Susceptible Rice Research Articles

Expression Alteration of Candidate Rice MiRNAs in Response to Sheath Blight Disease.

Background: MicroRNAs, as small non-coding RNAs, are recently reported to be involved in plant defense system against pathogens including fungi.Objective: In this research, it was intended to investigate candidate susceptible rice (Oryza Sativa) Osa-miRNA expression alteration following the infection by Rhizoctonia solani.Materials and Methods: To this aim, literature review suggested eight conserved plant miRNAs that are involved in other plant-pathogen interactions. Then, sixty days old rice plants (Hashemi, susceptible cultivar) were inoculated with R. solani and candidate miRNA expression alterations were investigated 2 hpi (hours post inoculation), 2 dpi (days post inoculation) and 6 dpi.Results: RT-qPCR analysis suggested four subgroups of candidate miRNAs based on the time of their responses to the pathogenesis of R. solani. While Osa-miR-156 was early-responsive, Osa-miR159 was the last-responsive and Osa-miR167, Osa-miR171, Osa-miR408, and Osa-miR444 were late responsive to R. solani infection. Osa-miR166 and Osa-miR393 were non-responsive to this infection, compared to the mock-inoculated control group. Consistently, Os-SPL3 and Os-MADS known target genes were expressed in reverse correlation to Osa-miR156 and Osa-miR444, respectively.Conclusions: From these data, it is suggested that both early (Osa-miR-156) and late (Osa-miR167, Osa-miR171, Osa- miR408, Osa-miR444) responsive miRNAs might be involved in R. solani infection in rice plants.

RESISTANCE EVALUATION OF MODERN RICE VARIETIES TO BROWN PLANTHOPPER Nilaparvata lugens STÅL

Resistance evaluation of modern rice varieties to brown planthopper Nilaparvata lugens STÅL. The research was performed to understand the resistance of modern rice varieties to the field population of brown planthopper (BPH). The research studied BPH settling preference, numbers of laid eggs, and functional plant loss index (FPLI) of resistant and susceptible rice varieties. The results showed BPH were less settle and laid fewer eggs on resistant varieties. BPH significantly settled longer on TN1 than other varieties after 24 hours. The numbers of eggs laid on rice resistant varieties (Inpari 13, Inpari 31, Inpari 33, RH, and PTB33) were fewer compared to TN1. FPLI value in TN1 was the highest among the tested rice varieties. Inpari 13 had better resistance to BPH compared to Inpari 31 and Inpari 33. In managing BPH in endemic areas, we recommend Inpari 13, Inpari 31, and Inpari 33 to be planted in rotation.

Comparative transcriptome analysis of Tilletia horrida infection in resistant and susceptible rice (Oryza sativa L.) male sterile lines reveals potential candidate genes and resistance mechanisms

Rice kernel smut (RKS), caused by the basidiomycete fungus Tilletia horrida, is one of the most devastating diseases affecting the production of male sterile lines of rice (Oryza sativa) worldwide. However, the molecular mechanisms of resistance to T. horrida have not yet been explored. In the present study, RNA sequencing analysis of rice male sterile lines, that are resistant and susceptible to RKS (Jiangcheng 3A and 9311A, respectively) was conducted after T. horrida infection. Transcriptomic analysis showed that a greater number of differentially expressed gene (DEGs) was observed in Jiangcheng 3A compared with 9311A after T. horrida inoculation. Furthermore, 4, 425 DEGs were uniquely detected in Jiangcheng 3A, and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of these DEGs revealed that oxidoreductase activity, peroxidase activity, cutin, suberine and wax biosynthesis, and flavonoid biosynthesis were key pathways for T. horrida resistance. In summary and based on transcriptome analysis, we suggest a preliminary regulatory mechanism for Jiangcheng 3A cultivar resistance response to T. horrida inoculation.

The gut bacterial flora associated with brown planthopper is affected by host rice varieties.

