Functional Bph14 from Rathu Heenati promotes resistance to BPH at the early seedling stage of rice (Oryza sativa L.) as revealed by QTL-seq

Virulence Adaptation by Rice Planthoppers and Leafhoppers to Resistance Genes and Loci: A Review

In recent decades, research on developing and deploying resistant rice has accelerated due to the availability of modern molecular tools and, in particular, advances in marker-assisted selection. However, progress in understanding virulence adaptation has been relatively slow. This review tracks patterns in virulence adaptation to resistance genes (particularly Bph1, bph2, Bph3, and bph4) and examines the nature of virulence based on selection experiments, responses by virulent populations to differential rice varieties (i.e., varieties with different resistance genes), and breeding experiments that interpret the genetic mechanisms underlying adaptation. The review proposes that varietal resistance is best regarded as a combination of minor and major resistance traits against which planthoppers develop partial or complete virulence through heritable improvements that are reversable or through evolutionary adaptation, respectively. Agronomic practices, deployment patterns, and herbivore population pressures determine the rates of adaptation, and there is growing evidence that pesticide detoxification mechanisms can accelerate virulence adaptation. Research to delay adaptation has mainly focused on gene pyramiding (i.e., including ≥ two major genes in a variety) and multilines (i.e., including ≥ two resistant varieties in a field or landscape); however, these strategies have not been adequately tested and, if not managed properly, could inadvertently accelerate adaptation compared to sequential deployment. Several research gaps remain and considerable improvements in research methods are required to better understand and manage virulence adaptation.

Substitution mapping and characterization of brown planthopper resistance genes from traditional rice cultivar 'Rathu Heenati' (Oryza sativa L.)

The brown planthopper (BPH; Nilaparvata lugens Stål) is a devastating pest that causes severe rice yield losses in Asia. Introducing multiple BPH resistance genes into rice cultivars is an effective and sustainable way to mitigate yield losses. A traditional rice cultivar, 'Rathu Heenati', has durable BPH resistance due to multiple resistance genes (including BPH3 and BPH17) and quantitative trait loci (QTLs). However, these genes have not been used in Japanese rice breeding owing to limited genetic information. To identify markers tightly linked to BPH3 and BPH17 introgressed into the 'Sagabiyori' (susceptible) genetic background, we performed substitution mapping. BPH3 was delimited between RM3132 and RM589 on chromosome 6, and BPH17 between RM16493 and RM16531 on chromosome 4. We also performed QTL analysis to identify additional BPH resistance genes from 'Rathu Heenati' and detected a QTL, denoted as qBPH3.1, on chromosome 3. The effect of pyramiding BPH3 and BPH17 was significantly greater against virulent BPH populations than that of either gene alone. The combination of BPH3, BPH17 and qBPH3.1 from 'Rathu Heenati' might be facilitated to improve commercial Japanese cultivars with more robust BPH resistance.

Development and characterization of near-isogenic lines for brown planthopper resistance genes in the genetic background of japonica rice 'Sagabiyori'

The brown planthopper (BPH: Nilaparvata lugens Stål) is one of the most destructive insects in rice production. The use of host plant resistance has potential to reduce damage caused by BPH. The heat tolerance japonica rice 'Sagabiyori', with superior grain quality and high soluble starch in the stem, is highly susceptible to damage by BPH. Here, to enhance its BPH resistance, we developed seven near-isogenic lines (NILs) carrying BPH2, BPH17-ptb, BPH32, BPH3, BPH17, BPH20, and BPH21 through marker-assisted selection and evaluated resistance to two BPH populations. Most lines were more resistant to the Hadano-1966 BPH population than Sagabiyori but were less effective against the highly virulent Koshi-2013 population. Nevertheless, in antixenosis tests, Koshi-2013 settled less on all NILs than on Sagabiyori. In addition, adult mortality and the percentage of fresh weight loss of lines carrying BPH17 and BPH3 indicated that these lines have higher resistance to Koshi-2013 than Sagabiyori. Current study revealed that BPH resistance of Sagabiyori became stronger by transferring BPH3 and BPH17 genes. Thus, BPH3 and BPH17 might be valuable for breeding programs to enhance BPH resistance of high grain quality rice varieties with heat tolerance.

Recent Advances in Molecular Mechanism and Breeding Utilization of Brown Planthopper Resistance Genes in Rice: An Integrated Review

Over half of the world's population relies on rice as their staple food. The brown planthopper (Nilaparvata lugens Stål, BPH) is a significant insect pest that leads to global reductions in rice yields. Breeding rice varieties that are resistant to BPH has been acknowledged as the most cost-effective and efficient strategy to mitigate BPH infestation. Consequently, the exploration of BPH-resistant genes in rice and the development of resistant rice varieties have become focal points of interest and research for breeders. In this review, we summarized the latest advancements in the localization, cloning, molecular mechanisms, and breeding of BPH-resistant rice. Currently, a total of 70 BPH-resistant gene loci have been identified in rice, 64 out of 70 genes/QTLs were mapped on chromosomes 1, 2, 3, 4, 6, 8, 10, 11, and 12, respectively, with 17 of them successfully cloned. These genes primarily encode five types of proteins: lectin receptor kinase (LecRK), coiled-coil-nucleotide-binding-leucine-rich repeat (CC-NB-LRR), B3-DNA binding domain, leucine-rich repeat domain (LRD), and short consensus repeat (SCR). Through mediating plant hormone signaling, calcium ion signaling, protein kinase cascade activation of cell proliferation, transcription factors, and miRNA signaling pathways, these genes induce the deposition of callose and cell wall thickening in rice tissues, ultimately leading to the inhibition of BPH feeding and the formation of resistance mechanisms against BPH damage. Furthermore, we discussed the applications of these resistance genes in the genetic improvement and breeding of rice. Functional studies of these insect-resistant genes and the elucidation of their network mechanisms establish a strong theoretical foundation for investigating the interaction between rice and BPH. Furthermore, they provide ample genetic resources and technical support for achieving sustainable BPH control and developing innovative insect resistance strategies.