Susceptible Rice Varieties Research Articles

Identification of Heat-Tolerant Genes in Non-Reference Sequences in Rice by Integrating Pan-Genome, Transcriptomics, and QTLs.

The availability of large-scale genomic data resources makes it very convenient to mine and analyze genes that are related to important agricultural traits in rice. Pan-genomes have been constructed to provide insight into the genome diversity and functionality of different plants, which can be used in genome-assisted crop improvement. Thus, a pan-genome comprising all genetic elements is crucial for comprehensive variation study among the heat-resistant and -susceptible rice varieties. In this study, a rice pan-genome was firstly constructed by using 45 heat-tolerant and 15 heat-sensitive rice varieties. A total of 38,998 pan-genome genes were identified, including 37,859 genes in the reference and 1141 in the non-reference contigs. Genomic variation analysis demonstrated that a total of 76,435 SNPs were detected and identified as the heat-tolerance-related SNPs, which were specifically present in the highly heat-resistant rice cultivars and located in the genic regions or within 2 kbp upstream and downstream of the genes. Meanwhile, 3214 upregulated and 2212 downregulated genes with heat stress tolerance-related SNPs were detected in one or multiple RNA-seq datasets of rice under heat stress, among which 24 were located in the non-reference contigs of the rice pan-genome. We then mapped the DEGs with heat stress tolerance-related SNPs to the heat stress-resistant QTL regions. A total of 1677 DEGs, including 990 upregulated and 687 downregulated genes, were mapped to the 46 heat stress-resistant QTL regions, in which 2 upregulated genes with heat stress tolerance-related SNPs were identified in the non-reference sequences. This pan-genome resource is an important step towards the effective and efficient genetic improvement of heat stress resistance in rice to help meet the rapidly growing needs for improved rice productivity under different environmental stresses. These findings provide further insight into the functional validation of a number of non-reference genes and, especially, the two genes identified in the heat stress-resistant QTLs in rice.

Genome-wide identification of long non-coding (lncRNA) in Nilaparvata lugens's adaptability to resistant rice.

BackgroundThe brown planthopper (BPH), Nilaparvata lugens (Stål), is a very destructive pest that poses a major threat to rice plants worldwide. BPH and rice have developed complex feeding and defense strategies in the long-term co-evolution.MethodsTo explore the molecular mechanism of BPH’s adaptation to resistant rice varieties, the lncRNA expression profiles of two virulent BPH populations were analyzed. The RNA-seq method was used to obtain the lncRNA expression data in TN1 and YHY15.ResultsIn total, 3,112 highly reliable lncRNAs in TN1 and YHY15 were identified. Compared to the expression profiles between TN1 and YHY15, 157 differentially expressed lncRNAs, and 675 differentially expressed mRNAs were identified. Further analysis of the possible regulation relationships between differentially expressed lncRNAs and differentially expressed mRNAs, identified three pair antisense targets, nine pair cis-regulation targets, and 3,972 pair co-expressed targets. Function enriched found arginine and proline metabolism, glutathione metabolism, and carbon metabolism categories may significantly affect the adaptability in BPH when it is exposed to susceptible and resistant rice varieties. Altogether, it provided scientific data for the study of lncRNA regulation of brown planthopper resistance to rice. These results are helpful in the development of new control strategies for host defense against BPH and breeding rice for high yield.

Alternately Rearing with Susceptible Variety Can Delay the Virulence Development of Insect Pests to Resistant Varieties

Resistant crop varieties can usually decrease the population density of insect pests; however, they can also easily cause the occurrence of highly virulent pest populations when repeatedly grown. Whether herbivorous insects feeding intermittently on a susceptible variety affects their subsequent virulence has rarely been investigated. In this paper, we examined the variations in the virulence of the brown planthopper (BPH), Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), by alternately rearing three resistant rice varieties, Mudgo, ASD7, and Rathu Heenati, with a susceptible rice variety (TN1) in indoor experiments. The results showed that, while the susceptible rice variety was used in alternate rearing for several generations, the BPHs exhibited a higher intrinsic rate of increase (rm) and were identified as less virulent to all three resistant varieties. Such virulence reduction by experience with a susceptible variety could delay the progression of resistance-breaking toward resistant varieties. The results suggested that careful alternation with susceptible varieties in fields is a potential method for pest variety-resistance management.

