Genetic inheritance of resistance to cowpea aphid-borne mosaic virus in cowpea

Cowpea aphid-borne mosaic virus (CABMV) is a major virus disease in Uganda that causes substantial loss of the cowpea crop especially in growth and yield. The mode of gene action conferring resistance to the virus is not well understood. The objective of the study was to determine the genetic inheritance of resistance in cowpea crosses. Three susceptible (S) cowpea landraces that are commonly grown by farmers were crossed with five introduced resistant cowpea varieties in accordance with a North Carolina mating design II scheme. The F₁, F₂ and BC₁F₁ progenies generated were evaluated in the field together with their parents. They were then infected with two infection methods namely: by spreader-rows of S cultivar (Ebelat) and artificial inoculation of virus extracts. The results obtained showed that general combining ability (GCA) and specific combining ability (SCA) effects were significant, indicating that both additive and non-additive gene effects controlled virus infection. The results further demonstrated that the GCA effects (59.8?%) were more important than SCA effects (40.2?%) in determining virus resistance in the cowpea varieties. Utilisation of good general combiners of the varieties MU-93, IT82D-516-2, SECOW-2W and IT85F-2841 in hybridisation to improve virus resistance in cowpea crosses would be recommended. The result of this study provided an indication that CABMV resistance was conditioned by more than one recessive gene in eight populations, but also revealed resistance to be conditioned by a single recessive gene in the other seven populations. Observation of continuous distribution of progenies for severity data in the F₂ populations also confirmed significance of quantitative inheritance for CABMV resistance. Therefore, the significance of GCA effects suggests that recurrent selection could be applied to accumulate the additive genes for resistance in F₂ populations.     

Wheat streak mosaic virus resistance in eight wheat germplasm lines

Wheat streak mosaic virus (WSMV) is a destructive pathogen in wheat (Triticum aestivum L.). Host resistance is the most effective way to control this virus. To date, Wsm2 is the only wheat resistance gene that is genetically mapped. The objective of this study was to identify germplasm lines that might carry resistance genes different from Wsm2. Eight newly reported resistant germplasm lines were examined by allelic tests. To validate the allelic test results, five of them were further analysed for the inheritance of WSMV resistance. A Wsm2‐linked marker was also genotyped on populations developed for the inheritance study. Our results suggested that the WSMV resistance in lines CItr9358, PI225288, PI243652, PI245439, PI245526 and PI478095 was controlled by either Wsm2 or a gene very closely linked to Wsm2. The resistance in PI243753 and PI321730, however, is likely controlled by a gene different from, but linked to Wsm2. The resistance in PI321730 might also involve some minor genes. This study provided useful information for breeders to select appropriate resistant lines to improve WSMV resistance in wheat.     

Resistance of early-maturing European maize germplasm to sugarcane mosaic virus (SCMV) and maize dwarf mosaic virus (MDMV)

Sugarcane mosaic virus (SCMV) and maize dwarf mosaic virus (MDMV) are the most important viruses of maize in Europe. In field and greenhouse experiments, 122 early-maturing European maize inbreds (45 flint and 77 dent lines) were evaluated for their reaction to artificial inoculation by SCMV and MDMV. Three dent inbreds (D21, D32, FAP1360 A) with complete resistance and four dent inbreds (D06, D09, R2306, FAP1396A) with partial resistance against both potyviruses under both greenhouse and field conditions were identified. All other inbreds were highly susceptible to both SCMV and MDMV. Selection for virus resistance in maize breeding could be performed with only one virus at a time because all inbreds resistant to SCMV were also resistant to MDMV. Rank correlations between percentages of infected plants in greenhouse and field trials ranged from 0.51 to 0.72 for both SCMV and MDMV, suggesting that prescreening of breeding materials for virus resistance can be performed in the greenhouse but final evaluation in multilocation trials in the field is recommended.     

Cercosporiosis resistance in coffee germplasm collection

Cercosporiosis, or brown eye spot, is currently one of the main diseases of the coffee tree. It is caused by Cercospora coffeicola Berk. & Cooke. Nevertheless, genetic resistance to this disease has not yet been explored in any depth. Our objectives (a) were evaluate the response of 124 accessions from the germplasm collection of the Minas Gerais State (GC), Brazil, and eight commercial cultivars of C. arabica to cercosporiosis and (b) determine the best way to perform early progenies selections via controlled greenhouse experiments. Three controlled greenhouse experiments (1–3) were run in different seasons to determine the best way to proceed the selection. The seedlings were inoculated with a four isolates mixture obtained from different regions. The experimental data were analyzed individually (1–3), in a joint analysis, and as repetitions of a randomized complete block design. In each analysis we estimated genetic parameters and E-BLUP (empirical best linear unbiased predictor) genotypic values of the access. There was genetic variability to C. coffeicola resistance among the coffee tree accessions germplasm collection. Therefore, genetic improvements could be obtained by selection. Experimental repetitions in different seasons increase the selection efficiency and reliability of resistant genotypes with low cercosporiosis severity. The genotype Sarchimor MG 8840 showed the highest resistance level followed by Guatenano and the Timor Hybrid UFV 377-34, Timor Hybrid UFV 376-14 BE 5, and Wush–Wush × Timor Hybrid UFV 366-08.     

