Mountainous Region Agricultural Research Institute (MARI), Aichi Agricultural Research Center(AARC) was established in Inabu town (later Toyota city), Aichi Prefecture, in 1933. MARI is situated in latitude 35 degrees 13 minutes north and longitude 137 degrees east and located 505 m above the sea level. The mean yearly temperature is 11.8°C, it has about 1,500 sunshine hours a year, and rainfall in a year is about 2,100 mm. These environmental conditions are suitable for blast. We have been breeding rice with blast resistance in these areas where outbreak of rice blast often occurs. MARI has contributed to rice cultivation in Japan by breeding scores of rice blast resistant cultivars. In particular, the rice cultivars bred by introducing blast field resistance of the upland rice cultivar, Sensho, are being cultivated not only in mountainous regions of a temperate district where outbreak of rice blast often occurs, but also at rice breeding laboratories all over Japan as mother plants for breeding. Since 1967, MARI was assigned by the Ministry of Agriculture and Fisheries as the experimental station for breeding superior cultivars for mountainous regions in the temperate district in Japan. The main cultivars bred by this project are Mine-asahi which have good kernel quality and good eating quality, Chiyonishiki and Mine-hibiki, which are resistant to rice blast, and others. At present, we are introducing the chromosomal region of field resistance to blast from Sensho by QTL (Quantitative trait loci) analysis and various genes from Yunnan cultivars and native gene sources into the cultivars with good eating quality, and breeding highly rice blast resistant lines.

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The effects of the night temperature on CO₂ exchange rate and organic acid accumulation in the leaves of two crassulacean acid metabolism (CAM) plants, Kalanchoë pinnata and Ananas comosus (pineapple), were examined under a fixed day-temperature condition of 30°C. With the increase of the night temperature, the CO₂ exchange rate decreased in both species, and K. pinnata completely lost nocturnal CO₂ uptake under a high night temperature (30/37°C in day/night) condition (HNT). Malate accumulation in the leaves of pineapple and K. pinnata in the morning decreased with increasing night temperature, but that in the afternoon was not influenced by the night temperature. Diurnal changes of ten kinds of metabolites were investigated under HNT. Pineapple accumulated a large amount of nocturnal malate under HNT, but K. pinnata did not. Four kinds of hexose-phosphate (hexose-P) were accumulated at the same levels during the day/night cycle under HNT in both plant species. Nocturnal accumulation of oxaloacetate (OAA) was observed but phosphoenolpyruvate (PEP) was kept at a high level both in day and night under HNT in both plant species. The concentrations of malate required for 50% inhibition of the activities of day and night forms of PEP carboxylase (PEPC) from the pineapple leaves were 1.2 and 0.7 mM, respectively, whereas those from the K. pinata leaves were 3.7 and 2.0 mM, respectively. In both plants, NAD-MDH activity in vitro increased with increasing temperature. It is therefore suggested that under HNT, phosphorylation may not be the major factor controlling PEPC activity in pineapple, and therefore CAM mode in pineapple was maintained under HNT. The nighttime phosphorylation of PEPC in K. pinnata would disappear under HNT leading to the loss of nocturnal malate accumulation.

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The ratio of dry-matter increase in seed (S) to that in shoot (W), referred to as R_S/W, during the seed-filling period may reflect the balance between the assimilate supply and the sink capacity of harvest organs. In the determinate soybean, cv. Tamahomare, R_S/W during the seed-filling period was nearly the same under various growing conditions including shading and thinning of plants. Therefore, the S in the determinate soybean seems to correlate with the W under various conditions. However, the correlation of the S with the W in indeterminate soybeans in which shoot growth continues during the seed-filling period is unknown. In this study, three soybean cultivars [Glycine max (L.) Merr.], Tamahomare (determinate), Tozan69 (indeterminate) and Peking (semi-indeterminate), were grown under shading and thinning conditions during the seed-filling period. The R_S/W approximated a positive linear regression in the three cultivars. R_S/W was approximately 0.5 in each cultivar. Positive correlations were observed between W and S, pod number or total node number in all cultivars. However, the seed number per pod and individual seed weight were not significantly influenced either by shading or thinning in any cultivar. Hence the rate of partition of assimilate to seeds seems to be determined by pod number. Harvest index was stable except when W was extremely low as when plants were heavily shaded. Our results suggested that the R_S/W, harvest index and the yield-determining processes of the determinate and the indeterminate soybeans are fundamentally the same.

