The high-yielding capacity of some Chinese rice varieties with more than 1000 gm^-2 of brown rice yield was verified and the process of yield formation examined in Yunnan Province, China. Through our research, it became clear that the high efficiency in the use of absorbed nitrogen during the formation of the rice grain contributed to their high-yielding capacity. To explore the potential of these high-yielding rice varieties other than for daily food, we evaluated their suitability for Japanese sake brewing. The physical and chemical propert ies of Yu-Za 29, ChiJing 9 and He-Xi 24 rice, harvested in Yunnan Province, were evaluated for the brewing of sake and compared with that of Nipponbare (one of Japan’s high -yielding rice varieties), Yamadanishiki and Iwai (two white -core rice varieties that are used exclusively for brewing sake), all harvested in Japan. As a result, it became clear that Chi-Jing 9 was more suitable for brewing sake than Nipponbare. Moreover, sake brewed from this variety has a better aroma and taste than that brewed from Nipponbare.

The effect of fertilization on growth of water yam (Dioscorea alata L.) is not fully understood. The importance of nitrogen application has been demonstrated; however, the required minimum amount remains unknown. This study examined growth of water yam under low fertile soil conditions on Miyako Island, Okinawa Prefecture, Japan, from April 2013 to January 2014. Growth with urea application (N treatment) and without urea (control) was compared. N treatment had no effect on growth or tuber yield in soil with poor organic matter. Although yellowish leaves were observed in control plants, they continued to grow till the end of harvest. The findings suggest that water yam (cv. No. 511) is able to grow under poor fertile soil conditions such as the Holocene limestone soil of Miyako Island. The δ¹⁵N values of the N-treated plants suggested that nitrogen was absorbed from the urea; however, the source of nitrogen in the control plants was not identified. Moreover, the δ¹⁵N values of the control plants decreased with growth as in sweet potato, which are known to associate with nitrogen-fixing endophytes. In line with this, growth comparisons of N-treated and control plants suggest that water yam also absorbs nitrogen from the air, although further clarification is required.

An improved shoot micropropagation protocol of Simmondsia chinensis (Link) Schneider (jojoba) through axillary-bud proliferation from nodal explants using combination of 6-benzyladenine (BA) and thidiazuron (TDZ) has been developed. Axillary buds were sprouted from nodal segments within two weeks on Murashige and Skoog (MS) medium supplemented with different combinations of BA and TDZ. The presence of TDZ in initiation medium increased the rate of explants with sprouting buds. To avoid adverse effects of prolonged exposure of explants to TDZ, cultures were transferred to TDZ-free MS medium fortified with various concentrations of BA for further multiplication, proliferation and elongation of induced shoots. The highest number of shoots per explant (29.5 ± 1.3) was achieved when 2.5 mgL^-1 BA and 5.0 mgL^-1 TDZ-exposed explants were sub-cultured for 6 weeks on MS medium containing 1.0 mgL^-1 BA. Elongated shoots were rooted on 1/2 MS medium augmented with 2.5 mgL^-1 IBA, which resulted in the highest average number of roots per shoot (7.4 ± 0.9). The regenerated plants were acclimatized and transferred to a growth chamber with 75% survival rate. Our results suggested that combination of BA and TDZ was effective for shoots multiplication and sprouting buds of jojoba explants, and that this protocol would be useful for the large-scale micropropagation of elite jojoba genotypes.

Jojoba is an important oil crop that produces unique wax ester in seeds. Genetic transformation of jojoba, however, has not been reported yet. In this study, we used nodal segments as explants for transformation of jojoba by an Agrobacterium strain harbouring a plasmid containing the GUS gene with an intron, as well as the hygromycin resistance gene. Multiple shoots were regenerated from axillary buds of the nodal segments that were infected by the Agrobacterium strain. GUS activity was detected by histochemical assay in nodal segments as well as in the regenerated shoots that suggests jojoba cells were stably transformed and regenerated. Sonication and shaking treatments of the explants did not significantly affect on the transformation efficiency, but rather negatively affected on shoot regeneration. To obtain the effective hygromycin concentration for the selection of transgenic shoots, we examined hygromycin sensitivity of non-transgenic shoots on jojoba explants, and found that none of the shoots survived on the medium with 30 mg L^-1 of hygromycin. Regenerated shoots of Agrobacterium-treated explants were then selected on the same medium, and hygromycin-resistant shoots were observed with frequencies of 3.3 - 16.4 %. We also detected expression of the GUS gene in the hygromycin-resistant shoots by RT-PCR and GUS staining. This study is the first report of the successful introduction and expression of a foreign gene into jojoba, and will lead to generation of transgenic jojoba plants useful for the tropical and subtropical agriculture.