Gut microbiota plays vital roles in the development, evolution and environmental adaptation of the host insects. The brown planthopper (BPH) is one of the most destructive pests of rice, but little is known about its gut microbiota. In this study, we investigated the gut bacterial communities in two BPH populations feeding on susceptible and resistant rice varieties by high-throughput amplicon sequencing. Our results revealed that the gut bacterial communities in BPH were species diverse. A total of 29 phyla and 367 genera were captured, with Proteobacteria and Acinetobacter being the most prominent phylum and genus, respectively. Comparative analysis showed that significant differences in the profile of gut bacterial communities existed between the two BPH populations. The species richness detected in the population feeding on the resistant rice variety was significantly higher than that in the population rearing on the susceptible rice variety. Although the most dominant gut bacteria at all taxonomic levels showed no significant differences between the two BPH populations, the relative abundances of two subdominant phyla (Firmicutes and Bacteroidetes) and two subdominant classes (Bacteroidia and Clostridia) were significantly different. FAPROTAX analysis further indicated that host rice varieties might induce changes of the gut bacterial flora in BPH, as significant differences in five metabolism-related functional categories (fermentation, methylotrophy, xylanolysis, nitrate reduction and ureolysis) were detected between the two BPH populations. Our results are informative for studies which focused on the interactions between BPH and its symbiotic microbes and could also provide the basis of future BPH biological management.

Ser-653-Asn substitution in the acetohydroxyacid synthase gene confers resistance in weedy rice to imidazolinone herbicides in Malaysia.

The continuous and sole dependence on imidazolinone (IMI) herbicides for weedy rice control has led to the evolution of herbicide resistance in weedy rice populations across various countries growing IMI herbicide-resistant rice (IMI-rice), including Malaysia. A comprehensive study was conducted to elucidate occurrence, level, and mechanisms endowing resistance to IMI herbicides in putative resistant (R) weedy rice populations collected from three local Malaysian IMI-rice fields. Seed bioassay and whole-plant dose-response experiments were conducted using commercial IMI herbicides. Based on the resistance index (RI) quantification in both experiments, the cross-resistance pattern of R and susceptible (S) weedy rice populations and control rice varieties (IMI-rice variety MR220CL2 and non-IMI-rice variety MR219) to imazapic and imazapyr was determined. A molecular investigation was carried out by comparing the acetohydroxyacid synthase (AHAS) gene sequences of the R and S populations and the MR220CL2 and MR219 varieties. The AHAS gene sequences of R weedy rice were identical to those of MR220CL2, exhibiting a Ser-653-Asn substitution, which was absent in MR219 and S plants. In vitro assays were conducted using analytical grade IMI herbicides of imazapic (99.3%) and imazapyr (99.6%) at seven different concentrations. The results demonstrated that the AHAS enzyme extracted from the R populations and MR220CL2 was less sensitive to IMI herbicides than that from S and MR219, further supporting that IMI herbicide resistance was conferred by target-site mutation. In conclusion, IMI resistance in the selected populations of Malaysian weedy rice could be attributed to a Ser-653-Asn mutation that reduced the sensitivity of the target site to IMI herbicides. To our knowledge, this study is the first to show the resistance mechanism in weedy rice from Malaysian rice fields.

Comparative iTRAQ proteomic profiling of proteins associated with the adaptation of brown planthopper to moderately resistant vs. susceptible rice varieties.

The brown planthopper (BPH), Nilaparvata lugens (Stål), is a destructive pest that poses a significant threat to rice plants worldwide. To explore how BPHs adapt to the resistant rice variety, we analyzed proteomics profiles of two virulent N. lugens populations. We focused on Biotype Y, which can survive on the moderately resistant rice variety YHY15, and Biotype I, which can survive on the susceptible rice variety TN1. We performed protein quantitation using the isobaric tag for relative and absolute quantification (iTRAQ) and then compared the expression patterns between two virulent N. lugens populations and found 258 differentially expressed proteins (DEPs). We found that 151 of the DEPs were up-regulated, while 107 were down-regulated. We evaluated transcript levels of 8 expressed genes from the iTRAQ results by qRT-PCR, which revealed transcriptional changes that were consistent with the changes at the protein level. The determination of the protein changes in two virulent N. lugens populations would help to better understanding BPH adaptation to resistant rice varieties and facilitate the better design of new control strategies for host defense against BPH.