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The transient changes in seminal root elongation rate, osmotic potential, water potential, and turgor pressure in maize after the onset of stress treatments were examined using polyethylene glycol 6000 to evaluate the process of osmotic adjustment in root. Maize seedlings were exposed to different intensities of osmotic stress for 1, 3, 5, 10, and 20 minutes, and 2, 6, 12, and 24 hours. Seminal roots shrunk immediately after the onset of the -0.41 and -0.89 MPa stress treatments, due to dehydration. However, roots gradually resumed elongation from 5 minutes after the onset of the stress treatment. The osmotic potential in the root elongating zone dropped drastically with the onset of stress followed by a gradual decrease for 6 hours. We quantitatively analyzed the relative importance of the factors that contributed to the reduction of osmotic potential, and found that 46% reduction of osmotic potential was caused by tissue dehydration and 54% by solute accumulation 20 minutes after start of -0.89 MPa treatment. At hour 12, however, only 7% reduction of osmotic potential was caused by tissue dehydration and 93% by solute accumulation. In the root elongating zone, turgor pressure decreased immediately after the onset of the stress treatment due to the larger decline of water potential than that of the osmotic potential. However, from minute 20 onwards, turgor pressure started to recover due to osmotic adjustment. These results indicated that osmotic adjustment develops immediately after exposure to osmotic stress, especially in the root elongating zone, and substantially contributed to the maintenance of turgor pressure and root growth.

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The changes in the accumulation of compatible solutes in the seminal root and leaves of maize were examined under four osmotic stress conditions to elucidate the expression pattern of osmotic adjustment. Maize seedlings were exposed to different intensities of osmotic stress for 1, 3, 5, 10, and 20 minutes, and 2, 6, 12, and 24 hours using polyethylene glycol 6000. Segments were obtained from the elongating zone of the root, elongated zone of the root and mature part of leaves. The concentrations of potassium ion and some amino acids under osmotic stress began to increase within 20 minutes after the onset of stress treatment in the root elongating zone. From hour 2, reducing sugars contributed mainly to the change of osmolarity. The amino acids that responded most quickly to the osmotic-stress treatment were Asp, Glu, Asn and Thr, which started to increase within 20 minutes, followed by Ser and Ala, which increased from hour 2 to 6, and Pro which increased from hour 12 to 24. Moreover, in the roots at hour 24, the proportion of potassium ion to total solutes decreased with the increase in the stress intensity. The proportion of amino acids to total solute in the root elongating zone was higher in the -0.13 MPa treatment group and that of the reducing sugars in the root elongated zone was higher in the -0.13 MPa and -0.41 MPa treatment groups than in the -0.08 and -0.89 MPa treatment groups. These results suggested that the kinds of solutes that contributed to osmotic adjustment differed depending on the duration and intensity of osmotic stress.

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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.

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Cell division and cell death in the cell division zone of the roots of rye seedlings under salt stress were analyzed quantitatively. Cell division was examined by immunological staining with anti-5-bromo-2'-deoxyuridine (BrdU) and cell death by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL). In the 0-700 μm portion from the root tip, which is the cell division zone, the frequency of cell division increased linearly during BrdU treatment. Therefore, the frequency of cell division under salt stress was compared with that in the control at 7 hours after application of BrdU. In the 250 mM NaCl solution (salt stress), the frequency of cell division was decreased and that of cell death was increased as compared with the control resulting in the inhibition of root elongation. In the presence of 50 and 100 mM NaCl, the frequency of cell division was also significantly increased and cell death was hardly detected, and root growth was unchanged as compared with the control. These results suggested that the increase of cell division complemented the decrease of cell elongation due to salt stress, and consequently maintained root growth under mild salt stress conditions.

