Inheritance of resistance to angular leaf spot in common bean and validation of the utility of resistance linked markers for marker assisted selection out side the mapping population

Inheritance of resistance to angular leaf spot (ALS) disease caused by Phaeoisariopsis griseola (Sacc.) Ferr was investigated in two common bean cultivars, Mexico 54 and BAT 332. Both Andean and Mesoamerican backgrounds were used to determine the stability of the resistance gene in each of the two cultivars. Resistance to P. griseola was phenotypically evaluated by artificial inoculation with one of the most widely distributed pathotypes, 63–39. Evaluation of the parental genotypes, F₁, F₂ and backcross populations revealed that the resistance to angular leaf spot in the cultivars Mexico 54 and BAT 332 to pathotype 63–39 is controlled by a single dominant gene, when both the Andean and Mesoamerican backgrounds were used. Allelism test showed that ALS resistance in Mexico 54 and BAT 332 to pathotype 63–39 was conditioned by the same resistance locus. Resistant and susceptible segregating populations generated using Mexico 54 resistant parent were selected for DNA extraction and amplification to check for the presence /absence of the SCAR OPN02 and RAPD OPE04 markers linked to the Phg-2 resistance gene. The results indicated that the SCAR OPN02 was not polymorphic in the study populations and therefore of limited application in selecting resistant genotypes in such populations. On the other hand, the RAPD OPE04 marker was observed in all resistant individuals and was absent in those scored susceptible based on virulence data. Use of the RAPD OPE04 marker in marker-assisted selection is underway.     

Molecular marker-assisted selection for development of common bean lines resistant to angular leaf spot

The objective of this work was to develop homozygous common bean lines carrying angular leaf spot resistance genes derived from the cultivars ‘Mexico 54’, ‘MAR 2’ and ‘BAT 332’ through marker‐assisted selection. Molecular markers SCAR OPN02₈₉₀, RAPD OPE04₅₀₀ and OPAO12₉₅₀ linked to the resistance genes of ‘Mexico 54’, ‘MAR 2’ and ‘BAT 332’, respectively, were used in segregating backcross‐derived populations to selection. DNA fingerprinting was used to select homozygous BC₂F₃ and BC₁F₃ resistant plants genetically closer to the recurrent parent. Two homozygous BC₂F_2:3 and two and five BC₁F_2:3 families derived from ‘Ruda’ vs. ‘Mexico 54’ (RM), ‘MAR 2’ (RMA) and ‘BAT 332’ (RB) crosses were selected, respectively. After only one (RMA, RB) or two backcrosses (RM), five and eight BC₁F₃ lines derived from RMA and RB, respectively, and seven BC₂F₃ lines derived from RM, with 14.9–16.6, 16.9–18.6 and 9.3–11.1% of relative genetic distances to the recurrent parent were selected. This is the first report of lines resistant to angular leaf spot carrying genes of the cultivars ‘Mexico 54’, ‘MAR 2’ and ‘BAT 332’ developed with the aid of molecular markers.     

DNA marker-assisted selection to pyramid rust resistance genes in “carioca” seeded common bean lines

This work reports a gene pyramiding approach assisted by DNA markers used to develop “carioca” seeded common bean (Phaseolus vulgaris L.) elite lines harboring three different rust resistance genes. Rust is among the most destructive diseases that attack P. vulgaris and cause serious damage worldwide. The rust resistance genes Ur-5 (from ‘Mexico 309’), Ur-11 (from ‘BelMiDak RR-3’), and Ur-14 (from ‘BRS Pioneiro’, a “carioca” seeded cultivar derived from the resistance source ‘Ouro Negro’) were combined in the “carioca” seeded bean cultivar ‘Rudá’. Firstly, two different backcross programs were conducted separately to produce progenies harboring individually the Ur-5 and Ur-11 genes. Molecular fingerprinting analysis was used to select plants genetically similar to ‘Rudá’ in the backcross cycles to accelerate the recurrent-background recovery. The obtained progenies were initially intercrossed and then crossed with ‘BRSMG Pioneiro’ (Ur-14). The final F₁ plants derived from these crosses were screened with DNA markers linked to the three rust resistance genes: SI19 (Ur-5), SAE19 (Ur-11) and OPX11 (Ur-14). The plants selected as harboring all the alleles of interest were used to obtain the next generations. The selection based on DNA markers was conducted up to the F_4:5 generation. We were able to select F_4:7 progenies showing all the DNA markers associated to the genes of interest and resistant to all specific races of U. appendiculatus used for phenotypically detecting each one of the rust resistance genes. Yield evaluations show that these selected lines are as productive as the recurrent parent ‘Rudá’ and high-performing control cultivars grown in Brazil.     

