ORIGINAL RESEARCH article

Front. Microbiol., 24 June 2025

Sec. Microbe and Virus Interactions with Plants

Volume 16 - 2025 | https://doi.org/10.3389/fmicb.2025.1614122

Delineating the source of resistance to bean common mosaic virus (BCMV) and bean common mosaic necrosis virus (BCMNV) in common bean (Phaseolus vulgaris) cultivars of Jammu and Kashmir, a North-Western Himalayan region

  • 1. DNA Fingerprinting and Advanced Plant Virology Laboratory, AICRP-NSP, Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir, Srinagar, India

  • 2. Dryland Agricultural Research Station (DARS), Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir, Budgam, India

  • 3. Division of Genetics and Plant Breeding, Faculty of Agriculture (FoA), Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir, Sopore, India

Abstract

Bean common mosaic virus (BCMV) and bean common mosaic necrosis virus (BCMNV) are among the most challenging constraints for common bean production in Northern states of India due to their easy transmission through aphids and seeds. Highly valuable Indian common bean varieties and landraces are more susceptible to BCMV and BCMNV and very few varieties exhibit resistance to these viruses. Resistance towards these viruses is governed by a single dominant (I) gene and a few recessive genes (bc-1, bc-2, bc-3, bc-4, bc-ud, and bc-ur). This study aims to identify common bean genotypes bearing multiple resistant genes, each working with a different mode of action. A total of 123 genotypes of common beans were mechanically inoculated with BCMV and BCMNV isolates and molecular markers (SW13, ROC11, BCMV-CAPS, ENM-FWe/Rve) were used to identify the presence of two major resistant genes (I and bc-3). Out of these, 23 genotypes were found phenotypically resistant to both viruses. Furthermore, molecular screening was performed in which 13 hypersensitive resistant genotypes bearing a single dominant gene (I) were confirmed through SW13 and BCMV-CAPS markers. Additionally, ROC11/420, ENMF/R markers identified 4 genotypes bearing the recessive (bc-3) gene conferring complete resistance to the virus without executing hypersensitive response (HR). A valuable gene combination of both I, bc-3 (Ibc-3, Host group-12) genes in 3 genotypes was also established in the screened germplasm. However, in 3 phenotypically resistant genotypes, neither the I gene nor bc-3 gene was identified. The virus accumulation in the resistant genotypes was also understood properly through a time course experiment in a qPCR assay. This extensive identification of resistant common bean genotypes against BCMV and BCMNV can be readily included in the common bean breeding program of the Northern states of India for virus resistance.

1 Introduction

Bean common mosaic virus (BCMV) and bean common mosaic necrosis virus (BCMNV) are one of the most widespread viruses infecting common beans (Phaseolus vulgaris L.) and other cultivated legumes with worldwide distribution (; ; ). These viruses belong to the genus Potyvirus within the family Potyviridae. They possess a single-stranded (+) RNA genome of approximately 10 kilobases that encodes a large polyprotein precursor which is subsequently cleaved into 10 functional proteins (; ). Both viruses are non-persistently transmitted by probing aphids and are seed-borne, with a transmission efficiency of up to 80% (Wani et al., 2023; ). The major symptoms induced by BCMV on bean plants were mosaic, necrosis, chlorosis, etiolation and deformation, whereas BCMNV strains induce severe necrosis of bean plants (; ; Rashid et al., 2022; Wani et al., 2023).

In India, especially in the Northern Himalayan region, valuable local bean varieties are becoming increasingly susceptible to diverse strains of BCMV and BCMNV, leading to heavy yield losses in hilly areas compared to the Northern plains. Also, BCMNV-induced whole plant necrosis was reported from Jammu and Kashmir (; Rashid et al., 2022) in which identifying resistant sources goes unrecognized. To overcome these viruses, we must identify and utilize resistant genotypes through germplasm screening and incorporate them into breeding programs. Resistance to BCMV and BCMNV is conferred by a single dominant (I) gene and six recessive genes namely bc-1, bc-2, bc-3, bc-4, bc-ud, and bc-ur (; Soler-Garzón et al., 2024; Soler-Garzón et al., 2021a; Soler-Garzón et al., 2021b). The dominant (I) gene confers resistance against BCMV-BCMNV through a hypersensitive response (HR) on the primary leaves, whereas recessive genes confer absolute resistance toward specific viral strains (). Genotypes exhibiting HR present nervure localized necrosis on the primary inoculated leaves and demonstrate the presence of the dominant “I” gene for resistance (; ; Vallejos et al., 2006; ). At temperatures exceeding 30°C, some bean cultivars possessing the I gene experience strong whole plant necrosis (WPN), when infected with BCMNV and BCMV: NL-2 and NL-6 strains (). This interaction leads to a disease known as black root (; ). Hence, to prevent the WPN induced by BCMNV and BCMV (NL-2 and NL-6), genotypes bearing the “I” gene must be protected with extra “bc” recessive genes, especially in high-temperature areas (; ; ). Although the non-necrotic strains cannot induce WPN in genotypes bearing the dominant I gene, the presence of an extra recessive gene will protect the bean plants from extreme HR when the temperature exceeds 30°C and provide additional protection ().

