The culture procedure was examined to improve the shoot regeneration rate from apple leaf segments, using the culture growth period, composition of plant growth regulators in the medium, leaf area, and vitrification rate as indexes. The apple cultivar ‘Fuji’ was used as the plant material. Each ‘Fuji’ apple had a different culture growth period. The culture growth period is the number of days from the date the plants were placed in the culture system to the date they were used in the experiment. Three types of shoot regeneration media with different concentrations of plant growth regulators were used. The shoot regeneration rates were lower in all three media with a 6-month culture growth period. Therefore, the 6-month treatment was considered unsuitable for experiments of shoot regeneration from leaf segments. The addition of high concentrations of cytokinin was effective in improving the shoot regeneration rate with the 6-month treatment; however, no significant effect was observed in the 1-year or 7.5-month treatments. In the 6-month treatment, there was a significant correlation between leaf area in the first month after the beginning of incubation and the regeneration rate in the third month for all three types of media. Therefore, it was considered that an increase in leaf area was necessary to improve the regeneration rate. The tendency to require a larger leaf area to increase the regeneration rate on all media decreased with an increase in the culture growth period. The leaf area increased with increasing concentrations of thidiazuron and an increased cytokinin/auxin ratio. It was also found that a higher thidiazuron concentration or cytokinin/auxin ratio in the regeneration medium led to more vitrification. The shorter the culture growth period, the higher the rate of vitrification. The shoot regeneration rates exceeded 90% in some petri dishes with MBNZ511 medium after culture growth periods of one year or 7.5 months. In these cases, the average leaf area in the first month after the beginning of incubation was more than 30 mm². Therefore, it is inferred that transformants using the Agrobacterium method could be efficiently obtained by selecting leaf segments larger than 30 mm² in the first month after the beginning of incubation. The shoot regeneration potential from leaf segments is an inherent character of individuals.

Near-isogenic lines (NILs) with introduced external gene alleles are good breeding materials for developing novel rice cultivars with a high agronomic performance. We developed NILs by introducing the Ghd7, Hd1, and Hd16 gene alleles showing an early or late heading date in the genetic backgrounds of three rice cultivars, “Shinko 538”, “Fusaotome”, and “Chiba 28”. The NILs were developed within 5 years by using continuous backcrossing and whole genome DNA marker-assisted selections with each backcrossed generation. The NILs with an introduced early-heading-date allele of the Ghd7 gene had a heading date 9 to 13 days earlier, in comparison with their recurrent cultivar, “Shinko 538”. The NILs with an early-heading-date allele of the Hd16 gene had a heading date from about 1 day earlier to about 8 days later. In the genetic backgrounds of “Fusaotome” and “Chiba 28”, NILs with the late-heading-date alleles of the Hd1, Hd16, and Hd1 + Hd16 genes had heading dates which were about 13 days, 3 days, and 28 days later, respectively, than their recurrent cultivars. The agronomic traits were nearly the same between recurrent cultivars and the NILs with the late-heading-date alleles of the Hd1 gene in the genetic backgrounds of “Fusaotome” and “Chiba 28”. By comparing the evaluation scores in previously developed NILs, the Ghd7, Hd17, and Hd18 gene alleles stably improved the heading date and other agronomic traits, while the Hd1 and Hd16 gene alleles showed variations depending on the recurrent parents and growth environment. For the efficient development of novel climate-resilient rice cultivars derived from NILs, it is necessary to elucidate in detail the genetic interactions between each introduced gene allele and its genetic background.

High temperatures over 35℃ at anthesis induces spikelet sterility. There is a concern that high-temperature-induced spikelet sterility will decrease rice yield due to global warming. We have developed near-isogenic lines (NILs) carrying the QTL (qEMF3) for avoiding high-temperature-induced sterility at anthesis by flowering at a cooler temperature in the early morning in the indica genetic background. We demonstrated that high-temperature-induced sterility can be reduced by using NILs. However, it has not been proved whether qEMF3 induces early-morning flowering (EMF) in the genetic background of japonica rice, and whether it produces the effect of avoiding high-temperature-induced sterility.

In this study, qEMF3 was introduced into the genetic background of four japonica rice cultivars, “Hitomebore”, “Hinohikari”, “Nikomaru”, and “Toyomeki”, by backcrossing. By using the NILs, early-morning flowering and the avoidance of high-temperature-induced sterility were verified. In a pot test of high-temperature treatment at only one flowering day in growth chambers in which the temperature was raised from 6:00 a.m., each qEMF3 NIL flowered 2–4 hours earlier than the recurrent parent cultivar under all genetic backgrounds. qEMF3 NILs mostly finished flowering by 10:30 a.m., when the temperature reached 35°C.

As a result, each qEMF3 NIL did not encounter high-temperature stress conditions at anthesis and could maintain a high level of fertility. On the other hand, in an experiment conducted on a concrete-framed paddy field in a greenhouse in Kagoshima Prefecture in Japan, where continuous high-temperature treatment at around 35℃ was performed during the heading stage, each qEMF3 NIL showed a higher seed fertility rate than the recurrent parent cultivar. From this, it was concluded that the EMF QTL (qEMF3) is an effective QTL for mitigating high-temperature-induced sterility even in the genetic background of japonica rice.

‘ITOSAI No. 1’ is a new Chinese cabbage F₁ cultivar that shows extremely late bolting. Late-bolting BrFLC genes derived from ‘Leafy Parental Green No. 2’ were introduced to the parents of the Chinese cabbage F₁ cultivar ‘Tiny-chouchou’ with backcrossing and DNA marker selection. In spring sowing under a low temperature, ‘ITOSAI No. 1’ showed extremely late bolting compared to commercial late-bolting F₁ cultivars. Other characteristics of ‘ITOSAI No. 1’, except the late bolting, are almost the same as ‘Tiny-chouchou’, including no trichomes. It is suitable for use in salads. Whereas the existing commercial F₁ cultivars bolted after 10 to 20 days of chilling treatment, ‘ITOSAI No. 1’ needs more than 40 days to induce bolting. ‘ITOSAI No. 1’ is an epoch-making cultivar which enables us to cultivate Chinese cabbage in spring without heating and covering materials.

‘Yumeikoro’ was selected from the progeny of a cross between ‘Irish Cobbler’ and ‘Kitakei-39’ at Hokkaido Research Organization Kitami Agricultural Experiment Station. ‘Yumeikoro’ has resistance to the potato cyst nematode (Globodera rostochiensis; Ro1) and moderately resistance to common scab (Streptomyces turgidiscabies). Its agronomic performance has been tested for eight years (2014–2022) at Kitami Agricultural Experiment Station. Vine maturity of ‘Yumeikoro’ was early, which similar to that of ‘Irish Cobbler’. The mean tuber weight of ‘Yumeikoro’ was higher than that of ‘Irish Cobbler’. The yield of marketable tubers (60–260 g) of ‘Yumeikoro’ was higher than that of ‘Irish Cobbler’. Eye depth of its tubers was shallower than that of ‘Irish Cobbler’. Fleshy substance was medium. ‘Yumeikoro’ will be cultivated instead of ‘Irish Cobbler’ in the areas infected with potato cyst nematode of Hokkaido and also is expected to contribute to stable potato production in Hokkaido.