Development and characterization of common black bean lines resistant to anthracnose,rust and angular leaf spot in Brazil

Anthracnose, rust and angular leaf spot caused by Colletotrichum lindemuthianum, Uromyces appendiculatus and Pseudocercospora griseola, respectively, are economically important diseases affecting the common bean production in Brazil. The BIOAGRO/UFV bean breeding program developed Rudá-R, a dry bean line with ‘carioca’ seed type, containing the following disease resistance genes: Co-4, Co-6 and Co-10 (anthracnose); Ur-ON (rust) and Phg-1 (angular leaf spot). To transfer this combination of disease resistance genes present in Rudá-R to a black-seeded bean, a backcrossing program aided by molecular markers was conducted, involving Rudá-R (donor genitor) and Diamante Negro (recurrent genitor). Forty black-seeded BC₃F_3:6 lines were obtained with combinations of at least three markers linked to the indicated disease resistance genes. The lines were evaluated for resistance to the three mentioned pathogens. Eight of the lines were homozygous and resistant to all four evaluated races of C. lindemuthianum, but susceptible to race 2047. Four of the lines were homozygous and resistant to two races of U. appendiculatus. Twenty of the lines were homozygous and resistant to the two races of P. griseola tested. Grain yield of the BC₃F_3:6 lines was evaluated during the ‘winter’ season of 2006 and the ‘dry’ season of 2007. All lines had statistically equal or higher yields than Rudá-R and Diamante Negro. Lines were identified that not only were high yielding but also resistant to the three pathogens tested. These lines are potential genotypes for further testing and for release as new black common bean varieties.     

Genetics of angular leaf spot resistance in the Andean common bean accession G5686 and identification of markers linked to the resistance genes

Angular leaf spot (ALS), caused by the fungus Phaeoisariopsis griseola is an economically important and widely distributed disease of common bean. Due to the co-evolution of P. griseola with the large and small seeded bean gene pools, stacking Andean and Mesoamerican resistance genes is a strategy most likely to provide lasting resistance to ALS disease. This strategy requires identification and characterization of effective Andean and Mesoamerican resistance genes, and the development of molecular markers linked to these genes. This study was conducted to elucidate the genetics of ALS resistance in the Andean accession G5686 using an F₂ population derived from a G5686 × Sprite cross. Segregation analysis revealed that three dominant and complementary genes conditioned resistance of G5686 to P. griseola pathotype 31-0. Three microsatellite markers, Pv-ag004, Pv-at007 and Pv-ctt001 segregated in coupling phase with the resistance genes in G5686. Microsatellites Pv-ag004 and Pv-ctt001, located on opposite ends of linkage group B04 segregated with resistance genes Phg _G5686A , Phg _G5686B at 0.0 and 17.1 cM, respectively, while marker Pv-at007, localized on linkage group B09 segregated with resistance gene Phg _G5686C at 12.1 cM. Parental surveys showed that these markers were polymorphic in Andean and Mesoamerican backgrounds. The usefulness of G5686 ALS resistance genes in managing the ALS disease, and the potential utility of identified molecular markers for marker assisted breeding are discussed.     