Recessive resistance to BCMV-BCMNV is conferred by six recessive genes: four strain-specific bc-1, bc-2, bc-3, and bc-4 genes and two strain-unspecific bc-ur and bc-ud resistant genes (Soler-Garzón et al., 2021a; Soler-Garzón et al., 2021b; Soler-Garzón et al., 2024; ). Strain-specific genes confer resistance to specific strains of BCMV-BCMNV. However, the bc-3 gene is exceptional in providing resistance to common beans against all strains of BCMV-BCMNV (; ) except for a BCMV isolate 1755a (PG-VIII) that was able to overcome the bc-3 resistance (). The strain-non-specific gene (bc-ud) is required for the complete action of the strain-specific genes (; Soler-Garzón et al., 2021a; Soler-Garzón et al., 2021b). A new gene “bc-ur” at the Bc-u locus on chromosome Pv05 was recently recognized as another strain-non-specific gene that interacts with bc-ud and also with the other recessive genes for conferring resistance against BCMV (; Soler-Garzón et al., 2024). To identify common bean varieties possessing these multiple resistance genes, reliable methods are necessary. Marker-assisted selection can be used as a consequence to efficiently select genotypes with desirable resistance genes. Molecular markers have been identified to be effective in identifying resistance genes in common beans against BCMV and BCMNV. identified a Randomly Amplified Polymorphic Marker (RAPD): OW13, linked to the I gene, which was later developed into a Sequence Characterized Amplified Region (SCAR) marker: SW13 () that was more reliable and widely used. Molecular markers were also developed for the identification of recessive genes (Tang and Feng, 2022). Since most of these markers were dominant, progeny testing is necessary to distinguish between homozygous and heterozygous plants. Therefore, the use of co-dominant Cleaved Amplified Polymorphic Sequence (CAPS) marker was suggested for precise and efficient selection of BCMV-resistant genotypes compared to dominant markers ().

As a proof of concept, the current study was conducted to identify common bean genotypes bearing the dominant I gene, recessive bc-3 gene and combination of both I and bc-3 genes (Ibc-3) for resistance with different modes of action based on phenotypic evaluation and molecular screening utilizing SCAR and CAPS markers. The pathogenicity and resistance mechanism during virus-plant interaction were studied. The resistant genes were later cloned, sequenced and aligned to identify the nucleotide differences and their implementation against virus resistance.

2 Materials and methods

2.1 Collection and maintenance of plant materials, viral isolates and inoculation method

123 genotypes of common beans, including 53 collections obtained from the National Bureau of Plant Genetic Resources (NBPGR)-New Delhi and 68 lines maintained by All India Co-ordinated Research Project (AICRP)- Seed Crops, AICRP-Pulses and Division of Genetics and Plant Breeding (Wadura, SKUAST-K) with truly unknown disease reaction to BCMV-BCMNV were evaluated in this study. All plants were grown under two treatments (T1: BCMV, T2: BCMNV) and three replicates in a growth chamber under ambient conditions of 26°C temperature and 70% relative humidity. For every genotype, non-inoculated control and mock-inoculated plants were maintained. The BCMV and BCMNV isolates (MW675689; OK094708), identified in our previous study (Rashid et al., 2022), were maintained through periodical propagation on Nicotiana benthamiana plants and were used to mechanically inoculate test plants at the primary leaf stage. The viral inoculum was prepared by homogenizing infected leaf tissue in 100 mM potassium phosphate buffer (pH 7.0) with 0.5% celite added directly to the viral inoculum just before inoculation (Wani et al., 2025). Ten days after planting, the first trifoliate leaves were mechanically inoculated with both BCMV and BCMNV isolates individually to identify the presence of the dominant hypersensitive I gene and recessive bc-3 gene. All the treatments were performed in triplicates with non-inoculated control and mock-inoculated plants maintained separately.

