Brown Planthopper Resistance Research Articles

Area-wide survey and monitoring of insecticide resistance in the brown planthopper, Nilaparvata lugens (Stål), from 2020 to 2023 in China

The brown planthopper (BPH), Nilaparvata lugens (Stål), is a notorious pest affecting Asian rice crops. The evolution of insecticide resistance in BPH has emerged as a significant challenge in effectively managing this pest. This study revealed the resistance status of BPH to nine insecticides in ten provinces and Shanghai City in China from 2020 to 2023. Monitoring results showed that the resistance of BPH to triflumezopyrim, nitenpyram, and dinotefuran increased rapidly. The average resistance ratio of BPH to triflumezopyrim increased from 2.5 to 7.1 fold, nitenpyram from 18.3 to 37.7 fold, and dinotefuran from 119.5 to 268.1 fold. All populations remained extremely high resistance to imidacloprid, thiamethoxam, and buprofezin. Most field populations of BPH maintained moderate resistance to chlorpyrifos and sulfoxaflor, and high resistance to pymetrozine by rice stem dipping method. However, considering the reproduction-inhibiting character of pymetrozine, susceptible to low resistance levels to pymetrozine were monitored by Insecticide Resistance Action Committee (IRAC) NO.005 method. This result indicated that pymetrozine might lose efficacy in the control of application generation, but it could significantly inhibit the reproduction of field populations of BPH. Additionally, we compared the expression levels of 11 nicotinic acetylcholine receptor (nAChR) genes, the targets of nAChR competitive modulators, in four field populations (FY23, YH23, LJ23, LP23) and susceptible strain. The expression level of nAChR α4 was significantly reduced in all field populations, while α1, α2, α6, and α7 were significantly reduced in some field populations. Our findings provide valuable information for resistance management strategies in N. lugens and offer new insights into the resistance mechanisms of nAChR competitive modulators.

ACL1-ROC4/5 complex reveals a common mechanism in rice response to brown planthopper infestation and drought

Brown planthopper (BPH) is the most destructive insect pest of rice. Drought is the most detrimental environmental stress. BPH infestation causes adaxial leaf-rolling and bulliform cells (BCs) shrinkage similar to drought. The BC-related abaxially curled leaf1 (ACL1) gene negatively regulates BPH resistance and drought tolerance, with decreased cuticular wax in the gain-of-function mutant ACL1-D. ACL1 shows an epidermis-specific expression. The TurboID system and multiple biochemical assays reveal that ACL1 interacts with the epidermal-characteristic rice outermost cell-specific (ROC) proteins. ROC4 and ROC5 positively regulate BPH resistance and drought tolerance through modulating cuticular wax and BCs, respectively. Overexpression of ROC4 and ROC5 both rescue ACL1-D mutant in various related phenotypes. ACL1 competes with ROC4/ROC5 in homo-dimer and hetero-dimer formation, and interacts with the repressive TOPLESS-related proteins. Altogether, we illustrate that ACL1–ROC4/5 complexes synergistically mediate drought tolerance and BPH resistance through regulating cuticular wax content and BC development in rice, a mechanism that might facilitate BPH-resistant breeding.

Identification and candidate analysis of a new brown planthopper resistance locus in an Indian landrace of rice, paedai kalibungga.

The online version contains supplementary material available at 10.1007/s11032-024-01485-6.

Brown planthoppers manipulate rice sugar transporters to benefit their own feeding

The feeding of piercing-sucking insect herbivores often elicits changes in their host plants that benefit the insect.1 In addition to thwarting a host's defense responses, these phloem-feeding insects may manipulate source-sink signaling so as to increase resources consumed.2,3 To date, the molecular mechanisms underlying herbivore-induced resource reallocation remain less investigated. Brown planthopper (BPH), an important rice pest, feeds on the phloem and oviposits into leaf sheaths. BPH herbivory increases sugar accumulations 5-fold in the phloem sap of leaf sheaths and concurrently induces the expression of two clade III SWEET genes, SWEET13 and SWEET14, in leaf tissues, but not in leaf sheaths of attacked rice plants. Mutations of both genes by genome editing attenuate resistance to BPH without alterations of known chemical and physical defense responses. Moreover, BPH-elicited sugar levels in the phloem sap were significantly reduced in sweet13/14 mutants, which is likely to attenuate BPH feeding behavior on sweet13/14 mutants. In one of the two field seasons tested, the sweet13/14 mutants showed comparable yield to wild types, and in the other season, the mutants demonstrated stronger BPH resistance. These preliminary results suggested that the mutations in these SWEET transporters could enhance BPH resistance without yield penalties. Given that sweet13/14 mutants also exhibit resistance to bacterial blight pathogen, Xanthomonas oryzae pv. oryzae, these SWEET genes could serve as excellent molecular targets for the breeding of resistant rice cultivars.

