Self-(in)compatibility inheritance and allele-specific marker development in yellow mustard (Sinapis alba)

Yellow mustard (Sinapis alba) has a sporophytic self-incompatibility reproduction system. Genetically stable self-incompatible (SI) and self-compatible (SC) inbred lines have recently been developed in this crop. Understanding the S haplotype of different inbred lines and the inheritance of the self-(in)compatibility (SI/SC) trait is very important for breeding purposes. In this study, we used the S-locus gene-specific primers in Brassica rapa and Brassica oleracea to clone yellow mustard S-locus genes of SI lines Y514 and Y1130 and SC lines Y1499 and Y1501. The PCR amplification results and DNA sequences of the S-locus genes revealed that Y514 carried the class I S haplotype, while Y1130, Y1499, and Y1501 had the class II S haplotype. The results of our genetic studies indicated that self-incompatibility was dominant over self-compatibility and controlled by a one-gene locus in the two crosses of Y514 × Y1499 and Y1130 × Y1501. Of the five S-locus gene polymorphic primer pairs, Sal-SLGI and Sal-SRKI each generated one dominant marker for the SI phenotype of Y514; Sal-SLGII and Sal-SRKII produced dominant marker(s) for the SC phenotype of Y1501 and Y1499; Sal-SP11II generated one dominant marker for Y1130. These markers co-segregated with the SI/SC phenotype in the F₂ populations of the two crosses. In addition, co-dominant markers were developed by mixing the two polymorphic primer pairs specific for each parent in the multiplex PCR, which allowed zygosity to be determined in the F₂ populations. The SI/SC allele-specific markers have proven to be very useful for the selection of the desirable SC genotypes in our yellow mustard breeding program.     

A simple method to estimate the percentage of hybridity in canola (Brassica napus) F1 hybrids

We have developed an efficient PCR-based system that uses RAPD markers for the certification of F₁ hybrids of canola. These markers were selected by screening five parental lines used in three crosses X, Y and Z with 131, 131 and 322 primers respectively. Stable DNA fragments that were homozygous and specific to the male inbreds were used to certify F₁ hybrid populations. The hybrid production system was based on self-incompatibility (SI) alleles that prevent self-pollination of the female parent. The efficiency of two S-alleles was compared under both field and greenhouse conditions. The percentage of hybridity was estimated in different F₁ populations. We found a significant difference between the two alleles for their efficiency in controlling selfing; both alleles were stable under greenhouse conditions, one allele appeared less reliable under field conditions.     

Genetic mapping and QTL analysis for yield and agronomic traits with an F2:3 population derived from a waxy corn × sweet corn cross

We constructed a framework map using SSR markers in the F₂ population derived from a cross between a waxy corn inbred line and a sweet corn inbred line. We constructed a genetic linkage map of the F_2:3 population employing 295 SSR markers on 158 F₂ individuals produced from the cross. The map comprised a total genomic length of 2,626.5 cM in 10 linkage groups and an average distance between markers of 8.9 cM. The number of loci per linkage group ranged from 27 (chr. 5) to 34 (chr. 7). The genetic distance per linkage group ranged from 213.6 cM (chr. 10) to 360.6 cM (chr. 2). Χ ² tests revealed that 254 markers (86.1 %) distributed over all 10 chromosomes exhibited a Mendelian segregation ratio of 1:2:1. A total of 14 quantitative trait loci (QTLs) for days to silking (DTS), plant height (PH), ear height (EH), ear height ratio (ER), ear length (L-ear), and setted ear length (L-sear) were found in the 158 F₂ progeny. They were mapped to chromosomes 1, 2, 3, 7, 8, and 10. Among them, one QTL was associated with DTS, three with PH, six with EH, one with ER, two with L-ear, and one QTL was related to L-sear. In our study, we found that four QTLs: qDTS1, qEH1a, qEH1b, and qPH1, were clustered between umc2390 and umc1603 on chromosome 1. These new QTLs identified by the present study could serve as useful molecular markers in selecting for yield and agronomic traits in maize. The results of this study may improve the identification and characterization of genes responsible for yield and agronomic traits in waxy corn and sweet corn.     

Developmental and environmental factors affecting level of self-incompatibility response in <Emphasis Type="Italic">Brassica rapa</Emphasis> L.

