Measures against High Temperatures and Breed Developments for “Small Chrysanthemums” and “Gladiolus” in Ibaraki Prefecture

Date of interview	August 24, 2021
Targets	Makoto Miyagi, Chief Special Skills Instructor, Special Skills Instructor Office, Ibaraki Agricultural Center Hidenori Ichige, Section Chief, and Kota Yoshiya, Chief, Flowering Plants Laboratory, Horticultural Institute Takeru Gonai, Section Chief, and Fumihiko Inazaki, Engineer, Fruit Tree and Flowering Plant Breeding Laboratory, Plant Biotechnology Institute

Please give us an outline of the Horticultural Institute and the Plant Biotechnology Institute of the Ibaraki Agricultural Center.

Mr. Ichige: The Ibaraki Agricultural Center currently has 5 research institutes. Of these, the Horticultural Institute is in charge of cultivation tests on fruit trees, vegetables, and horticulture crops. There are 6 laboratories in the Horticultural Institute, and the Flowering Plants Laboratory conducts tests and research on cultivation of major flowering plants in Ibaraki Prefecture, such as small chrysanthemums, roses, and gladiolus.

Mr. Gonai: The Plant Biotechnology Institute develops new breeds of horticulture crops, and is currently working to reduce the length of the period for breed development by combining the old biotechnologies such as tissue culture and leading-edge technologies such as DNA markers with the main hybridization breeding.
Small chrysanthemums have the largest yield as cut flowers in Ibaraki Prefecture. They are major production items for which Ibaraki Prefecture occupies the top position in the share of the wholesale market in Tokyo during the summer. The Plant Biotechnology Institute is also the only institute in Japan that breeds gladiolus.

Please tell us about the characteristics of the cultivation of small chrysanthemums, which are major products of Ibaraki Prefecture, and the measures against climate change.

Mr. Yoshiya: Small chrysanthemums increase in demand and unit price especially during the obon festival and the equinoctial week, which are held from July to September. While it is important that we make stable shipments during this period, we have had occasions where the shipment peak shifted so that it was too early or too late in recent years. One of the reasons for this is that the reaction of small chrysanthemums to the temperature varies depending on the growth stage.
Although an appropriate temperature is required during the stages from planting to flower bud differentiation, the flowering time is advanced as the growth is accelerated if it is exposed to high temperatures that are above the level of a normal year. Within the last few years, temperatures were relatively high in spring and the flowering time advanced in 2014, 2015, and this year.

Flowering adjustment under lighting is a conventional method that has been used as a measure against high temperatures during the first half of growth. Since small chrysanthemums are short-day plants, the length of the night controls flowering. If the night is sufficiently long, there is more flowering stimulation and the flowering is advanced. We therefore adopt a technique to expose the plants to artificial light at night to suppress the flower bud differentiation.
In addition, based on the tests on small chrysanthemum breeds, we have recently come to understand that lighting during the late time from 12 midnight to 4 a.m. is more effective in suppressing flower bud differentiation instead of lighting from 10 p.m. to 2 a.m., which was used in the conventional method. Although some expressed concerns about deterioration in quality with this “lighting from midnight to early morning,” we observed no such effects.

Meanwhile, exposure to high temperatures suppresses flowering stimulation during the latter half of growth from the flower bud differentiation stage and later, and flowering becomes delayed. While it is assumed that the common measures such as shading with materials and watering between the ridges may be effective, these are not very practical for small chrysanthemums. We are therefore trying to select the breeds that are resistant to flowering delay under high temperatures. We have specified 6 breeds in 2014, and added 6 more breeds in 2019.

Can I ask the same questions for gladiolus?

Mr. Inazaki: Shipment of the gladiolus from Ibaraki Prefecture occurs from May to November with the peak in June to August. High temperatures and strong sunlight have indeed become problematic during this period, and we suffer “spike burn,” which causes the parts around the spike to wither and die, more and more often because of it. When spike burn occurs, the product grade may become lower, or shipment must be forgone in the worst case. The Plant Biotechnology Institute is therefore working on the development of breeds that do not suffer spike burn as much.

We started from elucidating the weather conditions that tended to cause spike burn. In our outcomes from last year, we found that the exposure to high temperatures before blooming caused spike burns. We therefore planted multiple breeds that had different levels of resistance to spike burn, and minutely observed the reaction of each breed against temperature. Since the difference between breeds that are more resistant to spike burn and those that are not becomes evident when the temperature exceeds 34 to 35C in particular, we are currently trying to evaluate the resistance to spike burn by raising and planting them so that the blooming time would match the timing when they are exposed to high temperatures.

As the spike burn resistant breed, we are applying for variety registration for “Hitachi Kirameki (provisional name),” which is a flower color mutant that occurred from “Princess Summer Yellow,” a breed that was already evaluated as resistant to spike burn, and we will try to realize its dissemination in the production field as soon as possible.

Are there cultivation methods to prevent spike burn besides breed improvement?

Mr. Inazaki: Some people have adopted shade culture as a measure against spike burn. It is a simple shading method where straight pipes are installed between ridges so that the shading net can be placed over them and fixed to them. While this does not completely prevent spike burn, it is used as an effective method to prevent severe cases. However, there are issues such as requirement of labor in installation, having everything including the shading net collapse when there is a strong wind, and high material expenses. Others are also attempting to lower the temperature by spraying water, but we are working with a goal to create resistant breeds that do not require such efforts.

What are the requests that are sent from the producers?

Mr. Gonai: In addition to selection and development of breeds that do not delay in blooming under high temperatures, there are some requests about small chrysanthemums, which suffer withered leaves from the bottom of the plant and decrease in product value when it is cultivated under unfavorable weather conditions or soil conditions. Some suspect that the humidified state of the soil caused by heavy rains, which are becoming more frequent in recent years in addition to the high temperatures, may be causing the withering of bottom leaves, and we are beginning to receive requests for elucidation of the causes of withering and discovery of specific measures.

Finally, please tell us what gives you the sense of satisfaction in your daily work, difficulties, and future prospects.

Mr. Yoshiya: Climate change is an issue that will continue for a long time in the future. While I fear that it may become a cat-and-mouse situation where the measures will no longer be enough as the temperature keeps rising even when we come up with measures, I hope to keep working speedily to ensure stable incomes for the producers, etc.

Mr. Ichige: The Institute has the role to conduct testing and research, and transmit the outcomes to the producers. I hope to deliver outcomes of research that would meet the expectations of the producers and disseminate the breeds, techniques, etc. in the future.

Mr. Inazaki: I expect that the standard requirement for gladiolus will be that it is resistant to spike burn if the temperature keeps rising in the future. I will continue working on development of such breeds. I would also like to focus on the development of white and pink gladiolus, which are higher in demand than other colors.

Mr. Gonai: The goal of breed development changes in time. The traits that are demanded will also change due to climate change. While it is difficult to have a long-term prospect as persons in charge may be transferred, I hope to keep working by properly determining the characteristics that will be demanded in the future so that we can provide excellent breeds to the producers.