Genetic mapping of quantitative resistance to race 5 of Pseudomonas syringae pv. phaseolicola in common bean

Halo-blight is an important worldwide bacterial disease of common bean (Phaseolus vulgaris L.) caused by Pseudomonas syringae pv. phaseolicola. Nine races of the pathogen and five race-specific resistance genes have been previously described. However, a quantitative response to this pathogen has also been described. The objective of this study was to identify halo-blight resistance loci linked to molecular markers that could be used in resistance breeding. Chromosomal regions related to race 5 halo-blight resistance were localized on a genetic map of RAPD and AFLP molecular markers and constructed by the analysis of a “Jules” × “Canela” F₂ progeny. “Jules” shows quantitative resistance to halo-blight and “Canela” is a very appreciated but susceptible Spanish bean landrace. Two QTL for resistance to halo-blight were mapped in two linkage groups. There were four large groups, with 14–22 molecular markers each, five with 4–8 markers each, and three with 2 or 3 markers each.     

An allelic series at the Co-1 locus conditioning resistance to anthracnose in common bean of Andean origin

In this study, we characterized the genetic resistance of the Andean bean cultivars Kaboon and Perry Marrow and their relation to other sources of anthracnose resistance in common bean. Based on the segregation ratio (3R:1S) observed in two F₂ populations we demonstrated that Kaboon carries one major dominant gene conferring resistance to races 7 and 73 of Colletotrichum lindemuthianum. This gene in Kaboon is independent from the Co-2 gene and is an allele of the Co-1 gene present in Michigan Dark Red Kidney (MDRK) cultivar. Therefore, we propose the symbol CO-1 ² for the major dominant gene in Kaboon. The Co-1 is the only gene of Andean origin among the Co anthracnose resistance genes characterized in common bean. When inoculated with the less virulent Andean race 5, the segregation ratio in the F₂ progeny of Cardinal and Kaboon was 57R:7S (p = 0.38). These data indicate that Kaboon must possess other weaker dominant resistance genes with a complementary mode of action, since Cardinal is not known to possess genes for anthracnose resistance. Perry Marrow, a second Andean cultivar with resistance to a different group of races, was shown to possess another resistant allele at the Co-1 locus and the gene symbol Co-1 ³ was assigned. In R × R crosses between Perry Marrow and MDRK or Kaboon, no susceptible F₂ plants were found when inoculated with race 73. These findings support the presence of a multiple allelic series at the Andean Co-1 locus, and have major implications in breeding for durable anthracnose resistance in common bean. This revised version was published online in July 2006 with corrections to the Cover Date.     

RAPD and SCAR markers for resistance to acochyta blight in lentil

Resistance to ascochyta blight of lentil (Lens culinaris Medikus),caused by the fungus Ascochyta lentis, is determined by a single recessive gene, ral ₂, in the lentil cultivar Indian head. Sixty F₂ individuals from a cross between Eston (susceptible) and Indian head (resistant) lentil were analyzed for the presence of random amplified polymorphic DNA (RAPD) markers linked to the ral ₂gene, using bulked segregant analysis (BSA). Out of 800 decanucleotide primers screened, two produced polymorphic markers that co-segregated with the resistance locus. These two RAPD markers, UBC227₁₂₉₀and OPD-10₈₇₀, flanked and were linked in repulsion phase to the gene ral ₂ at 12 cm and 16 cm, respectively. The RAPD fragments were converted to SCAR markers. The SCAR marker developed from UBC227₁₂₉₀ could not detect any polymorphism between the two parents or in the F₂. The SCAR marker developed from OPD-10₈₇₀ retained its polymorphism. The polymorphic RAPD marker UBC227₁₂₉₀ and the SCAR marker developed from OPD-10₈₇₀ can be used together in a marker assisted selection program for ascochyta blight resistance in lentil. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular markers linked to genes for specific rust resistance and indeterminate growth habit in common bean

Bulked segregant analysis was utilized to identify random amplified polymorphic DNA (RAPD) markers linked to genes for specific resistance to a rust pathotype and indeterminate growth habit in an F2 population from the common bean cross PC-50 (resistant to rust and determinate growth habit) × Chichara 83-109 (susceptible to rust and indeterminate growth habit). Six RAPD markers were mapped in a coupling phase linkage with the gene ( Ur-9) for specific rust resistance. The linkage group spanned a distance of 41 cM. A RAPD marker OA4.1050 was the most closely linked to the Ur-9 gene at a distance of 8.6 cM. Twenty-eight RAPD markers were mapped in a coupling phase linkage with the gene ( Fin) for indeterminate growth habit. The linkage group spanned a distance of 77 cM. RAPD markers OQ3.450 and OA17.600 were linked to the Fin allele as flanking markers at a distance of 1.2 cM and 3.8 cM, respectively. The RAPD markers linked to the gene for specific rust resistance of Andean origin detected here, along with other independent rust resistance genes from other germplasm, could be utilized to pyramid the different genes into a bean cultivar for durable rust resistance.     

