Seedlessness

Thanks to some informative comments on my post about figs and wikipedia my knowledge of botany is slowly improving and my admiration of figs steadily increasing. Many species of figs are pollinated by symbiotic wasps, but there are other fig varieties that develop edible, seedless figs through a process called parthenocarpy. A dominant mutation in the plant allows unfertilized flowers to stay on the tree and develop into yummy figs. While these seedless fruits are delicious, the plants that produce them are sterile, able to reproduce only through human intervention.

Fig trees are particularly easy to propagate seedlessly by simply planting new branch shoots, and this simplicity made figs one of the earliest domesticated plants. Recent archaeobotanic evidence suggests that fig trees were possibly the earliest plants to be domesticated, approximately 11,400 years ago, a thousand years before the domestication of grains. By cracking open carbonized figs found in an early Neolithic village, the archeologists realized that the villagers were eating and storing seedless parthenocarpic figs, suggesting that they were also likely planting cuttings from the tree, intentionally creating domesticated parthenocarpic fig trees from the wild mutant variety which can make both seeded and seedless figs.

Propagation of naturally occurring seedless varieties is just one way to get seedless fruit. Wild bananas are full of hard seeds that make them impossible to eat, but crossing strains of bananas that have four sets of chromosomes (tetraploid) to strains that have only two (diploid) yields sterile triploid bananas. The odd number of chromosomes can't be split evenly during meiosis, making it impossible for the cell to produce the gametes that mix to become the seeds, making triploid bananas edible.

Parthenocarpy can also be artificially induced in multiple species of plants through application of chemical growth regulators on the developing flower or through genetic engineering. Pollination activates the production of several plant hormones that in turn start off the process that makes the fruits. Injecting the hormones into the proto-figs makes seedless figs in otherwise normal plants, as detailed in this fun PDF of an article from 1948 discussing early studies of chemical induced fruit development. Instead of externally applying the hormones, genes that activate hormone production can also be engineered into normal plants so that the hormone will be produced even in the absence of pollination.

Seedless fruits are great for eating, but because they are propagated clonally, without mixing genes from two plants together as occurs during pollination, the dearth of genetic diversity can make populations especially susceptible to infection and disease. Agricultural and genetic tools to increase diversity in farms and orchards and to develop more resistant strains can be used together to keep seedless varieties alive. The history of plant domestication, breeding, and, much more recently, genetic engineering is long and fascinating and something I'm hoping to learn a lot more about--any good reading recommendations?