Inheritance of resistance to watermelon mosaic virus in the cucumber line TMG-1: tissue-specific expression and relationship to zucchini yellow mosaic virus resistance

The inbred cucumber (Cucumis sativus L.) line TMG-1 is resistant to three potyviruses:zucchini yellow mosaic virus (ZYMV), watermelon mosaic virus (WMV), and the watermelon strain of papaya ringspot virus (PRSV-W). The genetics of resistance to WMV and the relationship of WMV resistance to ZYMV resistance were examined. TMG-1 was crossed with WI-2757, a susceptible inbred line. F₁, F₂ and backcross progeny populations were screened for resistance to WMV and/or ZYMV. Two independently assorting factors conferred resistance to WMV. One resistance was conferred by a single recessive gene from TMG-1 (wmv-2). The second resistance was conferred by an epistatic interaction between a second recessive gene from TMG-1 (wmv-3) and either a dominant gene from WI-2757 (Wmv-4) or a third recessive gene from TMG-1 (wmv-4) located 20–30 cM from wmv-3. The two resistances exhibited tissue-specific expression. Resistance conferred by wmv-2 was expressed in the cotyledons and throughout the plant. Resistance conferred by wmv-3 + Wmv-4 (or wmv-4) was expressed only in true leaves. The gene conferring resistance to ZYMV appeared to be the same as, or tightly linked to one of the WMV resistance genes, wmv-3.     

Genes for resistance to zucchini yellow mosaic in tropical pumpkin

Four cultigens of Cucurbita moschata resistant to zucchini yellow mosaic virus were crossed with the susceptible 'Waltham Butternut' and with each other in order to clarify the mode of inheritance of resistance and relationships among the genes involved. Five loci were segregating, with genes for resistance Zym-0 and Zym-4 carried by 'Nigerian Local' and one of them also carried by 'Nicklow's Delight,' Zym-1 carried by 'Menina,' and zym-6 carried by 'Soler.' A recessive gene carried by 'Waltham Butternut,' zym-5, is complementary with the dominant Zym-4 of 'Nigerian Local,' that is, the resistance conferred by Zym-4 is only expressed in zym-5/zym-5 individuals. Gene zym-6 appears to be linked to either Zym-0 or Zym-4, and it is also possible that Zym-1 is linked to one of them as well.     

Multiple alleles for zucchini yellow mosaic virus resistance at the zym locus in cucumber

 Sources of resistance to several potyviruses have been identified and characterized within the cucumber (Cucumis sativus L.) germplasm. Resistance to zucchini yellow mosaic virus (ZYMV) is present in inbred lines derived from the Dutch hybrid Dina (Dina-1) and from the Chinese cultivar ‘Taichung Mou Gua’ (TMG-1). Tests of allelism indicated that the genes for resistance to ZYMV in TMG-1 and Dina-1 are at the same locus; however, the two genotypes exhibited different phenotypes in response to cotyledon inoculation with ZYMV. Dina-1 exhibited a distinct veinal chlorosis and accumulation of virus limited to the first and/or second true leaves, while TMG-1 remained symptom-free and did not accumulate virus. The distinct veinal chlorosis phenotype in Dina-1 was dominant to the symptom-free phenotype in TMG-1 and was shown not to be due to a separate gene. These results indicate that a series of alleles differing in effectiveness and dominance relationships occurs at the zym locus such that Zym>zym ^Dina>zym ^TMG-1. In addition to ZYMV resistance, TMG-1 is also resistant to watermelon mosaic virus (WMV), the watermelon strain of papaya ringspot virus (PRSV-W) and the Moroccan watermelon mosaic virus (MWMV); the WMV and MWMV resistances are at the same locus, or tightly linked to the zym locus. Dina-1 also was found to be resistant to PRSV-W and MWMV. The gene for MWMV resistance in Dina-1 appeared to be at the same locus or tightly linked (<1% recombination) to the gene for ZYMV resistance. In contrast to the response to ZYMV inoculation, Dina-1 does not exhibit distinct veinal chlorosis when inoculated with PRSV-W or MWMV. Collectively, these observations suggest that the gene(s) conferring resistance to ZYMV, WMV, and MWMV may be part of a gene cluster for potyvirus resistance in cucumber. Received: 12 November 1996 / Accepted: 25 April 1997     

