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Low transfer of radioactive cesium (radiocesium) from soil to grains of agricultural crops is desirable to ensure food safety for humans and animals. Although the transfer of radiocesium from soil ...

To mitigate radioactive cesium from soil to plant, increasing and maintaining the exchangeable potassium (ExK) level during growth is widely accepted after Tokyo Electric Company's Fukushima Dai-ichi Nuclear Plant accident in Japan. This is because the antagonistic relationship between soil solution K and

Radiocesium (RCs) discharged by the Fukushima Daiichi Nuclear Power Plant (Tokyo Electric Power Co., Inc.) accident has extensively contaminated agricultural land in Fukushima Prefecture and its ne...

Non-exchangeable K released from soil minerals can reduce radiocesium transfer to plants, as well as exchangeable K. We investigated the effect of non-exchangeable K on radiocesium transfer to soybean, and the non-exchangeable K extraction method most suitable for estimating the transfer risk. In Fukushima Prefecture, Japan, 106 soils were collected from 89 soybean fields during 2014-2018 to analyze non-exchangeable K contents using three methods: boiling nitric acid extraction, tetraphenyl‑boron extraction, and mild tetraphenyl‑boron extraction. The non-exchangeable K contents quantified by the former two methods were dependent on the amount of micas, which are K-bearing minerals. The non-exchangeable K content by mild tetraphenyl‑boron extraction depended on the amount of K fertilizer application and K-fixing minerals but not on micas, indicating that it reflects fertilizer K fixed by the minerals. The soil-to-plant transfer factor of radiocesium was most correlated with the non-exchangeable K content by the mild extraction (r

Decreasing the transfer of radioactive cesium (RCs) from soil to crops has been important since the deposition of RCs in agricultural soil owing to the Fukushima nuclear power plant accident of 2011. We investigated the genotypic variation in RCs accumulation in 234 and 198 hexaploid wheat (Triticum spp.) varieties in an affected field in 2012 and 2013, respectively. The effects of soil exchangeable potassium (ExK) content to RCs accumulation in wheat varieties were also evaluated. A test field showed fourfold differences in soil ExK contents based on location, and the wheat varieties grown in areas with lower soil ExK contents tended to have higher grain RCs concentrations. RCs concentrations of shoots, when corrected by the soil ExK content, were positively significantly correlated between years, and RCs concentrations of shoots were significantly correlated with the grain RCs concentration corrected by the soil ExK content. These results indicated that there were genotypic variations in RCs accumulation. The grain to shoot ratio of RCs also showed significant genotypic variation. Wheat varieties with low RCs accumulations were identified. They could contribute to the research and breeding of low RCs accumulating wheat and to agricultural production in the area affected by RCs deposition.

The effect of soil exchangeable (plant-available) potassium (ExK) content on cesium (Cs) absorption and translocation in buckwheat was evaluated in a field contaminated with radioactive Cs (134Cs and 137Cs, RCs) in 2013. The RCs concentration in buckwheat was significantly positively correlated with the naturally occurring stable Cs (133Cs, SCs) concentration, and was lower at higher soil ExK content. The RCs and SCs were actively absorbed by buckwheat until the flowering stage. The soil ExK content was significantly negatively correlated with soil exchangeable RCs and SCs (ExRCs and ExSCs) concentrations. Greater RCs and SCs absorption by buckwheat in soils with low ExK contents was mainly due to higher soil ExRCs and ExSCs concentrations. Reproductive organs showed the largest differences in SCs concentration between low-ExK and high-ExK plots. The root–shoot and shoot–reproductive organs translocations of SCs markedly decreased with increasing soil ExK content. In the root–shoot and shoot–reproductive organs translocations, the discrimination of SCs and K decreased with decreasing soil ExK content. Our main findings were as follows: (1) because RCs are mainly taken up at the earlier growth stage, potassium should be applied as a basal fertilizer to decrease the RCs concentration in buckwheat; (2) lower soil ExK content led to higher soil ExRCs concentrations, resulting in greater RCs absorption by buckwheat; (3) the high Cs absorption and translocation and weaker discrimination between Cs and K in low ExK content soil may be due to the expression of K transporter(s) with weak discrimination between Cs and K.