Integration of molecular breeding and multi-resistance screening for developing a promising restorer line Guihui5501 with heavy grain, good grain quality, and endurance to biotic and abiotic stresses.

Rice, a critical staple on a global scale, faces escalating challenges in yield preservation due to the rising prevalence of abiotic and biotic stressors, exacerbated by frequent climatic fluctuations in recent years. Moreover, the scorching climate prevalent in the rice-growing regions of South China poses obstacles to the cultivation of good-quality, heavy-grain varieties. Addressing this dilemma requires the development of resilient varieties capable of withstanding multiple stress factors. To achieve this objective, our study employed the broad-spectrum blast-resistant line Digu, the brown planthopper (BPH)-resistant line ASD7, and the heavy-grain backbone restorer lines Fuhui838 (FH838) and Shuhui527 (SH527) as parental materials for hybridization and multiple crossings. The incorporation of molecular markers facilitated the rapid pyramiding of six target genes (Pi5, Pita, Pid2, Pid3, Bph2, and Wxb ). Through a comprehensive evaluation encompassing blast resistance, BPH resistance, cold tolerance, grain appearance, and quality, alongside agronomic trait selection, a promising restorer line, Guihui5501 (GH5501), was successfully developed. It demonstrated broad-spectrum resistance to blast, exhibiting a resistance frequency of 77.33% against 75 artificially inoculated isolates, moderate resistance to BPH (3.78 grade), strong cold tolerance during the seedling stage (1.80 grade), and characteristics of heavy grains (1,000-grain weight reaching 35.64 g) with good grain quality. The primary rice quality parameters for GH5501, with the exception of alkali spreading value, either met or exceeded the second-grade national standard for premium edible rice varieties, signifying a significant advancement in the production of good-quality heavy-grain varieties in the southern rice-growing regions. Utilizing GH5501, a hybrid combination named Nayou5501, characterized by high yield, good quality, and resistance to multiple stresses, was bred and received approval as a rice variety in Guangxi in 2021. Furthermore, genomic analysis with gene chips revealed that GH5501 possessed an additional 20 exceptional alleles, such as NRT1.1B for efficient nitrogen utilization, SKC1 for salt tolerance, and STV11 for resistance to rice stripe virus. Consequently, the restorer line GH5501 could serve as a valuable resource for the subsequent breeding of high-yielding, good-quality, and stress-tolerant hybrid rice varieties.

Exploring the Resistance of Pigmented Rice to Brown Planthopper (Nilaparvata lugens Stål) by Phenotypic and Genotypic Analyses

Developing new pigmented rice varieties that meet consumers' preferences requires addressing resistance to brown planthopper (BPH), a highly destructive insect pest of rice. To effectively manage this pest, it is essential to explore BPH resistance genes from rice germplasms and incorporate them into elite varieties. The objective of this study was to identify the source of resistance among local and improved pigmented rice varieties in Indonesia against field BPH. Furthermore, the study aimed to characterize their genetic diversity using molecular markers associated with Bph genes and functional markers for these genes. Eighty-eight local varieties from the Indonesian Agricultural Gene Bank, collected across 18 provinces between 1971 and 2019, and four improved varieties, were evaluated using the standard seed box screening test method. Among these entries, 6 local accessions and 1 improved variety exhibited moderate resistance. Genetic analysis of these entries and three randomly selected susceptible entries using 12 SSR and InDel markers associated with Bph gene loci showed that the moderately resistant entries had higher allele numbers (11 to 13) compared to the susceptible entries (4 to 7). These markers could distinguish the resistant group from the susceptible ones in cluster analysis. Genotyping using functional markers further showed that the moderately resistant entries had 2 to 4 combinations of Bph genes. In contrast, the susceptible entries contained neither Bph genes nor only one gene. Local accessions with a 2 to 4 Bph gene combination can be donors of BPH resistance in improving pigmented rice varieties.