Temperature differentially modulates the transcriptome response in Oryza sativa to Xanthomonas oryzae pv. oryzae infection

Bacterial blight is caused by the pathogen Xanthomonas oryzae pv. oryzae (Xoo). Genome scale integrative analysis on the interaction of high and low temperatures on the molecular response signature in rice during the Xoo infection has not been conducted yet. We have analysed a unique RNA-Seq dataset generated on the susceptible rice variety IR24 under combined exposure of Xoo with low 29/21 °C (day/night) and high 35/31 °C (day/night) temperatures. Differentially regulated key genes and pathways in rice plants during both the stress conditions were identified. Differential dynamics of the regulatory network topology showed that WRKY and ERF families of transcription factors play a crucial role during signal crosstalk events in rice plants while responding to combined exposure of Xoo with low temperature vs. Xoo with high temperatures. Our study suggests that upon onset of high temperature, rice plants tend to switch its focus from defence response towards growth and reproduction.

First report of Bakanae disease caused by Fusarium proliferatum on rice in Turkey

The Bakanae disease caused by Gibberella fujikuroi species complex is one of the major fungal diseases of rice. It is present in the major rice production areas in the world. In 2016, field surveys were conducted from rice germination to maturity. Four isolates of Fusarium proliferatum associated with Bakanae disease were obtained from infected rice plants and identified using morphological and molecular-based methods. Pathogenicity tests were carried on susceptible rice variety. Initially, pale green to yellowing of leaves and thinner plants were observed. Then, these plants turned brownish and died, while control plants showed no symptoms. All isolates were found to be pathogenic. The disease severity values ranged from 27 to 66%. To our knowledge, this is the first report of the presence of F. proliferatum causing Bakanae disease on rice in Turkey.

A Synthetic Cytokinin Improves Photosynthesis in Rice under Drought Stress by Modulating the Abundance of Proteins Related to Stomatal Conductance, Chlorophyll Contents, and Rubisco Activity.

Drought susceptible rice cultivar PTT1 (Pathumthani1) was treated with drought (−72 kPa) and CPPU (N-2-(chloro-4-pyridyl)-N-phenyl urea) @ 5 mg/L at tillering and grain-filling stages. Plants were tested for the effect of synthetic cytokinin on the parameters influencing the process of photosynthesis. Exogenous spray of CPPU improved the stomatal conductance of rice leaves, which was severely reduced by drought. The abundance intensities of proteins, associated with the stomatal conductance (ZEP, NCED4, PYL9, PYL10, ABI5, SnRK4, Phot1, and Phot2), were also in agreement with the positive impact of CPPU on the stomatal conductance under drought stress. Among the photosynthetic pigments, Chl b contents were significantly reduced by drought stress, whereas CPPU treated plants retained the normal contents of Chl b under drought stress. Subsequently, we examined the abundance intensities of chlorophyll synthase and HCR proteins, implicated in the biosynthesis of chlorophyll pigments and the conversion of Chl b to Chl a, respectively. The results indicated a drought-mediated suppression of chlorophyll synthase. However, CPPU treated plants retained normal levels of chlorophyll synthase under drought stress. In addition, drought stress induced HCR proteins, which might be the cause for reduced Chl b contents in drought stressed plants. Further, CPPU treatment helped the plants sustain photosynthesis at a normal rate under drought stress, which was comparable with well-watered plants. The results were further confirmed by examining the abundance intensities of two key proteins, RAF1 and Rubisco activase, implicated in the assembly and activation of Rubisco, respectively. CPPU treatment reversed the drought mediated suppression of these proteins at both of the growth stages of rice under drought stress. Based on the results, it can be suggested that synthetic cytokinins help the plants sustain photosynthesis at a normal rate under drought stress by positively influencing the determinants of photosynthesis at a molecular level.

