Performance of different fish species for controlling weeds in rainfed lowland rice field

A field experiment was conducted during wet season to evaluate the performance of different fish species for biocontrol of weeds in rainfed waterlogged rice fields with fingerlings of three exotic carps – grass carp, Ctenopharyngodon idella (Val.) (Cyprinidae, Cypriniformes), silver barb, Puntius gonionotus (Bleeker) (Cyprinidae, Cypriniformes) and common carp, Cyprinus carpio (L.) (Cyprinidae, Cypriniformes) – and three Indian major carps – rohu, Labeo rohita (Ham.) (Cyprinidae, Cypriniformes), catla, Catla catla (Ham.) (Cyprinidae, Cypriniformes), mrigal, Cirrhinus mrigala (Ham.) (Cyprinidae, Cypriniformes). A total of 13 major weeds under the categories of grassy, sedges, broadleaf and aquatic weeds were observed in the rice fields. Grass carp reduced maximum weed biomass (weed control efficiency [WCE] 63% at 60 days after transplanting [DAT] and 62% at 100 DAT) followed by silver barb and common carp. Among the Indian carps, only rohu was effective in control of weeds (WCE, 23% at 60 DAT). The grain yield of rice (variety Varshadhan) slightly increased (4.2–4.5 t/ha), but straw yield was significantly higher (10.2–10.7 t/ha) under rice-fish farming. Fish yield was significantly higher in exotic carps (270–288 kg/ha/90days) due to higher specific growth rates (1.8–2% body weight/day). The study indicated that exotic carps (grass carp, silver barb and common carp in order) were more effective than Indian carps for control of weed in rainfed lowland rice fields and among the Indian carps, rohu showed potential for weed control.     

Seed vigour and water relations in wheat

The laboratory germination (criterion radicle emergence) of seven seed lots of winter wheat cv. Slejpner was similar. However, they differed in vigour as demonstrated by differences in germination after controlled deterioration carried out at a range of seed moisture contents, at two temperatures and for different times. A vigour assessment for each lot was quantified by calculating a value for the seed lot constant K_i, of the viability equation. Germination in lower water potentials reduced the uptake of water, radicle and coleoptile emergence and radicle and coleoptile extension. There was no difference in the water uptake of seed lots differing in vigour. However, seed lots of lower vigour showed less radicle emergence, less coleoptile emergence and shorter radicles than higher vigour seed lots in low water potentials. Similarly, controlled deterioration resulted in reduced radicle and coleoptile emergence and growth compared to unaged seed, and also to a greater sensitivity to low water potentials. The implications for field establishment are discussed.     

Phosphorus cycling in rainfed lowland rice ecosystems on sandy soils

Phosphorus cycling in rainfed lowland rice ecosystems is poorly understood. Soil drying and grazing of rice straw during the long dry season, the growth of volunteer pastures during the early wet season, and intermittent loss of soil-water saturation while the rice crop is growing are important distinguishing characteristics of the rainfed lowlands in relation to P cycling. We studied P cycling in an acid sandy rainfed lowland soil that covers about 30% of the rice growing area of Cambodia. Soils with similar properties in comparable rainfed sub- ecosystems occur in Laos and northeast Thailand. We developed a general schema of P pools and fluxes in the crop and soil for rice-based cropping systems in the rainfed lowlands of Cambodia. The schema was derived from a number of field experiments carried out over five consecutive cropping seasons to quantify the residual value of P fertiliser, P mass balances, soil P fractions, the effect on subsequent rice crops of crop residues and volunteer pastures incorporated into the soils, and the dynamics of P turnover in the soil. With a single rice crop yielding 2.5–3 t ha⁻¹, application of 8–10 kg P ha⁻¹ maintained yields and a small positive P balance in the soil. However, the soil P balance was sensitive to the proportion of rice straw returned to the soil. Volunteer pastures growing during the early wet season accumulated significant amounts of P, and increased their P uptake when soils were previously fertilised with P. These pastures recycled 3–10 kg P ha⁻¹ for the succeeding rice crops. While inorganic soil P pools extractable with ion exchange resins and 0.1 M NaOH appeared to be the main source of P absorbed by rice, microbial and organically-bound P pools responded dynamically to variation in soil water regimes of the main wet, dry and early wet seasons. The schema needs to be developed further to incorporate site-specific conditions and management factors that directly or indirectly affect P cycling, especially loss of soil-water saturation during the rice cropping cycle. The paper discusses the application of results for acid sandy soils to other significant rice soils in the rainfed lowlands of southeast Asia.     