Evaluation of resistance to melon yellow spot virus in a cucumber germplasm collection

Melon yellow spot virus (MYSV), a member of the genus Tospovirus, is a serious thrips‐transmitted virus of cucurbits in Japan. Resistant cultivars provide an effective means for reducing the impact of the disease; however, no MYSV‐resistant cucumber has been reported. Susceptibilities of 398 cucumber accessions originating from 26 countries were evaluated by mechanical inoculation of MYSV. Thirteen accessions from South Asia, South East Asia and unknown origin had low disease severity indices (DSIs), and 10 of them showed no necrotic lesions on inoculated leaves. No or little positive reaction was detected by DAS‐ELISA analysis of inoculated leaves of these accessions. 27028930 showed resistance to a melon isolate (MYSV‐S) of MYSV, and ‘Yamakyuri‐1’ showed moderate resistance to a cucumber isolate (FuCu05P).     

Identification of new sources of resistance to Striga gesnerioides in cowpea germplasm

There have been reports of breakdown of striga resistance in previously resistant cowpea cultivars in Burkina Faso. This could be attributed to new striga races emerging or to an increase in the aggressiveness of current striga races. Therefore, cowpea genotypes were evaluated in fields infested with S. gesnerioides at three striga hot spots in Burkina Faso and in pots under artificial infestation with striga races SR 1, SR 5 and SR Kp to identify new, adapted and striga‐resistant sources. Cowpea genotypes showed differential reactions for striga resistance over sites and for striga races in pot experiments, indicating differences in the races involved, and SR Kp was reported as a new race. Resistant sources conferring site‐specific or multiple striga‐race resistance were identified. Genotypes 58‐57, Sanga 2, IT84S‐2049, IT98K‐205‐8, IT93K‐693‐2, KVx771‐10, KVx775‐33‐2, KVx61‐1, Gorom local, Mouride and Melakh conferred resistance to all three striga races. These genotypes are potential donor parents for breeding new, adapted and striga‐resistant genotypes. Cowpea landraces including Moussa local and Niaogo local with farmers' preferred traits were susceptible and need improvement for striga resistance.     

Characterization of resistance to powdery mildew (Erysiphe pisi) in a germplasm collection of Lathyrus sativus

Lathyrus sativus has a considerable potential for dry land‐farming systems but can be severely damaged by powdery mildew infection. Little is known about the availability of resistance against powdery mildew and the underlying mechanisms in the Lathyrus genus. A range of resistance reactions was identified in a collection of Iberian‐cultivated L. sativus germplasm. In most cases a compatible reaction to powdery mildew with no macroscopically visible necrosis was observed. Nevertheless, accessions with reduced disease severity despite being of a high infection type have been identified. The genes responsible for this partial resistance will be potentially useful for the development of durable resistant cultivars of Lathyrus spp., and may also be of value for the improvement of other related cultivated leguminous plants.     

Genetic analysis of gene‐specific resistance to mungbean yellow mosaic virus in mungbean (Vigna radiata)

Six intervarietal crosses involving two resistant and three susceptible genotypes of mungbean were attempted with the objectives to determine the mode of inheritance of gene‐specific Mungbean Yellow Mosaic Virus (MYMV) resistance. An infector row technique along with artificial inoculation was used for evaluating parents, F₁, F₂ and F₃ plants for MYMV resistance. Disease scoring for MYMV indicated that F₁s were highly susceptible as were the susceptible parents while resistant parent exhibited resistant reaction. The F₂ progeny segregated in the ratio of 9 S:3 MS:3 MR:1 R suggesting that the resistance was governed by digenic recessive genes (r_m1 and r_m2). When one gene (r_m1) was present in the homozygous recessive condition in different plants, it conferred moderately susceptible (MS) reaction, whereas when other gene (r_m2) was in homozygous condition, moderately resistant (MR) reaction was obvious. When both genes (r_m1 and r_m2) were present together in the homozygous recessive condition, resistant reaction (R) was observed. The F₂ segregation explained on the basis of phenotypic expression was further confirmed by F₃ segregation.     

