Effects of Toxic Levels of Aluminium on Seedling Parameters of Rice under Hydroponic Culture

The presence of Al in the rhizosphere of rice in acid soil restricts root growth and significantly reduces crop productivity.In this study,the effects of Al(30,60 and 90μg/mL)on seedling root growth,number of primary roots per seedling,seedling shoot length,number of leaves per seedling,seedling fresh weight,and seedling dry weight were studied.Rice genotypes were classified into three different classes,namely,tolerant,moderately tolerant,and susceptible,based on root tolerance index.The method of hydroponic culture was modified,and elaborated in the text.Toxic levels of Al in nutrient solution significantly decreased seedling root growth,number of primary roots,seedling shoot length,number of leaves per seedling,seedling fresh weight,and seedling dry weight.Few genotypes showed longer root length at 30μg/mL Al in nutrient solutions compared with the control.High levels of Al in nutrient solutions were highly toxic for rice seedlings.Based on root tolerance index,Radhunipagal,Gobindobhog,Badshabhog,Kalobhog,UBKVR-11,UBKVR-16,UBKVR-18,Khasha and IVT4007-B were classified as tolerant genotypes,and these genotypes may be used as donors for breeding of Altoxicity tolerance.     

Resistance Evaluation to Sheath Blight in Transgenic Rice Lines

Resistance of forty-one homozygous rice lines transformed with chitinase gene (RC24) and β-1,3 -glucanse gene (β-1,3-Glu) to sheath blight was analyzed by inoculation. Among different lines, the resistance had significant differences according to the result by cluster analysis. The lines could be categorized into resistant, moderately resistant, moderately susceptible and susceptible types, while 92.1% of which belonging to moderately resistant or moderately susceptible type. For different resistant or susceptible lines, the resistance to rice sheath blight was remarkable correlated with the chitinase activity of transgenic lines except resistant type lines, in which enzyme activity coded by target gene was lower than moderately resistant type. The chitinase activity of transgenic lines tested at different time after inoculation or different organs of the same plant was uniform, which suggested that the expression of chitinase gene was constitutive in nature. Check varieties‘ chitinase activity would change at different time after inoculation and reach a peak at sometime, but it had no difference at various parts of the same plant.     

Resistance Evaluation to Sheath Blight in Transgenic Rice Lines

Resistance of forty-one homozygous rice lines transformed with chitinase gene (RC24) and β-1,3 -glucanse gene β-1,3-Glu) to sheath blight was analyzed by inoculation. Among different lines, the resistance had significant differences according to the result by cluster analysis. The lines could be categorized into resistant, moderately resistant, moderately susceptible and susceptible types, while 92.1% of which belonging to moderately resistant or moderately susceptible type. For different resistant or susceptible lines, the resistance to rice sheath blight was remarkable correlated with the chitinase activity of transgenic lines except resistant type lines, in which enzyme activity coded by target gene was lower than moderately resistant type. The chitinase activity of transgenic lines tested at different time after inoculation or different organs of the same plant was uniform, which suggested that the expression of chitinase gene was constitutive in nature. Check varieties chitinase activity would change at different time after inoculation and reach a peak at sometime, but it had no difference at various pans of the same plant.     

Association and Heritability Studies for Drought Resistance under Varied Moisture Stress Regimes in Backcross Inbred Population of RiceAssociation and Heritability Studies for Drought Resistance under Varied Moisture Stress Regimes in Backcross Inbred Population of Rice

Drought stress is one of the major constraints affecting rice production and yield stability in the rainfed regions. To understand the physiological basis of drought resistance related component traits, we used a backcross inbred population of rice under three kinds of moisture regimes viz., non-stress, moderate （24.48%） and severe stress （73.97%） conditions which reflect the differential responses of the genotypes to varying stress intensities. The plot yield, 1000-grain weight, panicle exsertion and canopy air temperature difference exhibited high heritability under the control conditions, whereas spikelet sterility and single plant yield exhibited high heritability under the moderate stress conditions. Traits such as days to 50% flowering, plant height and osmotic potential showed high heritability under the severe stress conditions. Plot yield under stress was significantly and positively correlated with harvest index and 1000-grain weight, but negatively associated with leaf rolling score and days to 50% flowering. The drought susceptibility index and drought response index were negatively correlated between each other both under the moderate and severe stress conditions. The derived traits viz., difference in panicle length between the control and the severe stress was associated with osmotic adjustment measured under field conditions. Difference in plant height and panicle length was negatively associated with plot yield under stress.     