Oilseed sunflower (Helianthus annuus L.) has a lower seed yield and harvest index than other oil crops, and consequently produces a large amount of residue such as stem, receptacle, and oil cake. Our study attempted to use these residues as biochar for improving soil fertility, sunflower growth, and yield in subtropical island, Okinawa, Japan. To reveal the synergistic effect of biochar and inorganic fertilizer, we established four treatments: biochar (B), biochar + fertilizer (BF), fertilizer (F), and control, using biochar derived from bagasse (Exp. 1) and sunflower residue (Exp. 2). As a result, biochar application improved soil fertility, including soil electrical conductivity and mineral concentration. In spite of the initial positive effect of biochar application to plant growth this effect became negative later. The reason for this response might be the reduction of the net assimilation rate (NAR) during the later growth stage due to nitrogen deficiency after biochar application. Biochar application had a positive effect on sunflower growth during the early growth stage when the leaf area index (LAI) was dominant for the crop growth rate (CGR), while this effect became negative during the later growth stage when the NAR was dominant for the CGR. Further research is required to determine the effects of biochar application depending upon application methods, plant growth stages, and plant species.

The relationship between nitrogen absorption and growth of lesser yam (Dioscorea esculenta L.) is not clearly understood. The results of our previous experiment that lesser yam was able to grow under poor fertile soil conditions without nitrogen fertilization; however, the source of nutrition was not identified. This study, which was conducted from April 2015 to January 2016 aimed to determine whether nitrogen-fixing endophytic bacteria are associated with lesser yam. Growth with urea (N treatment), with cow manure (CM treatment) and without nitrogen (control) was compared. N and CM treatment had a positive effect on growth and tuber yield in soil with poor organic matter. Control plants presented with yellowish leaves, but grew until harvest and had a tuber yield comparable with other treatments. Changing natural isotope values (δ¹⁵N) under N and CM treatment suggested that nitrogen was absorbed from the urea and cow manure, respectively; however, the source of nitrogen in the control plants was not identified. Isolation of nitrogen-fixing endophytic bacteria using an acetylene reduction activity test and phylogenetic analysis of 16S rRNA gene sequences revealed five species of in the stem and roots of the lesser yam plants. These species were shown to be related to species in the genera Azospirillum, Devosia, Klebsiella, Rhizobium and Xanthomonas. The Rhizobium sp. was found in stem and the others were observed in the roots of lesser yam. All these species are known as nitrogen fixing bacteria and associate with plants growth. This is the first report to identify nitrogen-fixing endophytic bacteria associated with lesser yam.

Increasing rice yield in rainfed fields is one of the major agricultural challenges in Cambodia. As an answer to this challenge, we focused on the System of Rice Intensification (SRI), which has been reported to increase rice yield while reducing water use, and has actually been adopted by many farmers. To elucidate how SRI can increase rice yield under water constraint in rainfed fields, we conducted an interview study with 106 farming households in Popel commune, Tram Kak District, Takeo Province of Cambodia in 2015, and asked them about the wet season rice in 2014. The farmers cultivated rice in total of 167 fields, of which 35 fields were under SRI practices whereas 132 fields were under conventional ones. We found that SRI was practiced more often in fields where supplementary water was available from ponds, rivers, and tube wells than those without it. In the former fields, SRI increased rice yield, whereas it did not in the latter fields. In SRI fields without supplementary water, younger seedlings planted earlier should have experienced severer water stress than those in conventional fields, and lost advantage of SRI to develop more tillers and thereby more grains. The dependency of yield increase by SRI on supplementary water availability implies that the prospect of rice yield increase via greater adoption of SRI would hinge on the capacity to increase supplementary water availability in the rainfed fields.