Seed and seedling vigour in relation to crop growth and yield

In theory, seed germination, vigour and size (three aspects of seed quality) may influence crop yield through both indirect and direct effects. The indirect effects include those on percentage emergence and time from sowing to emergence. These influence yield by altering plant population density, spatial arrangement, and crop duration. Direct effects on subsequent plant performance are more difficult to discern. A number of different approaches to testing the hypothesis that seed quality affects subsequent plant performance (implicit in some definitions of vigour) are illustrated. The results show that it is possible to detect such effects in some circumstances.     

Prediction of nitrogen availability and rice yield in lowland soils: Nitrogen mineralization parameters

Field experiments were conducted under flooded soil conditions using Maahas clay amended with urea and rice straw-sesbania mixtures during the wet and dry seasons. Parallel laboratory incubation tests were done. The objectives were 1) to determine N mineralization patterns and establish the relationship between mineralization parameters and either N availability or grain yield, and 2) to correlate the results of organic N mineralization studies in the laboratory with data from field experiments. The N mineralization patterns of flooded soils in the laboratory followed a logistic function. In laboratory studies, mineralization potential was positively correlated with extractable soil NH₄ ⁺-N at the end of the incubation period (cumulative available N). Likewise, mineralization potential calculated from laboratory studies was positively correlated with N uptake and grain yield from field studies. Extractable (NH₄ ⁺+NO₃ ^–)-N in the field correlated positively with extractable NH₄ ⁺-N in the laboratory. The extractable NH₄ ⁺-N from laboratory incubations at 14 days after transplanting, panicle initiation, and maturity was also highly and positively correlated with grain yield from field experiments.     

广东早稻高产的适宜气温指标

选取了广东典型生态区的曲江、高要、广州、汕头和湛江5个代表性试验点进行地理分期播种试验,各试验点均采用3个主栽品种、设置6个播期,观测早稻不同发育期、测定其产量及其产量构成因子。结合附近气象站同期观测资料,采用数理统计和变异系数等方法,分析平均气温对早稻产量及产量构成因子的影响,确定了广东早稻高产不同生育期的适宜气温指标。结果表明:全生育期平均气温为23～24℃,其中出苗-分蘖期为18～21℃、分蘖-孕穗期为21～25℃、孕穗-齐穗期为24～28℃、齐穗-成熟期为27～30℃。     

Phosphorus nutrition of rice in relation to flooding and temporary loss of soil-water saturation in two lowland soils of Cambodia

In the rainfed lowlands, temporary loss of soil-water saturation during crop growth is a common factor limiting rice (Oryza sativa L.) yield but its effects on phosphorus (P) availability are poorly understood. Rice plants were transplanted into pots containing soils that were either continuously flooded, maintained at field capacity or flooded and then dried to field capacity for 3 weeks during the vegetative stage. A black clay soil (Kandic Plinthaquult) and a sandy soil (Plinthustalf) from south-east Cambodia were compared with or without amendments by rice straw and P fertilizer. Under continuously flooded conditions, the growth of rice was vigorous without straw addition and there was a strong response of rice growth to the addition of P fertilizer. The soil underwent reduction, which increased pH from 4.2 to 5.5 or 6.0, in the black clay or sandy soil, respectively. By contrast, a loss of soil-water saturation 3 weeks before panicle initiation (PI) markedly impaired the growth of rice. This was not through any effect of water stress, and the growth reductions were not as strong as with continued loss of soil-water saturation from transplanting to PI. Fluctuations in soil pH and Eh corresponded closely to changes in soil-water regimes. Growth reductions were attributed to reduced shoot P levels resulting from the decline in P availability during the loss of soil-water saturation. The addition of rice straw stimulated soil reduction and lessened changes in soil pH and Eh during the loss of soil-water saturation in both soils. Straw addition enhanced P uptake by the rice plants during loss of soil-water saturation, but its beneficial effects could not be attributed to the direct addition of P, N or K to the soils. Thus the application of rice straw may be effective in lessening the effects of temporary loss of soil-water saturation on rice growth in lowland rice soils by minimising the decline in P availability. This revised version was published online in August 2006 with corrections to the Cover Date.     