A survey of Nicotiana germplasm for resistance to Tomato spotted wilt virus (TSWV)

The reaction to Tomato spotted wilt virus (TSWV) was evaluated in 94 accessions of Nicotiana, originating from the Institute of Soil Science and Plant Cultivation tobacco germplasm collection in Pu?awy, Poland. Tests for resistance were conducted under greenhouse conditions using single TSWV isolate collected from tobacco plantation in Lublin district, Poland. The presence of the virus was verified using DAS-ELISA. SCAR markers associated with TSWV resistance gene were applied. The members of the section Alatae, the genus Nicotiana: N. alata, N. forgetiana, and Nicotiana x sanderae as well as N. tabacum cultivars: ‘Polalta’ and ‘Wiktoria’ with the TSWV resistance gene introduced from N. alata, displayed the hypersensitive reaction (HR) against TSWV (grade 0 on symptom intensity scale). In some of those accessions, the virus spread from the initially infected areas eliciting systemic hypersensitive reaction (SHR). Five accessions of N. alata and three of Nicotiana x sanderae were composed of 6.3–50.0 % of plants in which SHR symptoms appeared. In all of N. forgetiana plants HR reaction was followed by systemic infection (SHR). In N. tabacum ‘Wiktoria’ 21.1 % of plants showed HR reaction, while the remaining were susceptible (S). All of the genotypes which responded with HR or SHR reaction to TSWV infection demonstrated the presence of SCAR markers linked to the resistance gene. The remaining eighty tested accessions were identified as being susceptible upon exposure to TSWV.     

Inheritance of resistance to the Moroccan watermelon mosaic virus in the cucumber line TMG-1 and cosegregation with zucchini yellow mosaic virus resistance

Inbred lines derived from the Chinese cucumber (Cucumis sativus L.) cultivar, ‘Taichung Mou Gua’ (TMG), have been shown to be resistant to several potyviruses including: zucchini yellow mosaic virus (ZYMV), zucchini yellow fleck virus (ZYFV), watermelon mosaic virus (WMV) and the watermelon strain of papaya ringspot virus (PRSV-W). Recently, an additional virus that infects cucurbits, the Moroccan watermelon mosaic virus (MWMV), has been determined to be a distinct member of the potyvirus group. This study demonstrates that TMG-1 possesses resistance to MWMV. Rub or aphid inoculated TMG-1 seedlings remain free of symptoms. Progeny analyses of the F₁, F₂ and backcross generations show that resistance to MWMV is conferred by a single recessive gene (proposed designation, mwm). Sequential inoculation of progeny possessing resistance to ZYMV followed by MWMV (or MWMV followed by ZYMV) and analysis of F₃ families derived from F₂ individuals selected for resistance to ZYMV indicate that both resistances are conferred by the same gene, or two tightly linked genes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inheritance and linkage analysis of resistance to zucchini yellow mosaic virus, watermelon mosaic virus, papaya ringspot virus and powdery mildew in melon

A melon (Cucumis melo L.) breeding line derived from PI 414723 is resistant to three potyviruses,watermelon mosaic virus (WMV), zucchini yellow mosaic virus (ZYMV), papaya ringspot virus (PRSV), and to powdery mildew (PM). The inheritance and linkage relationships of these four resistances were studied in a segregating F2 population and derived F3 families from a cross between cultivar Top Mark and the resistant breeding line. Dominant monogenic inheritance of all four resistances was observed. We report that line 414723-4S3, which was initially selected as a source of ZYMV and WMV resistance, is also a source of dominant monogenic resistances to PRSV and PM race 1. We also report on genetic linkage (significant departure from independent segregation, χ² = 58.1, p≪ 0.0001) between resistance to WMV and ZYMV. The map distance between these loci was estimated to be 7.5 cm. The genes for resistance to PM and PRSV segregated independently from each other, and from ZYMV and WMV resistance. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic analysis of Fusarium wilt resistance in cowpea (Vigna unguiculata Walp.)

This study investigated the inheritance of resistance to Fusarium oxysporum f.sp. tracheiphilum (Fot) in cowpea lines. Resistant and susceptible cowpea lines were crossed to develop F₁, F₂ and backcross populations. Reaction to Fot was evaluated in 2015 and 2016 using seed soak and modified root‐dip inoculation methods. The expression of resistance reaction in the F₁ and segregation in F₂ generations indicated the role of dominant gene controlling Fot in cowpea. These results were further supported by the result of backcross (BC₁P₁F₁ and BC₁P₂F₁) progeny tests. The backcross of F₁ with the resistant parent produced progeny that were uniformly resistant, whereas backcross of F₁ with the susceptible parent produced progeny that segregated into 1:1 ratio. The F₂ segregation ratio in the reciprocal cross showed no evidence of maternal effect in the inheritance of the resistance. Allelism test suggests that the gene for resistance in TVu 134 was the same in TVu 410 and TVu 109‐1. We also identified an SSR marker, C13‐16, that cosegregated with the gene conferring resistance to Fot in cowpea.     