2.2 Screening of common bean germplasm against BCMV-BCMNV

2.2.1 Phenotypic evaluation

Disease reaction and symptoms of each virus were recorded every 2 days post inoculation (dpi) from 0 to 30 dpi and the genotype is classified as resistant/susceptible at 30th dpi. Disease severity was scored on a 0–3 scale according to Odu (), where 0 = no disease symptoms/HR on plants, 1 = mild foliar disease symptoms, 2 = moderate foliar disease symptoms and 3 = severe distortion, malformation of leaves or stem and stunting. Resistant genotypes that exhibited no symptoms or HR were re-sown and re-inoculated to confirm resistance. Both symptomatic and asymptomatic plants were further tested using an RT-PCR assay to confirm the presence of the virus.

2.2.2 Genotypic evaluation

123 genotypes were screened for I and bc-3 gene resistance irrespective of the plant reaction to the virus (Table 2). Two SCAR markers (SW13 and ROC11) and two CAPS markers (BCMV-CAPS and ENM-FWe/Rve) were used for selection and their thermal conditions are given in Table 1. These markers were chosen due to their proven reliability and close linkage to the I and bc-3 genes. SCAR markers were initially used to identify the genotypes bearing resistant genes and CAPS markers were later used for revalidation. Pooled leaves of three replicates per genotype were collected at 30 dpi and stored in a deep freezer at −80°C. DNA was extracted from the young leaves of 10-day-old plants using a DNeasy plant mini kit (Qiagen). Total RNA was isolated from 100 mg of leaf tissue using TRIzol reagent as per the user guidelines (Invitrogen, Thermo Scientific). 1 μg of RNA was used as a template for cDNA synthesis using the Revert-Aid cDNA synthesis kit (Thermo Scientific) in a total volume of 20 μL. 2 μL of cDNA was used in the RT-PCR assay to test the presence of virus in both susceptible and resistant plants. PCR cycling conditions are listed in Table 1. PCR reactions were performed in 25 μL volumes, each containing 1 μL of 50 ng genomic DNA as a template, 12.5 μL of GoTaq green dye master mix (Promega, Madison, United States), 10 μM of each primer (20 pmol for SW13). For CAPS markers, 5 μL of PCR products were digested with 1 μL of 10X Reaction buffer (Thermo Scientific) and 1 μL of the restriction enzyme (Taq1 for I gene, Rsa1 for bc-3 gene) in a total volume of 15 μL. The digested products were then separated on a 2% agarose gel. The complete nucleotide sequence of both I and bc-3 genes corresponding to the BCMV-CAPS and ENM-FWe/Rve amplified product were purified and sanger sequenced at Medauxin genomics, Bangalore, http://www.medauxin.com/. The sequences were aligned and analyzed using the BioEdit 7.0 sequence alignment editor. BLASTn analysis of the ENM-FWe/Rve amplicon sequence was performed to identify similarities with known bc-3 gene sequences in reported cultivars.

TABLE 1

MarkerGeneSequence and thermal conditionsAmplicon lengthReferences
SW13I5′-CACAGCGACATTAATTTTCCTTTC-3′
5′-CACAGCGACAGGAGGAGCTTATTA-3′
One cycle at 94°C for 4 min; 35 cycles of 94°C-10 s, 63°C- 40 s, 72°C- 2 min.
690 bp
CAPS (Taq1)5′-AGGAGGAAGAACGGTGGTC-3′
5′-TTTGGTGGTAATTTGAAAATGG-3′
One cycle at 94°C for 5 min; 35 cycles of 94°C-30 s, 58°C- 30 s, 72°C- 30 s. followed by restriction digestion
300 bp
ROC11bc-35′-CCAATTCTCTTTCACTTGTAACC-3′
5′-GCATGTTCCAGCAAACC-3′
One cycle at 94°C for 2 min; 30 cycles at 92°C-10 s, 65°C- 10 s, 72°C for 25 s.
420 bp
ENM-FWe/Rve (Rsa1)5′- ACCGATGAGCAAAACCCTA -3′
5′- CAACCAACTGGTATCGGATT-3′
One cycle at 95°C-3 min; 40 cycles at 94°C-20 s, 58°C-20 s, 72°C – 20 s. Followed by restriction digestion
541 bp (381/160)
BCMV CP (For RT-PCR and qPCR)Coat protein5′- AGTTGTTCCTCGGCATTCAAA-3′
5′- TACGGCCTCTCGGAATTTCT-3′
One cycle at 95°C-2 min; 35 cycles 95°C-30 s, 55°C-30 s, 72°C-1 min. Final extension of 72°C for 10 min.
414 bpWani et al., 2025
BCMNV (for RT-PCR and qPCR)5′- ATGAACAGTGTGGCGAAGTG-3′
5′- GCTTTGTTGGGCTCTTCAAC-3′
One cycle at 95°C-2 min; 35 cycles 95°C-30 s, 55°C-30 s, 72°C-1 min. Final extension of 72°C for 10 min.
834 bpRashid et al., 2022

List of Markers used in the study and their thermal conditions.

