Geographic and research center origins of rice resistance to asian planthoppers and leafhoppers: Implications for rice breeding and gene deployment

2017 by the authors. This study examines aspects of virulence to resistant rice varieties among planthoppers and leafhoppers. Using a series of resistant varieties, brown planthopper, Nilaparvata lugens, virulence was assessed in seedlings and early-tillering plants at seven research centers in South and East Asia. Virulence of the whitebacked planthopper, Sogatella furcifera, in Taiwan and the Philippines was also assessed. Phylogenetic analysis of the varieties using single-nucleotide polymorphisms (SNPs) indicated a clade of highly resistant varieties from South Asia with two further South Asian clades of moderate resistance. Greenhouse bioassays indicated that planthoppers can develop virulence against multiple resistance genes including genes introgressed from wild rice species. Nilaparvata lugens populations from Punjab (India) and the Mekong Delta (Vietnam) were highly virulent to a range of key resistance donors irrespective of variety origin. Sogatella furcifera populations were less virulent to donors than N. lugens; however, several genes for resistance to S. furcifera are now ineffective in East Asia. A clade of International Rice Research Institute (IRRI)-bred varieties and breeding lines, without identified leafhopper-resistance genes, were highly resistant to the green leafhopper, Nephotettix virescens. Routine phenotyping during breeding programs likely maintains high levels of quantitative resistance to leafhoppers. We discuss these results in the light of breeding and deploying resistant rice in Asia

Brown Planthopper (N. lugens Stal) Feeding Behaviour on Rice Germplasm as an Indicator of Resistance

BACKGROUND: The brown planthopper (BPH) Nilaparvata lugens (Stal) is a serious pest of rice in Asia. Development of novel control strategies can be facilitated by comparison of BPH feeding behaviour on varieties exhibiting natural genetic variation, and then elucidation of the underlying mechanisms of resistance. METHODOLOGY/PRINCIPAL FINDINGS: BPH feeding behaviour was compared on 12 rice varieties over a 12 h period using the electrical penetration graph (EPG) and honeydew clocks. Seven feeding behaviours (waveforms) were identified and could be classified into two phases. The first phase involved patterns of sieve element location including non penetration (NP), pathway (N1+N2+N3), xylem (N5) [21] and two new feeding waveforms, derailed stylet mechanics (N6) and cell penetration (N7). The second feeding phase consisted of salivation into the sieve element (N4-a) and sieve element sap ingestion (N4-b). Production of honeydew drops correlated with N4-b waveform patterns providing independent confirmation of this feeding behaviour. CONCLUSIONS/SIGNIFICANCE: Overall variation in feeding behaviour was highly correlated with previously published field resistance or susceptibility of the different rice varieties: BPH produced lower numbers of honeydew drops and had a shorter period of phloem feeding on resistant rice varieties, but there was no significant difference in the time to the first salivation (N4-b). These qualitative differences in behaviour suggest that resistance is caused by differences in sustained phloem ingestion, not by phloem location. Cluster analysis of the feeding and honeydew data split the 12 rice varieties into three groups: susceptible, moderately resistant and highly resistant. The screening methods that we have described uncover novel aspects of the resistance mechanism (or mechanisms) of rice to BPH and will in combination with molecular approaches allow identification and development of new control strategies

Not Available

Not AvailableBackground: A major pest of rice, the Asian rice gall midge (Orseolia oryzae Wood-Mason), causes significant yield losses in the rice growing regions throughout Asia. Feeding by the larvae induces susceptible plants to produce nutritive tissue to support growth and development. In order to identify molecular signatures during compatible interactions, genome wide transcriptional profiling was performed using SSH library and microarray technology. Results: Results revealed up-regulation of genes related to primary metabolism, nutrient relocation, cell organization and DNA synthesis. Concomitantly, defense, secondary metabolism and signaling genes were suppressed. Further, real-time PCR validation of a selected set of 20 genes, in three susceptible rice varieties (TN1, Kavya and Suraksha) during the interaction with the respective virulent gall midge biotypes, also revealed variation in gene expression in Kavya as compared to TN1 and Suraksha. Conclusions: These studies showed that virulent insects induced the plants to step up metabolism and transport nutrients to their feeding site and suppressed defense responses. But Kavya rice mounted an elevated defense response during early hours of virulent gall midge infestation, which was over-powered later, resulting in host plant susceptibilityNot Availabl

Not Available

Not AvailableHost plant resistance is the preferred management strategy for Asian rice gall midge (Orseolia oryzae), a serious pest in many rice-growing countries. Identification of simple sequence repeat (SSR) markers that are tightly linked to pest resistance genes can accelerate development of gene pyramids for durable/multiple resistance. Based on conventional and molecular allelism tests, we report herein that rice genotype Aganni possesses Gm8 gene, conferring hypersensitive independent (HR– type) resistance to gall midge biotypes GMB1, GMB2, GMB3, GMB4, and GMB4M. The gene Gm8 was mapped to chromosome 8 within a 400-kbp region, and the SSR markers RM22685 and RM22709 flank the gene closely. Using these closely linked flanking markers, nine other gall midge-resistant genotypes were identified as carrying the same gene Gm8. Through marker-assisted selection, Gm8 has been introgressed into an elite bacterial blight-resistant cultivar, Improved Samba-Mahsuri (IS).Not Availabl

