The development of tetraploids is one of the useful methods for breeding horticultural plants. However, it is difficult to obtain the perfect tetraploid by chromosome doubling on colchicine treatment. In this study, the colchicine treatment of seedlings of Catharanthus roseus induced chimeras with each tissue of L1, L2, and L3 layers composed from 2x or 4x. The percentage of polyploids containing chimeras was the highest with 24-hour treatment with colchicine at 10 mM (DMSO 5%). Regarding the relation between ploidy of L1–3 layers in the leaf of the obtained polyploid and the leaf width/leaf length ratio, the ploidy of L1 and L3 layers was not involved in the leaf width/leaf length ratio. Leaves with an L2 layer of 4x were roundish and the leaf width/leaf length ratio was significantly higher than in leaves with an L2 layer consisting of 2x. Therefore, the ploidy of the L2 layer was involved in the determination of the leaf shape.

To establish a practical method to identify tree peony cultivars, we attempted to develop a method to distinguish 353 tree peony cultivars cited in the “Botan meikan” directory using Random Amplified Polymorphic DNA (RAPD) markers. Using 29 primers, 48 RAPD markers that identify polymorphisms among peony cultivars were obtained. All of the cultivars, except eight bud mutation groups and two presumed synonymous cultivars, could be distinguished using the 48 RAPD markers. Parents, offspring, and sibling cultivars could be distinguished using these markers. On the comparison of RAPD band patterns between cultivar groups, specific bands of each cultivar group were obtained. To confirm the effectiveness of the developed markers, cultivar identification was performed using specimens in an exhibition garden. The cultivar names inferred from RAPD markers were matched with the labeled names in 91.4% of the tested individuals. Thus, the RAPD markers developed in this study are effective for the curation of tree peony cultivars.

Using questionnaire surveys, this study investigated cultivar usage and its relationship with several parameters on tourist farms in the Kanto, Shikoku, and Kyushu-Okinawa regions of Japan. From the results, in addition to picking and direct sales, Shikoku and Kyushu-Okinawa farms supplied fruits to other businesses. However, in all investigated regions, most of the tourist farms used four cultivars, including early flowering and high-yielding cultivars, as well as some late flowering and low-yielding cultivars. According to responses to questions on farm priorities, we concluded that farms use both early and late flowering cultivars to standardize the harvest time and fruit quality rather than to prolong the harvest time. Finally, farms in all regions focused on fruit quality, disease resistance, and continuous flowering. These characteristics are important in the breeding of suitable cultivars for tourist farms.

Tachibana (Citrus tachibana (Makino) Tanaka) is a citrus species indigenous to Japan. It has been known since before the Nara period (~800 AD), and several wild populations are present in forests along the Pacific coast, from Tokai to Kyushu Island. Although tachibana was previously regarded as consisting of a single genotype, recent research with DNA markers suggested there are at least three different genotypes. Previous work was carried out across different wild populations, but little is known about the genetic diversity within each population, or among populations. In this study, wild tachibana trees of a population in Heda, Shizuoka (n = 64; 24 in Ida area and 40 in Kamiya area) were sampled to explore the population’s genetic diversity and promote utilization and conservation. Using DNA marker analysis for both nuclear and organelle genomes, we confirmed that, in total, 60 plants (22 in Ida and 38 in Kamiya) had a tachibana-A strain genotype. Four unidentified citrus plants in the sample were genotyped as Natsudaidai (C. natsudaidai Hayata). No selfed or hybrid offspring were found in either area. The observations suggest that it may be difficult to obtain hybrids from tachibana-A as seed parents, and another DNA marker analysis of open-pollinated seeds showed similar results. The survey revealed several young tachibana trees in the population, and we suggest that vegetative propagation by polyembryonic seeds may facilitate asexual maintenance of this tachibana population.