Low cadmium (Cd) transfer from the soil to edible parts of crop plants is important to minimize toxicity to humans and animals. We previously showed that Cd accumulation in grains differs substantially among varieties of common wheat ( Triticum aestivum L.). In this study, we investigated the factors responsible for these differences by comparing the absorption and partitioning of Cd among wheat varieties with distinct grain Cd concentrations. Three varieties with low grain Cd concentrations (low-Cd/G varieties) and one standard variety were cultivated in a field (under natural conditions) and in pots with Cd application at four growth stages (emergence, jointing, flowering, and grain-filling). The Cd concentration and content in the whole plant and grains were determined at the seedling, flowering, grain-filling, and maturity stages in the field experiment. Cd concentration, content, and partitioning in different plant segments were determined at the maturity stage in the pot experiment. In the field experiment, there were significant differences in Cd partitioning to grains between low-Cd/G varieties and the standard variety. Cd application at different growth stages in the pot experiment indicated the remobilization of Cd from shoots to grains and direct transport of Cd from roots to grains. In the pot experiment, lower Cd absorption was detected in low-Cd/G varieties than in the standard variety and the low-Cd/G varieties exhibited differences in Cd sequestration among plant parts, including the root, leaf, lower stem, first internode, rachis, and/or glume. These results suggest that several factors related to Cd absorption and translocation, such as root traits and xylem and phloem transport, affect the accumulation of Cd in grains in common wheat. Understanding and elucidating the contribution of each of these factors might facilitate the development of common wheat varieties with minimal grain Cd accumulation.

This study assessed soil contamination with high radioactive cesium (R–Cs) concentration in buckwheat grains by lodging, and assessed the possibility of R–Cs reduction in grain through post-harvest preparation. Analysis of buckwheat grain produced in farmers’ fields and reports from farmers indicated that grain from fields that had lodging showed higher R–Cs than grain from fields with no lodging. A field experiment demonstrated that R–Cs in grain after threshing and winnowing (TW) was about six times higher in lodged plants than in nonlodged plants. In lodged plants, R–Cs in grain was decreased to about one-fourth by polishing, and was decreased to about one-seventh by ultrasonic cleaning, compared with R–Cs in grain after TW. These results demonstrate that R–Cs of buckwheat grain of lodged plants can be decreased by removing soil from the grain surface by polishing and winnowing.

Tokyo Electric Power Company's Fukushima Dai-ichi nuclear power plant released radioactive cesium (Cs) into the environment after the Great East Japan Earthquake of March 11, 2011. After radioactive Cs fell onto agricultural fields, radioactive nuclide levels in some buckwheat ( Fagopyrum esculentum Moench) grain subsequently exceeded new standard limits for radioactive materials, including that for radioactive Cs (100 Bq kg −1 ) established by the Japanese government in 2012. A survey of soils and buckwheat grain from 68 farmers’ fields in 2012 revealed that soil exchangeable potassium (K) concentration was significantly and negatively correlated with radioactive Cs concentration in the grain. The effect of K application on the reduction of radioactive Cs concentration in the grain was confirmed by pot and field experiments conducted respectively in 2012 and 2013. This effect might result from the similarity of ion forms of K and Cs and/or the lower exchangeable Cs concentrations at higher exchangeable K concentrations in soil. Based on these results, farmers were recommended to establish a soil exchangeable K concentration of 250 mg kg −1 (300 mg kg −1 in K 2 O) before applying basal fertilizer. After this recommendation, the soil K concentrations of farmers’ fields increased, causing an overall decrease in radioactive Cs concentrations of buckwheat grain produced in 2013. Consequently, no grain sample from this year exceeded the standard limits for radioactive Cs level across the affected area in Japan. These efforts contributed greatly to the rehabilitation and reconstruction of agriculture in the area contaminated with radioactive Cs.