Analyses of the Root-Knot Nematode (Meloidogyne graminicola) Transcriptome during Host Infection Highlight Specific Gene Expression Profiling in Resistant Rice Plants

The plant-parasitic nematode Meloidogyne graminicola causes considerable damages to rice (Oryza sativa) culture. Resistance to M. graminicola in the related species Oryza glaberrima reduces root penetration by juveniles and stops further nematode development. M. graminicola genes expressed during O. sativa infection were previously characterized but no information is available about the molecular dialogue established with a resistant plant. We compared the M. graminicola transcriptomes of stage-two juveniles (J2s) before and during infection of susceptible or resistant rice. Among 36,121 M. graminicola genes surveyed, 367 were differentially expressed during infection of resistant or susceptible plants. Genes encoding cell wall-degrading enzymes, peptidases and neuropeptides were expressed for a longer time in resistant plants compared to susceptible plants. Conversely, genes related to nematode development were not activated in the resistant host. The majority of M. graminicola effector genes had similar expression patterns, whatever the host genotype. However, two venom allergen-like protein (VAP)-encoding genes were specifically induced in resistant plants and Mg-VAP1 silencing in J2s reduced their ability to colonize roots. This study highlighted that M. graminicola adapts its gene expression to the host susceptibility. Further investigation is required to assess the role of Mg-VAPs in the rice–nematode interaction.

Silicon nanoparticle-pulsing mitigates fluoride stress in rice by fine-tuning the ionomic and metabolomic balance and refining agronomic traits

The present manuscript investigates the roles of silicon nanoparticles (SiNPs) in ameliorating fluoride toxicity in the susceptible rice cultivar, IR-64. Fluoride toxicity reduced overall growth and yield by suppressing grain development. Fluoride stress alarmingly increased the accumulation of cobalt, which together with fluoride triggered electrolyte leakage, malondialdehyde, methylglyoxal and hydrogen peroxide accumulation and NADPH oxidase activity. The overall photosynthesis was compromised due to chlorosis and inhibited Hill activity. Nano-Si-priming efficiently ameliorated molecular injuries and restored yield by reducing fluoride bioaccumulation particularly in the grains. The level of non-enzymatic antioxidants like anthocyanins, flavonoids, phenolics and glutathione was stimulated upon SiNP-priming. Nano-Si-pulsing removed fluoride-mediated inhibition of glutathione synthesis by activating glutathione reductase. Glutathione was utilized to activate glyoxalases and associated enzymes like glutathione-S-transferase and glutathione peroxidase. Uptake of nutrients like silicon, potassium, zinc, copper, iron, nickel, manganese, selenium and vanadium improved seedling health even during prolonged fluoride stress. Nano-Si-pulsing produced a nanozymatic effect, since high level of crucial co-factors like copper, zinc and iron stimulated the activity of superoxide dismutase, catalase, ascorbate peroxidase and guaiacol peroxidase, which synergistically with other enzymatic and non-enzymatic antioxidants scavenged reactive oxygen species and promoted fluoride tolerance. Overall, the study supported by statistical modelling using principal component analysis, t-distributed stochastic neighbour embedding and multidimensional scaling, established the potential of SiNP to promote safe rice cultivation and precision farming even in fluoride-infested environments.

SWATH-MS-based quantitative proteomics reveals a uniquely intricate defense response in Cnaphalocrocis medinalis-resistant rice

Cnaphalocrocis medinalis is a major insect pest of rice in Asia. A few defensive enzymes were reported to show higher activities in a resistant rice line (Qingliu) than in a susceptible rice line (TN1) upon leaffolder infestation. However, the overall molecular regulation of the rice defense response against leaffolder herbivory is unknown. Here, differential proteomic analysis by SWATH-MS was performed to identify differentially expressed proteins between the two rice varieties, Qingliu and TN1, at four time points of leaffolder herbivory, 0, 6, 24, and 72 h. Gene Ontology (GO) enrichment of the differentially expressed proteins indicated overrepresentation of (1) photosynthesis, (2) amino acid and derivative metabolic process, and (3) secondary metabolic process. Phenylalanine ammonia lyase and chalcone synthase, which catalyze flavonoid biosynthesis, and lipoxygenase, which catalyzes jasmonic acid biosynthesis, exhibited higher expression in Qingliu than in TN1 even before insect herbivory. Momentary activation of the light reaction and Calvin cycle was detected in Qingliu at 6 h and 24 h of insect herbivory, respectively. At 72 h of insect herbivory, amino acid biosynthesis and glutathione-mediated antioxidation were activated in Qingliu. A defense response involving jasmonic acid signaling, carbon remobilization, and the production of flavonoids and glutathione could underlie the resistance of Qingliu to leaffolder.