Effects of imidacloprid combined with validamycin on the population fitness and symbiotic of Nilaparvata lugens (Hemiptera: Delphacidae)

Using a high-efficiency insecticide in combination with fungicides that have different mechanisms of action is a conventional method in the current management of brown planthopper (BPH) resistance. In this study, we investigate the separate and combined effects of the low-toxicity fungicide validamycin and the non-cross-resistant insecticide imidacloprid on the fitness and symbiosis of BPH. These research results indicate that when the proportion of active ingredients in validamycin is combined with imidacloprid at a ratio of 1:30, the toxicity ratio and co-toxicity coefficient are 1.34 and 691.73, respectively, suggesting that the combination has a synergistic effect on the control of BPH. The number of yeast-like symbiotic (YLS) and dominant symbiotic (Noda) in the imidacloprid + validamycin groups were significantly lower than the other three treatment groups (validamycin, imidacloprid, and water). The results of the study on population fitness show that the lifespan of the BPH population in validamycin, imidacloprid, and imidacloprid + validamycin was shortened. Notably, the BPH populations in the imidacloprid + validamycin groups were significantly lower than other groups in terms of average generation cycle, intrinsic growth rate, net reproduction rate, finite rate of increase, and fitness. The Real-time quantitative PCR showed that validamycin and imidacloprid + validamycin can significantly inhibit the expression of the farnesyl diphosphate farnesyl transferase gene (EC2.5.1.21) and uricase gene (EC1.7.3.3), with imidacloprid + validamycin demonstrating the most pronounced inhibitory effect. Our research results can provide insights and approaches for delaying resistance and integrated management of BPH.

The Development of Multi-Resistant Rice Restorer Lines and Hybrid Varieties by Pyramiding Resistance Genes against Blast and Brown Planthopper

Rice blast, caused by the fungus Magnaporthe oryzae, and brown planthopper (BPH) infestation are two of the most destructive problems of rice production in China. The development of multi-resistant varieties is widely recognized as the most efficient and environmentally friendly approach to controlling crop diseases and pests. Functional molecular markers (FMMs) have been developed from functional variants in the genic region associated with trait variation, greatly enhancing the efficiency of identifying and pyramiding valuable genes in crop breeding. In this study, two FMMs and a multiplex PCR amplification system were developed for two major broad-spectrum BPH resistance genes, Bph6 and Bph9. With the assistance of FMMs in the multi-resistant rice restorer-line development pipeline, two lines (Huahui7713 and Huahui3006) with blast and BPH resistance were developed by pyramiding three resistance genes Pigm, Bph6 and Bph9. Two new hybrid rice varieties, Weiliangyou7713 and Xuanliangyou3006, derived from Huahui7713 and Huahui3006, have been developed and commercialized in China. Weiliangyou7713 and Xuanliangyou3006 exhibit enhanced resistance to both blast and BPH, while maintaining optimal yield and grain quality. The adoption of Weiliangyou7713 continues to expand, now being cultivated on a large scale, which is promising for its future role in reducing the dependence on chemical fungicides and pesticides in rice production. This suggests that the implementation of Huahui7713 and Huahui3006 in targeted breeding programs could be highly beneficial for developing rice varieties with strong resistance to blast and BPH.

Fine mapping and breeding application of two brown planthopper resistance genes derived from landrace rice.

The Brown planthopper (Nilaparvata lugens Stål; BPH) is known to cause significant damage to rice crops in Asia, and the use of host-resistant varieties is an effective and environmentally friendly approach for controlling BPH. However, genes limited resistance genes that are used in insect-resistant rice breeding programs, and landrace rice varieties are materials resources that carry rich and versatile genes for BPH resistance. Two landrace indica rice accessions, CL45 and CL48, are highly resistant to BPH and show obvious antibiosis against BPH. A novel resistance locus linked to markers 12M16.983 and 12M19.042 was identified, mapped to chromosome 12 in CL45, and designated Bph46. It was finely mapped to an interval of 480 kb and Gene 3 may be the resistance gene. Another resistance locus linked to markers RM26567 and 11MA104 was identified and mapped to chromosome 11 in CL48 and designated qBph11.3 according to the nominating rule. It was finely mapped to an interval of 145 kb, and LOC_Os11g29090 and LOC_Os11g29110 may be the resistance genes. Moreover, two markers, 12M16.983 and 11MA104, were developed for CL45 and CL48, respectively, using marker-assisted selection (MAS) and were confirmed by backcrossing individuals and phenotypic detection. Interestingly, we found that the black glume color is closely linked to the BPH resistance gene in CL48 and can effectively assist in the identification of positive individuals for breeding. Finally, several near-isogenic lines with a 9311 or KW genetic background, as well as pyramid lines with two resistance parents, were developed using MAS and exhibited significantly high resistance against BPHs.

