Agronomy

1. Elucidation of the high-yield mechanism of the super high-yielding variety “Hokuriku 193

It is generally believed that crop yield is related to both sink capacity (e.g., the number of paddy seeds per rice plant) and source capacity (e.g., the ability to fill the sink with organic matter: e.g., photosynthesis and biomass productivity). The recently bred super high-yielding variety “Hokuriku 193” has been reported to be able to achieve a yield 1.5 times higher than that of common varieties. This is due to the superiority of Hokuriku　 193 in terms of both sink and source capacity.

How does Hokuriku 193 achieve such excellent source performance? If this can be clarified, it will provide clues for the development of more high-yielding varieties in the future. To elucidate this point, we conducted a comparative study between Hokuriku No. 193 and other major varieties. The results showed that Hokuriku 193 has a unique three-dimensional structure in terms of the plant body and leaf expansion, and that it may have a form that can efficiently receive solar radiation. The high efficiency of sunlight reception means that the amount of photosynthesis can be increased and the plant can grow faster and larger even when grown under the same conditions. Such morphological characteristics may contribute to the super-high yield of Hokuriku No. 193. We are currently working to elucidate the mechanism and verify it using a simulation model.

2. Soybean crop shift in anticipation of climate change

This research was partially supported by the Strategic Innovation Creation Program “Building a Sustainable Food Chain that Provides an Abundance of Food”.

Soybean has been cultivated in Japan for a long time and is becoming increasingly important due to its excellent processability and nutritional value. However, soybean production in Japan is currently stagnant and unable to meet the increasing demand. Despite various breeding and cultivation improvement efforts, the yield per acre has been stagnant for several decades, and the self-sufficiency rate of soybeans for food use has remained in the low 20% range. One of the major reasons for this stagnation is that the rainy season coincides with the soybean sowing season in Honshu and southward, and soybean is severely damaged by humidity in the early stages of growth. Soybean is naturally susceptible to heavy rainfall and flooding, and we are concerned that the situation will become even more serious as the weather becomes more severe due to global warming.

Therefore, we are testing a cultivation system that avoids periods of high weather risk by drastically changing the soybean cultivation period from the previous one. Specifically, we have developed an extremely early sowing system, in which cultivation begins in early April, more than two months earlier than before, and an extremely late sowing system, in which cultivation begins in mid-August or later, more than two months later than before. Of course, the temperatures and day lengths during the growing season are completely different from those of normal cultivation, so normal growth cannot be expected simply by growing conventional varieties at different times of the year. For this reason, we are searching for the best combination of cultivation environment and variety by introducing varieties originally grown in Hokkaido or genetic resources from overseas that have growth characteristics rarely found in domestic soybean varieties. This has proven possible to obtain yields comparable to those of conventional cultivation. It is expected that this research will establish a cultivation system that is resistant to climate change and can produce soybeans stably in the future.