Molecular characterization and screening of Xanthomonas oryzae pv. oryzae, isolated from Pakistan for prediction of bacterial leaf blight-resistant basmati rice

Bacterial leaf blight (BLB) is a devastating disease of rice caused by Xanthomonas oryzae pv.oryzae (Xoo), severely affects grain quality and reduces yield in all rice-growing areas of Pakistan. The pathogen is highly dynamic and quickly evolves itself when encountered with new resistant genes, hence, the knowledge about existing virulence range within the pathogen population and availability of corresponding resistance gene source is of immense importance. The present study focused on molecular dissection and evaluating the effectiveness of different resistance gene combinations against Xoo isolates collected from seven major rice-growing districts of Punjab Pakistan. Phenotypic characterization of collected Xoo isolates has shown that all of them were rod-shaped Gram-negative bacteria. However, oryzae species and oryzae pathovar were confirmed in only 22 out of 50 isolates using multiplex PCR. Analysis of loop-mediated isothermal amplification validated the lineage and close relatedness of Pakistani Xoo isolates with the already reported Asian Xoo population. Pathogenicity test on susceptible rice variety Super Basmati has shown that out of twenty-two tested Xoo isolates, four isolates from three different districts fell into the most virulent category with an average lesion length of ≥15 cm. Pathotyping of selected resistant rice lines against Xoo isolates distributed 22 isolates into nine pathotypes based on their interaction with R genes. Current molecular and phenotypic profiling of isolated Pakistani Xoo isolates may serve as a valuable reference for global comparison to manage BLB disease of rice in real-time.

Culture condition and variation in the pathogenicity of Ustilagonoidea virens isolates causing false smut disease of rice

False smut of rice caused by Ustilagonoidea virens was previously considered a minor disease of rice or rather a sign of bumper harvest, hence the disease was also known by the name Lakshmi disease. However, the disease is gaining much importance at present and is reported to occur in most of the rice growing areas of world in moderate to severe forms. Rice which is cultivated throughout the year in West Bengal is also observed to produce the symptoms of the disease every year in varying degree of severity. Effect of light and different temperature on mycelial growth of Ustilagonoidea virens in BOD incubator was tested. It was found that temperature of 28oC and dark condition favors mycelial growth. Twelve different isolates of Ustilagonoidea virens collected from different districts of West Bengal were isolated in laboratory and tested for their variability in Pathogenicity using the susceptible rice variety Swarna (MTU 7029). 2 ml of inoculum suspension of each isolates were injected to rice plant at booting stage with three replications, whereas in control plants 2 ml of sterilized water was injected and percent grain infection was calculated and analyzed. All the inoculated plants were observed to produce typical false disease symptom with varying degree of severity indicating variation in pathogenicity among the isolates. Percent grain infection ranged from 1.461% to 7.936%. Isolate Uv5 from Alipudwar district was found to be significantly more virulent as compared to other isolates with 7.936% grain infection followed by isolate Uv4 (Jalpaiguri district) and Uv3(Nadia district)  with 5.050% and 4.557% grain infection respectively. Significantly lower infection was observed in isolate Uv9 collected from Coochbehar district with 1.461% grain infection followed by isolate Uv2 (North 24 Parganas district) and Uv12 (Hooghly district) with 1.912 and 3.279% grain infection.

Identification of the rice genes and metabolites involved in dual resistance against brown planthopper and rice blast fungus.