2.3 qRT-PCR analysis

qPCR assay was carried out to study the best resistant genotypes inhibiting the replication and systemic movement of the virus in different resistant plants (I, bc-3, and Ibc-3). For assays, resistant genotypes possessing the I (WB-352), bc-3 (EC-127645), and Ibc-3 (EC-116117) genes for resistance were selected along with a highly susceptible plant (IC-437141). All plants were inoculated with BCMV-BCMNV isolates and RNA was extracted from these genotypes at two development stages (Day 4 and Day 8). For every genotype, uninoculated resistant plants were used as an untreated control. Reactions were performed in the Rotor-Gene Q Real-Time PCR system (QIAGEN) using a 20 μL reaction mixture, including 10 μL SYBR green master mix (Thermo Scientific), 1 μL each of forward and reverse primers (BCMV-CP and BCMNV, 10 μm, Table 1), 2 μL cDNA and 6 μL of Nuclease-free water. The cycling conditions were set at an initial hold of 95°C for 2 min, followed by cycling for 35 times at 95°C-30 s, 60°C-30 s and 72°C- 60 s. Following the final PCR cycle, melting curve analysis was performed on the samples by heating them from 70 to 95°C, with a rise of 0.3°C for each step for the detection of specific and non-specific PCR products. Each sample was assayed in three replicates, including the actin gene, used as an internal control. The comparative quantification report was used to construct the box plots using REST 2008 software (QIAGEN). For both qPCR and RT-PCR, BCMV and BCMNV specific primers (Rashid et al., 2022; Wani et al., 2025) were used to detect both viruses (Table 1).

3 Results

3.1 Plant reaction to BCMV/BCMNV

Based on the phenotypic evaluation from the screening experiment, 23 genotypes were found resistant to both BCMV and BCMNV. The resistant plants were categorized into two groups, hypersensitive and absolute, based on the presence or absence of necrosis symptoms on the inoculated leaves. The results were presented under three experimental groups based on the selection of resistant genotypes assisted by molecular markers: Group 1: characterized by the sole presence of the I gene, Group 2: characterized by the sole presence of the bc-3 gene, and Group 3: characterized by the presence of both I and bc-3 genes (Ibc-3).

3.2 Phenotypic and genotypic evaluation of plant materials bearing I gene

BCMV and BCMNV isolates induced typical mosaic, necrosis, mottling, leaf crinkling and deformations in susceptible cultivars and accurately distinguished the resistant genotypes carrying the dominant “II” gene from the susceptible “ii” genotypes. Of all the 123 plant materials screened for BCMNV resistance, 13 genotypes presented localized and systemic vein necrosis that suggested the presence of “I” gene conditioning resistance through “Temperature Insensitive Necrosis (TIN)” in bean plants (Figure 1b, Supplementary File S1). The tested BCMNV isolate induced initial necrotic lesions on resistant plant materials that appeared at 4 dpi and expanded quickly, reaching the entire leaf veins and a nervure necrotic vein reaction was noticed at 10–12 dpi (Figure 1b, Supplementary File S1). Similarly, from the tested 123 plant materials, 23 genotypes conferred resistance to BCMV. However, infection with BCMV didn’t induce TIN in those genotypes conditioning HR to BCMNV and conferring extreme immunity (Figure 1a). Also, few genotypes induced mild necrosis of primary leaves infected with BCMV, demonstrating the incomplete dominant nature of the I gene as described by , that I/i genotypes respond to BCMV infection also through an HR.

FIGURE 1

When a SCAR marker SW13 was utilized to screen all the genotypes for identifying the I gene, the marker consistently identified the plant materials presenting localized vein necrosis on the inoculated leaf. SW13 marker linked to the I gene amplified a 690 bp product from 16 genotypes (Table 2) that specified the presence of the dominant I gene for resistance (Figure 2a). However, three genotypes (EC-400444, EC-271540, and WB-6, Table 2), identified by the marker were susceptible to virus inoculation. They were later found to have mutations in the I gene at four nucleotide positions (Figure 3). To overcome these mutated forms, another co-dominant marker (BCMV-CAPS, Table 1) linked to the I gene was utilized. This marker is based on the presence of single nucleotide difference (A/G) between I gene-bearing resistant (II) and susceptible (ii) plants. Resistant plants have “A” allele while susceptible plants have “G” allele. PCR products (311 bp) of resistant genotypes on digestion with TaqI (Restriction site: TCGA) generated products of 201 and 110 bp, whereas susceptible plants remain un-cleaved (311 bp) by TaqI (Figure 2b) due to point mutations and absence of the restriction site (TCGA-TCGG). CAPS analysis based on these closely linked SNPs identified only true resistant plants bearing the I gene for resistance. PCR products from resistant and susceptible genotypes, containing the I gene corresponding to CAPS marker, were purified and sanger sequenced. Sequence alignment revealed point mutations between resistant and susceptible plants. One of these mutations created a Taq1 restriction site, as illustrated in Figure 3.