Tagging of Brown Planthopper Resistance Genes in F2s of IR50 × Ptb33 of Rice by Using Bulked Segregant Analysis

Brown planthopper(Nilaparvata lugens St?l) is one of the most damaging pests causing hopper burn in rice,and thereby reducing the productivity and also the quality of the product.The effective management strategy to control this pest is the identification and transfer of desirable genes to local rice cultivars.The most important approach for developing resistant cultivars is the identification of markers,which can help in marker-assisted selection of more durable resistant genotype.The susceptible parent IR50 and the resistant parent Ptb33,and their F2 populations were used in bulked segregant analysis for identification of resistant genes with random amplified polymorphic DNA marker(RAPD) primers.The primers OPC7 and OPAG14 showed both dominant and susceptible specific banding pattern so called co-dominant markers.Moreover,OPC7697 and OPAG14680 showed resistant specific bands and thus being in coupling phase,whereas OPC7846 and OPAG14650 showed susceptible specific genotypic bands in bulked segregant analysis.Therefore,the coupling phase markers,OPC7697 and OPAG14680,are considered to be more useful in marker-assisted selection of rice genotypes in crop improvement.     

Phenotypic Expression of Whitebacked Planthopper Resistance in the Newly Established japonica ／ indica Doubled Haploid Rice Population

A new doubled haploid (DH) rice population was established from a cross between WBPH-resistant japonica Chunjiang 06 (C J-06) and susceptible indica TN1. Sucking inhibitory and ovicidal resistance of the DH rice lines were evaluated on the basis of non-preference response of WBPH immigrants and honeydew excretion by WBPH females, and appearance of watery lesions in the necrotic discoloration of leaf sheaths ovipositied by WBPH,respectively. Both the major gene resistance to WBPH, sucking inhibitory and ovicidal resistance, showed 1 (resistant): 1 (susceptible) segregation ratio in the DH population. Relative density of WBPH populations and damage scores in the DH population indicated combined functions of both the major resistance genes as well as QTLs affecting the host plant response to WBPH infestations. Thus, the newly developed CJ-06/-I-N1 DH population could be a useful material to analyze major genes and QTLs for WBPH resistance in japonica rice.     

Changes of glucosidase activity and insect body weight of the whitebacked planthopper after fed on resistant rice plants

Glucosidase is an important digestive enzyme in insect. The plant-sucking insect, the whitebacked planthopper Sogatella furcifera, ingests rice phloem sap and must use this enzyme to decompose the main sugar source of disaccharide sucrose into monosaccharide glucose and fructose for normal absorption. In studying the resistant mechanism, we investigated the changes of glycosides activity and insect body weight of S. furcifera after fed on the highly-resistant rice variety Rathu Heenati (RHT) and susceptible TN1 The 4-, 6-and 8-week old rice plants of RHT and TN1 were enclosed with mylar cages. The brachypters were introduced into cages and collected at 3 days after infestation and weighed. The uncaged insect served as control. Insects were homogenized with citrate buffer and centrifuged. Homogenates and substrate (p-nitrophenyl-a-glucoside) solution were incubated at 33℃ for 2 b and added with Tris-HCl buffer for interruption enzymatic reaction. The absorbance of color solutions was measured at 420 nm.     

Changes in Methamidophos Resistance and Fitness of Hybrids in Different Strains of Nilaparvata lugens

A resistant strain selected successively in the laboratory for 17 generations had 198.63-fold resistance to methamidophos. The resistant levels and fitness of progenies from the resistant strain and susceptible strain or field population were closer to those of the resistant strain than those of the susceptible strain or field population. The changes in the resistant levels of the hybrid were propitious to the resistance development, however, the changes of the fitness went to the contrary. The effects of the migration on the development of methamidophos resistance in Nilaparvata lugens were discussed in the aspects of the migration of Nilaparvata lugens, the resistant levels of progenies and the changes of the fitness.     