Brown planthopper (BPH) and blast disease jointly or individually cause big yield losses every year. To identify genes and metabolites with potential contributions to the dual resistance against both biotic-stress factors, we carried out a transcriptome and metabolome analysis for susceptible and resistant rice varieties after BPH and rice blast infestations. Coexpression network analysis identified a modular pattern that had the highest correlation coefficients (0.81) after the BPH and rice blast (-0.81) treatments. In total, 134 phenylpropanoid biosynthesis pathway-related genes were detected in this group. We found that the flavanone 3-hydroxylase gene (OsF3H) had opposite expression trends in response to BPH and rice blast infestations whereas the OsF3'H had similar expression patterns. Genetics analysis confirmed that the OsF3H gene knockdown lines demonstrated the opposite resistance phenotypes against BPH and rice blast, whereas the OsF3'H knockout lines enhanced rice resistance against both pests. Consistently, our metabolomics analysis identified the metabolite eriodictyol, one putative essential product of these two genes, that was more highly accumulated in the resistant rice variety of RHT than in the susceptible variety MDJ. This study highlights a useful strategy for identifying more genes and metabolites that have potential synergistic effects on rice against to multiple biotic stresses.

Identification of a Negative Regulator for Salt Tolerance at Seedling Stage via a Genome-Wide Association Study of Thai Rice Populations.

Salt stress is a major limiting factor in crop production and yield in many regions of the world. The objective of this study was to identify the genes responsible for salt tolerance in Thai rice populations. We performed a genome-wide association study with growth traits, relative water content, and cell membrane stability at the seedling stage, and predicted 25 putative genes. Eleven of them were located within previously reported salt-tolerant QTLs (ST-QTLs). OsCRN, located outside the ST-QTLs, was selected for gene characterization using the Arabidopsis mutant line with T-DNA insertion in the orthologous gene. Mutations in the AtCRN gene led to the enhancement of salt tolerance by increasing the ability to maintain photosynthetic pigment content and relative water content, while the complemented lines with ectopic expression of OsCRN showed more susceptibility to salt stress detected by photosynthesis performance. Moreover, the salt-tolerant rice varieties showed lower expression of this gene than the susceptible rice varieties under salt stress conditions. The study concludes that by acting as a negative regulator, OsCRN plays an important role in salt tolerance in rice.

Seeds Phenotypes Characterization of Promising Tungro-Resistant Rice Lines

Breeding activities to produce a new site-specific rice varieties resistant to tungro require of suitable genetic materials as cross-breeding materials. This research aims to determine the seed phenotypic characters of promising tungro resistant rice lines and their similarity. The research was conducted using a completely randomized design with treatment of 42 promising tungro-resistant rice lines, 1 resistant rice variety (Inpari 7) and 1 susceptible rice variety (TN1), that each of which was repeated 3 times. The characters were observed included of quantitative and qualitative characters. Observation of seed characters was carried out based on the standard system of characterization and evaluation of rice plants. The similarity of seed characters was analyzed by using the NTSYS pc version 2.1 program and displayed in the form of a dendrogram. The results showed that most of the tested lines had the same quantitative characters as the Inpari 7 variety. The value of variability of diversity was included in the broad category of >4, with the lowest similarity coefficient of 63% and the highest of 94%. The similarity analysis based on the seed characters resulted in 2 large groups consisting of 41 lines belonging to the Inpari 7 group and 1 line belonging to the TN1 group. The lines that were incorporated in the Inpari 7 group were further divided into two subgroups of 39 and 2 lines, respectively. The results of this research are preliminary data to obtain an information of the relationship between seed characters and tungro resistance properties.

