What type of research are you engaged in?

Fig. 1: Blue honeysuckle

Have you heard of the blue honeysuckle? The blue honeysuckle (Fig. 1) is a plant that grows wild in Hokkaido. It has extremely high nutritional value, as can be seen from the fact that the Ainu value it highly as an elixir of youth, and its berries are recognized as a special berry (small fruit) product of Hokkaido. I discovered this plant on a farm the year I was appointed to Hokkaido University, and loved it as soon as I tried the berries, which were sweet and sour at the same time. I had studied plant improvement at graduate school, so I decided to try applying this to selective breeding of blue honeysuckle plants. My breeding objectives are twofold – to produce a large fruit with a hard skin, and to produce a good flavor.

 

What methods are you using in your research?

Fig 2 Field studies, searching for blue honeysuckle

The blue honeysuckle grows wild in various areas of Hokkaido, so I began researching by collecting some of these wild plants. The more varieties you can collect, the broader your improvements can be. I went searching in the Tomakomai Yufutsu Wetlands, Yokotsudake near to Hakodate, Kushiro Wetlands in eastern Hokkaido, the Bekanbeushi Wetlands, the Kiritappu Wetlands, and the Shibetsu Wetlands, among other places. I was in my school’s mountaineering club, and have always enjoyed reading maps and looking at vegetation, so I really enjoyed implementing a field survey (Fig. 2) while looking for blue honeysuckle. It was like searching for hidden treasure.

Once I started looking at the blue honeysuckle plants I found, I discovered something interesting. Plants with one set of ordinary plant chromosomes are known as diploids (diploidy), but among the collection of wild blue honeysuckle plants there were a group of diploids (with 18 chromosomes) and a group of tetraploids (with 36 chromosomes). The diploids were only found in one part of eastern Hokkaido (Kushiro Wetlands and Bekanbeushi Wetlands), while the tetraploids were spread across other regions. It is still a mystery how this sort of distribution occurred, and I am still engaged in research into the differences in DNA sequence between the different blue honeysuckles from different regions.

My research so far has shown that there are diploid and tetraploid versions. This is significant in implementing selective breeding. In general, when the number of chromosomes increases a plant’s tissue and organs can be expected to become larger. Kyoho (“giant”) grapes are a well-known example of a tetraploid. In order to increase the size of the blue honeysuckle fruit, therefore, I began to engage in polyploidy breeding (research into the production of various polylpoids).

At this point, you have to focus on the endosperm. The endosperm is the part that of rice or maize that is eaten, but it has the function of nurturing the embryo, and so it is full of nutrients. This part does not become a plant, but is a type of tissue that degenerates when the embryo has been nurtured. The ploidy level of endosperm ploidy has 1.5 times the number of chromosomes of the rest of the tissue as a result of double fertilization. In the case of blue honeysuckle, the endosperm in diploid plants was triploid (27 chromosomes), and the endosperm in tetraploid plants was hexaploid (54 chromosomes). If I succeeded in extracting the endosperm alone, culturing its tissue, and turning it into a plant, I believed I would be able to establish a new method of polyploidy breeding.

Fig. 3 Process of regenerating a plant from endosperm

The endosperm is special tissue designed to store nutrients, and until now it has been considered that it would not become a plant. So what if we use endosperm from a younger stage, before it begins to store nutrients? I began experimenting immediately. After culturing around 2,000 endosperms, in a few months a few plants regenerated. We had demonstrated that plant endosperm had the capacity to regenerate into a plant. I studied the number of chromosomes and found that it was hexaploid – the same as the endosperm. This could probably be described as a new polyploidy breeding method (Fig. 3).

To date, through crossbreeding, we have produced diploid, triploid, tetraploid, pentaploid, hexaploid and octaploid versions. So do these polyploids have larger fruit? In fact, it takes several years for blue honeysuckle to fruit, so I am still waiting for the plants to grow that far.

 

What are you aiming for next?

My objective in breeding blue honeysuckle was to create a plant with good-flavored fruit. In order to do this, I am crossbreeding the plants with their wild relatives. I am also working on crossbreeding wild raspberries, which grow naturally in Hokkaido, with cultivated raspberries.

I believe it is interesting to find plants that grow wild in Japan, and to contribute to their selective breeding. I like fieldwork, and I am also interested in detailed experimentation using a microscope, and biotechnology. Being able to combine fieldwork and biotechnology, and produce new varieties in the laboratory, is truly fascinating.