Mapping of a novel recessive brown planthopper resistance gene bph46 from wild rice (Oryza nivara)

Mapping of a novel recessive brown planthopper resistance gene bph46 from wild rice (Oryza nivara)

Genome-wide association study and genomic prediction for resistance to brown planthopper in rice.

The brown planthopper (BPH) is the most destructive insect pest that threatens rice production globally. Developing rice varieties incorporating BPH-resistant genes has proven to be an effective control measure against BPH. In this study, we assessed the resistance of a core collection consisting of 502 rice germplasms by evaluating resistance scores, weight gain rates and honeydew excretions. A total of 117 rice varieties (23.31%) exhibited resistance to BPH. Genome-wide association studies (GWAS) were performed on both the entire panel of 502 rice varieties and its subspecies, and 6 loci were significantly associated with resistance scores (P value < 1.0e-8). Within these loci, we identified eight candidate genes encoding receptor-like protein kinase (RLK), nucleotide-binding and leucine-rich repeat (NB-LRR), or LRR proteins. Two loci had not been detected in previous study and were entirely novel. Furthermore, we evaluated the predictive ability of genomic selection for resistance to BPH. The results revealed that the highest prediction accuracy for BPH resistance reached 0.633. As expected, the prediction accuracy increased progressively with an increasing number of SNPs, and a total of 6.7K SNPs displayed comparable accuracy to 268K SNPs. Among various statistical models tested, the random forest model exhibited superior predictive accuracy. Moreover, increasing the size of training population improved prediction accuracy; however, there was no significant difference in prediction accuracy between a training population size of 737 and 1179. Additionally, when there existed close genetic relatedness between the training and validation populations, higher prediction accuracies were observed compared to scenarios when they were genetically distant. These findings provide valuable resistance candidate genes and germplasm resources and are crucial for the application of genomic selection for breeding durable BPH-resistant rice varieties.

Combined miRNA and mRNA sequencing reveals the defensive strategies of resistant YHY15 rice against differentially virulent brown planthoppers.

The brown planthopper (BPH) poses a significant threat to rice production in Asia. The use of resistant rice varieties has been effective in managing this pest. However, the adaptability of BPH to resistant rice varieties has led to the emergence of virulent populations, such as biotype Y BPH. YHY15 rice, which carries the BPH resistance gene Bph15, exhibits notable resistance to biotype 1 BPH but is susceptible to biotype Y BPH. Limited information exists regarding how resistant rice plants defend against BPH populations with varying levels of virulence. In this study, we integrated miRNA and mRNA expression profiling analyses to study the differential responses of YHY15 rice to both avirulent (biotype 1) and virulent (biotype Y) BPH. YHY15 rice demonstrated a rapid response to biotype Y BPH infestation, with significant transcriptional changes occurring within 6 hours. The biotype Y-responsive genes were notably enriched in photosynthetic processes. Accordingly, biotype Y BPH infestation induced more intense transcriptional responses, affecting miRNA expression, defenserelated metabolic pathways, phytohormone signaling, and multiple transcription factors. Additionally, callose deposition was enhanced in biotype Y BPH-infested rice seedlings. These findings provide comprehensive insights into the defense mechanisms of resistant rice plants against virulent BPH, and may potentially guide the development of insect-resistant rice varieties.

Dissecting brown planthopper resistance genes in Oryza and its wild relatives: A review

Dissecting brown planthopper resistance genes in Oryza and its wild relatives: A review

Brown planthopper infestation on rice reduces plant susceptibility to Meloidogyne graminicola by reducing root sugar allocation.

