Effects of 42-year long-term fertilizer management on soil phosphorus availability, fractionation,adsorption–desorption isotherm and plant uptake in flooded tropical rice

Soil phosphorus(P) fractionation, adsorption, and desorption isotherm, and rice yield and P uptake were investigated in flooded tropical rice(Oryza sativa L.) following 42-year fertilizer and manure application. The treatments included low-input [unfertilized control without N, P, or K(C0N0)], farmyard manure(FYM)(C1N0), NP(C0NP), NPK(C0NPK), FYM + NP(C1NP), and high-input treatment, FYM + NPK(C1NPK). Grain yield was increased significantly by 74%over the control under the combined application of FYM + NPK. However, under low- and high-input treatments, yield as well as P uptake was maintained at constant levels for 35 years.During the same period, high yield levels and P uptake were maintained under the C0 NP, C0 NPK,and C1 NPK treatments. These are unique characteristics of a tropical flooded ecosystem, which is a self-sustaining system for rice production. The Fe–P fraction was highest compared to the Ca–P and Al–P fractions after 42 years of fertilizer application and was significantly higher under FYM + NPK treatment. The P adsorption capacity of soil was highest under the low-input treatment and lowest under long-term balanced fertilization(FYM + NPK). In contrast, P desorption capacity was highest under NPK and lowest in the control treatment. Long-term balanced fertilization in the form of FYM + NPK for 42 years lowered the bonding energy and adsorption capacity for P in soil but increased its desorption potential, increasing P availability to the plant and leading to higher P uptake and yield maintenance.

Leaf Photosynthetic Activity and Antioxidant Defense Associated with Sub1 QTL in Rice Subjected to Submergence and Subsequent Re-aeration

The influence of submergence on photosynthesis and antioxidant capacities in rice varieties Swarna and Swarna-Subl with or without Sub1 QTL were evaluated under control, simulated complete submergence and subsequent re-aeration. The leaf photosynthetic rate and stomatal conductance decreased in the both varieties during the progression of submergence as compared to the control plants, but significant varietal differences were observed after 1 d of submergence. Submergence also altered the PSII activity, as reflected in a decrease in the values of Fo, Fm and Fv/Fm and degradation of chlorophyll, more in Swarna than in Swarna-Subl. During early submergence period, the activities of superoxide dismutase （SOD）, ascorbate peroxidase （APX）, dehydroascorbate reductase （DHAR）, glutathione reductase （GR） against reactive oxygen species were increased in the both varieties. However, with the progress of submergence period （after 7 d）, the activities of SOD, catalase （CAT）, APX, guaiacol peroxidase （GPX）, GR and DHAR declined, more in Swarna than in Swarna-Subl. During re-aeration, Swarna-Subl showed significant increase of above antioxidant enzymes but not in Swarna, Swarna-Subl improves photosynthetic activity, showing higher photosynthetic rate compared to Swarna under submergence and subsequent re-aeration because of less degradation of chlorophyll, higher stomatal conductance, and efficient PSII activity along with better antioxidant protection from oxidative damage.

Seed Priming Improves Agronomic Trait Performance under Flooding and Non-flooding Conditions in Rice with QTL SUB1

Farmers in South East Asia are adopting rice crop establishment methods from transplanting to direct wet or dry seeding as it requires less labour and time and comparatively less energy than transplanting. In contrast to irrigated condition, in rainfed lowland, direct seeding is a common practice. Early flooding controls weeds but decreases seedling establishment in direct seeded rice. Anaerobic germination is an important trait to counteract damages caused by early flooding. Management options which can help in crop establishment and improve crop growth under flooding might remove the constraints related to direct seeding. The investigation was carried out with two near isogenic lines Swarna and Swarna- Sub1. Swarna-Subl is tolerant to submergence whereas Swarna is susceptible. Seed priming was done with water and 2% Jamun （Syzygium cumini） leaf extract, and it improved seedling establishment under flooding. Acceleration of growth occurred due to seed pretreatment, which resulted longer seedling and greater accumulation of biomass. Seed priming greatly hastened the activities of total amylase and alcohol dehydrogenase in Swarna-Subl than in Swarna. Swarna-Subl outperformed Swarna when the plants were cultivated under flooding. Weed biomass decreased significantly under flooding compared to non-flooding conditions. Seed priming had positive effects on yield and yield attributing parameters both under non-flooding and early flooding conditions.