Inheritance of anthracnose resistance in the common bean cultivar Widusa

Snap bean (Phaseolus vulgaris L.) cultivar, Widusa, was crossed to Michigan Dark Red Kidney (MDRK), Michelite, BAT 93, Mexico 222, Cornell 49–242, and TO cultivars to study the inheritance of resistance to anthracnose in Widusa. The segregation patterns observed in six F₂ populations supported an expected 3R:1S ratio suggesting that Widusa carries a single dominant gene conditioning resistance to races 7, 65, 73, and 453 of Colletotrichum lindemuthianum, the causal organism of bean anthracnose. Allelism tests conducted with F₂ populations derived from crosses between Widusa and Cornell 49–242 (Co-2), Mexico 222 (Co-3), TO (Co-4), TU (Co-5), AB 136 (Co-6), BAT 93 (Co-9), and Ouro Negro (Co-10), inoculated with races 7, 9, 65 and 73, showed a segregation ratio of 15R:1S. These results suggest that the anthracnose resistance gene in Widusa is independent from the Co-2, Co-3, Co-4,Co-5, Co-6, Co-9, and Co-10 genes. A lack of segregation was observed among 200 F₂ individuals from the cross Widusa/MDRK, and among 138 F₂ individuals from the cross Widusa/Kaboon inoculated with race 65, suggesting that Widusa carries an allele at the Co-1 locus. We propose that the anthracnose resistance allele in Widusa be named Co-1 ⁵ as Widusa exhibits a unique reaction to race 89 compared to other alleles at the Co-1 locus. RAPD marker A18₁₅₀₀ co-segregated in repulsion-phase linkage with the Co-1 ⁵ gene at a distance of 1.2 cM and will provide bean breeders with a ready tool to enhance the use of the Co-1 ⁵ gene in future bean cultivars.     

Characterization of resistance to angular leaf spot of common bean (Phaseolus vulgaris L.) breeding line SPS50HB

The common bean (Phaseolus vulgaris L.) makes an important contribution to the human diet, particularly in Africa and Latin America. Because angular leaf spot (ALS), caused by the fungal pathogen Pseudocercospora griseola, is one of the most severe foliar diseases of the bean plant, an important priority is to identify genes encoding resistance. The present study focused on the resistance shown by the Mesoamerican common bean breeding line SPS50HB. From the pattern of segregation for resistance displayed in an F₂ population bred from a cross between SPS50HB and the ALS-susceptible Ethiopian variety Red Wolaita, it was concluded that the resistance of SPS50HB is controlled by two unlinked dominant genes. An allelism test indicated that one of these genes was either identical with, allelic to, or closely linked to the major gene Phg-2 carried by variety Mexico 54. The sequence-characterized amplified region assays OPEO4 and PF13, which are diagnostic for an ALS resistance gene carried by the germplasm accession G10909, both tracked a possible second gene present in SPS50HB.     

Development of RAPD markers associated with common bunt resistance to race T1 (Tilletia tritici) in spelt wheat

Common bunt caused by Tilletia tritici and T. laevis has occurred worldwide and reduces yield and quality in common and durum wheats. The development of DNA markers linked to bunt resistance to race T1 in the cross, ‘Laura’(S) בRL5407’ (R), was carried out in this study based on the single head derived F_4:5 and single seed derived F_4:6 populations. Bulked segregant analysis was used to identify two random amplified polymorphic DNA (RAPD) markers linked to the gene for resistance to race T1 in the spelt wheat ‘RL5407′. The two markers identified, UBC548₅₉₀ and UBC274₉₈₈, flanked the resistance gene with a map distance of 9.1 and 18.2 cM, respectively. The former was linked in repulsion phase to bunt resistance while the later was in coupling phase. The two RAPD markers and the common bunt‐resistance gene all segregated in Mendelian fashion. Use of these two RAPD markers together could assist in incorporating the bunt‐resistance gene from spelt wheat into common wheat cultivars by means of marker‐assisted selection.     