Apple blotch (Marssonina blotch), which is caused by Diplocarpon mali Harada & Sawamura (anamorph Marssonina coronaria (Ell. & J. J. Davis) J. J. Davis), is one of the major diseases of cultivated apple (Malus × domestica Borkh.) in Japan. The aim of this study was to develop a reliable index to assess the resistance of apples to Apple blotch, and evaluate resistance levels of various apple genotypes. At first, we observed the degree of disease development on natural infection with Diplocarpon mali. in the field of Apple Research Station, Institute of Fruit Tree and Tea Science, NARO. Among 12 varieties, dwarfing rootstocks, Marubakaido and Mitsubakaido revealed that the disease incidence and disease severity index were high among cultivated apples, whereas no disease symptom was found in Mitsubakaido; the disease incidence and disease severity index in Marubakaido, ‘M. 9EMLA’ and ‘M. 26EMLA’, were low compared with those in cultivated apples, ‘JM1’ and ‘JM7’. A strong positive correlation was observed between the values of the disease severity index and rate of defoliation obtained by the inoculation test and the degree of disease development, expressed as the disease incidence and disease severity index, caused by natural infection with Diplocarpon mali. in the field. Resistance levels of seventy apple genotypes including rootstocks and wild Malus species, inoculated with the conidial suspensions artificially, were classified by the values of the disease severity index as: resistance < 0.3, 0.3 ≦ moderate resistance < 0.6, 0.6 ≦ susceptible; similarly, the genotypes were classified by the values of defoliation as: resistance < 0.1, 0.1 ≦ moderate resistance < 0.4, 0.4 ≦ susceptible. Inoculation tests indicated that the resistance levels of several wild Malus species, Tarehanakaido (Malus halliana), Mitsubakaido (Malus sieboldii), Nikkozumi (Malus baccata), Bracteata (Malus coronaria), Malus angustifolia, and Malus ioensis, were rated as adequately resistant to Apple blotch, while cultivated apples including scab-resistant varieties such as ‘Florina’, ‘Freedom’, ‘Remo’, ‘Retina’, and dwarfing rootstocks of ‘M.9E’, ‘M.26E’, ‘JM1’, and ‘JM7’ were susceptible. Marubakaido and some wild Malus species belonging to Malus platycarpa, Malus pratii, Malus sieversii, Malus florentina, and Malus honanensis were rated as moderately resistant.

We evaluated the crossability of 20 Bouvardia cultivars/lines and determined their usefulness as breeding materials. A total of 20 Bouvardia cultivars/lines were examined: one Bouvardia longiflora line, two B. ternifolia lines, four 4x-hybrid cultivars, nine 8x-hybrid cultivars, and four polyploid (8x) lines produced from the 4x-hybrids treated with colchicine. Reciprocal crosses were performed using all 20 cultivars/lines as seed parents, and 13 cultivars/lines as pollen parents. The seed set percentage, number of seeds per capsule, germination rate, and number of seedlings per flower were recorded. Based on crossing results, female and male fertility was scored from 0 to 5, and self-fertility was scored from 0 to 4. There were 137 cross combinations in total. Seeds were obtained from 68 combinations (50%) and seedlings were obtained from 59 combinations (43%). Female fertility was recorded in 18 cultivars/lines (scores 2–5) and was generally low in the 4x-hybrid cultivars. However, fertility significantly recovered in their polyploid lines (8x). Male fertility was recorded in 10 cultivars/lines (scores 2–5) and was medium to high (scores 3–5) in the lines of two species (B. longiflora and B. ternifolia) and many 8x hybrid cultivars. Five cultivars/lines were self-fertile. Sixteen cultivars/lines, including polyploids, had medium to high scores (≥3) for one or more fertility type (male, female, and self), and were considered to be useful cross-breeding materials.

We developed a labor-saving fertilizer application method in ‘Ishiji’ satsuma mandarin whereby the nitrogen quantity of summer and autumn fertilizer can be reduced by 30%, using controlled-release fertilizer to reduce the working time for spreading fertilizer under permeable and reflective sheet mulching on steep sloping orchards. The developed fertilizer application method reduced the working time by 20% per year compared with the control of three times a year, because autumn fertilizer application and mulch opening and closing could be omitted. The 30% reduction in the quantity of summer and autumn fertilizer nitrogen had no influence on the yield or fruit quality for 3 years. From the above, it was suggested that the working time can be reduced and the yield and fruit quality are unaffected when using the developed fertilization method.