Development and Characterization of Elite Doubled Haploid Lines from Two Indica Rice Hybrids

Despite significant yield advantage over inbred rice, the adoption rate of hybrid rice in India is very low due to the high seed cost and poor quality of the produce. To alleviate the problem, we initiated a doubled haploid （DH） breeding approach to develop new lines from two elite indica rice hybrids （CRHR5 and CRHR7） through rapid fixation of homozygosity in the recombinants. In vitro culture of the rice anthers resulted in 243 and 186 fertile DH lines of CRHR5 and CRHR7, respectively. Flow cytometric and pollen fertility analyses confirmed the DH ploidy status of the regenerations. Morpho-agronomic evaluation revealed 100% uniformity and stability for all the characters in the DH lines of both hybrids. Nineteen promising DH lines of each hybrid were advanced to A2 generation for yield evaluation. The yield levels of the DH lines ranged from 5 097-6 965 kg/hm^2 for CRHR5 and 5 141-7 235 kg/hm^2 for CRHR7, which were at par or higher than the parental hybrids. Physico-chemical characterization and cooking quality analyses revealed significant and acceptable values for grain length and width, alkali spreading value, amylose content and water uptake ratio of the selected DH lines. Three DH lines, CR5-10, CR5-49, CR5-61 from CRHR5, and four DH lines, CR7-5, CR7-7, CR7-12 and CR7-52 from CRHR7, showed significant grain yield and quality characteristics and have been recommended for multi-location trials for subsequent release as new indica doubled haploid rice varieties.

Iron Nutrition <i>vis-à-vis</i>Aconitase Activity and Ferritin Accumulation in Tropical <i>Indica</i>Rice Cultivars Differing in Grain Iron Concentration

Effect of Fe nutrition on Fe acquisition, aconitase enzyme activity and assimilation of the element in ferritin protein was studied in two indica rice cultivars viz. Sharbati and Lalat having contrasting grain Fe concentration. Young rice seedlings were grown in hydroponics with different levels of Fe. For comparison, the two cultivars were also grown in the field under natural conditions of rice culture. Iron accumulation, aconitase activity and ferritin level were higher in the high Fe containing cultivar, Sharbati than that in the low Fe containing cultivar, Lalat. While aconitase activity increased consistently with the increase in concentration of Fe in the growing medium, the same was not found to be true for accumulation of ferritin protein. The leaf ferritin level increased up to a certain level of Fe in the growing medium and declined thereafter. Levels of Fe in the growing medium giving maximum ferritin synthesis were found to be different in the two rice cultivars. In both cultivars, aconitase activity attained maximum level after 20 days of panicle emergence (heading). Pattern of Fe accumulation in the leaves in response to increasing Fe level in the nutrient solution paralleled with that of the aconitase activity indicating a positive correlation. It was concluded that accumulation of both ferritin protein and aconitase enzyme were influenced not only by the Fe level in the growing medium but also by the internal Fe concentration of the two cultivars.

Nitrogen Fertilizer Optimization and Cultivar Selection for Rice Grown near Mountainous Slopes in Orissa,India—A Field Experiment and Simulation Model Study

Degradation of the natural resource base has led to decline in crop yields or stagnation that caused food shortages at varying degrees among mountain families. Rice, the major staple food in Asia, is suffering from lack of suitable cultivar and N fertilizer management, when grown near mountainous slopes under rain-fed agro-ecosystem. An investigation through a field experiment and simulation study was conducted at United Nations University, Tokyo to select suitable rice cultivars and N fertilizer level for the rice grown near mountainous slopes in Orissa, India. The field experiment was conducted during wet season （June to November） of 2001 at Kasiadihi village of Dhenkanal district, Orissa, India with eight popular rice cultivars of medium （120～130 d） and long duration （135～150 d） group and four N levels （0, 40, 80 and 120 kg·ha^-1）. Highest grain yield of 5,680 kg·ha^-1 was obtained from cultivar Ranjit of long duration group followed by 4,730 kg·ha^-1 from cultivar Mahamaya of medium duration group, across N levels. CERES-Rice model was used to simulated grain yield of these two selected cultivars using historical weather data of the past 18 years （1983～2000）. Long duration cultivar Ranjit registered higher yield with lower stability as compared medium duration cultivar Mahamaya over the past 18 years. An optimum N fertilizer level of 80 kg·ha^-1 was recommended for rice grown under rain-fed ecosystem near mountainous slopes in Orissa, India to attain optimum yield potential of cultivar.