Stability of the association of molecular markers with common bacterial blight resistance in common bean (Phascolus vulgaris L.)

Common bacterial blight (CBB) caused hy Xanthomonas campestrts pv. phaseoli is an important disease of common bean (Phaseolus vulgaris L.) throughout the world. Two random amplified polymorphic DNA (RAPD) markers (R7313 and R4865) linked to genes for CBB resistance, that were transferred to P- vulgaris by an interspecific cross with Phaseohus acutifoluis. Were identified in a previous study. The current study was conducted to examine the use of these markers for selecting CBB resistant material from 85 F_5,6, lines derived from crosses between two of the resistant lines used previously in the linkage study and susceptible breeding lines. The results showed that these two markers were located on the same linkage group and explained 22% (P = 0.0002) of the variation in response to CBB in the current population. Seventy per cent of the lines that had both markers were classified as resistant in a disease test of the F_5,6, lines, whereas 73% of the lines that had neither of the RAPD markers were susceptible. The results indicated that the marker-disease resistance associations remained stable in a plant breeding programme and that they can be used lor marker-assisted selection of CBB-resistant beans.     

Introgressing resistance to bacterial and viral diseases from the middle American to Andean common bean

The genetic base of cultivars within market classes of common bean (Phaseolus vulgaris L.) is narrow. Moreover, small- and medium-seeded Middle American cultivars often possess higher yield and resistance to abiotic and biotic stresses than their large-seeded Andean counterparts. Thus, for broadening the genetic base and breeding for higher yielding multiple stress resistant Andean cultivars use of inter-gene pool populations is essential. Our objective was to determine the feasibility of introgressing resistance to Been common mosaic virus (BCMV, a potyvirus), and the common [caused by Xanthomonas campestris pv. phaseoli (Xcp) and X. campestris pv. phaseoli var. fuscans (Xcpf)] and halo [caused by Pseudomonas syringae pv. phaseolicola (Psp)] bacterial blights from the Middle American to Andean bean, using gamete selection. Also, we investigated the relative importance of the use of a landrace cultivar versus elite breeding line as the last parent making maximum genetic contribution in multiple-parent inter-gene pool crosses for breeding for resistance to diseases. Two multiple-parent crosses, namely ZARA I = Wilkinson 2 /// ‘ICA Tundama’ / ‘Edmund’ // VAX 3 / PVA 773 and ZARA II = ‘Moradillo’ /// ICA Tundama / Edmund // VAX 3 / PVA 773 were made. From the F₁ to F₅ single plant selection was practiced for resistance to the common and halo bacterial blights in both populations at Valladolid, Spain. The parents and F₅-derived F₆ breeding lines were evaluated separately for BCMV, and common and halo bacterial blights in the greenhouse at Filer and Kimberly, Idaho in 2001. They were also evaluated for the two bacterial blights, growth habit, seed color and 100-seed weight at Valladolid in 2002. All 20 F₁ plants of ZARA I were resistant or intermediate to common and halo bacterial blights in the greenhouse, but their F₂ and subsequent families segregated for both bacterial blights. Segregation for resistant, intermediate, and susceptible plants for common bacterial blight occurred in the F₁ of ZARA II. Simple correlation coefficient for common bacterial blight between the F₁ and F₁-derived F₂ families was positive (r = 0.54 P < 0.05) for ZARA II. From the F₂ to F₅ the number of families resistant to both bacterial blights decreased in both populations. Only four of 20 F₁ plants in ZARA I resulted in seven F₆ breeding lines, and only one of 32 F₁ plants in ZARA II resulted in one F₆ breeding line resistant to the three diseases. None of the selected breeding lines had seed size as large as the largest Andean parent. The use of elite breeding line or cultivar as the last parent making maximum genetic contribution to the multiple-parent inter-gene pool crosses, relatively large population size in the F₁, and simultaneous selection for plant type, seed traits as well as resistance to diseases would be crucial for introgression and pyramiding of favorable alleles and quantitative trait loci (QTL) of interest between the Andean and Middle American beans.     