Classification of a collection of sesame germplasm using multivariate analysis

Sesame (Sesamum indicum L.) is an important edible oil crop. Meteorological factors such as temperature, rainfall, and the amount of solar radiation determine the yield potential of sesame. To identify phenotypic diversity and to infer genotypic backgrounds in a collection of 250 sesame germplasm accessions, we classified the germplasm based on variation in morphological traits using principal component (PC) and cluster analysis. The sesame germplasm was grouped based on five PCs, which accounted for 82.3% of total variation. The first PC (PC1) was positively correlated with days to flowering, days to maturity, and number of capsules per plant, whereas the second PC (PC2) was negatively correlated with all characteristics except capsule-bearing stem length. The third component (PC3) was highly positively correlated with capsule length and plant height. We constructed a scatter diagram of the first two PCs (PC1 vs. PC2), revealing four distinct groups of eigenvectors. Most sesame germplasm was widely distributed among Groups I, II, III, and IV. Group III showed a wide range of distribution in the diagram. Otherwise, the distribution of the 250 germplasm accessions was more compact in a scatter diagram of PC1 vs. PC3 compared with PC1 vs. PC2. Groups I, II, III, and IV contained 142, 102, 2, and 3 sesame germplasm accessions, respectively. The two germplasm in Group III were collected from different regions, as were the three germplasm in Group IV. The results show that the distribution of sesame origin is wider than the regions examined in view of phenotypic diversity.     

Identification and characterization of resistance to rust (Uromyces ciceris-arietini (Grognot) Jacz. & Boyd) in a germplasm collection of Cicer spp.

A collection consisting of 140 accessions of chickpea (Cicer arietinum L.) and 109 accessions of related wild species (Cicer spp.) was screened for resistance to chickpea rust (Uromyces ciceris-arietini (Grognot) Jacz. & Boyd). Varying levels of partial resistance were identified, based on a reduced disease severity and area under disease progress curve without any macroscopically visible host cell necrosis. Higher levels of resistance were observed in wild Cicer species, but neither associated with hypersensitivity. Components of resistance have been macros- and microscopically studied in selected C. arietinum accessions. Resistance was expressed as longer latent period and lower infection frequency, which were associated with increased percentage of early aborted colonies, reduced number of haustorial mother cells and haustoria per colony, and reduced colony size.     

甘蓝抗芜菁花叶病毒育种研究进展

摘要：本文简述了甘蓝TuMV抗性种质资源的现状和各种分子生物技术应用发展的前景,从TuMV的发生、甘蓝抗TuMV种质资源的挖掘,甘蓝对TuMV的抗性规律,植-病互作分子机制,甘蓝抗TuMV分子标记的开发与应用和基因工程技术在甘蓝抗TuMV育种中的应用等方面综述了近年来的研究进展,为今后甘蓝抗性育种提供参考和借鉴。     

Evaluation and verification of resistance to Meloidogyne hapla Chitwood in a Cannabis germplasm collection

A collection of Cannabis accessions was evaluated for resistance to the root-knot nematode Meloidogyne hapla Chitwood in a seedling test. After inoculation with a larval suspension, significant variation was found for the number of galls and egg masses on the seedling roots. These parameters were considered as estimates for nematode infection and larval multiplication, respectively. A subset of the tested accessions was grown on a naturally infested arable field to study the relation between the test results and host characteristics in the field. The ranking order of accessions for the number of galls in the seedling test agreed well with that for the number of root galls on juvenile plants in the field. Therefore the test provides a useful indication for nematode infection. The number of egg masses in the seedling test and the population density of Meloidogyne measured in post-treatment soil samples of the field trial, showed a comparable ranking of accessions. Differences between accessions in the field were however smaller and not statistically significant.     

A new resistance gene to PepYMV (Pepper yellow mosaic virus) in Capsicum annuum L.

Pvr4 locus, commonly associated with a co-dominant CAPS marker, confers monogenic dominant resistance to potyvirus complex in Capsicum spp. Aiming to investigate whether the resistance found in resistant genotypes not bearing Pvr4 marker is due to allelism in the Pvr4 locus, or due to a new locus of the pvr series, segregation analyses of an F₂ population obtained from a cross between two pepper lines “Myr-29-10” (P₁) (resistant to PepYMV, showing a single band of 444 bp, Pvr4/Pvr4) and “PIM-025” (P₂) (resistant to PepYMV, showing a single band of 458 bp, Pvr4⁺/Pvr4⁺) were performed. According to the results, there is strong evidence that the locus controlling PepYMV resistance in PIM-025 (P₂) is not Pvr4. These results provide evidence that those resistant genotypes, bearing a susceptible band pattern in the Pvr4 locus (458 bp, Pvr4⁺/Pvr4⁺), carry a different gene from those described in the literature up to the present time.