen.

"Pollen viability was examined by recording the number of viable as well as non-viable microspores in anthers just before anthesis, as it could be an efficient and rapid indicator of female fertility. It was thought that competency in meiotic restitution in microspores could indicate similar competency in megaspores. Pollen fertility was compared among seeded diploids and edible triploids of Musa and correlated with ovule fertility. Viability was examined using the Alexander's pollen stain procedure. The seeded diploid species M. acuminata, M. balbisiana, and M. ornata had 3 times more viable pollen than the edible tetraploids (AAAB). M. balbisiana and M. ornata had significantly more viable pollen than M. acuminata. The tetraploids contained 3 times more viable pollen than the edible triploids AAA […] The AAA triploid Gros Michel had the highest percentage of viable pollen at 13% […] "

Pollen fertility in Musa : Viability in cultivars grown in Southern Australia, J. A. Fortescue, D. W. Turner, Australian Journal of Agricultural Research, January 2004
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