RAPD markers linked to resistance to downy mildew disease in soybean

To determine and utilize RAPD markers linked to resistance to downymildew incited by Peronospora manshurica in soybean, a resistantcultivar `AGS129' was crossed to a susceptible cultivar `Nakhon Sawan 1'(NS1). F₂ and BC₁ populations were advanced from the F₁ and evaluatedfor resistance to the disease. ²-test demonstrated that the resistancewas controlled by a single dominant gene (Rpmx). Near-isogenic lines(NILs) and bulked segregant analysis (BSA) were used to identify RAPDmarkers linked to the gene. Six DNA bulks namely F₅(R), F₅(S),BC₆F₃(R), BC₆F₃(S), F₂(R) and F₂(S) were set up by pooling equalamount of DNA from 8 randomly selected plants of each disease responsetype. A total of 180 random sequence decamer oligonucleotide primerswere used for RAPD analysis. Primer OPH-02 (5 TCGGACGTGA 3 andOPP-10 (5 TCCCGCCTAC 3) generated OPH-02₁₂₅₀ and OPP-10₈₃₁fragments in donor parent and resistant bulks, but not in the recurrentparent and susceptible ones. Co-segregation analysis using 102 segregatingF₂ progenies confirmed that both markers were linked to the Rpmxgene controlling downy mildew disease resistance with a genetic distance of4.9 cm and 23.1 cm, respectively. Marker OPH-02₁₂₅₀ was presentin 13 of 16 resistant soybean cultivars and absent in susceptible cultivars,thus confirming a potential for MAS outside the mapping population.     

Molecular mapping of black rot resistance locus Xca1bo on chromosome 3 in Indian cauliflower (Brassica oleracea var. botrytis L.)

Black rot is the most devastating disease of cauliflower worldwide causing severe damage to crop. The identification of markers linked to loci that control resistance can facilitate selection of plants for breeding programmes. In the present investigation, F₂ population derived from a cross between ‘Pusa Himjyoti’, a susceptible genotype, and ‘BR‐161’, a resistant genotype, was phenotyped by artificial inoculation using Xcc race 1. Segregation analysis of F₂ progeny indicated that a single dominant locus governed resistance to Xcc race 1 in ‘BR‐161’. Bulk segregant analysis in resistant and susceptible bulks of F₂ progeny revealed seven differentiating polymorphic markers (three RAPD, two ISSR and two SSR) of 102 markers screened. Subsequently, these markers were used to genotype the entire F₂ population, and a genetic linkage map covering 74.7 cM distance was developed. The major locus Xca1bo was mapped in 1.6‐cM interval flanked by the markers RAPD 04₈₃₃ and ISSR 11₆₃₅. The Xca1bo locus was located on chromosome 3. The linked markers will be useful for marker‐assisted resistance breeding in cauliflower.     

Molecular mapping of a new gene for resistance to frogeye leaf spot of soya bean in 'Peking'

Amplified fragment length polymorphism (AFLP) and microsatellite (simple sequence repeat, SSR) techniques were used to map the _RGSp_eking gene, which is resistant to most isolates of Cercospora sojina in the soya bean cultivar ‘Peking’. The mapping was conducted using a defined F₂ population derived from the cross of ‘Peking’(resistant) בLee’(susceptible). Of 64 EcoRI and MseI primer combinations, 30 produced polymorphisms between the two parents. The F₂ population, consisting of 116 individuals, was screened with the 30 AFLP primer pairs and three mapped SSR markers to detect markers possibly linked to Rcs_Peking. One AFLP marker amplified by primer pair E‐AAC/M‐CTA and one SSR marker Satt244 were identified to be linked to Res_Peking. The gene was located within a 2.1‐cM interval between markers AACCTA178 and Satt244, 1.1 cM from Satt244 and 1.0 cM from AACCTA178. Since the SSR markers Satt244 and Satt431 have been mapped to molecular linkage group (LG) J of soya bean, the Res_Peking resistance gene was putatively located on the LG J. This will provide soya bean breeders an opportunity to use these markers for marker‐assisted selection for frogeye leaf spot resistance in soya bean.     