Plants are simultaneously attacked by different pests that rely on sugars uptake from plants. An understanding of the role of plant sugar allocation in these multipartite interactions is limited. Here, we characterized the expression patterns of sucrose transporter genes and evaluated the impact of targeted transporter gene mutants and brown planthopper (BPH) phloem-feeding and oviposition on root sugar allocation and BPH-reduced rice susceptibility to Meloidogyne graminicola. We found that the sugar transporter genes OsSUT1 and OsSUT2 are induced at BPH oviposition sites. OsSUT2 mutants showed a higher resistance to gravid BPH than to nymph BPH, and this was correlated with callose deposition, as reflected in a different effect on M. graminicola infection. BPH phloem-feeding caused inhibition of callose deposition that was counteracted by BPH oviposition. Meanwhile, this pivotal role of sugar allocation in BPH-reduced rice susceptibility to M. graminicola was validated on rice cultivar RHT harbouring BPH resistance genes Bph3 and Bph17. In conclusion, we demonstrated that rice susceptibility to M. graminicola is regulated by BPH phloem-feeding and oviposition on rice through differences in plant sugar allocation.

Insecticide resistance triggers a reduction of virulence to host‐plant defenses in the brown planthopper

AbstractPlants produce various phytochemicals against herbivory, but phytophagous insects have encountered phytochemicals in the co‐evolutionary history between plants and insects. Selection pressure exerted by phytochemicals triggers a preadaptation to insecticide resistance in insect pests that is due to detoxification systems that are common to phytochemicals and insecticides in the insect's body. We investigated the interaction between the host plant resistance of rice cultivars and the brown planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae). Forty brown planthopper resistance gene loci (BPHs) that are related to phytochemicals in various cultivars of rice inhibit feeding by N. lugens, but this planthopper has developed virulence to resistant rice cultivars possessing some genes. Nilaparvata lugens has also developed resistance to some insecticides as a rapid adaptation to human‐driven selection. We tested the hypothesis that the evolution of insects' resistance to an insecticide is promoted by their encounters with phytochemicals. We compared the virulence of imidacloprid‐resistant and control N. lugens strains toward seven rice cultivars that possess different genes, and we observed that the imidacloprid‐resistant N. lugens had reduced virulence to three rice cultivars, Rathu Heenati (BPH3, BPH17), Babawee (BPH4), and Balamawee (BPH27, three quantitative trait loci), meaning that the development of imidacloprid resistance has a negative impact on the virulence of N. lugens to three cultivars. Our results indicate trade‐offs rather than a co‐relationship between the evolution of insecticide resistance and encounters with host plant defense.

Defense Regulatory Network Associated with circRNA in Rice in Response to Brown Planthopper Infestation

The brown planthopper (BPH), Nilaparvata lugens (Stål), a rice-specific pest, has risen to the top of the list of significant pathogens and insects in recent years. Host plant-mediated resistance is an efficient strategy for BPH control. Nonetheless, BPH resistance in rice cultivars has succumbed to the emergence of distinct virulent BPH populations. Circular RNAs (circRNAs) play a pivotal role in regulating plant–environment interactions; however, the mechanisms underlying their insect-resistant functions remain largely unexplored. In this study, we conducted an extensive genome-wide analysis using high-throughput sequencing to explore the response of rice circRNAs to BPH infestations. We identified a total of 186 circRNAs in IR56 rice across two distinct virulence groups: IR-IR56-BPH (referring to IR rice infested by IR56-BPH) and IR-TN1-BPH, along with a control group (IR-CK) without BPH infestation. Among them, 39 circRNAs were upregulated, and 43 circRNAs were downregulated in the comparison between IR-IR56-BPH and IR-CK. Furthermore, in comparison with IR-CK, 42 circRNAs exhibited upregulation in IR-TN1-BPH, while 42 circRNAs showed downregulation. The Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis revealed that the targets of differentially expressed circRNAs were considerably enriched in a multitude of biological processes closely linked to the response to BPH infestations. Furthermore, we assessed a total of 20 randomly selected circRNAs along with their corresponding expression levels. Moreover, we validated the regulatory impact of circRNAs on miRNAs and mRNAs. These findings have led us to construct a conceptual model that circRNA is associated with the defense regulatory network in rice, which is likely facilitated by the mediation of their parental genes and competing endogenous RNA (ceRNA) networks. This model contributes to the understanding of several extensively studied processes in rice-BPH interactions.