Dynamics of bacterial blight disease in resistant and susceptible rice varieties

Bacterial blight (X. oryzae pv. oryzae) is a serious disease in rice across the world. To better control the disease, it is important to understand its epidemiology and how key aspects of this (e.g. infection efficiency, and spatial spread) change according to environment (e.g. local site conditions and season), management, and in particular, variety resistance. To explore this, we analysed data on the disease progress on resistant and susceptible varieties of rice grown at four sites in the Philippines across five seasons using a combination of mechanistic modelling and statistical analysis. Disease incidence was generally lower in the resistant variety. However, we found no evidence that the primary infection efficiency was lower in resistant varieties, suggesting that differences were largely due to reduced secondary spread. Despite secondary spread being attributed to splash dispersal which is exacerbated by wind and rain, the wetter sites of Pila and Victoria in south Luzon tended to have lower infection rates than the drier sites in central Luzon. Likewise, we found spread in the dry season can be substantial and should therefore not be ignored. In fact, we found site to be a greater determinant of the number of infection attempts suggesting that other environmental and management factors had greater effect on the disease than climate. Primary infection was characterised by spatially-random observations of disease incidence. As the season progressed, we observed an emerging short-range (1.6 m–4 m) spatial structure suggesting secondary spread was predominantly short-range, particularly where the resistant variety was grown.

Diversity Control in Early Transcribed ROS/RNS-balancing Genes: A Common Mechanism for Healthy Resilience?

Diversity Control in Early Transcribed ROS/RNS-balancing Genes: A Common Mechanism for Healthy Resilience?

Disease resistance of improved MR220 lines against Pyricularia oryzae Cavara and their preliminary agronomic performance

Blast disease caused by Pyricularia oryzae is one of the most destructive fungal diseases of rice in Malaysia. Utilisation of resistant varieties is the most efficient management approach towards reducing yield losses. The line IRTP21683 with the Pi9 gene has shown strong resistance against the isolate MPO988.3 of pathotype P<sub>0.0</sub>, the most prevalent P. oryzae pathotype in Malaysia. Crossing of IRTP21683 was undertaken with the recurrent parent MR220, a susceptible elite Malaysian rice variety, using a marker assisted backcrossing technique with two simple sequence repeat markers, RM19776 and RM7311, as the tag for the Pi9 gene. Twenty BC<sub>3</sub>F<sub>4</sub> lines with the Pi9 gene were resistant when challenged with MPO 988.3. The cluster analysis based on seven agronomic parameters showed that the resistant BC<sub>3</sub>F<sub>4</sub> lines could be divided into four groups, of which the members in group 1 and 2 have shown comparable or better performance than MR220. Five lines in group 1, B220PI9-3-48, B220PI9-3-76, B220PI9-3-77, B220PI9-3-79 and B220PI9-3-82 showed outstanding yield performance with early maturation.

Methylation patterns of Tf2 retrotransposons linked to rapid adaptive stress response in the brown planthopper (Nilaparvata lugens)

Transposable elements (TEs) exhibit vast diversity across insect orders and are one of the major factors driving insect evolution and speciation. Presence of TEs can be both beneficial and deleterious to their host. While it is well-established that TEs impact life-history traits, adaptations and survivability of insects under hostile environments, the influence of the ecological niche on TE-landscape remains unclear. Here, we analysed the dynamics of Tf2 retrotransposons in the brown planthopper (BPH), under environmental fluctuations. BPH, a major pest of rice, is found in almost all rice-growing ecosystems. We believe genome plasticity, attributed to TEs, has allowed BPH to adapt and colonise novel ecological niches. Our study revealed bimodal age-distribution for Tf2 elements in BPH, indicating the occurrence of two major transpositional events in its evolutionary history and their contribution in shaping BPH genome. While TEs can provide genome flexibility and facilitate adaptations, they impose massive load on the genome. Hence, we investigated the involvement of methylation in modulating transposition in BPH. We performed comparative analyses of the methylation patterns of Tf2 elements in BPH feeding on resistant- and susceptible-rice varieties, and also under pesticide stress, across different life-stages. Results confirmed that methylation, particularly in non-CG context, is involved in TE regulation and dynamics under stress. Furthermore, we observed differential methylation for BPH adults and nymphs, emphasising the importance of screening juvenile life-stages in understanding adaptive-stress-responses in insects. Collectively, this study enhances our understanding of the role of transposons in influencing the evolutionary trajectory and survival strategies of BPH across generations.