We performed artificial self-pollination throughout the period of sexual reproduction in six inbred lines of Brassica rapa, a plant with sporophytic self-incompatibility (SI). The level of SI changed between each pollination date in all lines, suggesting the effects of both internal and external factors. To further investigate the potential factors affecting the changes in the level of SI, multiple regression was performed, with plant line, seeding date, and temperature and humidity on the day of pollination (external factors) and plant age (internal factor) as explanatory variables. The factors affecting the change in the level of SI differed between the lines, and temperature and plant age had especially large effects. The level of SI was reduced by maximum temperatures >24°C on the pollination day, but this effect was no longer significant at maximum temperatures >28°C. High temperatures before flowering also influenced the reduction of SI. The level of SI was particularly reduced at plant age 0.75 (i.e., the last quarter of the flowering period), and a significant positive interaction between average temperature and plant age was found. This is the first study to quantify the change in the level of SI in plants across the entire period of sexual reproduction and to analyze the relationship between the change in rate of seed set and various external and internal factors.     

Dominance Relationship between Two Self-Incompatible<Emphasis Type="Italic">Brassica campestris</Emphasis> Haplotypes in Response to CO<Subscript>2</Subscript> Gas

InBrassica, self-incompatibility (SI) can be overcome by CO₂ application, an effective method for obtaining numerous inbred lines for F, commercial seed. We previously reported two different S-alleles ofBrassica campestris, S⁷³³ and S⁷³⁴, with extremely different degrees of susceptibility to this gas. In the current study, we raised a cross-population between those two genetic lines, and analyzed their reaction level of self-incompatibility to CO₂ (RLSICO₂). Here, all 40 of our progeny from the F₁ cross-population were susceptible, maintaining high values of RLSICO₂. This suggests that the susceptible line, S⁷³⁴, is dominant to the insusceptible line, S⁷³³. We also generated an F₂ selfing-population of each crossed progeny, S⁷³³♀ S⁷³⁴♂ and S⁷³³♂ S⁷³⁴♀, to assess the RLSICO₂ of each individual. PCR-RFLP analysis was performed to determine the S-genotype of the F₂ population. The S⁷³⁴ allele segregated in a theoretical ratio of the dominant trait, and the RLSICO₂ was consistent with the dominance relationship. Therefore, we have now demonstrated that high RLSICO₂ in β.campestris is controlled by a dominant gene. Both authors contributed equally to this work     

Fine genetic mapping of a locus controlling short internode length in melon (Cucumis melo L.)

Compact and dwarfing vining habits in melon (Cucumis melo L.; 2n = 2x = 24) may have commercial importance since they can contribute to the promotion of concentrated fruit set and can be planted in higher plant densities than standard vining types. A study was designed to determine the genetics of dwarfism associated with a diminutive (short internodes) melon mutant line PNU-D1 (C. melo ssp. cantalupensis). PNU-D1 was crossed with inbred wild-type melon line PNU-WT1 (C. melo ssp. agrestis), and resultant F₁ progeny were then self-pollinated to produce an F₂ population that segregated as dwarf and vining plant types. Primary stem length of F₂ progeny assessed under greenhouse conditions indicated that a single recessive gene, designated mdw1, controlled dwarfism in this population. To identify the chromosomal location associated with mdw1, an simple sequence repeat (SSR)-based genetic linkage map was constructed using 94 F₂ progeny. Using 76 SSR markers positioned on 15 linkage groups spanning 462.84 cM, the location of mdw1 was localized to Chromosome 7. Using the putative dwarfing-associated genes, fine genetic mapping of the mdw1 genomic region was facilitated with 1,194 F₂ progeny that defined the genetic distance between mdw1 and cytokinin oxidase gene, a candidate gene for compact growth habit (cp) in cucumber, to be 1.7 cM. The candidate gene ERECTA (serin/threonine kinase) and UBI (ubiquitin) were also mapped to genomic regions flanking mdw1 at distances of 0.6 and 1.2 cM, respectively.     

Characterization and Fine Mapping of a Necrotic Leaf Mutant in Maize (Zea mays L.)