Near-isogenic lines (NILs), carrying different combinations of Ppd-1 genes in the genetic background of an early-maturity cultivar Abukumawase were grown at two sites for two years to elucidate the effects of photoperiodic response genes on the growth and yield of early-maturity wheat ( Triticum aestivum L.) in central and southwestern Japan. Photoperiod-insensitive genes, Ppd-B1a and Ppd-D1a , accelerated young spike development, and this effect was predominant with Ppd-B1 with no additive effect among them. Ppd-B1a and Ppd-D1a also advanced the jointing stage, heading, and maturity, and the effect of Ppd-B1a on the jointing stage and heading was stronger than that of Ppd-D1a. An additive effect of two genes was detected for heading. Besides, Ppd-B1a and Ppd-D1a reduced culm length and grain weight, although the reduction effect on grain weight was not significant. Meanwhile, the mean temperature from double ridge formation stage to heading was lower in NILs with photoperiod-insensitive genes than in NILs with photoperiod-sensitive gene, and there was a significant correlation between mean temperature from double ridge formation stage to terminal spikelet formation stage and spikelet number per spike as well as between mean temperature from terminal spikelet formation stage to heading and grain number per spikelet. Therefore in a genetic background of extremely early-maturity line of spring type wheat, photoperiod-insensitive genes accelerated wheat growth and reduced spikelet numbers in central and southwestern Japan, and the effect of Ppd-B1a was stronger than that of Ppd-D1a.

Fusarium head blight (FHB) remains a serious problem that causes yield and grain quality losses, and mycotoxin accumulation in wheat production in western Japan. A 3-year field trial with artificial FHB inoculation was conducted to evaluate varietal characteristics of FHB resistance among 31 wheat cultivars/lines cultivated in western Japan, including one standard line. Severity of FHB, frequency of Fusarium-damaged kernels (FDK), deoxynivalenol concentration (DON), nivalenol concentration (NIV), and grain yield showed significant differences among years and among cultivars/lines. Interaction between years and cultivars/lines was also significant in these traits, but F values were larger for cultivars/lines than for the interaction. Correlation analysis showed that cultivars/lines with lower FHB severities tended to have lower FDK, DON and NIV, and a higher yield. Resistance to kernel infection (RKI), residuals calculated by regressing FDK against FHB severity, and resistance to mycotoxin accumulation (RTA), residuals calculated by regressing DON + NIV against FDK, also differed significantly among cultivars/lines. These results indicated that varietal differences in response to FHB symptom development, RKI and RTA exist among wheat cultivars/lines in western Japan. Such information is important to aid producers in controlling the disease and for breeders to improve FHB resistance and reduce mycotoxin accumulation in commercial wheat cultivars.

Fusarium head blight (FHB), caused by Fusarium graminearum, is a serious disease of wheat (Triticum aestivum L.) associated with contamination by the mycotoxin deoxynivalenol (DON). The FHB-resistant wheat cultivar ‘Sumai 3’ has been used extensively around the world. The existence of variation in FHB resistance among ‘Sumai 3’ accessions has been discussed. In this study, genetic variation among ‘Sumai 3’ accessions collected from six countries were identified using SSR markers; our results demonstrate unique chromosome regions in Sumai 3-AUT and Sumai 3-JPN (‘Sumai 3’ accessions from Austria and Japan, respectively). Field evaluation indicated strong resistance to FHB in Sumai 3-AUT. The polymorphic rate (number of polymorphic markers/number of available markers × 100) based on a DArT array was 12.5% between the two ‘Sumai 3’ accessions. Genotyping for DNA markers flanking FHB-resistant quantitative trait loci (QTLs) revealed genetic variations for the QTL regions on 5AS and 2DS; however, no variation was observed for the QTL regions on 3BS and 6B. Thus, the variation in FHB resistance among ‘Sumai 3’ accessions in the field is due to genetic diversity.