Recent Progress in Rice Broad-Spectrum Disease Resistance.

Rice is one of the most important food crops in the world. However, stable rice production is constrained by various diseases, in particular rice blast, sheath blight, bacterial blight, and virus diseases. Breeding and cultivation of resistant rice varieties is the most effective method to control the infection of pathogens. Exploitation and utilization of the genetic determinants of broad-spectrum resistance represent a desired way to improve the resistance of susceptible rice varieties. Recently, researchers have focused on the identification of rice broad-spectrum disease resistance genes, which include R genes, defense-regulator genes, and quantitative trait loci (QTL) against two or more pathogen species or many isolates of the same pathogen species. The cloning of broad-spectrum disease resistance genes and understanding their underlying mechanisms not only provide new genetic resources for breeding broad-spectrum rice varieties, but also promote the development of new disease resistance breeding strategies, such as editing susceptibility and executor R genes. In this review, the most recent advances in the identification of broad-spectrum disease resistance genes in rice and their application in crop improvement through biotechnology approaches during the past 10 years are summarized.

Balancing selection and wild gene pool contribute to resistance in global rice germplasm against planthopper.

Interactions and co-evolution between plants and herbivorous insects are critically important in agriculture. Brown planthopper (BPH) is the most severe insect of rice, and the biotypes adapt to feed on different rice genotypes. Here, we present genomics analyses on 1,520 global rice germplasms for resistance to three BPH biotypes. Genome-wide association studies identified 3,502 single nucleotide polymorphisms (SNPs) and 59 loci associated with BPH resistance in rice. We cloned a previously unidentified gene Bph37 that confers resistance to BPH. The associated loci showed high nucleotide diversity. Genome-wide scans for trans-species polymorphisms revealed ancient balancing selection at the loci. The secondarily evolved insect biotypes II and III exhibited significantly higher virulence and overcame more rice varieties than the primary biotype I. In response, more SNPs and loci evolved in rice for resistance to biotypes II and III. Notably, three exceptional large regions with high SNP density and resistance-associated loci on chromosomes 4 and 6 appear distinct between the resistant and susceptible rice varieties. Surprisingly, these regions in resistant rice might have been retained from wild species Oryza nivara. Our findings expand the understanding of long-term interactions between rice and BPH and provide resistance genes and germplasm resources for breeding durable BPH-resistant rice varieties.

Effectiveness of Bacteria Isolated from Peat Swamp Forests to Control Rice Dirty Panicle Fungi in Thailand

Rice dirty panicle disease is one of the most important problems in Thailand. The fungal pathogens were reported to be many species including Curvularia lunata, Bipolaris oryzae, Fusarium incarnatum, Sarocladium oryzae, Trichoconis padwickii and Cercospora oryzae. Biological control is an alternative method for controlling this disease and reducing the application of fungicides. Therefore, this study aimed to evaluate the antagonistic potential of bacteria isolated from peat swamp forests in Thailand. A total of 513 bacterial isolates were collected and screened in the laboratory using the dual culture method. The results revealed that three of the 513 bacterial strains (IBK-4, IBK-8 and IBK-5) were highly inhibitory to the fungal pathogens including C. lunata, B. oryzae and F. incarnatum. These three strains were identified as Bacillus (IBK-4 and IBK-8) and Brevibacillus (IBK-5) based on 16S rRNA sequencing. Then, these three strains were evaluated on a susceptible rice variety by inoculation with three fungal pathogens. The results indicated that Bacillus strain IBK-8 had the highest efficiency to control the disease development as observed in the disease severity and index. The results of this study indicated that bacterial strains from peat swamp forests have the potential to be antagonistic to plant pathogens.

Biogenic silver nanoparticles as an antibacterial agent against bacterial leaf blight causing rice phytopathogen Xanthomonas oryzae pv. oryzae.

