1. How Breeders Choose One Winning Variety from Thousands of Cross-Bred Trees
Supermarket grapes and apples have variety names on their bags. These names belong to trees that someone cross-bred, grew, and selected. According to the Akita Prefectural Fruit Tree Experiment Station, the most common method for improving fruit varieties is "cross-breeding." This involves crossing two varieties to get seeds, planting them, and then choosing the best-tasting and best-looking trees from those that bear fruit [1].
For the Akita apple "Senshu," breeders used 7 varieties to create 15 different combinations and grew about 7,500 seedlings. The chosen apple is said to be one tree grown from 71 seeds resulting from a cross between "Toukou" and "Fuji" [1]. Breeders grow thousands of trees but select only a very few. So, how long do you wait after planting until the fruit is ready to eat?
2. Why It Takes Nearly 10 Years from Seed to First Fruit
Fruit trees grown from seeds take nearly 10 years to bear fruit [1]. Breeding of the "Senshu" apple began with a cross in 1966 (Showa 41). It took 7 years for the first fruit to appear and 14 years until it was officially registered as a variety [1].
The Shine Muscat grape began with a cross between "Akitsu 21" and "Hakunan" in 1988. Seeds were planted in 1989, and primary selection happened in 1997. From 1999, tests were conducted in 30 locations across 28 prefectures to see if the grape suited different regions. It received a name registration in 2003 and variety registration in 2006 [3]. Subtracting 1988 from 2006 gives 18 years. If counting only to name registration, it is 15 years. Kagawa Prefecture introduces it as a grape with thin skin where the whole fruit can be eaten [4].
Other fruits also take time. The Ehime citrus "Kanpei" took 16 years from cross to registration [6]. The Nagano apple "Shinanosweet" was crossed in 1978 (Showa 53) and registered in 1996 (Heisei 8). Another Nagano apple, "Shinano Dolce," started with a different cross in 1983 (Showa 58) and was registered in 2005 (Heisei 17) [7]. Calculating from these years gives 18 and 22 years respectively. Since breeders wait over a decade, they need ways to shorten this time. What can be sped up?
3. How Grafting Young Seedlings Can Speed Up Fruiting
The wait is long because young seedlings do not bear fruit early. Researchers study ways to make seedlings fruit sooner. In Kumamoto Prefecture, citrus trees usually take about 5 years from cross to fruit. By using "approach grafting" on young seedlings, fruit appeared in about 4 years, shortening the time by 1 year [5].
In Ehime Prefecture, for the "Kanpei" citrus, fruit began to appear in the 3rd year of growing the "high-grafted" trees. Breeders then performed primary selection on promising lines and cut down those with no potential. The remaining lines were grafted again for secondary selection, tested for local adaptability, and then registered [6]. Because space for growing trees is limited, removing unpromising trees early saves time and effort for the whole project. However, these methods only shorten the wait by about 1 year. Are there ways to avoid waiting before fruit appears?
4. How Natural Branch Mutations Can Become New Varieties
Sometimes, only one branch on a tree has fruit of a different color. This natural change is called a "branch mutation" (gardeners also call it a "sport"). According to Akita Prefecture, using branch mutations allows breeders to keep the original taste while improving fruit color or ripening time. From the "Fuji" apple, "Yataka" (which ripens early) and "Mishimafuji" (which has better color) were found [1].
Ehime Prefecture notes that for Satsuma mandarins, branch mutations have a wider range of variation than seedlings, making it easier for groundbreaking new lines to arise. Branch mutations like "Miyagawa Wase" have supported the citrus industry, and many were discovered by producers. "Nichiou 1" is a branch mutation of "Okitsu Wase" [6].
While branch mutations are attractive for saving waiting years, they happen at unpredictable times. Is there a way to create changes with human hands?
Sometimes a branch bears fruit with a different color or ripening time, while qualities such as taste stay the same.
5. How Gamma Rays Helped Create a Disease-Resistant Pear
The famous Japanese pear "Nijisseiki" has a weakness: it is susceptible to black spot disease. Resistance to this disease is determined by one gene. It was found that Nijisseiki had a "heterozygous" state for this gene. Scientists decided to use radiation to change the gene to a "homozygous recessive" state [8].
In 1962, trees were planted in a field exposed to gamma rays. In 1981, when fungicide spraying was stopped, only one branch showed no symptoms of black spot disease [8]. This branch was propagated by grafting and tested. On June 22, 1990, it was registered as "Gold Nijisseiki" (Nashi Norin 15). From planting to naming, 28 years passed [8].
Radiation is not "aimed" at specific genes. It causes random changes in the tree's DNA. Scientists then search for the one with the desired trait. In this case, humans found the single branch without disease symptoms [8]. Searching takes time too. To shorten it further, researchers also use DNA markers to help select promising seedlings.
6. How DNA Markers Identify Promising Seedlings Before They Fruit
The National Agriculture and Food Research Organization (NARO) reported that they used DNA markers to select 172 apple seedlings that carry the "Rvi6" gene for resistance to apple scab [9]. DNA markers are indicators that help predict traits at the seedling stage, narrowing down candidates without waiting for fruit. This allows breeders to choose promising seedlings early.
The report states that fruit trees and tea are crops that take years to grow, making efficient breeding methods important [9].
In Okayama Prefecture, research on peaches involves using DNA markers at the young seedling stage, before planting. This predicts pollen fertility and flesh color (white, yellow, or red) to remove bad individuals before they are planted. This is necessary because peach trees are large and many cannot be grown [10].
It is not clear from these documents exactly how many years this saves. However, reducing the number of trees before planting or before fruiting saves space and labor.
7. How to Work Out a Fruit's Breeding Years from Its Variety Name
If you have fruit at home, look at the variety name on the bag or sticker. You can search for that name with a parent or guardian on pages for "Fruit Tree Experiment Stations" or prefectural agricultural experiment stations. These pages often list the parent varieties and the year of the cross.
Subtracting the year of registration from the year of the cross tells you how many years it took to create that fruit. For example, Shine Muscat took 18 years from 1988 to 2006 [3].
When reading, check if the source uses the "year of cross," "year of name registration," or "year of variety registration." For Shine Muscat, it is 15 years to name registration and 18 years to variety registration, so the number changes depending on the method. Many national and prefectural documents are available as PDFs and include timelines and selection details. The parent combination for "Fuji" is also found in Akita Prefecture's materials [2].