Maize (Zea mays L.) is a commercially important crop. Its yield can be reduced by mutations in biosynthetic and degradative pathways that cause death. In this paper, we describe the necrotic leaf (nec-t) mutant, which was obtained from an inbred line, 81647. The nec-t mutant plants had yellow leaves with necrotic spots, reduced chlorophyll content, and the etiolated seedlings died under normal growth conditions. Transmission electron microscopy revealed scattered thylakoids, and reduced numbers of grana lamellae and chloroplasts per cell. Histochemical staining suggested that spot formation of nec-t leaves might be due to cell death. Genetic analysis showed that necrosis was caused by the mutation of a recessive locus. Using simple sequence repeat markers, the Nec-t gene was mapped between mmc0111 and bnlg2277 on the short arm of chromosome 2. A total of 1287 individuals with the mutant phenotype from a F₂ population were used for physical mapping. The Nec-t gene was located between markers T31 and H8 within a physical region of 131.7 kb.     

The effects of inbreeding and low temperature on the pattern of chromosome synapsis in the ovarian nurse cell nuclei of Drosophila melanogaster strains

The effects of inbreeding and low temperature on the pattern of homologous chromosome synapsis in ovarian nurse cell nuclei of Drosophila melanogaster strains were studied. Exposure to decreased temperature (16°C) caused a noticeable increase in the rate of asynapses of homologous chromosomes, whereas this effect was insignificant for F₃₀ inbreeding generation. Long-term inbreeding has a substantial effect on the relative positions of chromosomes in the nurse cell nuclei. This is visually evident only in the interstrain hybrids between highly inbred strains LA (F₉₂₈) and HA (F₉₂₈) or between either strain and laboratory strain Canton S or the flies from the natural population, where abnormalities in homologous chromosome synapsis are observed in virtually all nuclei.     

Molecular mapping of a male fertility restorer locus of Brassica oleracea using expressed sequence tag-based single nucleotide polymorphism markers and analysis of a syntenic region in Arabidopsis thaliana for identification of genes encoding pentatricopeptide repeat proteins

An F₂ population was developed from a cross between a mur-cytoplasmic male sterile broccoli line and a restorer Chinese kale line. Phenotypic analysis of F₂ plants indicated that the pollen fertility is controlled by two genes and segregated in a duplicate gene interaction mode with a ratio of 15:1. A total of 236 single nucleotide polymorphism (SNP) markers were developed utilizing 1,448 primers designed for production of expressed sequence tag (EST)-SNP markers of Raphanus sativus and analyzed by the dot-blot technique in 205 F₂ individuals. A linkage map was constructed with a total of 142 markers and these markers were assigned to nine linkage groups together with simple sequence repeat markers mapped previously on the published linkage maps of Brassica oleracea. The linkage map spanned 909 cM with an average marker distance of 6.4 cM. A fertility restorer locus (Rfm1) was mapped on LG1, corresponding to chromosome 3, along with a flower color locus at a distance of 25 cM. SNP markers flanking the Rfm1 locus were BoCL2642s at a distance of 2.5 cM on one side and BoCL2901s at a distance of 7.5 cM on the other side. All the SNP markers showed homology with Arabidopsis thaliana and Brassica rapa genome sequences. Three pentatricopeptide repeat genes of the P-subfamily, particularly expressed in buds of the restorer line, were identified and these genes could be potential candidate fertility restorer genes.     

Characterization and mapping of <Emphasis Type="Italic">Rpi1</Emphasis>, a gene that confers dominant resistance to stalk rot in maize

The maize inbred lines 1145 (resistant) and Y331 (susceptible), and the F₁, F₂ and BC₁F₁ populations derived from them were inoculated with the pathogen Pythium inflatum Matthews, which causes stalk rot in Zea mays. Field data revealed that the ratio of resistant to susceptible plants was 3:1 in the F₂ population, and 1:1 in the BC₁F₁population, indicating that the resistance to P. inflatum Matthews was controlled by a single dominant gene in the 1145×Y331 cross. The gene that confers resistance to P. inflatum Matthews was designated Rpi1 for resistance to P. inflatum) according to the standard nomenclature for plant disease resistance genes. Fifty SSR markers from 10 chromosomes were first screened in the F₂ population to find markers linked to the Rpi1 gene. The results indicated that umc1702 and mmc0371 were both linked to Rpi1, placing the resistance gene on chromosome 4. RAPD (randomly amplified polymorphic DNA) markers were then tested in the F₂population using bulked segregant analysis (BSA). Four RAPD products were found to show linkage to the Rpi1 gene. Then 27 SSR markers and 8 RFLP markers in the region encompassing Rpi1 were used for fine-scale mapping of the resistance gene. Two SSR markers and four RFLP markers were linked to the Rpi1 gene. Finally, the Rpi1 gene was mapped between the SSR markers bnlg1937 and agrr286 on chromosome 4, 1.6 cM away from the former and 4.1 cM distant from the latter. This is the first time that a dominant gene for resistance to maize stalk rot caused by P. inflatum Matthews has been mapped with molecular marker techniques.     