Identification of RAPD and SCAR markers linked to northern leaf blight resistance in waxy corn (Zea mays var. ceratina)

Exserohilum turcicum causes northern corn leaf blight (NCLB), an important disease occurring in maize producing areas throughout the world. Currently, the development of cultivars resistant to E. turcicum seems to be the most efficient method to control NCLB damage. Marker-assisted selection (MAS) enables breeders to improve selection efficiency. The objective of this work was to identify random amplified polymorphic DNA (RAPD) and sequence characterized amplified region (SCAR) markers associated with NCLB resistance. Bulked segregant analysis (BSA) was used to search for RAPD markers linked to NCLB resistance genes, using F₂ segregating population obtained by crossing a susceptible inbred ‘209W’ line with a resistant inbred ‘241W’ line. Two hundred and twenty-two decamer primers were screened to identify four RAPD markers: OPA07₅₂₁, OPA16₄₅₇, OPB09₅₂₀, and OPE20₅₃₆ linked to NCLB resistance phenotype. These markers were converted into dominant SCAR markers: SCA07₄₉₆, SCA16₄₂₀, SCB09₄₆₄, and SCE20₄₂₉, respectively. The RAPD and SCAR markers were developed successfully to identify NCLB resistant genotypes in segregating progenies carrying NCLB resistant traits. Thus, the markers identified in this study should be applicable for MAS for the NCLB resistance in waxy corn breeding programs.     

Inheritance of resistance to four cucurbit viruses in Cucurbita moschata

Cucurbita moschata cv. Nigerian Local has been used as a source of resistance to Zucchini yellow mosaic virus (ZYMV), Watermelon mosaic virus (WMV), Papaya ringspot virus W (PRSV-W) and Cucumber mosaic virus (CMV) in breeding both Cucurbita moschata and Cucurbita pepo. We used the F₁, F₂ and BC₁ generations derived from the cross C.-moschata cv. Waltham Butternut × Nigerian Local to study the inheritance of resistance to each of the viruses. We confirmed monogenic dominant resistance to ZYMV previously attributed to Zym, and we report monogenic dominant resistance to WMV and CMV which we propose to designate Wmv and Cmv, respectively. A single recessive gene, which we propose to designate prv, controls resistance to PRSV. DNA samples were extracted from a Waltham Butternut BC₁ F₁ population screened with ZYMV and analyzed using randomly amplified polymorphic DNA markers. No RAPD markers linked to ZYMV resistance were found. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inheritance and linkage of a gene for resistance to race 4 of fusarium wilt and RAPD markers in chickpea

Several races of Fusarium oxysporum Schlechtend.:Fr f. sp. ciceris (Padwick) Matuo and K. Sato cause economic losses from wilting disease of chickpea ( Cicer arietinum L.). While the genetics of resistance to race 1 have been reported, little is known of the genetics of resistance to race 4. We undertook a study to determine the inheritance of resistance and identified random amplified polymorphic DNA markers (RAPDs) linked to the gene for resistance. For the investigation, we used 100 F₅ derived F₇ recombinant inbred lines (RILs) that had been developed from the cross of breeding lines C-104 x WR-315. Results indicated that resistance is controlled by a single recessive gene. The RAPD markers previously shown to amplify fragments linked to race 1 resistance also amplified fragments associated with race 4 resistance. The RAPD loci, CS-27₇₀₀, UBC-170₅₅₀ and the gene for resistance to race 4 segregated in 1:1 ratios expected for single genes. Both RAPD markers were located 9 map units from the race 4 resistance locus and were on the same side of the resistance gene. Our results indicated that the genes for resistance to race 1 and 4 are 5 map units apart. The need to determine the genomic locations of race specific resistance genes and the possibility that these genes are clustered to the same genomic region should be investigated. This revised version was published online in July 2006 with corrections to the Cover Date.