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The callus induction potential of 15 indica rice genotypes from Indonesia was examined in comparison with that of the japonica rice Nipponbare. Callus was induced from embryos of mature seeds and root segments on MS and CI media. There was genotype×medium×explant interaction for inducing white/cream/yellow callus with an organized structure (callus type I and II) and for callus browning, but not for callus induction ability and diameter of callus. Genotypes significantly differed in inducing high quality of calluses depending on medium and explant used. Four indica types, Fatmawati, Ciapus, BP-23 and BP-360-3, had callus induction-related traits similar to those of Nipponbare. These genotypes would be useful for tissue-culture based research and for crop improvement, particularly for genetic transformation. Culturing seed explant on MS was more suitable for callus induction than either root explant on MS or both explants on CI medium.

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Establishment of a suitable system for plant regeneration of rice calluses derived from mature seed is a prerequisite for genetic transformation using callus as the target tissue. Selecting the most suitable medium and assessing the genotype performance for in vitro response are essential requirement for this purpose. The experiment with five Indonesian rice genotypes showed that callus-proliferation capacity (CPC) and callus-growth capacity were significantly affected by genotype and CPC by medium. The shoot-regeneration capacity and plantlet-regeneration capacity were affected by the interaction effect between genotype and medium. However for green plant-regeneration capacity, it was affected independently by genotype and medium. Culture media D1 and NB₅ were the most suitable media for callus subculture and plant regeneration, respectively. Genotypes Fatmawati and BP-140 consistently performed best in the callus subculture and plant regeneration.

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This study was designed to determine whether or not the difference in the physical properties between white-core and non-white-core kernels of the rice varieties for sake brewing is associated with their starch properties. We used two rice cultivars for sake brewing, Senbon-nishiki and Yamada-nishiki, from three different plots in Hiroshima prefecture. Hardness values of kernels were significantly higher in non-white-core than in white-core kernels in both varieties. Vickers hardness (VH) values were lowest at the center of the kernel in both types of kernels. VH values of white-core tissues of white-core kernels were significantly lower than those of corresponding tissues of non-white-core kernels. No significant differences were observed between the two types of kernels in VH values of the surrounding translucent tissues and in the starch properties (amylose content, pasting properties analyzed using a rapid viscoanalyzer and gelatinization properties analyzed using a differential scanning calorimetry). These results suggest that the difference in physical properties between the two types of kernels of the rice varieties for sake brewing are associated with the difference in structure of endosperm cells and not in starch properties.

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The spring-type cultivar (Triticum aestivum L.) is usually sown in November. However, the sowing time is sometimes delayed considerably because of much rain in October, and the seed bed does not become suitably dry for sowing due to cold temperature. To find a solution to this problem, we compared the yielding ability of wheat sown early (early-sown group) with wheat sown at the standard date (standard group) in Yamaguchi. The grain yield for nine cultivars averaged for three growing seasons, 1999/2000, 2001/2002 and 2002/2003 was 230 gm^-2 in the early-sown group, and significantly lower than that in the standard group (334 gm^-2). The spike number and grain number per spike were lower in the early-sown group than in the standard group. Akitakko, Iwainodaichi, Airakomugi had a higher grain yield, and Akitakko had a higher spikelet number per spike and higher grain number per spike than the other cultivars when sown earlier. Iwainodaichi showed higher spike number when sown earlier. Airakomugi showed higher grain number per spike and grain weight when sown earlier. Akitakko was the only cultivar that showed a higher grain yield by early sowing.

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