Seed conglomeration: a disruptive innovation to address restoration challenges associated with small‐seeded species

Small‐seeded species are an integral component of many natural systems. However, small‐seeded species are often omitted from restoration projects due to limited flow through seeders, low broadcast distance, and inconsistent seeding rates. To address these problems, we developed a novel technique within a rotary coater that allows for the conglomeration of small, low‐purity seeds using a combination of clay, compost, water, and a polymer binder. We used Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis), which has a seed size of approximately 1 mm or less, as a model species to evaluate the technology. We demonstrated improved flowability of conglomerates over untreated (control) seeds through measurements of the Hausner ratio (8% decrease), the angle of repose (21% decrease), and delivery through a broadcast seeder. Seeding rates of conglomerated seed were more consistent than control seed over rugged terrain. Conglomerates were also broadcast 2.2 times further than control seed, which may mitigate the overall cost of implementing this technology. Laboratory trials demonstrated that the final germination of conglomerated seed averaged 15% higher than control seed. Field trials at two sites demonstrated that seedling emergence was similar for control and conglomerated seed. With no deleterious effects observed from the conglomeration treatment, additional research is merited for using conglomerates as a platform to apply various additives, such as fungicides, plant growth hormones, fertilizers, and biologicals. The potential outcomes of these strategies may have a significant impact on future seeding attempts by improving seed delivery and increasing overall seeding success.     

Overexpression of the leucine‐rich receptor‐like kinase gene LRK2 increases drought tolerance and tiller number in rice

Drought represents a key limiting factor of global crop distribution. Receptor‐like kinases play major roles in plant development and defence responses against stresses such as drought. In this study, LRK2, which encodes a leucine‐rich receptor‐like kinase, was cloned and characterized and found to be localized on the plasma membrane in rice. Promoter–GUS analysis revealed strong expression in tiller buds, roots, nodes and anthers. Transgenic plants overexpressing LRK2 exhibited enhanced tolerance to drought stress due to an increased number of lateral roots compared with the wild type at the vegetative stage. Moreover, ectopic expression of LRK2 seedlings resulted in increased tiller development. Yeast two‐hybrid screening and bimolecular fluorescence complementation (BiFC) indicated a possible interaction between LRK2 and elongation factor 1 alpha (OsEF1A) in vitro. These results suggest that LRK2 functions as a positive regulator of the drought stress response and tiller development via increased branch development in rice. These findings will aid our understanding of branch regulation in other grasses and support improvements in rice genetics.     

Receptor‐like kinase OsSIK1 improves drought and salt stress tolerance in rice (Oryza sativa) plants

Receptor‐like kinases (RLKs) play essential roles in plant growth, development and responses to environmental stresses. A putative RLK gene, OsSIK1, with extracellular leucine‐rich repeats was cloned and characterized in rice (Oryza sativa). OsSIK1 exhibits kinase activity in the presence of Mn²⁺, and the OsSIK1 kinase domain has the ability to autophosphorylate and phosphorylate myelin basic protein (MBP). OsSIK1 promoter‐GUS analysis revealed that OsSIK1 is expressed mainly in the stem and spikelet in rice. The expression of OsSIK1 is mainly induced by salt, drought and H₂O₂ treatments. Transgenic rice plants with overexpression of OsSIK1 show higher tolerance to salt and drought stresses than control plants. On the contrary, the knock‐out mutants sik1‐1 and sik1‐2, as well as RNA interference (RNAi) plants, are sensitive to drought and salt stresses. The activities of peroxidase, superoxide dismutase and catalase are enhanced significantly in OsSIK1‐overexpressing plants. Also, the accumulation of H₂O₂ in leaves of OsSIK1‐overexpressing plants is much less than that of the mutants, RNAi plants and control plants, as measured by 3,3′‐diamino benzidine (DAB) staining. We also show that OsSIK1 affects stomatal density in the abaxial and adaxial leaf epidermis of rice. These results indicate that OsSIK1 plays important roles in salt and drought stress tolerance in rice, through the activation of the antioxidative system.     