Suppression of a leucine-rich repeat receptor-like kinase enhances host plant resistance to a specialist herbivore.

The mechanisms by which herbivores induce plant defenses are well studied. However, how specialized herbivores suppress plant resistance is still poorly understood. Here, we discovered a rice (Oryza sativa) leucine-rich repeat receptor-like kinase, OsLRR-RLK2, which is induced upon attack by gravid females of a specialist piercing-sucking herbivore, the brown planthopper (BPH, Nilaparvata lugens). Silencing OsLRR-RLK2 decreases the constitutive activity of mitogen-activated protein kinase (OsMPK6) and alters BPH-induced transcript levels of several defense-related WRKY transcription factors. Moreover, silencing OsLRR-RLK2 reduces BPH-induction of jasmonic acid and ethylene but promotes the biosynthesis of both elicited salicylic acid and H2 O2 ; silencing also enhances the production of volatiles emitted from rice plants infested with gravid BPH females. These changes decrease BPH preference and performance in the glasshouse and the field. These findings suggest that OsLRR-RLK2, by regulating the plant's defense-related signaling profile, increases the susceptibility of rice to BPH, and that BPH infestation influences the expression of OsLRR-RLK2, suppressing the resistance of rice to BPH.

Three Proteins (Hpa2, HrpF and XopN) Are Concomitant Type III Translocators in Bacterial Blight Pathogen of Rice.

Type III (T3) proteic effectors occupy most of the virulence determinants in eukaryote-pathogenic Gram-negative bacteria. During infection, bacteria may deploy a nanomachinery called translocon to deliver T3 effectors into host cells, wherein the effectors fulfill their pathological functions. T3 translocon is hypothetically assembled by bacterial translocators, which have been identified as one hydrophilic and two hydrophobic proteins in animal-pathogenic bacteria but remain unclear in plant pathogens. Now we characterize Hpa2, HrpF, and XopN proteins as concomitant T3 translocators in rice bacterial blight pathogen by analyzing pathological consequences of single, double, and triple gene knockout or genetic complementation. Based on these genetic analyses, Hpa2, HrpF, and XopN accordingly contribute to 46.9, 60.3, and 69.8% proportions of bacterial virulence on a susceptible rice variety. Virulence performances of Hpa2, HrpF, and XopN were attributed to their functions in essentially mediating from-bacteria-into-rice-cell translocation of PthXo1, the bacterial T3 effector characteristic of transcription factors targeting plant genes. On average, 61, 62, and 71% of PthXo1 translocation are provided correspondingly by Hpa2, HrpF, and XopN, while they cooperate to support PthXo1 translocation at a greater-than-95% extent. As a result, rice disease-susceptibility gene SWEET11, which is the regulatory target of PthXo1, is activated to confer bacterial virulence and induce the leaf blight disease in rice. Furthermore, the three translocators also undergo translocation, but only XopN is highly translocated to suppress rice defense responses, suggesting that different components of a T3 translocon deploy distinct virulence mechanisms in addition to the common function in mediating bacterial effector translocation.

Exogenous Glutathione-Mediated Drought Stress Tolerance in Rice (Oryza sativa L.) is Associated with Lower Oxidative Damage and Favorable Ionic Homeostasis