Cantaloupe line CZW-30 containing coat protein genes of cucumber mosaic virus,zucchini yellow mosaic virus,and watermelon mosaic virus-2 is resistant to these three viruses in the field

Cantaloupe line CZW-30 containing coat protein gene constructs of cucumber mosaic cucumovirus (CMV), zucchini yellow mosaic potyvirus (ZYMV), and watermelon mosaic virus 2 potyvirus (WMV-2) was investigated in the field over two consecutive years for resistance to infections by CMV, ZYMV, and/or WMV-2. Resistance was evaluated under high disease pressure achieved by mechanical inoculations and/or natural challenge inoculations by indigenous aphid vectors. Across five different trials, homozygous plants were highly resistant in that they never developed systemic symptoms as did the nontransformed plants but showed few symptomatic leaves confined close to the vine tips. Hemizygous plants exhibited a significant delay (2–3 weeks) in the onset of disease compared to control plants but had systemic symptoms 9–10 weeks after transplanting to the field. Importantly, ELISA data revealed that transgenic plants reduced the incidence of mixed infections. Only 8% of the homozygous and 33% of the hemizygous plants were infected by two or three viruses while 99% of the nontransformed plants were mixed infected. This performance is of epidemiological significance. In addition, control plants were severely stunted (44% reduction in shoot length) and had poor fruit yield (62% loss) compared to transgenic plants, and most of their fruits (60%) were unmarketable. Remarkably, hemizygous plants yielded 7.4 times more marketable fruits than control plants, thus suggesting a potential commercial performance. This is the first report on extensive field trials designed to assess the resistance to mixed infection by CMV, ZYMV, and WMV-2, and to evaluate the yield of commercial quality cantaloupes that are genetically engineered.     

Inheritance of hypersensitive resistance to Bean yellow mosaic virus in narrow-leafed lupin (Lupinus angustifolius)

In narrow‐leafed lupin (Lupinus angustifolius), segregation for the necrotic (systemic hypersensitive) response to infection with a necrotic strain of Bean yellow mosaic virus (BYMV‐N) was studied in progeny plants from six crosses. The parents were two cultivars that always developed necrosis when infected (Danja and Merrit) and two genotypes that always responded without necrosis (90L423‐07‐13 and P26697). In the four possible combinations of crosses between the different necrotic and non‐necrotically reacting genotypes, segregation for the necrotic response in F₂ progeny plants always fitted a 3:1 ratio (necrotic: non‐necrotic). All F₂ progeny plants from the cross between the two non‐cultivar genotypes became infected without necrosis while 99% of the F₂ from the cross between the two cultivars developed necrosis. These results indicate that the systemic necrotic response to infection with BYMV‐N is probably controlled by a single dominant hypersensitivity gene for which we propose the name Nbm‐1. However, its expression seemed influenced by independently segregating modifier genes in the genetic background since necrosis developed at widely different rates within affected F₂ progeny plants resulting in staggered killing.     

Inheritance of resistance to yellow mosaic virus in blackgram (Vigna mungo (L.) Hepper)

Summary The inheritance of resistance to mungbean yellow mosaic virus (MYMV) was studied in blackgram (Vigna mungo (L.) Hepper). The highly resistant donors Pant U-84 and UPU-2 and a highly susceptible line, UL-2, their F₁'s, F₂'s and backcrosses were grown with spreader located every 5 to 6 rows. The resistance was found to be digenic and recessive in all the crosses and free from cytoplasmic effect.     

Spread of zucchini yellow mosaic potyvirus in squash in Hungary

The temporal and spatial distribution of zucchini yellow mosaic potyvirus (ZYMV) was studied in a 3000‐m² zucchini squash field. The first infected plants were found 4 weeks after the field was exposed to virus source plants. The infection increased to nearly 74% by the end of the study. Alate aphids were active from the beginning of the study and 43 species were trapped in the field. Flights of vector species Acyrthosiphon pisum and Myzus persicae peaked during the fourth week which resulted in high virus incidence 4 weeks later. There was a significant correlation between the number of vectors caught in yellow pan traps and the number of infected plants in the field. In laboratory studies evaluating 11 aphid species, Aphis pomi de Geer was identified as a new vector species of ZYMV. Although this aphid was not caught in our field studies, it may be an important contributor in other areas where cucurbits are grown in close proximity to apple or other hosts of this aphid.     

