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Cnaphalocrocis medinalis Guenée is a noxious rice pest during cultivated periods. Cnaphalocrocis medinalis moths lay eggs on leaf surfaces, and larvae longitudinally roll the leaves to hide inside the leaf buds and feed on the upper epidermis and mesophyll tissues. In this study, we evaluated the female oviposition preference and larval performance of C. medinalis on six insect-resistant and six insect-susceptible rice genotypes. Female moth choice and no-choice oviposition preferences were studied. The number of eggs laid on the leaf varies among selected rice genotypes; however, female adults prefer to lay more eggs on both some resistant and susceptible rice genotypes. Furthermore, newly hatched larvae showed no observed differences in preference for both specific resistant and susceptible rice genotypes. The time taken by larvae for leaf selection varied significantly after inoculation on different genotypes at the maximum tillering and heading stages of rice plants. Compared with susceptible genotypes, leaf selection time was prolonged in resistant genotypes. In addition, the time taken for folding primary vegetative and flag leaves by larvae varied among the selected rice genotypes; larvae required more time to fold leaves of resistant than susceptible genotypes. In host antibiosis tests, larval and pupal survival and pupal weight were higher in susceptible than resistant genotypes. The results showed that the time required by larvae for leaf rolling and host antibiosis should be considered as the most crucial factors for rice genotypes resistant to C. medinalis.

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 glutathionemediated 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. Rice production in Asia is affected by a harmful insect pest, Cnaphalocrocis medinalis (Guenée) (Lepidoptera: Pyralidae), also known as the rice leaffolder 1. Leaffolder caterpillars feed on mesophyll tissues, interfering with photosynthesis and then reducing yield 2. The affected leaf blades appear white, so heavily infested fields may have 'scorched'-looking patches. This insect herbivore can complete three life cycles during each rice cropping season in Taiwan 3,4. The application of chemical insecticides is the main method used to control pest populations in rice fields 5. However, this method of pest control is rendered less effective because the caterpillars build a feeding chamber by folding a leaf longitudinally with silk, and the chamber indirectly protects the pests from the chemical spray. When plants are infested by insect pests, they can differentiate diverse types of insects based on the insect elicitors or the nature of the damage caused by the insects 6. The plants immediately activate various defensive signaling pathways, including those associated with mitogen-activated protein kinase (MAPK) and phytohormones, such as jasmonic acid (JA), salicylic acid (SA) and ethylene (ET) 7. Chewing insects are generally known to trigger JA signaling pathways, while phloem-feeding insects trigger the SA signaling pathway 8. The JA and SA signaling pathways also participate in antagonistic crosstalk in plant-insect herbivory interactions 8. Because the signaling pathways triggered by different herbivorous insects vary, the production of downstream defensive proteins and secondary metabolites is...

Background Outbreaks of insect pests in paddy fields cause heavy losses in global rice yield annually, a threat projected to be aggravated by ongoing climate warming. Although significant progress has been made in the screening and cloning of insect resistance genes in rice germplasm and their introgression into modern cultivars, improved rice resistance is only effective against either chewing or phloem-feeding insects. Results In this study, the results from standard and modified seedbox screening, settlement preference and honeydew excretion tests consistently showed that Qingliu, a previously known leaffolder-resistant rice variety, is also moderately resistant to brown planthopper (BPH). High-throughput RNA sequencing showed a higher number of differentially expressed genes (DEGs) at the infestation site, with 2720 DEGs in leaves vs 181 DEGs in sheaths for leaffolder herbivory and 450 DEGs in sheaths vs 212 DEGs in leaves for BPH infestation. The leaf-specific transcriptome revealed that Qingliu responds to leaffolder feeding by activating jasmonic acid biosynthesis genes and genes regulating the shikimate and phenylpropanoid pathways that are essential for the biosynthesis of salicylic acid, melatonin, flavonoids and lignin defensive compounds. The sheath-specific transcriptome revealed that Qingliu responds to BPH infestation by inducing salicylic acid-responsive genes and those controlling cellular signaling cascades. Taken together these genes could play a role in triggering defense mechanisms such as cell wall modifications and cuticular wax formation. Conclusions This study highlighted the key defensive responses of a rarely observed rice variety Qingliu that has resistance to attacks by two different feeding guilds of herbivores. The leaffolders are leaf-feeder while the BPHs are phloem feeders, consequently Qingliu is considered to have dual resistance. Although the defense responses of Qingliu to both insect pest types appear largely dissimilar, the phenylpropanoid pathway (or more specifically phenylalanine ammonia-lyase genes) could be a convergent upstream pathway. However, this possibility requires further studies. This information is valuable for breeding programs aiming to generate broad spectrum insect resistance in rice cultivars.

Background Taichung Native 1 (TN1), a variety of rice ( Oryza sativa L.) developed in Taiwan, has played a key role in the green revolution of this major staple crop because of its semi-dwarf characteristics. Due to its susceptibility, it has been used as a susceptibility indicator in rice insect and pathogen resistance studies worldwide. While within-variety differences have been reported for agronomic traits in other rice varieties, no study has addressed the within-variety consistency of pathogen and insect susceptibility of TN1, which would influence the result interpretation of plant-pest interaction studies. Therefore, the objective of this study was to evaluate the genomic consistency and to assess a range of agronomic and insect susceptibility traits in three representative accessions of TN1 in Taiwan. Results Among these three accessions, two were identical across 43,325 genome-wide single nucleotide polymorphisms (SNPs) while the third one differed at four SNPs. Of the three accessions of TN1, there were minor differences in seed length, seed breadth, length/width ratio, number of leaves and tillers, and number of unfilled seeds. Besides, there was no effect on relative growth rate of Cnaphalocrocis medinalis larvae fed on the three accession sources. Furthermore, there is no different on plant susceptibility among these three accessions against C. medinalis and Nilaparvata lugens . Conclusion Our study indicates that it is appropriate to use TN1 in Taiwan to test for rice insect susceptibility as it yields consistent results.