Silver nanoparticles (Ag NP) were produced utilizing leaf extract of rice cultivar Taichung native-1. Various factors like leaf extract, silver nitrate concentrations, and duration of autoclaving were standardized during synthesis. Nanoparticles were analyzed with UV-visible absorption spectroscopy (UV-vis), dynamic light scattering, zeta potential, X-ray diffraction and transmission electron microscopy techniques. The synthesis was noted at 0.4% extract, 0.6mM silver nitrate, 30min of autoclaving and NP formation was confirmed from 424nm peak in UV-vis. NP showed zeta potentialof - 27mV, face-centered cubic (fcc) crystal nature and sized around 16.5 ± 5.9nm. Biogenic NP synthesized from susceptible rice variety were used as an antibacterial agent against phytopathogen Xanthomonas oryzae pv. oryzae (Xoo), the causative agent of bacterial leaf blight (BLB) disease in rice. Antibacterial effect of Ag NP was evaluated using in vitro assays and in vivo efficacy under greenhouse conditions. Results confirmed effective inhibition of Xoo growth and colony formation by Ag NP and found to be the more powerful antibacterial agent. Besides, Ag NP treatment (10µg/mL) caused an enhancement in seedling vigor index. Pots treated with Ag NP (15μg/mL) in vivo in greenhouse showed disease severity of 26.6% and disease decrease over control of 49.2%, at a much lower NP concentration than earlier reported studies. Thus, the current report implies using the leaf extract synthesized Ag NP to control and BLB disease management in field conditions.

Pathotype profiling, distribution and virulence analysis of Xanthomonas oryzae pv. oryzae causing bacterial blight disease of rice in Bangladesh

AbstractBacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is a serious threat to rice production in the world. Identification of Xoo races pattern, distribution and deployment of race‐specific resistant genes is a sustainable strategy to develop bacterial blight resistant varieties. In this study, a total of 118 isolates of Xoo were collected from 8 rice‐growing regions of Bangladesh to identify the existing pathotypes of Xoo. All tested isolates were virulent on the susceptible rice varieties viz. IR24, Purbachi and BR11. The tested isolates were evaluated on 13 near‐isogenic lines of rice and each line consisted of a single bacterial blight resistant gene viz Xa1, Xa2, Xa3, Xa4, xa5, Xa7, xa8, Xa10, Xa11, xa13, Xa14, Xa21 and Xa23. Based on reaction patterns of 118 isolates of Xoo on near‐isogenic lines, 12 pathotypes/races were first time identified in Bangladesh. Race 1, Race 2 and Race 3 were predominantly distributed in the most of the areas of Bangladesh and considered as major races containing the maximum number of isolates (48%, 14% and 11% respectively). Among these, Race 1 was the most prevalent and widely distributed while Race 5 was the most virulent circumventing all of the resistance genes tested. Race 1 was recorded from six rice‐growing regions of Bangladesh. Host plant R‐genes xa5, xa8, xa13, Xa21 and Xa23 have been found as effective against bacterial blight based upon resistance frequencies and the reactions of near‐isogenic lines and pyramid lines. The bacterial blight resistant gene Xa21 showed a resistant reaction against 11 of 12 races (i.e. 94.91% of the isolates tested). Effective genes and information of races generated from this study could be deployed for the development of race‐specific bacterial blight resistant varieties in Bangladesh.