Oligogenic inheritance for resistance to Zucchini yellow mosaic virus in Cucurbita pepo

‘True French’ is an open‐pollinated cultivar of the Zucchini (Courgette) Group of Cucurbita pepo and is susceptible to Zucchini yellow mosaic virus (ZYMV). Using C. moschata‘Menina’ as the source of ZYMV resistance and following six generations of backcrossing, a true‐breeding line nearly isogenic to ‘True French’, designated 381e, was recovered that carried ZYMV resistance, albeit not at as high a level as in ‘Menina’. ‘True French’ and accession 381e were crossed, and their reciprocal F₁, F², and backcross progenies were grown in a chamber and inoculated with a highly virulent, non‐aphid‐transmissible strain of ZYMV. Nearly all F¹ plants and all plants of the backcross to 381e were classified as resistant. Segregation to resistant and susceptible individuals occurred in the backcross to the susceptible parent, in accordance with a 3:5 three‐gene ratio of resistant: susceptible. The F₂ segregated in accordance with a ratio of 45 resistant : 19 susceptible, which would be obtained if there was one major gene for resistance, Zym‐1 (Zym), and two other genes, herein designated Zym‐2 and Zym‐3, both of which for complementary to Zym‐1. The presence of Zym‐1 and either Zym‐2 or Zym‐3 is necessary for resistance to be expressed in young plants, but the presence of all three might be necessary for resistance to continue to be expressed during subsequent development of the plants. Evidently, Zym‐2 and Zym‐3 are ubiquitous in C. moschata but their susceptible alleles are much more common in C. pepo. As the level of resistance of 381e to ZYMV is not as high as that of C. moschata‘Menina’, additional, as yet unidentified, genes must be involved in conferring high resistance to this virus.     

Analysis of the autoproteolytic activity of the recombinant helper component proteinase from zucchini yellow mosaic virus

The multifunctional helper component proteinase (HC-Pro) of potyviruses contains an autoproteolytic function that, together with the protein 1 (P1) and NIa proteinase, processes the polyprotein into mature proteins. In this study, we analysed the autoproteolytic active domain of zucchini yellow mosaic virus (ZYMV) HC-Pro. Several Escherichia coli-expressed MBP:HC-Pro:GFP mutants containing deletions or point mutations at either the N- or C-terminus of the HC-Pro protein were examined. Our results showed that amino acids essential for the proteolytic activity of ZYMV HC-Pro are distinct from those of the tobacco etch virus HC-Pro, although the amino acid sequences in the proteolytic active domain are conserved among potyviruses.     

Inheritance and allelism tests of Raiden soybean for resistance to soybean mosaic virus

The gene symbol Rsv2 was previously assigned to the gene in the soybean [Glycine max (L.) Merr.] line OX670 for resistance to soybean mosaic virus (SMV). The Rsv2 gene was reported to be derived from the Raiden soybean (PI 360844) and to be independent of Rsv1. Accumulated data from our genetic experiments were in disagreement with this conclusion. In this study, Raiden and L88-8431, a Williams BC5 isoline with SMV resistance derived from Raiden, were crossed with two SMV-susceptible cultivars to investigate the mode of inheritance of SMV resistance in Raiden. They were also crossed with five resistant cultivars to examine the allelomorphic relationships of the Raiden gene with other reported genes at the Rsv1 locus. F1 plants, F2 populations, and F2-derived F3 (F2:3) lines were tested with SMV strains G1 or G7 in the greenhouse or in the field. The individual plant reactions were classified as resistant (R, symptomless), necrotic (N, systemic necrosis), or susceptible (S, mosaic). The F2 populations from R x S crosses segregated in a ratio of 3 (R + N):1 S and the F2:3 lines from Lee 68 (S) x Raiden (R) exhibited a segregation pattern of 1 (all R):2 segregating:1 (all S). The F2 populations and F2:3 progenies from all R x R crosses did not show any segregation for susceptibility. These results demonstrate that the resistance to SMV in Raiden and L88-8431 is controlled by a single dominant gene and the gene is allelic to Rsv1. The heterozygous plants from R x S and R x N crosses exhibited systemic necrosis when inoculated with SMV G7, indicating a partial dominance nature of the resistance gene. Raiden and L88-8431 are both resistant to SMV G1-G4 and G7, but necrotic to G5, G6, and G7A. Since the resistance gene in Raiden is clearly an allele at the Rsv1 locus and it exhibits a unique reaction to the SMV strain groups, assignment of a new gene symbol, Rsv1-r, to replace Rsv2 would seem appropriate. Further research is ongoing to investigate the possible existence of the Rsv2 locus in OX670 and its relatives.     