Water,Nitrogen and Plant Density Affect the Response of Leaf Appearance of Direct Seeded Rice to Thermal Time

Field experiments were conducted in the Ebro Delta area (Spain), from 2007 to 2009 with two rice varieties:Gleva and Tebre. The experimental treatments included a series of seed rates, two different water management systems and two different nitrogen fertilization times. The number of leaves on the main stems and their emergence time were periodically tagged. The results indicated that the final leaf number on the main stems in the two rice varieties was quite stable over a three-year period despite of the differences in their respective growth cycles. Interaction between nitrogen fertilization and water management influenced the final leaf number on the main stems. Plant density also had a significant influence on the rate of leaf appearance by extending the phyllochron and postponing the onset of intraspecific competition after the emergence of the 7th leaf on the main stems. Final leaf number on the main stems was negatively related to plant density. A relationship between leaf appearance and thermal time was established with a strong nonlinear function. In direct-seeded rice, the length of the phyllochron increases exponentially in line with the advance of plant development. A general model, derived from 2-year experimental data, was developed and satisfactorily validated; it had a root mean square error of 0.3 leaf. An exponential model can be used to predict leaf emergence in direct-seeded rice.     

Analyses of gene effects and inheritance of resistance to bacterial blight in rice

We analyzed the resistant inheritance of a japonica variety, Jia23, to two bacterial blight pathogen strains, KS—6—6 and Zhe 173, representing respectively the two predominant pathogenic types (Ⅱ and Ⅳ) in the rice cropping area along the Yangtze River Valley. Jla23 was crossed with susceptible varieties, Ewan8 and 7416. F_1 plants were backcrossed with both resistant and susceptible parents to produce B_1 (F_1×P_1) and B_2 (F_2×P_2). All generations were planted during the late—season on an isolated field from Jun to Oct in 1994. Thirty—day—old seedlings were transplanted individually with a spacing of 13cm between plants and 17cm between rows. Concentration of inoculum was adjusted to 10~9 cells/ml. Three fully expanded leaves per plant were inoculated with each type of strains by clipping     

Susceptibility to Insecticides and Ecological Fitness in Resistant Rice Varieties of Field Nilaparvata lugens Stl Population Free from Insecticides in Laboratory

A population of rice brown planthopper(BPH) Nilaparvata lugens collected from a paddy field in Hangzhou was successively reared on susceptible rice Taichung Native 1(TN1) in a laboratory free from insecticides for more than 14 generations. The changes in susceptibility to insecticides and ecological fitness on different resistant rice varieties were monitored in each generation. The resistance ratio to imidacloprid sharply declined with the succession of rearing generations without insecticides from 359.94-fold at F1 to 6.50-fold at F14 compared with the susceptible strain, and the resistance ratio to chlorpyrifos was from 9.90-fold at F1 to 5.94-fold at F14. Nymphal duration and weights of newly hatched female adults were significantly affected by rice variety, generation and their interactions, but nymphal survival was significantly affected by the generation only. The ratio of brachypterous adults in males was affected by the generation and generation × variety interaction, whereas no difference was found in females. Nymphal duration extended with increasing generations, and the female nymphal duration was shorter in the susceptible variety TN1 than those in the resistant varieties IR26 and IR36. In addition, the female adult weight in TN1 was higher than those in IR26 and IR36. These results indicated that the resistance of field BPH population to insecticides was reversed after several generations of no-exposure to insecticides, and the ecological fitness in TN1 was higher than those in IR26 and IR36. These findings suggested the rational and reduced use of insecticides in combination with the manipulation of resistant rice varieties would be effective for BPH management.     

Physiological Macro-lesions Enhanced Resistance to Blast （Magnaporthe grisea） in Rice Near-isogenic Lines

Roll-leaf-1 （rl-1） and spot-leaf-1 （spl-1） were two near-isogenic lines, which were obtained after 3 to 4 backcrosses with early season indica rice Zhefu 802 as recurrent parent. Henna macro-lesions, referred as physiological or morphological markers, began to appear on leaves at 4.5- to 6.0-leaf stage. The rice seedlings were inoculated at 3.5-, 5.0- and 7.0-leaf stages with high pathogenic races Zhong A1 and Zhong B1 of Magnaporthe grisea, respectively. The resistance of rl-1, spl-1 and Zhefu 802 against blast was significantly different. The seedlings of Zhefu 802 at 3.5- to 7.0-leaf stage were susceptible to races Zhong A1 and Zhong B1 of M. grisea, whereas those of rl-1 and spl-1 at 3.5-, 5.0- and 7.0-leaf stages were susceptible, moderately resistant and resistant, respectively. These results suggested that the enhanced resistance of rl-1 and spl-1 related to the appearance of their morphological marker lesions. The experiment provided a basis for studying lesion mimic and hypersensitive response in association with disease resistance.     