Alleviation of Submergence Stress in Rice Seedlings by Plant Growth-Promoting Rhizobacteria With ACC Deaminase Activity

Submergence stress slows seed germination, imposes fatalities, and delays seedling establishment in rice. Seeds of submergence susceptible rice variety IR 42 were inoculated with four 1-aminocyclopropane-1-carboxylic acid (ACC) utilizing isolates viz., Bacillus sp. (AR-ACC1), Microbacterium sp. (AR-ACC2), Methylophaga sp. (AR-ACC3), and Paenibacillus sp. (ANR-ACC3) and subjected to submergence stress under controlled conditions for 7 days. Seeds treated with Microbacterium sp. AR-ACC2, Paenibacillus sp. ANR-ACC3, and Methylophaga sp. AR-ACC3 significantly enhanced the germination percentage (GP), seedling vigor index (SVI), and other growth parameters like root and shoot length and total chlorophyll contents, when compared with nonbacterized seeds submerged similarly. However, the values were statistically at par when control seeds were treated with l-α-(2-aminoethoxyvinyl) glycine hydrochloride (AVG), a known inhibitor of ethylene production. Results suggest that stress ethylene production was significantly reduced by around 85% in seedlings treated with Microbacterium sp. AR-ACC2 as compared with untreated control seeds under submergence. Paenibacillus sp. ANR-ACC3 and Methylophaga sp. AR-ACC3 were the next effective strains. Ethylene synthesis in seedlings was statistically at par with seeds treated with AVG suggesting ACC deaminase can effectively reduce ethylene levels in plants subjected to submergence. Bacillus sp. (AR-ACC1) was neither able to significantly promote seedling growth parameters nor inhibit ethylene production as compared with control seeds. Results suggest that flooded soil planted to rice harbor microorganisms with plant growth-promoting properties that can be used effectively to alleviate submergence stresses in susceptible rice varieties under field conditions.

Elevated temperatures diminish the effects of a highly resistant rice variety on the brown planthopper

This study compares the effects of temperature (constant at 15, 20, 25, 30 and 35 °C) on adult longevity, oviposition, and nymph development of the brown planthopper, Nilaparvata lugens, on susceptible and resistant rice varieties. The resistant variety contained the BPH32 gene. In our experiments, nymphs failed to develop to adults at 15, 20 and 35 °C on either variety. Host resistance had its greatest effect in reducing adult survival at 20–25 °C and its greatest effect in reducing nymph weight gain at 25 °C. This corresponded with optimal temperatures for adult survival (20–25 °C) and nymph development (25–30 °C). At 25 and 30 °C, adult females achieved up to three oviposition cycles on the susceptible variety, but only one cycle on the resistant variety. Maximum egg-laying occurred at 30 °C due to larger numbers of egg batches produced during the first oviposition cycle on both the susceptible and resistant varieties, and larger batches during the second and third oviposition cycles on the susceptible variety; however, resistance had its greatest effect in reducing fecundity at 25 °C. This revealed a mismatch between the optimal temperatures for resistance and for egg production in immigrating females. Increasing global temperatures could reduce the effectiveness of anti-herbivore resistance in rice and other crops where such mismatches occur.

Tibet Development and Breeding Application of the Fluorescence Molecular Marker of Rice Bacterial Blight Resistance Gene Xa7

In this study, the closely linked fluorescence molecular marker PM-Xa7 of  Xa7  gene was developed on the basis of sequence difference between the resistant variety ‘IRBB7’ containing  Xa7  and other nine bacterial blight susceptible rice varieties, and combine with PARMS technology (Penta-primer amplification refractory mutation system). Genotypes of  Xa7  were identified in 72 rice germplasm and the bacterial blight resistance level of ‘Mei B’ was improved by backcross and screening with this marker. The results showed that two rice germplasms containing  Xa7  were screened out from 72 rice germplasm; By introducing the resistant  Xa7  gene from ‘IRBB7’ into ‘Mei B’ with PM-Xa7, a stable new maintainer with resistance to bacterial blight was successfully obtained. The bacterial blight resistant fluorescence signal was detected in 289 plants and the bacterial blight susceptible fluorescence signal was detected in 93 plants of BC 2 F 2 population generated from ‘IRBB7’ and ‘Mei B’, and the genotypes were consistent with the phenotypes of  Xoo  inoculation. These research results indicated that PM-Xa7 can be effectively used for the marker-assisted breeding of bacterial blight resistant rice variety   with the resistant   Xa7  gene.