TABLE 2

S. NGenotypeDisease ratingSW13 (I gene)CAPS-BCMV (I gene)ROC11 (bc-3 gene)ENM-F/R (bc-3 gene)Resistant phenotypes
BCMVBCMNV
1.EC-4004441 ++
2.EC-4004542+
3.EC-3985122+
4.EC-4052171+
5.EC-2715553+
6.EC-181331+
7.EC-4004532+
8.EC-2714892+
9.EC-3250650 +++NVNVN
10.EC-4052100+NVNNVN
11.EC-3985772+
12.EC-249460NVNNVN
13.EC-4004282+
14.EC-2582793+
15.EC-3978241+
16.EC-4004390 +++NVNVN
17.EC-2855792+
18.EC-131000 ++ +NVNNVN
19.EC-1992052+
20.EC-1276450 ++ +NVNNVN
21.EC-2715401++
22.EC-2860711+
23.EC-4004082+
24.EC-4052090 ++MVNVN
25.EC-2715440 +NVNNVN
26.EC-3249762+
27.EC-3852590 +NVNNVN
28.EC-249563+
29.IC-3285583+
30.IC-0496962+
31.IC -0495592+
32.IC-2582592+
33.IC-2628312+
34.IC-3288962+
35.IC-0416652+
36.EC-3985672+
37.EC-1161170 ++ +NVNNVN
38.EC-4051932+
39.EC-285553+
40.IC-4371413+
41.IC-3810132+
42.IC-0390732+
43.IC-371502+
44.IC-3291541+
45.IC-0416502+
46.IC-0371372+
47.EC-4004501+
48.EC-4052082+
49.EC-2715302+
50.EC-3160262+
51.EC-3985001+
52.EC-9423862+
53.EC-3250780 +++MVNVN
54.WB-11370 +NVNNVN
55.WB-16700 +NVNNVN
56.WB-8462 +
57.KRC-221
58.SKAU-R-912
59.WB-6622
60.WB-13160NVNNVN
61.8362
62.SR 21
63.WB-2221
64.WB-13042
65.WB-3520 +++-MVNVN
66.WB-9202
67.16772
68.227211
69.N21
70.WB-3693
71.WB-1952
72.WB-592
73.WB-16781
74.SR-30 ++--NVNVN
75.WB-11293
76.WB-221
77.WB-2162
78.WB-1121
79.WB-352 (field)0 +++NVNVN
80.WB-N40 ++--NVNVN
81.WB-N10 ++--MVNVN
82.WB-61 ++
83.ALR-61+
84.ALR-312+
85.ALR-592+
86.ALR-491+
87.ALR-543+
88.ALR-663+
89.ALR-943+
90.ALR-12+
91.ALR-502+
92.ALR-561+
93.ALR-621+
94.ALR-343+
95.ALR-792+
96.ALR-783+
97.ALR-701+
98.ALR-82+
99.ALR-133+
100.ALR-901+
101.ALR-822+
102.ALR-51+
103.ALR-763+
104.Local A3+
105.Local B2+
106.Local C1+
107.Local-11+
108.Local-20 +++NVNVN
109.Local-32+
110.11292+
111.N-153+
112.Arka Komal2+
113.Shalimar French bean-10 +++NVNVN
114.SR-13+
115.SR-41+
116.SR-1012+
117.SKAU NSP-23+
118.SKAU NSP-32+
119.SKAU NSP-42+
120.SR-22+
121.SKAU-51+
122.NSP F-10 +++NVNVN
123.NSP F-20 +++NVNVN

Genotypes screened for resistance, phenotyping and resistance gene results.

VN: Resistant Genotypes that show Vein Necrosis (VN) on the inoculated leaves. NVN: Resistant Genotypes that display No Vein Necrosis (NVN) on the inoculated leaf. MVN: Resistant Genotypes that display Mild Vein Necrosis (MVN) on the inoculated leaf. SW13: “+” denotes presence of I gene as identified by the marker. “−” denotes absence of I gene as identified by the marker. BCMV-CAPS: “ + “ denotes presence of I gene after digestion of PCR amplicon (311 bp) with TaqI that generates products of 201 and 110 bp. “−” denotes absence of I gene after digestion of PCR amplicon (311 bp) with TaqI, which does not generate products of 201 and 110 bp and remains un-cleaved (311 bp). ROC11: “+” denotes absence of bc-3 gene. “−” denotes the presence of the bc-3 gene. ENM-F/R: “+” denotes presence of two signals (381 and 160 bp) after digestion with Rsa1 (resistant). “−” denotes presence of undigested 541-bp fragment after digestion with Rsa1 (susceptible). For the ENM-F/R test, only genotypes identified as carrying the bc-3 gene (using the ROC11/420 marker) were used.