Effect of azoxystrobin and kresoxim‐methyl on rice blast and rice grain yield in China

Sensitivity to azoxystrobin and kresoxim‐methyl of 80 single‐spore isolates of Magnaporthe oryzae was determined. The EC₅₀ values for azoxystrobin and kresoxim‐methyl in inhibiting mycelial growth of the 80 M. oryzae isolates were 0.006–0.056 and 0.024–0.287 µg mL^?1, respectively. The EC₅₀ values for azoxystrobin and kresoxim‐methyl in inhibiting conidial germination of the M. oryzae populations were 0.004–0.051 and 0.012–0.105 µg mL^?1, respectively. There was significant difference in sensitivity to azoxystrobin or kresoxim‐methyl between the tested isolates representing differential sensitivity to carbendazim (MBC) and kitazin P (IBP); however, there was no correlation between this difference in sensitivity to azoxystrobin or kresoxim‐methyl and sensitivity to MBC or IBP, indicating that there was no cross‐resistance between azoxystrobin or kresoxim‐methyl and MBC or IBP. In the protective and curative experiments, kresoxim‐methyl exhibited higher protective and curative activity than azoxystrobin when applied at 150 and 250 µg mL^?1 accordingly, while azoxystrobin exhibited stronger inhibitory activity against M. oryzae isolates than that of kresoxim‐methyl in the in vitro test. The results of field experiments also suggested that both azoxystrobin and kresoxim‐methyl at 187.5 g.a.i. ha^?1 gave over 73% control efficacy in both sites, exhibiting excellent activity against rice blast. Taken together, azoxystrobin and kresoxim‐methyl could be a good substitute for MBC or IBP for controlling rice blast in China, but should be carefully used as they were both at‐risk.     

High vapor pressure deficit drives salt‐stress‐induced rice yield losses in India

Flooded rice is grown across wide geographic boundaries from as far north as Manchuria and as far south as Uruguay and New South Wales, primarily because of its adaptability across diverse agronomic and climatic conditions. Salt‐stress damage, a common occurrence in delta and coastal rice production zones, could be heightened by the interactions between high temperature and relative humidity (vapor pressure deficit – VPD). Using temporal and spatial observations spanning 107 seasons and 19 rice‐growing locations throughout India with varying electrical conductivity (EC), including coastal saline, inland saline, and alkaline soils, we quantified the proportion of VPD inducing salinity damage in rice. While controlling for time‐invariant factors such as trial locations, rice cultivars, and soil types, our regression analysis indicates that EC has a nonlinear detrimental effect on paddy rice yield. Our estimates suggest these yield reductions become larger at higher VPD. A one standard deviation (SD) increase in EC from its mean value is associated with 1.68% and 4.13% yield reductions at median and maximum observed VPD levels, respectively. Yield reductions increase roughly sixfold when the one SD increase is taken from the 75th percentile of EC. In combination, high EC and VPD generate near catastrophic crop loss as predicted yield approaches zero. If higher VPD levels driven by global warming materialize in conjunction with rising sea levels or salinity incursion in groundwater, this interaction becomes an important and necessary predictor of expected yield losses and global food security.     

Proteomes of Leaf‐Growing Zones in Rice Genotypes with Contrasting Drought Tolerance

Plants require a distinctive cohort of enzymes to coordinate cell division and expansion. Proteomic analysis now enables interrogation of immature leaf bases where these processes occur. Hence, proteins in tissues sampled from leaves of a drought‐tolerant rice (IAC1131) are investigated to provide insights into the effect of soil drying on gene expression relative to the drought‐sensitive genotype Nipponbare. Shoot growth zones are dissected to estimate the proportion of dividing cells and extract protein for subsequent tandem mass tags quantitative proteomic analysis. Gene ontology annotations of differentially expressed proteins provide insights into responses of Nipponbare and IAC1131 to drought. Soil drying does not affect the percentage of mitotic cells in IAC1131. More than 800 proteins across most functional categories increase in drought (and decrease on rewatering) in IAC1131, including proteins involved in “organizing the meristem” and “new cell formation”. On the other hand, the percentage of dividing cells in Nipponbare is severely impaired during drought and fewer than 200 proteins respond in abundance when growing zones undergo a drying cycle. Remarkably, the proteomes of the growing zones of each genotype respond in a highly distinctive manner, reflecting their contrasting drought tolerance even at the earliest stages of leaf development.     

