Since the establishment of the International Rice Research Institute (IRRI) in 1960, IRRI’s breeding effort in varietal improvement for irrigated lowland has passed four decades. Breeding of semi-dwarf rice varieties such as IR8 at IRRI during first decade from 1960 to 1969 resulted in quantum leaps in yield potential, which marked the green revolution in Asia. During the second decade from 1970 to 1979, the primary emphasis of rice improvement has been directed towards incorporation of multiple disease and insect resistance and shortening of growth duration. Grain quality was the main target of crop improvement at IRRI during the third decade from 1980 to 1989. The fourth decade from 1990 to 1999 and beyond was focused again on the improvement of yield potential by developing hybrid rice and new plant type. Up to 1999, 46 indica inbred varieties and 2 indica/indica hybrid rice varieties were developed by IRRI and released in the Philippines for the irrigated lowland rice systems. Large-scale adoption of these improved varieties under modern crop management practices has resulted in a dramatic increase in rice production in major rice-growing countries. The hybrid varieties between indicas increased yield potential by 9% under the tropical conditions. New plant type (NPT) breeding has not yet resulted in an increase in yield potential. The second generation NPT developed by crossing tropical japonica with indica has demonstrated some promising results in terms of improvements in yield potential, disease and insect resistance, and grain quality.
Acidic fractions of the extracts from the three alfalfa cultivars Batasu, Rasen, and Yuba exhibited a varietial difference in the inhibitory effect on hypocotyls and radicle growth of alfalfa (cv. Nasuwakaba) and rice (cv. Koshihikari) seedlings. The extract from Rasen possessed the strongest inhibitory activity, and that of Batasu was the lowest. In a TLC bioassay with lettuce seedlings, inhibitory zones of the extracts were located at an Rf value of 0.6-0.8, and maximum exhibitory zones at Rfs of 0.7-0.8. However, the extracts of Rasen and Yuba contained an additional inhibitory zone at Rf of 0.1-0.2. Inhibitory zones were analyzed by HPLC. Eight phenolic compounds were identified in the extracts from Rasen and Batasu, and six compounds in that from Yuba. However, the content of these phenolic compounds varied with the cultivar. The content of each phenolic compound was the highest in Rasen, followed by Yuba and Batasu, although the content of p-hydroxybenzoic acid was equivalent in all cultivars. We suppose that the degree of inhibitory exhibition of allelopathy may be related to the presence and concentrations of allelochemicals (phenolic compounds), however, the allelopathic activity of the plant might be determined by interactions of all these compounds, not just a single chemical.
To clarify the factors responsible for the maintenance of a high rate of photosynthesis at the ripening stage in the high-yield rice cultivar Akenohoshi, as compared with that in a Japanese standard cultivar, Nipponbare, we investigated the nitrogen content of leaves, focusing on the accumulation and the partitioning of nitrogen in rice plants. The nitrogen content of leaves of plants that were grown in the field or in pots remained higher in Akenohoshi than in Nipponbare during the ripening stage, and there was a close correlation between the rate of photosynthesis and the nitrogen content irrespective of cultivar and treatment. The accumulation of nitrogen in the whole plant was greater in Akenohoshi than in Nipponbare before heading and during the ripening stage. The extent of partitioning of nitrogen to leaves was higher and that to ears was lower in Akenohoshi than in Nipponbare during the ripening stage. By application of additional nitrogen fertilizer to Nipponbare, the nitrogen content of leaves was increased as a result of the increased accumulation of nitrogen in the whole plant and the enhanced partitioning of nitrogen to leaves. Our results indicate that the higher nitrogen content of Akenohoshi leaves was due to the greater accumulation of nitrogen in the plant before heading and during the ripening stage and the more effective partitioning of nitrogen to leaves during the ripening stage, which resulted in the maintenance of a high rate of photosynthesis during ripening.