FIGURE 2

FIGURE 3

3.3 Phenotypic and genotypic evaluation of plant materials bearing the bc-3 gene

This resistant group included 4 genotypes that were resistant and symptomless after mechanical inoculation (BCMV and BCMNV) and were tested for the presence of the “bc-3” gene in PCR assays. Genotypes carrying this recessive resistance allele conferred complete immunity to both BCMV and BCMNV isolates (Figures 4a,b), without triggering any necrotic reaction on the inoculated leaves. Plant materials with the bc-3 gene never reacted with mosaic or necrosis and the only visible reaction was necrotic, in which pin-point necrotic spots developed on upper un-inoculated leaves in between 10 and 15 dpi infected with BCMNV (Figure 4) which were less prominent and did not extend into localized vein necrosis. No systemic necrosis can be exemplified as the plant materials are visibly healthy and recorded no symptoms throughout the 30-day phenotyping period.

FIGURE 4

The presence of the bc-3 gene in this group was confirmed by both ROC11 and ENM-FWe/Rve markers. The absence of SCAR marker ROC11/420 indicates the presence of bc-3 gene and its negative selection was initially used to eliminate the common bean genotypes lacking bc-3 disease resistance locus (Table 2). Subsequently, those genotypes bearing the bc-3 gene as identified by ROC11 marker were amplified using ENM-FWe/Rve marker. The genotypes which were not identified for the presence of bc-3 gene using ROC11 marker were not utilized to test with ENM-FWe/Rve marker. Digestion of PCR amplified products (541-bp fragment) with RsaI cleaved bc-3 carrying genotypes into 381- and 160-bp fragments, whereas the PCR products derived from the susceptible genotypes remain un-cleaved, due to the absence of mutations within the eIF4E gene. To confirm the presence of mutations in the eIF4E gene of resistant genotypes, the 541-bp PCR products were purified and sanger sequenced. Pairwise nucleotide sequence comparison was performed by using the Basic Local Alignment Search Tool (BLAST) and the partial coding sequence (541 bp) of genotypes carrying the bc-3 gene had a maximum identity of 100% to the published eIF4E gene sequence of the cultivar “IVT7214” (KT175572), reported to carry bc-3 gene.

3.4 Phenotypic and genotypic evaluation of plant materials bearing I and bc-3 gene

Three genotypes (EC-13100, EC-127645, EC-116117) bearing both I and bc-3 (Ibc-3) genes for resistance were identified from the screened germplasm. These genotypes presented no symptoms or any HR (Figures 5a,b) on both inoculated and upper un-inoculated leaves to both BCMV and BCMNV isolates. Hence, these genotypes were protected from BCMNV-induced necrosis and conditioned extreme resistance to the bean plants without subjecting them to HR. In this gene combinations (Ibc-3), the dominant I gene was protected from being necrotic by the presence of the bc-3 allele.

FIGURE 5

However, 3 resistant plant materials in which both I and bc-3 genes were not identified, the presence of other resistance genes or gene combination can be assumed, which protects the common beans against BCMV-BCMNV. Due to its minor influence on conferring resistance to the virus and also due to the limited availability of markers linked to these genes, its presence in the screened germplasm was not established. These genotypes conferred high resistance to the test isolates and the viral symptoms didn’t appear on both inoculated and upper uninoculated leaves till the entire phenotyping period of 30 dpi. In susceptible plants, the RT-PCR assay using BCMV and BCMNV primers yielded positive results, and did not detect the presence of the virus in resistant plants (Figure 6). Susceptible plants associated with the symptoms of mosaic, necrosis, leaf crinkling and puckering were amplified around 414 bp with BCMV CP primers and no BCMV presence was detected in resistant genotypes (Figures 6a,b). Whereas, BCMNV primers amplified the target virus with expected product size of 834 bp from susceptible genotypes (Figure 6c) and no BCMNV was detected from the RNA isolated from resistant genotypes.