Behavioral response of captive western lowland gorillas (Gorilla gorilla gorilla) to the death of silverbacks in multi‐male groups

In both free‐ranging and captive western lowland gorillas, a silverback provides protection and leadership, mediating conflict within a group. In the wild, when a dominant silverback dies the group will disperse or transfer to a solitary male, unless a subsequent male is present to inherit the group. In captivity, studies have focused on groups containing one male and therefore it is unclear how gorillas respond to the death or removal of a silverback in multi‐male groups. This study examined the behavior of a bachelor group (Cleveland Metroparks Zoo) and a multi‐male, mixed‐sex group (Pittsburgh Zoo and PPG Aquarium) following the death of two older silverbacks in 2005. Both of the younger but dominant males maintained their same level of dominance after the death. We predicted that agonism would increase after the death as groups struggled for social stablility. We did observe an increase in both agonism and displacements among the bachelor group, but only observed an increase in displacements among the mixed‐sex group. Although we predicted that there would be no change in solitary behavior, both groups decreased feeding and the mixed‐sex group increased self‐directed behavior post‐death. In the bachelor group, self‐directed behavior decreased and undesirable behavior increased. We also observed a difference in spatial distance after the death with members of the mixed‐sex group becoming more dispersed and members of the bachelor group more converged. This study demonstrates that there is a period of transition for multi‐male groups after the death or removal of the oldest silverback. Future research could integrate physiological measures with behavioral analyses before and after the death or removal of a prominent member of the group. Zoo Biol 29:16–29, 2010. © 2009 Wiley‐Liss, Inc.     

A rice lectin receptor‐like kinase that is involved in innate immune responses also contributes to seed germination

Seed germination and innate immunity both have significant effects on plant life spans because they control the plant's entry into the ecosystem and provide defenses against various external stresses, respectively. Much ecological evidence has shown that seeds with high vigor are generally more tolerant of various environmental stimuli in the field than those with low vigor. However, there is little genetic evidence linking germination and immunity in plants. Here, we show that the rice lectin receptor‐like kinase OslecRK contributes to both seed germination and plant innate immunity. We demonstrate that knocking down the OslecRK gene depresses the expression of α–amylase genes, reducing seed viability and thereby decreasing the rate of seed germination. Moreover, it also inhibits the expression of defense genes, and so reduces the resistance of rice plants to fungal and bacterial pathogens as well as herbivorous insects. Yeast two‐hybrid and co‐immunoprecipitation experiments revealed that OslecRK interacts with an actin‐depolymerizing factor (ADF) in vivo via its kinase domain. Moreover, the rice adf mutant exhibited a reduced seed germination rate due to the suppression of α–amylase gene expression. This mutant also exhibited depressed immune responses and reduced resistance to biotic stresses. Our results thus provide direct genetic evidence for a common physiological pathway connecting germination and immunity in plants. They also partially explain the common observation that high‐vigor seeds often perform well in the field. The dual effects of OslecRK may be indicative of progressive adaptive evolution in rice.     