The architecture of a grass population is determined by the spatial distribution and morphology of tillers. The demographic and phase changes of tillers were compared between an annual-like (Progrow) and perennial (Ruanui) lines of Lolium species. We investigated the developmental fate of axillary buds for 57 weeks after germination (WAG) under a constant condition. In general, a high production of seeds is positively correlated with the annual habit in plants. A high production of seeds was highly associated with % reproductive tillers in annual-like Progrow, which resulted from the death of non-reproductive or vegetative tillers before heading. However, no such tendency was observed in perennial Ruanui. This showed that the death of tillers is genetically regulated to contribute to the maximum success in fitness depending on the longevity. In addition, % reproductive tillers was distinctly reduced during the following regrowth in Ruanui, suggesting that a phase change in the tiller system took places during the growth. Microscopic observations of quiescent axillary buds showed that a phase change from reproductive to vegetative occurred at maturity in Ruanui but not in Progrow. As a result, numerous ears developed in Ruanui plants only when they were vernalized after first maturation (30 WAG), showing that the vernalized state gradually diminishes with time in Ruanui. Thus, the present results confirmed that the differential regulation in the developmental fate of axillary buds actually plays a role for determining the pattern of life history in Lolium.
The correlations of the reading of a portable chlorophyll meter (SPAD-502) with the chlorophyll and N contents of leaves of two faba bean (Vicia faba L.) cultivars, Japanese (Ryousai-issun) and Egyptian (Cairo 241), were examined. The SPAD readings positively correlated (p<0.01) with the chlorophyll contents and the r2 values were 0.99 and 1.00 for Ryousai-issun and Cairo 241, respectively. A close linear relationship (p<0.001) was observed between SPAD reading and total leaf N content at the pod development stage of faba bean plants with r2=0.88 and 0.99 for Ryousai-issun and Cairo 241, respectively. The SPAD reading was the highest in the 2nd to 4th leaves counted from the top (the youngest fully expanded leaves). The changes in leaf chlorophyll content of both cultivars from 3 weeks after transplanting to the ripening stage showed an incomplete “M” type curve. SPAD readings were significantly higher in Ryousai-issun than in Cairo 241 throughout the growth season. Organic fertilizers application improved faba bean plant growth. These results suggest that the SPAD-502 chlorophyll meter can be used to measure chlorophyll and nitrogen contents of faba bean leaves for quick screening faba bean genotypes.
The effects of paclobutrazol (PB) on podding habits and photosynthetic characteristics (CO2 assimilation rate, quantum yield of photosystem II (ΦPSII) and chlorophyll content) were examined in peanut. Application of PB at the start of the pod formation stage increased the percentage of podding, particularly in early-blooming flowers and seed yield. The major factor for this effect may be an acceleration of dry matter distribution to the early-bearing pods, which resulted from the inhibition of stem growth by PB. Application of PB at the early pod-formation stage increased chlorophyll content and ΦPSII, resulting in enhanced CO2 assimilation rates. In the long term, PB tended to increase crop growth rate and net assimilation rate though not significantly. The effects of PB on the photosynthetic characteristics, however, were observed only during a short period at a restricted growing stage, suggesting that an increase in the photosynthetic rate would not be the main factor for the PB-induced increase in seed yield.
The period from mid-March to April in the wheat-growing season in Japan corresponds to a wet period known as “Natanezuyu”. After this wet period, the weather remains rather dry until June. Fluctuations in soil moisture conditions during the growing season might be expected to affect the growth of wheat. Therefore, we compared the grain yield, dry matter production and ecophysiological characteristics of wheat grown with adequate moisture during the ripening stage after it had been grown under adequate (W-plot) or deficient (D-plot) soil moisture conditions for about one month before heading. The grain yield in the D-plot was higher by about 15 to 40% than that in the W-plot, with greater dry matter production. The larger dry weight in the D-plot resulted from a higher rate of crop growth before and after heading, which was due to a larger leaf area and higher net assimilation rate. During the ripening stage, leaf senescence of plants was delayed and the rate of photosynthesis fell more slowly in the D-plot than in the W-plot. Root systems developed better, resistance to water transport from root to leaves was lower, the exudation rate of roots was higher, and the cytokinin activity in xylem exudates from roots was higher in the D-plot. These characteristics of roots might have caused the significant difference in the growth and physiology of the aboveground parts of the plants. Our results indicate that encouragement of the development of the root systems, for example, by drainage during the wet period might be important for improving the grain yield of wheat in Japan.