Description of Aphelenchoides besseyi from Abnormal Rice with ＇Small Grains and Erect Panicles＇ Symptom in China

The abnormal rice with small grains and erect panicles were found on a large scale in China, which showed shortend rice panicle and decreased number of grains in comparison with normal rice, and the grain was small and black-brown, and some of them were distorted, while the flag leaf was normal. A kind of nematode of Aphelenchoides was isolated from the grains of rice variety Wuyujing 3 which performed ＇small grains and erect panicles＇ symptom. There were 2014 nematodes in one hundred grains infected, and up to 74 in single grain, 92 percent of the grains tested had nematodes in the infested panicles. The diagnosis characters of nematode include lateral fields about one-fourth as wide as body, with 4 incisures. The terminus bears a mucro of diverse shape with 3-4 pointed processes. The female post-vulval uterine sac extends less than 50% of distance from vulva to anus, no sperm in it. Oocytes usually arrange in 2-4 rows. The male spicules have a moderately developed rostrum. Morphological measurements showed it to be conspecific with Aphelenchoides besseyi Christie, 1942.     

The impacts of timing and insecticides at early stage of late rice on the population development of brown plant hopper （BPH）

Field experiments were carried out in northern Zhejiang Province. Three insecticides (methamidophos,Shachongshuang and triazophos) were used to control the rice leaffolder Cnaphalocrocis medinalis and rice striped stemborer Chilo suppressalis in rice fields during 18—27 days after transplantating. The impacts of timing and insecticides on the population development of brown planthopper Nilaparavata lugens was surveyed by direct counting on the plants or by tapping method.     

Variation in Yield and Physicochemical Quality Traits among Mutants of Japonica Rice Cultivar Wuyujing 3

To select elite germplasms, 112 mutants derived from japonica rice cultivar Wuyujing 3 were evaluated. The yield components such as panicle number per square meter, grain number per panicle, and grain weight were measured. The quality traits such as percentage of chalky grains(PCG), brown rice yield(BRY), milled rice yield(MRY), degree of milling(DM), amylose content(AC), protein content(PC), and relationships among traits were inverstigated. Results showed that grain yield ranged from 2.15 to 12.49 t/hm~2 with a mean of 6.4 t/hm~2 and number of grains per square meter contributed for 94.64% in grain yield variation. For quality traits, all rice mutants had short size(grain length ≤ 5.5 mm) and bold shape(grain length to width ratio = 1.10–2.00). Most of rice mutants(87.5%) had PCG values below 20%. All mutants had MRY values above 50%, AC values below 20%, and PC values below 10%. Percentage of chalky grains was significantly negatively correlated with MRY and positively correlated with DM. BRY and MRY were significantly negatively correlated with DM. PC was significantly and positively correlated with MRY and negatively correlated with DM, while AC had no significant correlation with these quality traits. It was concluded that there were 25 rice mutants which fulfilled the major requirements of Jiangsu standard japonica rice such as low percentage of chalky grains, low amylose content, optimal protein content, and which could be used as elite germplasms. Thus the mutants identified may lead to significant progress in improvement of rice quality.     

Bacterial Community in Different Populations of Rice Brown Planthopper Nilaparvata lugens （St~l）

The structures of bacterial communities in the brown planthopper （BPH） Nilaparvata lugens （St~l） from different geographic and resistant virulent populations were analyzed by using denatured gradient gel electrophoresis （DGGE）. Results showed that the bacterial communities in BPH nymph from the first to the fifth instars varied with nymphal growth and development. The bacterial communities in the first-instar BPH nymph were similar to those in adults. Nine geographic BPH populations were divided into three groups based on the cluster analysis of DGGE fingerprint. The first group was from the Philippines; the second group was from Thailand and Hainan, Yunnan and Zhejiang provinces of China; and the third group was from Vietnam and Guangxi, Hunan and Jiangxi provinces of China. BPH populations adapted to different resistant rice varieties. The BPH populations from Mudgo （with resistant gene Bphl） and ASD7 （with resistant gene bph2） differed with those of the susceptible rice variety TNI.     