FIGURE 6

3.5 qPCR-based assessment of virus accumulation

Resistant phenotypes of bean cultivars differed based on the presence or absence of the I gene. The two test isolates induced either local or systemic necrosis in resistant cultivars (WB-352) carrying the I gene, but not in those genotypes carrying Ibc-3 (EC-116117) and bc-3 (EC-127645) resistant genes. qPCR analysis of the RNA isolated from the upper leaves of three different genotypes (I, bc-3, and Ibc-3) at the 4th and 8th day post-inoculation revealed varying levels of BCMV-BCMNV expression across the genotypes. Cultivars carrying the I gene alone exhibited low-level viral expression on Day 4, where initial necrotic lesions appeared on the inoculated leaves and an increased expression at day 8 (Figure 7a) that corresponds to extensive vein necrosis that usually appears at 10 dpi. In contrast, no viral spread was detected in Ibc-3 (Figure 7c) and bc-3 (Figure 7b) genotypes up to 8 dpi, and these plants remained visibly healthy throughout the 30-day observation period. This suggests that genotypes carrying the I gene alone would enable the virus to replicate and allow for systemic movement inside the host plants without the symptoms being expressed that were affected in the other genotypes (Ibc-3, bc-3), where its replication and movement were inhibited. The melting and amplification curves of the tested genotypes were provided in Supplementary File S2.

FIGURE 7

4 Discussion

BCMV and BCMNV are two closely related viruses that pose a significant threat to global common bean production. These viruses can cause complete crop failure (up to 100% yield loss) and significantly reduce bean quality (Tang and Feng, 2022; Worrall et al., 2015). In response, identifying and developing common bean cultivars with broad genetic resistance to these viruses is crucial.

In this study, 123 common bean genotypes were inoculated to assess resistance and susceptibility to BCMV-BCMNV and to identify the plant materials bearing multiple resistant genes, each working with a different mode of action. Two forms of resistance were observed in the identified plant materials: some exhibited a hypersensitive reaction (HR) to the virus, while others remained resistant without exhibiting HR. Resistant plants exhibiting HR presented a vein necrosis of primary inoculated leaves between 7 and 10 dpi. Phenotypically, this necrotic vein reaction of inoculated primary leaves was the key feature in demonstrating the presence of the I gene (; ). This necrotic sign has been identified in most of the resistant cultivars (13 genotypes) in the screened germplasm and conferred resistance toward BCMV-BCMNV under controlled conditions (< 30°C). The evidence for the presence of the I gene was suggested by PCR using SW-13 and BCMV-CAPS markers. These results are in accordance with some previous studies that the I gene confers a high degree of resistance and complete immunity to BCMV strains below 30°C (; Vallejos et al., 2006; ) and induces a necrotic reaction on primary inoculated leaves to BCMNV, regardless of the temperature. However, the wide use of common bean genotypes bearing the I gene has led to BCMNV-induced systemic necrosis and in response, its susceptibility can be prevented if the I gene is “protected” in the presence of one of the recessive genes (bc-1, bc-2, or bc-3) (; Singh and Schwartz, 2010; ; ). We then focused on the presence of any recessive resistant gene in the remaining plant materials that were immune (without HR) to both BCMV and BCMNV. Interestingly, four resistant genotypes possessed the bc-3 gene, and three genotypes were in combination of both I and bc-3 genes (Ibc-3). However, some bean varieties with bc-3 resistance to BCMNV were also reported as susceptible to BCMV (). The recessive bc-3 gene encodes a mutated eukaryotic translation initiation factor (eIF4E) gene and was identified to be associated with resistance against BCMV-BCMNV in common beans. The VPg protein of the virus interacts with eIF4E proteins in plants and four-point mutations in the eIF4E gene impaired the interaction between eIF4E and VPg protein and also affected the replication of BCMV, thus conferring resistance in common beans (). These amino acid polymorphisms in eIF4E were also reported previously to confer recessive resistance to Potyviruses in Pisum sativum against pea seed-borne mosaic virus, Capsicum annuum against chili veinal mottle virus and potato virus Y (PVY), Hordeum vulgare against barley yellow mosaic virus, Citrullus lunatus against zucchini yellow mosaic virus, Lycopersicum esculentum against potato virus Y (PVY) and tobacco etch virus (TEV) (; ; ; ; ; Ruffel et al., 2002; Ruffel et al., 2006).