Cost-effective multiplex PCR assay for simultaneous detection of bacterial leaf blight, blast and brown planthopper resistance genes in rice

Cost-effective multiplex PCR assay for simultaneous detection of bacterial leaf blight, blast and brown planthopper resistance genes in rice

Phenotyping and genotyping of rice genotypes for brown planthopper resistance

Phenotyping and genotyping of rice genotypes for brown planthopper resistance

Identification and Functional Characterization of Two Major Loci Associated with Resistance against Brown Planthoppers (Nilaparvata lugens (Stål)) Derived from Oryza nivara.

The brown planthopper (BPH) is a highly destructive pest of rice, causing significant economic losses in various regions of South and Southeast Asia. Researchers have made promising strides in developing resistance against BPH in rice. Introgression line RPBio4918-230S, derived from Oryza nivara, has shown consistent resistance to BPH at both the seedling and adult stages of rice plants. Segregation analysis has revealed that this resistance is governed by two recessive loci, known as bph39(t) and bph40(t), contributing to 21% and 22% of the phenotypic variance, respectively. We later mapped the genes using a backcross population derived from a cross between Swarna and RPBio4918-230S. We identified specific marker loci, namely RM8213, RM5953, and R4M17, on chromosome 4, flanking the bph39(t) and bph40(t) loci. Furthermore, quantitative expression analysis of candidate genes situated between the RM8213 and R4M17 markers was conducted. It was observed that eight genes exhibited up-regulation in RPBio4918-230S and down-regulation in Swarna after BPH infestation. One gene of particular interest, a serine/threonine-protein kinase receptor (STPKR), showed significant up-regulation in RPBio4918-230S. In-depth sequencing of the susceptible and resistant alleles of STPKR from Swarna and RPBio4918-230S, respectively, revealed numerous single nucleotide polymorphisms (SNPs) and insertion-deletion (InDel) mutations, both in the coding and regulatory regions of the gene. Notably, six of these mutations resulted in amino acid substitutions in the coding region of STPKR (R5K, I38L, S120N, T319A, T320S, and F348S) when compared to Swarna and the reference sequence of Nipponbare. Further validation of these mutations in a set of highly resistant and susceptible backcross inbred lines confirmed the candidacy of the STPKR gene with respect to BPH resistance controlled by bph39(t) and bph40(t). Functional markers specific for STPKR have been developed and validated and can be used for accelerated transfer of the resistant locus to elite rice cultivars.

Molecular screening of local Indonesian rice to identified resistant varieties against brown planthopper (Nilaparvata lugens) attacks

Abstract. Puspito AN, Tigara MRN, Putra SID, Rozzita N, Ubaidillah M. 2023. Molecular screening of local Indonesian rice to identified resistant varieties against brown planthopper (Nilaparvata lugens) attacks. Biodiversitas 24: 5503-5512. Brown planthopper (Nilaparvata lugens Stal) is a significant pest in rice (Oryza sativa L.), resulting in a yield loss of around 20-80%. Environmentally friendly control involves looking for potential resistance in local Indonesian rice, because it’s naturally resistant to pests and diseases and has several tolerant mechanisms for dealing with stress. However, the resistance potential of local rice has not been widely studied, so it is necessary to carry out screening to identify the resistance possessed by local Indonesian rice and continue with molecular analysis to validate the presence of brown planthopper resistance genes. This study aimed to determine the possible resistance level of 24 Indonesian local rice varieties to brown planthopper pests. The research was conducted at the Agrotechnology Laboratory, Faculty of Agriculture, University of Jember. In June-November 2022. This research included screening using the third instar nymph brown planthopper, preference testing to analyze the preference level for each local rice variety and molecular analysis using six BPH markers (RM 247, RM 6869, RM 19291, g12140-2, RM 3331, and RM 5479) with the MAS technique. The results showed that in the preference test, Lahoten, Fatuk Masin, and Sukamandi had a higher preference value than other local Indonesian rice. In the screening, the average local rice with very resistant criteria is Leukat Medan, while those with moderately vulnerable criteria are Sukamandi. In the molecular analysis of local Indonesian rice, the Aek Sibundong variety had the most resistance, while the Kapuas and Sukamandi varieties had the least resistance.