Response of Osmotic Regulation Substance Content and Protective Enzyme Activities to Shading in Leaves of Different Rice Genotypes

Effects of shading at the flowering and grain filling stages on osmotic regulation substance content and protective enzyme activities in the leaves of different rice genotypes (e.g.,IIyou 498,Gangyou 188,Dexiang 4103,Gangyou 527 and Chuanxiang 9838) were investigated.The results showed that the malondialdehyde content of Gangyou 188 significantly increased under shading,whereas those of IIyou 498,Dexiang 4103,Gangyou 527 and Chuanxiang 9838 showed no significant differences compared to the control.The soluble sugar content significantly decreased in IIyou 498,Gangyou 188,Dexiang 4103 and Chuanxiang 9838,whereas it did not significantly increase in Gangyou 527 under the weak light conditions (shading).Moreover,the soluble protein content in the leaves of different genotypes tended to decrease under shading.Further,the protective enzyme activities in the leaves varied in different rice genotypes under the shading treatment.Based on the osmotic regulation substance content and the protective enzyme activities in the leaves of different rice genotypes,it was concluded that Gangyou 188 and Gangyou 527 had strong abilities to adapt to the low light conditions.In addition,the mechanism of damage to rice leaves in different genotypes under shading was discussed.     

SCAR Markers Assisted Selection for a Bentazon Susceptible Lethality Gene （ben） in Rice

In progenies resulting from crosses involving rice cultivar Norin 8m susceptible to bentazon as the donor of ben gene, SCARs tightly linked to ben were utilized for selection of ben. The homozygous and heterozygous genotypes with ben could be identified with the SCARs. The molecular markers offer a powerful tool for indirect selection of ben and can accelerate the introgression of ben into current rice cultivars.     

Effects of Bicarbonate and High pH Conditions on Zinc and Other Nutrients Absorption in Rice

Zinc deficiency was widely observed in calcareous soil where bicarbonate and high pH were always related with low zinc availability. In a hydroponic experiment, one zinc-efficient rice (IR36) and one zinc-inefficient rice (IR26) genotypes were employed to investigate the effects of bicarbonate and high pH conditions on absorption, transport of zinc and other nutrients (P, K, Ca, Mg, Fe, Cu, Mn) in rice. As compared with the control, high pH inhibited absorption, translocation and accumulation of zinc and other nutrients in both rice genotypes. Bicarbonate had minor effect on zinc-efficient rice genotype (IR36) whereas it could decrease zinc and other nutrient absorption in zinc-inefficient rice genotype (IR26). These results implied that increasing rice tolerance to bicarbonate is one of the most important strategies to improve rice adaptation for zinc-deficit calcareous soil.     

Preliminary Study on Resistance of the Rice Stem Borer （Chilo Suppressalis） to Fipronil

By means of topical application, fipronil resistance was surveyed in the rice stem borer, Chilo suppressalis, from 12 diferent areas in east China from 2001 to 2004. The rice stem borers in most regions of Jiangsu and Anhui were still susceptible to fipronil. But in Wuxi, Jiangsu Province and Cixi, Zhejiang Province, their sensitivity became decreased （resistance ratios were 3.1 and 3.6, respectively）, and the medium level of resistance （resistance ratio was 21.2） was found in Cangnan, Zhejiang Province. So, it was still at the early stage for fipronil resistance development in this pest. Synergism experiments showed that piperonyl butoxide（PBO） had a little effect on both susceptible and resistant borers （synergism ratios were 1.1-1.2）. Though triphenyl phosphate （TPP） and diethyl meleate （DEM） had no effect on the susceptible borers, they had significant synergism on fipronil in the resistant population to fipronil （synergism ratios were 1.8 and 1.6, respectively）, indicating esterase and glutathion S-transferase may be involved in the resistance mechanism. Bioassay with currently used insecticides indicated that triazophos （because of high resistance）, trichlorphon and acephate had very low toxicity to resistant borers. But diazinon, pyridaphenthion, decamethrin and avermeatin showed high toxicity and had no cross resistance to fipronil, which could be considered as substitute insecticides in the resistance managment.