Intraspecific variation in zucchini yellow mosaic virus transmission by Myzus persicae and the impact of aphid host plant

Three isofemale lines of Myzus persicae (Sulzer), two lines collected from and reared on a brassicaceous host, and one line collected from and reared on a malvaceous host, were evaluated for their efficiency of transmitting Zucchini yellow mosaic virus (family Potyviridae, genus Potyvirus, ZYMV). In the first experiment, the transmission efficiencies of two clones from Brassicaceae (B1 and B2) were 52.0 and 60.8%, respectively, and these transmissions were not significantly different. In a second experiment, the transmission efficiencies of the clone on Malvaceae (M1) and clone B2 were significantly different at 35.6 and 55.7%, respectively. Further experiments evaluated host-related mechanisms that may have contributed to the differential transmissions observed between clones M1 and B2. Studies on short-term feeding showed that aphids continuously reared on okra, Abelmoschus esculentus (L.) Moench (malvaceous host), and those that were reared on okra and allowed a 24-h preacquisition feeding period on mustard, Brassica juncea (L.) Czern (brassicaceous host), had significantly lower transmission than aphids continuously maintained on mustard. Aphids reared on mustard and allowed a 24-h preacquisition feeding period on okra had intermediate transmission efficiency. In long-term host association studies, we found that aphids reared on mustard had significantly higher transmission efficiency than those reared on okra, and aphids reared first on okra and then switched to mustard had a transmission efficiency that was intermediate and not significantly different from the other two treatments. Our study reveals the existence of intraspecific variation in the transmission of ZYMV by M. persicae, and it suggests that to accurately assess the transmission capability of ZYMV by this species, multiple clones should be examined. Furthermore, the host plant on which the aphid is reared as well as the host plant on which it feeds just before virus acquisition contribute to ZYMV transmission efficiency of M. persicae.     

Inheritance and allelism of resistance to soybean mosaic virus in Zao18 soybean from China

Soybean mosaic disease caused by soybean mosaic virus (SMV) occurs wherever soybean [Glycine max (L.) Merr.] is grown and is considered one of the most important soybean diseases in many areas of the world. Use of soybean cultivars with resistance to SMV is a very effective way of controlling the disease. China has rich soybean germplasm, but there is very limited information on genetics of SMV resistance in Chinese soybean germplasm and reaction of the resistance genes to SMV strains G1-G7. There also is no report on allelic relationships of resistance genes in Chinese soybeans with other named genes at the three identified loci Rsv1, Rsv3, and Rsv4. The objectives of this study were to examine reactions of Chinese soybean cultivar Zao18 to SMV strains G1-G3 and G5-G7, to reveal the inheritance of SMV resistance in Zao18 and to determine the allelic relationship of resistance genes in Zao18 with previously reported resistance genes. Zao18 was crossed with the SMV-susceptible cultivar Lee 68 to study the inheritance of resistance. Zao18 was also crossed with the resistant lines PI96983, L29, and V94-5152, which possess Rsv1, Rsv3, and Rsv4, respectively, to examine the allelic relationship between the genes in Zao18 and genes at these three loci. Our research results indicated that Zao18 possesses two independent dominant genes for SMV resistance, one of which is allelic to the Rsv3 locus; the other is allelic with Rsv1. The presence of both genes (Rsv1 and Rsv3) in Zao18 confers resistance to SMV strains G1-G7.     

The allelic relationship of genes giving resistance to mungbean yellow mosaic virus in blackgram

Summary The allelic relationship of resistance genes for MYMV was studied in blackgram (V. mungo (L.) Hepper). The resistant donors to MYMV — Pant U84 and UPU 2, and their F₁, F₂ and F₃ generations — were inoculated artificially using an insect vector, whitefly (Bemisia tabaci Genn.). The two recessive genes previously reported for resistance were found to be the same in both donors.Part of Ph.D. Thesis submitted by the senior author. Research Paper No. 4271     