Soil physical behaviour and crop responses to tillage in lowland rice soils of varying clay content

The influence of various tillage methods on two wetland rice soils in the Philippines is reported. The soils differed principally in clay content, 38% for the clay loam (clayey, mixed isohyperthermic Entic Hapludoll) while 56% for the clay (clayey, mixed noncalcareous, isohyperthermic Andaqueptic Haplaquoll). This had a marked effect on their response to tillage and varying water regime. The clay soil, under field conditions, showed little change in pore size distribution or soil water behaviour with different tillage methods. Crop (Rice, Oryza sativa L., var. IR20) yields were unaffected by tillage.In contrast, tillage effects were very marked in the clay loam soil, which consisted of a greenhouse and a field trial. In the greenhouse, which experienced severe dry periods, wet tillage not only increased the moisture retentivity but also the soil impedance at soil matric potential ()<–0.01 MPa. Seasonal average was <–1 MPa. Root length density decreased by 39% with dry tillage and by 56% with wet tillage compared with zero tillage. Grain yield however, did not vary with soil treatment. In the field, which experienced moderate dry spells, varied between –0.13 and –0.48 MPa. Root length density was significantly reduced at soil impedance >0.75 MPa. Wet tillage increased soil moisture storage which minimized the soil impedance during the dry cycle more effectively than did dry tillage. The crop performed best under wet tillage and least under zero tillage. Wet tillage in this soil was more effective under moderate than under severe water stress conditions.     

Improved oxidative tolerance in suspension‐cultured cells of C_4-pepctransgenic rice by H_2O_2 and Ca~(2+)under PEG-6000

To understand the molecular responses of PC(Overexpressing the maize C4-pepc gene, which encodes phosphoenolpyruvate carboxylase(PEPC)), to drought stress at cell level, we analyzed changes in the levels of signaling molecules(hydrogen peroxide(H2O2), calcium ion(Ca2t), and nitric oxide(NO)) in suspension-cultured PC and wild-type(WT)rice(Oryza sativa L.) cell under drought stress induced by 20%polyethylene glycol 6000(PEG-6000). Results demonstrated that PC improved drought tolerance by enhancing antioxidant defense, retaining higher relative water content, survival percentages, and dry weight of cells. In addition, PEPC activity in PC under PEG treatment was strengthened by addition of H2O2 inhibitor, dimethylthiourea(DMTU) and NO synthesis inhibitor, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide(c PTIO), respectively, while that in PC was weakened by addition of free calcium chelator, ethylene glycol-bis(b-aminoethylether)-N,N,N0,N0-tetraacetic acid(EGTA)t calcium channel outflow inhibitor, ruthenium red(RR) t plasma membrane channel blocker La(NO3)3, but EGTA t RR did Reseanot. Results also showed that NO and Ca2 twas lying downstream of H2O2 in drought-induced signaling. Calcium ion was also involved in the expression of C4-pepc in PC. These results suggested that PC could improve oxidative tolerance in suspension-cultured cells and the acquisition of this tolerance required downregulation of H2O2 and the entry of extracellular Ca2 tinto cells across the plasma membrane for regulation of PEPC activity and C4-pepc expression.     

Structural and functional responses of plant communities to climate change‐mediated alterations in the hydrology of riparian areas in temperate Europe

The hydrology of riparian areas changes rapidly these years because of climate change‐mediated alterations in precipitation patterns. In this study, we used a large‐scale in situ experimental approach to explore effects of drought and flooding on plant taxonomic diversity and functional trait composition in riparian areas in temperate Europe. We found significant effects of flooding and drought in all study areas, the effects being most pronounced under flooded conditions. In near‐stream areas, taxonomic diversity initially declined in response to both drought and flooding (although not significantly so in all years) and remained stable under drought conditions, whereas the decline continued under flooded conditions. For most traits, we found clear indications that the functional diversity also declined under flooded conditions, particularly in near‐stream areas, indicating that fewer strategies succeeded under flooded conditions. Consistent changes in community mean trait values were also identified, but fewer than expected. This can have several, not mutually exclusive, explanations. First, different adaptive strategies may coexist in a community. Second, intraspecific variability was not considered for any of the traits. For example, many species can elongate shoots and petioles that enable them to survive shallow, prolonged flooding but such abilities will not be captured when applying mean trait values. Third, we only followed the communities for 3 years. Flooding excludes species intolerant of the altered hydrology, whereas the establishment of new species relies on time‐dependent processes, for instance the dispersal and establishment of species within the areas. We expect that altered precipitation patterns will have profound consequences for riparian vegetation in temperate Europe. Riparian areas will experience loss of taxonomic and functional diversity and, over time, possibly also alterations in community trait responses that may have cascading effects on ecosystem functioning.