The supernodulating soybean genotype Sakukei 4 is potentially high-yielding. We characterized its leaf nitrogen (N) content, photosynthesis and growth at different developmental stages and under different dosages and types of N fertilizer, and compared it with its parental cultivar Enrei and the non-nodulating line En1282. At the pod-expansion and seed-filling stages, the N contents per leaf dry weight and per leaf area, and apparent photosynthetic rates (AP) were higher in Sakukei 4 than in the normal and the non-nodulating genotypes. The nodule activity per plant was also higher in Sakukei 4 than in Enrei during the reproductive stage. These traits varied less with the growing condition (field- or pot-grown) and dose or type of N fertilizer applied in Sakukei 4 than in the other genotypes. The superior ability of Sakukei 4 to maintain high leaf N and AP, however, did not enhance its growth performance, which tended to be inferior to that of Enrei. Further studies are needed to define the cultivation conditions optimal for an exploitation of the favorable traits of Sakukei 4.
Segments of rice leaves at different nodal positions were incubated in NaCl solutions for various periods, and the chlorophyll content, Na content, Cl content, Na/K ratio and the ultrastructure of excised leaf tissues were examined. The chlorophyll content of the leaf tissues decreased with increasing NaCl concentration and incubation period. Na and Cl contents of the leaf tissues also increased with increasing NaCl concentration, but the decrease in chlorophyll content by salt stress was greater in old than in young tissues even when both tissues contained comparable amounts of Na and Cl. The presence of benzylaminopurine (BAP) alleviated the salt stress-induced decrease in chlorophyll content, but did not significantly affect the element contents. Ultrastructural damages were apparent in the chloroplasts of the leaf tissues subjected to salt stress. In 0.1% NaCl-treated old leaf tissues, the thylakoids were swollen, the envelope was partly destroyed causing leakage of the chloroplast contents. However, these damages were alleviated by the addition of BAP to the NaCl solution. In young leaf tissues, the thylakoids were swollen by incubation in 1.0% NaCl solution, but no structural distortion was observed in a 0.1% NaCl solution even without BAP added. The present study suggests that the leaf tissues were damaged by an increasing salt content and became more sensitive to salt stress with advancing leaf age. BAP seemed to alleviate the damages by salt stress through retardation of leaf aging.
The contents of Na, K, Cl, chlorophyll and the foliar ultrastructure of rice seedlings grown in NaCl solution at various concentrations were investigated under light and dark conditions. The seedlings were first grown in water for 7 d under a light condition and then in NaCl solutions at various concentrations for 24 h under a light or dark condition. The Na and Cl contents in the 3rd leaves increased as the concentration of NaCl in the culture solution increased, and were significantly higher under a light condition than under a dark condition. The K content was scarcely influenced by the NaCl concentration under both conditions. The chlorophyll content in the 3rd leaves of the seedlings decreased as the NaCl concentrations of the culture solution increased under a light condition but not under a dark condition. In the 3rd leaves of the seedlings grown in the NaCl solution under a light condition, the thylakoids of chloroplasts in mesophyll cells were swollen and showed a wavy configuration. Under a dark condition, however, the thylakoids appeared intact under saline conditions although the leaves accumulated a large amount of Na and Cl than in a light condition. The present study suggests that the damages in the chloroplasts, such as a decrease in the chlorophyll content and the degradation of thylakoids, were caused by a light-dependent reaction and not directly by accumulation of excess salt.
In a hilly area in Lampung State, the southern end of Sumatra Island in Indonesia, coffee is commonly cultivated on hillsides with steep slopes and soil erosion affects sustainable coffee production. A field experiment on coffee cultivation was conducted for 4 years to evaluate the effects of alley cropping and no-tillage on the seed production of coffee and on erosion control in a steep slope area in this region. The cultivation of intercropped vegetables, red peppers, tomatoes, and long beans was introduced into the coffee fields when the coffee plants were small. No significant differences in the yields of either the coffee plants or the intercropped vegetables were noted among the treatments. Coffee shoot fresh weight, however, was slightly increased by no-tillage treatment. Soil erosion was reduced by 37% as a result of no tillage and by 64% with alley cropping. The amount of soil erosion for local farmers practice, tillage & no-alley, was more than four times that in no-tillage and alley treatment. These results indicate that alley cropping and no-tillage are effective for erosion control on coffee fields on steep slopes and that yield is not affected by these practices. The introduction of intercropped vegetables is beneficial in terms of farm economy, especially when the income from coffee cultivation is limited.