The Ppd-A1 genotype of 240 Japanese wheat cultivars and 40 foreign cultivars was determined using a PCR-based method. Among Japanese cultivars, only 12 cultivars, all of which were Hokkaido winter wheat, carried the Ppd-A1a allele, while this allele was not found in Hokkaido spring wheat cultivars or Tohoku-Kyushu cultivars. Cultivars with a photoperiod-insensitive allele headed 6.9-9.8 days earlier in Kanto and 2.5 days earlier in Hokkaido than photoperiod-sensitive cultivars. The lower effect of photoperiod-insensitive alleles observed in Hokkaido could be due to the longer day-length at the spike formation stage compared with that in Kanto. Pedigree analysis showed that 'Purple Straw' and 'Tohoku 118' were donors of Ppd-A1a and Ppd-D1a in Hokkaido wheat cultivars, respectively. Wheat cultivars recently developed in Hokkaido carry photoperiod-insensitive alleles at a high frequency. For efficient utilization of Ppd-1 alleles in the Hokkaido wheat-breeding program, the effect of Ppd-1 on growth pattern and grain yield should be investigated. Ppd-A1a may be useful as a unique gene source for fine tuning the heading time in the Tohoku-Kyushu region since the effect of Ppd-A1a on photoperiod insensitivity appears to differ from the effect of Ppd-B1a and Ppd-D1a.

Fusarium head blight (FHB), which is caused by Fusarium graminearum Schwabe [teleomorph: Gibberella zeae (Schwein.) Petch], is a devastating disease affecting wheat (Triticum aestivum L.) spikes, which considerably reduces grain yield and quality and produces mycotoxins that are harmful to humans and animals, especially in warm and humid climates, such as that of west Japan. Therefore, an important target of breeding programs is to improve FHB resistance in wheat. In general, wheat cultivars bred in west Japan exhibit high resistance to FHB worldwide. FHB resistance in wheat can be divided into resistance to initial infection (type I) and resistance to spread within the spike (type II). To improve FHB resistance in west Japanese wheat, we first improved the methods used to evaluate type I and II resistance separately. We then analyzed factors related to type I and II resistance using diverse materials. Finally, we selected a wheat line, ‘Norin PL-9,’ into which we integrated type I and II resistance, and applied for registration as the wheat parental line. The knowledge and materials developed in this study are useful for breeding FHB resistance in wheat where FHB outbreak is problematic. This review draws on a series of related studies.

The genotypes of photoperiod response genes Ppd-B1 and Ppd-D1 in Japanese wheat cultivars were determined by a PCR-based method, and heading times were compared among genotypes. Most of the Japanese wheat cultivars, except those from the Hokkaido region, carried the photoperiod-insensitive allele Ppd-D1a, and heading was accelerated 10.3 days compared with the Ppd-D1b genotype. Early cultivars with Ppd-D1a may have been selected to avoid damage from preharvest rain. In the Hokkaido region, Ppd-D1a frequency was lower and heading date was late regardless of Ppd-D1 genotype, suggesting another genetic mechanism for late heading in Hokkaido cultivars. In this study, only 11 cultivars proved to carry Ppd-B1a, and all of them carried another photoperiod-insensitive allele, Ppd-D1a. The Ppd-B1a/Ppd-D1a genotype headed 6.7 days earlier than the Ppd-B1b/Ppd-D1a genotype, indicating a significant effect of Ppd-B1a in the genetic background with Ppd-D1a. Early-maturity breeding in Japan is believed to be accelerated by the introduction of the Ppd-B1a allele into medium-heading cultivars carrying Ppd-D1a. Pedigree analysis showed that Ppd-B1a in three extra-early commercial cultivars was inherited from ‘Shiroboro 21’ by early-heading Chugoku lines bred at the Chugoku Agriculture Experimental Station.

Shiratae Nijo is a new two-rowed food barley cultivar bred at the National Agricultural Research Center for Kyushu Okinawa Region (KONARC) in collaboration with the National Institute of Crop Science (NICS) and released in 2009. Shiratae Nijo is a proanthocyanidin-free cultivar bred by backcross breeding using a leading cultivar Nishinohoshi as a recurrent parent and a foreign proanthocyanidin-free mutant ant28-494 as a non-recurrent parent. The agronomic characteristics of Shiratae Nijo are almost the same as those of Nishinohoshi which has high yield performance and high resistance to barley yellow mosaic virus (BaYMV) type I and powdery mildew. Like Nishinohoshi, Shiratae Nijo shows high resistance to Fusarium head blight (FHB) at the anthesis stage but is susceptible 10 days after anthesis. Shiratae Nijo exhibits significantly weaker seed dormancy than Nishinohoshi. Shiratae Nijo has excellent pearling quality, and the pearled grains show no discoloration and high whiteness after cooking because of the lack of catechin and proanthocyanidin in the grains.