Drought stress is a major concern for current agriculture as it limits plant growth and yield. An experiment was conducted with a drought susceptible rice (Oryza sativa L. cv. BRRI dhan29) to explore the potential functions and possible mechanisms of exogenous glutathione (GSH)-induced drought stress tolerance. Fifteen-day-old seedlings, GSH-pretreated or non-pretreated (0.2 mM GSH for 72 h), were subjected to PEG-induced (15% polyethylene glycol 6000) drought stress for 4 days. Rice plants exposed to drought stress displayed reduced growth, which was correlated with reduced chlorophyll content, water balance, antioxidant enzymes activities and mineral contents (K+, Ca2+ and Mg2+), as evidenced by principle component analysis (PCA) and heatmap clustering. The PCA also revealed that hydrogen peroxide (H2O2) and malondialdehyde (MDA) accumulations were strongly linked with the declined growth and development of rice plants under drought stress. Importantly, pretreatment with GSH improved the growth responses of rice plants to drought stress. GSH strengthened numerous physio-biochemical processes which were coupled with increased uptake of K+, Ca2+ and Mg2+, enhanced accumulation of soluble sugars, higher activities of enzymatic and non-enzymatic antioxidants. Moreover, GSH-pretreated seedlings under drought stress conditions had lower levels of O2·− , H2O2 and MDA which indicates successful adaptation of rice seedlings to drought stress. The results of PCA strongly supported that GSH conferred drought tolerance mostly by enhancing antioxidant activities and mineral homeostasis. Collectively, our findings provide an important prospect for use of GSH in modulating drought tolerance in rice plants. Breeding strategies should therefore be undertaken to increase the GSH content of rice plants as a means to increase drought tolerance.

In vitro mutagenesis to improve salt tolerance in rice (Oryza sativa L.)

Rice is the most important food crop in the world which has been severely affected with salinity. Aim of this study was to improve the salt tolerant ability of two moderately susceptible rice cultivars (White ponni and BPT-5204) using Ethyl Methane Sulfonate under in vitro condition. In this experiment salt tolerant callus were recovered in seeds treated with 0.5% EMS cultured on MS media supplemented with different concentrations of NaCl and sea water (starts with 0%, 0.5%. 1.0% and 1.5% NaCl to 10% and 25% seawater). The extant of salt tolerance was determined by callus growth parameters like callus induction frequency, relative growth rate and regeneration frequency. The reduction in growth parameters were more at 25% (v/v) sea water and 1.5% (w/v) NaCl treated media. Significant number of plants (17.23% and 22.49% plantlets respectively) was obtained in callus recovered in 3hr and 5hr EMS treated seeds cultured on 25% sea water and 1.5% NaCl treated media. Proline is an important osmaticm accumulated more under salt stress to maintain the turgor pressure and protect the plants from extreme desiccation. Under higher salt concentration BPT-5204 accumulated the higher amount of proline than white ponni. The plantlets obtained from higher concentration of salt can be transferred to field for the selection of elite lines.

<em>Meloidogyne graminicola</em> infestation in selected Sri Lankan rice varieties, <em>Oryza sativa</em> L.. and nemato-toxic effect of <em>Trichoderma viride</em> to reduce infectivity

Meloidogyne graminicola is a nematode parasite of rice, Oryza sativa L, in some rice growing areas in Sri Lanka. M. graminicola infestation levels in eight rice varieties namely Bg 407, Bg 366, Bg 403, Bg 251, Bg 369, Bg 380, Bg 310, and Bg 745 and nemato-toxic effect of Trichoderma viride against the nematode infectivity in a susceptible rice variety were evaluated in this study. Results revealed that varieties Bg 366 and Bg 251 were susceptible; varieties Bg 407, Bg 369, Bg 380, Bg 310, and Bg 745 were moderately susceptible while Bg 403 was moderately resistant to M. graminicola. There was a significant reduction of root galls (p = 0.000, F = 68.92) and weight of the fresh roots (p = 0.001, F = 12.89) of T. viride treated plants of a susceptible rice variety compared to the untreated tillers of same rice variety. This study concludes that none of the rice varieties tested were totally resistant to M. graminicola infestation, hence, T. viride treatment can be integrated into nematode management practices to reduce the nematode population in susceptible rice varieties.

Relationship of root aquaporin genes, OsPIP1;3, OsPIP2;4, OsPIP2;5, OsTIP2;1 and OsNIP2;1 expression with drought tolerance in rice