A qPCR experiment was conducted to study the resistance conferred by the three resistant groups (I, bc-3, Ibc-3) that affect the systemic movement of the virus. This assay (Figure 7) also suggests that systemic spread of the virus was drastically affected in genotypes bearing Ibc-3 genes with both BCMV and BCMNV being unable to replicate independently and spread to the uninoculated upper leaves. However, the genotypes bearing the I gene demonstrate a difference in virus spread in uninoculated upper leaves when compared to those genotypes bearing bc-3 and Ibc-3 genes. The systemic movement of virus in the bean genotypes carrying I alleles here demonstrated that BCMV replication occurs inside the host plants. It was also proven in the screening experiment that, bean genotypes carrying the I gene were immune to BCMV and a few genotypes also conditioned resistance to BCMV through a mild necrosis of primary leaves. Previous experiments with bean lines carrying I alleles also demonstrated that BCMV replication depends on the I allele’s dosage () and the virus could still replicate in genotypes carrying the I gene even at a low temperature (26°C) (). This suggests that BCMV/BCMNV strains are capable of replicating and undergoing intercellular movement within I-gene-containing common bean cultivars without expressing any viral symptoms and necrosis likely occurs when the virus spreads from the initially infected cell to a neighboring cell (; ; ). So, the best combination of genes in breeding for BCMV-BCMNV resistance was likely the Ibc-3 combination as they confer a broad spectrum of genetic resistance (; ; Singh and Schwartz, 2010; Worrall et al., 2015). This beneficial gene combination (Ibc-3) has been identified in some plant materials that provide promising resistance to BCMV-BCMNV also at temperatures above 30°C.

Hence, this study demonstrates the mechanism of resistance conferred by common bean cultivars bearing the dominant “I” and recessive “bc-3” genes and represents the influence of different genetic backgrounds on resistance to BCMV-BCMNV. Both SCAR (SW13 and ROC11) and CAPS (BCMV-CAPS and ENM-FWe/Rve) molecular markers used in this study were reliable for the identification of I and bc-3 genes. Importantly, there are no reported instances of recombinant viral strains overcoming resistance conferred by these genes in India. In this respect, this investigation was important to separate common bean cultivars with major genes for resistance. We can further introduce these genes directly into our elite common bean varieties that are susceptible to BCMV and can later be utilized in bean breeding program for virus resistance.

Statements

Data availability statement

The original contributions presented in the study are included in the article/Supplementary material, further inquiries can be directed to the corresponding author.

Author contributions

DM: Visualization, Writing – review & editing, Writing – original draft, Formal Analysis, Methodology, Validation, Software, Data curation, Conceptualization. SW: Validation, Writing – review & editing, Project administration, Formal Analysis, Supervision, Investigation, Software, Visualization, Methodology, Writing – original draft, Conceptualization. SB: Supervision, Data curation, Project administration, Conceptualization, Writing – review & editing, Resources, Funding acquisition. SR: Writing – review & editing, Investigation, Data curation, Validation, Formal Analysis, Visualization. AJ: Validation, Writing – review & editing, Methodology, Software. ZD: Resources, Funding acquisition, Visualization, Supervision, Project administration, Conceptualization, Writing – review & editing. SHW: Methodology, Conceptualization, Writing – review & editing, Project administration, Resources. PS: Data curation, Resources, Writing – review & editing, Supervision. GA: Supervision, Project administration, Writing – review & editing, Resources, Funding acquisition. AH: Conceptualization, Resources, Validation, Methodology, Writing – review & editing, Visualization, Investigation, Data curation, Formal Analysis, Supervision, Writing – original draft, Project administration, Funding acquisition.

Funding

The author(s) declare that financial support was received for the research and/or publication of this article. This work was funded by the SERB-DST (grant number: CRG/2022/003659), DST-PURSE (grant number: SR/PURSE/2022/124), and the ICAR- National Institute of Seed Science and Technology.

Acknowledgments

We acknowledge NBPGR-New Delhi, AICRP-NSP (Shalimar, SKUAST-K), and Division of Genetics and Plant Breeding (FOA, SKUAST-K) for providing seed material.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Generative AI statement

The authors declare that no Generative AI was used in the creation of this manuscript.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fmicb.2025.1614122/full#supplementary-material

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Summary

Keywords

BCMV, BCMNV, resistance, I-gene, bc-3 gene

Citation

Meghanath D, Wani S, Bashir S, Rashid S, Javaid A, Dar ZA, Wani SH, Sofi PA, Ali G and Hamid A (2025) Delineating the source of resistance to bean common mosaic virus (BCMV) and bean common mosaic necrosis virus (BCMNV) in common bean (Phaseolus vulgaris) cultivars of Jammu and Kashmir, a North-Western Himalayan region. Front. Microbiol. 16:1614122. doi: 10.3389/fmicb.2025.1614122

Received

18 April 2025

Accepted

30 May 2025

Published

24 June 2025

Volume

16 - 2025

Edited by

Nazia Manzar, National Bureau of Agriculturally Important Microorganisms (ICAR), India

Reviewed by

Jose Trinidad Ascencio-Ibáñez, North Carolina State University, United States

Nagamani Sandra, Indian Agricultural Research Institute (ICAR), India

Updates

Copyright

*Correspondence: Aflaq Hamid,

†These authors have contributed equally to this work and share first authorship

ORCID: Aflaq Hamid, orcid.org/0000-0001-6353-6070

Disclaimer

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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