In wheat (Triticum aestivum L.), Fusarium head blight (FHB) resistance is an important breeding target to reduce yield losses and mycotoxin contamination. We hypothesized that cleistogamous (CL, closed flowering) cultivars have a lower risk of FHB infection than chasmogamous (CH, opened flowering) cultivars because FHB infection usually occurs in the inside of florets or extracted anthers and FHB resistance in CL cultivars decreases mycotoxin accumulation. To test these hypotheses, we produced 126 recombinant inbred lines (RILs) derived from a cross between common wheat varieties ‘U24’ (CL variety) and ‘Saikai 165’ (CH variety). Although ‘U24’ and ‘Saikai 165’ are both resistant to FHB infection, ‘U24’ is susceptible to FHB spread, grain deterioration, and mycotoxin accumulation compared with ‘Saikai 165’. Among the RILs, there were significant differences in all of the tested traits. Although the CL RILs showed less initial FHB infection than CH RILs, there were no significant differences in grain deterioration and mycotoxin accumulation between the 2 groups. An FHB-resistant quantitative trait locus (QTL) located on chromosome 3BS increased resistance to FHB spread, grain deterioration, and mycotoxin accumulation; however, not all CL RILs with this QTL accumulated less mycotoxin than ‘Saikai 165’.

Fusarium head blight (FHB) is the most serious disease affecting wheat (Triticum aestivum L.) because of its impact on yield and grain quality and its associated mycotoxin accumulation. This study was conducted (1) to develop efficient methods to evaluate varietal resistance against fungal spread after infection, (2) to investigate varietal differences in resistance to FHB infection, FHB spread, and mycotoxin accumulation in 23 Asian varieties, and (3) to analyze relations among FHB-resistant types. Inoculation of Fusarium graminearum isolate, causing virulence to detached spikes, enabled evaluation of FHB spread in a shorter period and smaller space than conventional methods. Among the varieties, the FHB spread differed significantly. ‘Sumai 3’ and its derivatives showed higher resistance to FHB spread than other varieties. The FHB spread showed no significant correlation with FHB infection. It showed significant positive correlation with DON, but some varieties with high resistance to FHB spread showed moderately high DON. Results show that improved methods to evaluate FHB spread can be effective to screen numerous materials. The FHB resistance of western Japanese varieties depends mainly on resistance to FHB spread. For development of FHB resistant varieties, due attention should be devoted to DON.

Root growth into deep soil is an important factor for stable production in wheat under drought conditions. Root penetrating capacity (RP) shown by pot experiments with a paraffin-Vaseline layer (PV layer) may be a useful indicator estimating deep rooting ability of wheat genotypes. Previously, we identified genotypes of durum wheat (Triticum turgidum L. var. durum) and bread wheat (T aestivum L.) with diverse RP by the pot experiments. In this study, we investigated the root distribution of three Ethiopian landraces of durum wheat with high RP, three recent cultivars of durum wheat with low RP and one Japanese cultivar of bread wheat 'Haruyutaka' with low RP using: (1) pots with a PV layer, (2) root boxes, (3) artificial field and (4) a normal field to analyze the relationship between RP estimated by pot experiment and root development in the field. In the pot experiments, RP was evaluated by the number of roots penetrating through the PV layer (NRP). In the root-box and field experiments, the root distribution was evaluated by the number of roots on the vertical surface of soil as the root frequency (RF: root number cm^ soil surface). Ethiopian landraces had a significantly larger NRP than recent cultivars in the pot experiment. The root box and field experiments showed that Ethiopian landraces tended to have a higher RF than recent cultivars in deep soil layer. We concluded that RP estimated by pot experiments with a PV layer is a useful indicator of deep rooting ability under field conditions.