Not Available

Not AvailableThis chapter focuses on the progress made in using molecular tools in understanding resistance in rice to insect pests and breeding rice for multiple and durable insect resistance. Currently, molecular markers are being extensively used to tag, map, introgress, and clone plant resistance genes against gall midge, planthoppers, and leafhoppers. Studies on cloned insect resistance genes are leading to a better understanding of plant defense against insect pests under different feeding guilds. While marker-assisted breeding is successfully tackling problems in durable and multiple pest resistance in rice, genomics of plants and insects has identified RNAi-based gene silencing as an alternative approach for conferring insect resistance. The use of these techniques in rice is in the developmental stage, with the main focus on brown planthopper and yellow stem borer. CRISPR-based genome editing techniques for pest control in plants has just begun. Insect susceptibility genes (negative regulators of resistance genes) in plants are apt targets for this approach while gene drive in insect populations, as a tool to study rice-pest interactions, is another concept being tested. Transformation of crop plants with diverse insecticidal genes is a proven technology with potential for commercial success. Despite advances in the development and testing of transgenic rice for insect resistance, no insect-resistant rice cultivar is now being commercially cultivated. An array of molecular tools is being used to study insect-rice interactions at transcriptome, proteome, metabolome, mitogenome, and metagenome levels, especially with reference to BPH and gall midge, and such studies are uncovering new approaches for insect pest management and for understanding population genetics and phylogeography of rice pests. Thus, it is evident that the new knowledge being gained through these studies has provided us with new tools and information for facing future challenges. However, what is also evident is that our attempts to manage rice pests cannot be a one-time effort but must be a continuing one.Not Availabl

Suppressive subtraction hybridization reveals that rice gall midge attack elicits plant-pathogen-like responses in rice

Not AvailableThe Asian rice gall midge, Orseolia oryzae (Diptera: Cecidomyiidae), is the third most destructive insect pest of rice (Oryza sativa L.). Till date, 11 gall midge resistance gene loci have been characterized in different rice varieties. To elucidate molecular basis of incompatible (hypersensitive response plus [HR+] type) and compatible rice-gall midge interactions, two suppressive subtraction hybridization cDNA libraries were constructed. These were enriched for differentially expressed transcripts after gall midge infestation in two rice varieties (resistant Suraksha and susceptible TN1). In total, 2784 ESTs were generated and sequenced from the two libraries, of which 1536 were from the resistant Suraksha and 1248 were from the susceptible TN1. Majority (80%) of the ESTs was non-redundant sequences with known functions and was classified into three principal gene ontology (GO) categories and 12 groups. Upregulation of NBS-LRR, Cytochrome P450, heat shock proteins, phenylalanine ammonia lyase and OsPR10α genes from the Suraksha library, as revealed by real-time PCR, indicated that R gene mediated, salicylic acid related defense pathway is likely to be involved in gall midge resistance. Present study suggested that resistance in Suraksha against gall midge is similar in nature to the resistance observed in plants against pathogens. However, in TN1, genes related to primary metabolism and redox were induced abundantly. Results suggested that genes encoding translationally controlled tumor protein and NAC domain proteins are likely to be involved in the gall midge susceptibility.Not Availabl

Flanking SSR markers for the Asian gall midge (Orseolia oryzae) resistance genes

Screening of rice germplasm against Asian rice gall midge, Orseolia oryzae (Wood-Mason), biotypes in India has led to identification of over 300 resistant rice genotypes. However, only ten resistance genes have been characterized so far. Identification of new genes through classical allelism test is tedious and time consuming. We propose to use closely linked flanking Simple Sequence Repeat (SSR) markers in allelism tests for identification of resistance genes. Of the ten known gall midge resistance genes, eight have been tagged and mapped. The Gm1 and Gm2 genes have closely linked flanking markers. Hence SSR markers RM219 and RM444, flanking the gene Gm1, and RM317, RM241 along with the SCAR marker F8, flanking the gene Gm2, were selected for this study. Tests with one set of 13 genotypes likely to carry Gm1 and another set of 17 genotypes suspected to contain Gm2 suggested the presence of the respective allele in all the 13 and 15 genotypes from these sets, respectively. Classical allelism test perfectly matched with the markers test. There were two exceptions involving amplification with RM444 in cultivar Kavya and with RM241 in genotype AE20, suggesting a single recombination which could have resulted in the mismatch. All the three markers in the genotype Bhumansan and the two flanking markers RM317 and F8 in AE20 indicated the absence of the Gm2 allele. This was validated through a classical test, revealing a segregation ratio of 15 resistant: 1 susceptible F2 progeny of both the crosses between the Gm2 source Phalguna and these genotypes. We performed the allelism test with the markers on another set of 56 randomly selected gall midge resistant genotypes to discover possible sources of new resistance genes