Barley yellow mosaic virus is overcoming RYM4 resistance in Belgium

Barley yellow mosaic virus (BaYMV) is the causal agent of a soil-borne systemic mosaic disease on barley. It has been reported in Belgium since the 1980s. The control of this disease is managed almost exclusively through the use of resistant varieties. The resistance of most commercial barley cultivars grown in Europe is conferred mainly by a single recessive gene, rym4. This monogenic resistance provides immunity against BaYMV pathotype 1 and has been mapped on barley chromosome 3HL and shown to be caused by mutations in the translation initiation factor eIF4E. Another pathotype, BaYMV pathotype 2, which appeared in the late 1980s (in Belgium, in the early 1990s), is able to overcome the rym4-controlled resistance. Until recently, this pathotype remained confined to specific locations. During a systematic survey in 2003, mosaic symptoms were observed only on susceptible barley cultivars collected in Belgian fields. BaYMV was detected by ELISA and RT-PCR on the susceptible cultivars and only by RT-PCR on the resistant cultivars. In 2004, mosaic symptoms were observed on susceptible and resistant cultivars. BaYMV was detected by ELISA and RT-PCR on both cultivars. In addition to developing RT-PCR methods for detecting and identifying BaYMV and Barley mild mosaic virus (BaMMV), an RT-PCR targeting the VPg/NIa viral protein part of the genome, known to discriminate the two BaYMV pathotypes, was set up to accurately identify the pathotype(s) now present in Belgium. The sequences from the generated amplicons revealed the single nucleotide substitution resulting in an amino acid change from lysine to asparagine specific to BaYMV pathotype 2. The possible reasons for the change in the BaYMV pathotype situation in Belgium, such as climatic change or a progressive build-up of soil inoculum potential, will be discussed, as well as the use of eIF4E-based resistance.     

The effect on yield in courgette and marrow of the mild strain of zucchini yellow mosaic virus used for cross-protection

The effects on yield in courgette and marrow (Cucurbita pepo) crops resulting from inoculation with the mild strain of zucchini yellow mosaic virus (ZYMV:WK), have been determined in polythene-house trials and in three years of outdoor, commercial field trials. In polythene-house trials ZYMV:WK inoculated plants were up to 10 days later in flowering than uninoculated plants and their cumulative yields were between 5% and 26% less than uninoculated plants depending on the cultivar. In most field trials cumulative yields from inoculated plants were between 4% and 38% less than uninoculated plants depending on the site and cultivar, but in one trial the yield was 7% higher from inoculated plants. In all experiments, courgette and marrow fruits harvested from ZYMV:WK inoculated plants were symptomless and indistinguishable from fruit harvested from uninoculated plants. The mild leaf symptoms induced by ZYMV:WK infection did not intensify to severe leaf symptoms and where there were natural outbreaks of severe ZYMV infection, fruits from inoculated plants remained symptomless whilst those from uninoculated plants were severely affected and unmarketable.     

Durable field resistance to wheat yellow mosaic virus in transgenic wheat containing the antisense virus polymerase gene

Wheat yellow mosaic virus (WYMV) has spread rapidly and causes serious yield losses in the major wheat‐growing areas in China. Because it is vectored by the fungus‐like organism Polymyxa graminis that survives for long periods in soil, it is difficult to eliminate by conventional crop management or fungicides. There is also only limited resistance in commercial cultivars. In this research, fourteen independent transgenic events were obtained by co‐transformation with the antisense NIb8 gene (the NIb replicase of WYMV) and a selectable gene bar. Four original transgenic lines (N12, N13, N14 and N15) and an offspring line (N12‐1) showed high and durable resistance to WYMV in the field. Four resistant lines were shown to have segregated and only contain NIb8 (without bar) by PCR and herbicide resistance testing in the later generations. Line N12‐1 showed broad‐spectrum resistance to WYMV isolates from different sites in China. After growing in the infested soil, WYMV could not be detected by tissue printing and Western blot assays of transgenic wheat. The grain yield of transgenic wheat was about 10% greater than the wild‐type susceptible control. Northern blot and small RNA deep sequencing analyses showed that there was no accumulation of small interfering RNAs targeting the NIb8 gene in transgenic wheat plants, suggesting that transgene RNA silencing, a common mechanism of virus‐derived disease resistance, is not involved in the process of WYMV resistance. This durable and broad‐spectrum resistance to WYMV in transgenic wheat will be useful for alleviating the damage caused by WYMV.