The contamination of cadmium (Cd) into the food chain can be harmful because Cd causes chronic health problems. To evaluate the breeding potential reducing the Cd concentration in wheat grain, we compared Cd concentrations in 237 wheat genotypes including Japanese landraces, Japanese cultivars and introduced alien cultivars for breeding using grain samples collected from upland fields in 2004−5 and 2005−6 growing seasons. The Cd concentration in wheat grain significantly varied with the growing seasons and with the experimental fields. Cultivars bred in northern Japan, including the recent Japanese leading cultivar ‘Hokushin’, tended to have a low Cd concentration in grain compared with that bred in central and southern Japan. Simple correlation analysis between Cd concentration in grain and agronomic characteristics revealed that the Cd concentration in grain showed significant negative correlations with stem number, culm length and spikelet number per spike, and showed significant positive correlation with SPAD value (chlorophyll content) of flag leaf. Stepwise multipleregression analysis showed that the genotypic variation of Cd concentration in grain was associated with the culm length and spiklet number per spike. This study clarified the geographical pattern of genotypes with different Cd concentrations in grain in Japanese wheat cultivars. Cultivars originating from northern Japan may be useful genetic resources to develop cultivars with a low Cd concentration in grain to be grown in the areas where Cd accumulation in wheat grain is a problem.

The hard soil in the field is a major constraint for the cereal production because it mechanically restricts the root expansion and water absorption. The ability of root to penetrate into the hard soil is an important factor affecting yield stability of wheat (Triticum aestivum L.) under hard soil and drought conditions. We investigated the variation in the penetrating ability of roots (PA) among Japanese wheat cultivars and its relationship with other shoot and root characters to acquire basic information to develop the cultivars with a higher PA. The evaluation was conducted by the two experiments using the two groups of cultivars: 1) 43 Hokkaido cultivars in the first experiment, 2) 38 Honsyu, including Shikoku and Kyusyu, cultivars in the second experiment. In each experiment, one seedling of each cultivar was grown in a pot with a disc made of paraffin and Vaseline mixture (PV) as a substitute for the hard soil layer. The number of roots penetrating through the PV disc per plant (NRP), the number of seminal and crown roots reached the PV disc per plant (NRR) and the penetration index (PI = NRP/NRR) of each cultivar were evaluated as the traits related to PA. NRP significantly varied with the cultivar from 4.0 to 29.7 and 3.0 to 22.0 in the first and second experiments, respectively. NRP were significantly correlated with NRR (r=0.644** in the first and r=0.477** in the second experiment) and PI (r=0.863** in the first and r=0.811** in the second experiment), but the relationships between NRR and PI were not significant (r=0.260 in the first and r=0.190 in the second experiment). NRR was significantly correlated with the degree of winter growth habit (requirement of vernalization), root dry weight (DW) above the PV disc, the number of stems and leaf DW in each population. Correlations between PI and other characters were low or not significant. These results indicate that a large genotypic variation exists among Japanese wheat cultivars in NRP, and that PI is a suitable indicator of PA. Cultivars with a high PA detected in this study will be useful genetic resources of wheat to improve the yield stability under drought and hard soil conditions.

A pot cultivation experiment was conducted to elucidate the influence of the nonexchangeable potassium (K) of mica on radiocesium ((137)Cs) uptake by paddy rice (Oryza sativa L. cv. Koshihikari), and to evaluate the potential of mica application as a countermeasure to reduce radiocesium transfer from soil to paddy rice. The increase in the exchangeable K concentrations of soils, measured before planting, due to mica (muscovite, biotite, and phlogopite) application was negligible. However, in trioctahedral mica (biotite and phlogopite)-treated soil, the release of nonexchangeable K from the mica interlayer maintained the soil-solution K at a higher level during the growing season in comparison to the control, and consequently decreased the (137)Cs transfer factor for brown rice (TF). The sodium tetraphenylboron (TPB)-extractable K concentration of the soils, measured before planting, was strongly negatively correlated with the TF, whereas the exchangeable K concentration of the soils, also measured before planting, was not correlated with the TF. Therefore, we conclude that TPB-extractable K is more reliable than exchangeable K as a basis of fertilizer recommendations for radiocesium-contaminated paddy fields. Phlogopite-treated soils exhibited higher TPB-extractable K concentrations and lower TF values than biotite-treated soils. We thus conclude that phlogopite application is an effective countermeasure to reduce radiocesium uptake in paddy rice.