In this study, we aimed to develop a model for predicting dates of budding and full bloom of ‘Delaware’ grape under open field conditions based on the daily average temperature. To predict budding and full bloom dates of ‘Delaware’ grape, we analyzed field data from 1963 to 2019, with two methods adopted for the growth simulation model: accumulated temperature method and developmental rate (DVR) method. Strong negative correlations between the number of days for germination and temperature and the number of days for flowering and temperature were detected. The DVR method (starting date of February 21) showed the lowest Root Mean Square Error (RMSE) = 2.4 days for the prediction of budding dates. The RMSE of the DVR method = 2.1 days was the lowest for the prediction of full bloom dates. The findings of this study suggest that the developmental stages of grape can be predicted with practical accuracy by adopting an appropriate growth simulation model of targeted developmental stages.

Changes in the polymethoxyflavone (nobiletin, tangeretin, and sinensetin) and hesperidin contents in flavedo of Ponkan (Citrus reticulata Blanco) and Tachibana (Citrus tachibana Tanaka) during cultivation from July to December were investigated over several years. In 20 surveys conducted over 3 years (Ponkan) and 2 years (Tachibana), the nobiletin, tangeretin, sinensetin, and hesperidin content (mg・100 g^–1FW) was the highest in July and decreased significantly in the harvest period. Over the three years investigated, the nobiletin content in flavedo of Ponkan in December was 74, 46, and 40% of that in July, respectively. The nobiletin content in the flavedo of each fruit significantly increased with flavedo growth in 2017. In contrast, the nobiletin content did not increase in 2018. This could have been due to higher nobiletin degradation rather than flavedo growth. These results indicate that harvesting times of July, August, and September, earlier than common harvesting times could be more efficient time for the extraction and utilization of flavonoids. The relationship between the flavonoid content in the flavedo and fruit growth (maturity) as well as climatic factors remain to be elucidated.

Cryopreservation using the V cryo-plate method was estimated for cryobanking of Allium spp. The regrowth rate of cryopreserved shoot tips was almost 100%, and normal shoots grew without callus formation. A suitable method for garlic was as follows. Shoot tips were precultured for 2 days at 25°C on solidified 1/2MS medium containing 0.3 M sucrose. Osmoprotection treatment was performed in LS solution (2.0 M glycerol + 1.0 M sucrose) for 30 min at 25°C. The dehydration time of shoot tips by PVS2 was 30 min at 25°C. This optimized procedure could be applied to other Allium spp. and high regrowth rates (90–100%) were obtained. As shoot tips attached to the cryo-plate were immersed in liquid nitrogen directly in the V cryo-plate method, the speed of cooling and warming shoot tips is much faster than in vitrification and droplet-vitrification methods, resulting in achieving a high regrowth rate. The V cryo-plate may be applicable for effective cryo-banking of Allium spp.

The yellow-skin and red-fleshed apple cultivar ‘HFF60’ was bred on Fujisaki Experimental Farm of Hirosaki University. The potential parents of the cultivar elucidated by SSR markers are ‘Toko’ and “red-fleshed apple strain Parent A”, respectively. The shoot growth of ‘HFF60’ is vigorous like ‘Ohrin’; suitable training and pruning techniques were necessary to maintain a sufficient number of flower buds. In the Aomori region, the harvest season of this cultivar was from late September to early October. The cylindrical fruit usually had a fresh weight of 350 g with 12.4% soluble solids and around 0.5% titratable acidity at harvest. The flesh firmness readily decreased during the cold storage period and 1-MCP treatment could not prevent it. Pre-harvest AVG treatment was effective for maintaining the flesh firmness but it cannot be practically applied because of inhibiting flesh coloration. Thus, ‘HFF60’ was not suitable for long storage, but it has the attractive advantage that both growers and consumers can easily evaluate the flesh coloration non-destructively through the yellowish permeable skin. In order to promote this cultivar, we could emphasize not only the color contrast between skin and flesh for fresh consumption, but also highlight the utility for processing consumption.