Aquaporins are channel proteins that facilitate the passive uptake and transport of water, ions, molecules and regulate the water balance at the plant level. Genes for aquaporins are important since they play a major role in water uptake. The present study was therefore conducted to assess the relationship of aquaporins predominantly expressed in roots in response to drought tolerance. Transcript abundance of five rice aquaporin genes (PIP2;5, PIP1;3, PIP2;4, TIP2;1 and NIP2;1) in five rice genotypes (Banglami, ARC 10372, Inglongkiri, Ranjit and IR 64) under well-watered and drought stress conditions were measured using qRT-PCR. Significant variation in PIP relative transcript abundance in roots was observed between varieties under both well-watered and drought stress conditions. In roots, the expression levels of most OsPIPs were found to be increased in drought stress conditions. OsPIP1;3, OsPIP2;5, OsTIP2;1 and OsNIP2;1 were upregulated more in upland (drought tolerant) rice and Ranjit lowland (moderately drought tolerant) genotypes than drought susceptible lowland IR-64 rice in drought stress conditions and downregulated/unchanged in well-irrigated conditions. The OsPIP genes were identified as candidate genes based on their high expression under drought stress situations and played a significant role in water uptake and root development under water stress conditions. A positive correlation was observed between fold increase in aquaporin expression and degree of drought tolerance which suggest that these aquaporins genes might play an important role in root development under water stress situation to overcome stress.

The genetic associations between yield component traits and bacterial leaf blight resistance in rice (O. sativa L.)

Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is highly destructive to high-yielding susceptible rice cultivars. In severe epidemics, yield losses up to 75% have been reported. Considerable information on BLB resistant genes is available; however, genetic overlaps between BLB resistant and yield related traits largely remain unclear. Using two sets of backcross introgression inbred lines and one set of recombinant inbred lines, genetic associations between bacterial leaf blight resistance and yield component traits in three Xoo races were analyzed using Single Nucleotide polymorphism (SNP) markers. Fifteen quantitative trait loci conferring BLB resistant and 112 QTLs for yield and yield related traits were detected. Among 15 QTLs conferring bacteria leaf blight resistance, 14 QTLs overlapped with 39 QTLs for yield and yield related traits. The total resistance variation explained by additive QTLs (R2) ranged between 5-76% and epistasis QTLs ranged between 1-26%. Quantitative trait loci (QTLs) with the highest additive effects for BLB resistance were detected at positions os04-17305294 (on chr.4), os05-07310209 (on chr.5), os09-15240130 (on chr.9), os11-28421947 (on chr.11) and os12-25291547(on chr.12). The BLB resistance QTL at position os05-07310209 (on chr.5) overlapped with QTLs for 1000-grain weight, grain number per panicle, days to heading, grain length width ratio and grain yield per plant. The BLB resistance QTL at position os09-15240130 (on chr.9) overlapped with QTLs for grain yield per plant, panicle number, grain width and 1000-grain weight. The BLB resistance QTL at position os12-25291547-(on chr.12) overlapped with QTLs for 1000-grain weight, panicle number, grain yield per plant, filled grain number and grain width. Eleven percent of the 717 plants in this study were resistant to at least two Xoo races and had higher grain yield compared to both recurrent parents. Overlapping regions especially with already cloned genes and epistasis detected in this study offer opportunity to develop rice varieties which combine high yield and resistance to bacteria leaf blight.

Physiological and biochemical changes in susceptible and resistant rice cultivars induced by root-knot nematode, Meloidogyne graminicola

Screening of 50 rice varieties along with LALAT as local check, which showed evidence of damaging potential of Meloidogyne graminicola in terms of plant growth parameters and disease incidence. Disease intensity grade was classified on the basis of root knot index. Out of fifty varieties, 45 were moderately resistant to Meloidogyne graminicola while three varieties Ciherang Sub 1, IR 64 Sub 1and PSBRC 18 were susceptible with maximum number of egg mass per galls (6) while the rest 2 varieties, IRIOF 571 and IRIOF 602 showed resistant reactions. Observations were recorded in the biochemical modifications relating to various parameters like total chlorophyll, total sugar and starch contents, protein, phenol, nutrients (N, P, K, Ca, Mg, Fe) and proline content during post infection periods. The variation in total chlorophyll, total protein, proline and total sugar content in five cultivars i.e. IRIOF 571 and IRIOF 602 (Resistant), Ciherang Sub 1, IR 64 Sub 1and PSBRC 18 (susceptible) were studied 45 days after inoculation. Reduced percentage of total chlorophyll contents were observed in inoculated samples than the healthy counterparts. However, an increase in amount of total protein, phenol, proline and total sugar contents was observed in the diseased tissues.