Genetic analyses and mapping of a new thermo-sensitive genic male sterile gene in maize

The present study describes a novel thermo-sensitive genic male sterile (TGMS) line, Qiong68ms. To analyse the mode of fertility inheritance and tag the TGMS gene, a set of F₂, BC₁ and F_2:3 populations derived from a cross between Qiong68ms and K12 were evaluated for a period of 2 years. Classical genetic analyses and QTL mapping using the mean restoration percentage of the F_2:3 populations revealed that the fertility of Qiong68ms was likely to be governed by a single recessive gene, which was named tms3; the tms3 gene was mapped to a location between SSR markers umc2129 and umc1041, at a distance of 3.7 cM form umc2129 and 1.5 cM form umc1041. The molecular markers tightly linked with tms3 gene will aid in the transfer of the TGMS gene to various background inbred lines using the MAS method.     

Rapid and Targeted Introgression of Genes into Popular Wheat Cultivars Using Marker-Assisted Background Selection

A marker-assisted background selection (MABS)-based gene introgression approach in wheat (Triticum aestivum L.) was optimized, where 97% or more of a recurrent parent genome (RPG) can be recovered in just two backcross (BC) generations. A four-step MABS method was developed based on ‘Plabsim’ computer simulations and wheat genome structure information. During empirical optimization of this method, double recombinants around the target gene were selected in a step-wise fashion during the two BC cycles followed by selection for recurrent parent genotype on non-carrier chromosomes. The average spacing between carrier chromosome markers was <4 cM. For non-carrier chromosome markers that flanked each of the 48 wheat gene-rich regions, this distance was ∼12 cM. Employed to introgress seedling stripe rust (Puccinia striiformis f. sp. tritici) resistance gene Yr15 into the spring wheat cultivar ‘Zak’, marker analysis of 2,187 backcross-derived progeny resulted in the recovery of a BC₂F_2∶3 plant with 97% of the recurrent parent genome. In contrast, only 82% of the recurrent parent genome was recovered in phenotypically selected BC₄F₇ plants developed without MABS. Field evaluation results from 17 locations indicated that the MABS-derived line was either equal or superior to the recurrent parent for the tested agronomic characteristics. Based on these results, MABS is recommended as a strategy for rapidly introgressing a targeted gene into a wheat genotype in just two backcross generations while recovering 97% or more of the recurrent parent genotype.     

Identification of AFLP markers linked to resistance of cowpea (Vigna unguiculata L.) to parasitism by Striga gesnerioides

AFLP and bulked segregant analysis were used to identify molecular markers linked to resistance of cowpea [Vigna ungiculata (L.) Walp.] to parasitism by Striga gesnerioides (Willd.) Vatke. Segregation analysis of F₂ progeny from a cross of Tvx3236, a Striga-susceptible line, with IT82D-849, a resistant cultivar, showed that resistance to S. gesnerioides race 1 from Burkina Faso was controlled by a single dominant gene, designated Rsg2–1. Three AFLP markers were identified that are tightly linked to Rsg2–1: E-AAC/M-CAA₃₀₀ (2.6 cM), E-ACT/M-CAA₅₂₄ (0.9 cM), and E-ACA/M-CAT_140/150 (0.9 cM), which appears to be codominant. Segregation analysis of a different F₂ population resulting from a cross of the Striga-susceptible line IT84S-2246–4 with Tvu 14676, a S. gesnerioides race 3 resistant line, showed that resistance to S. gesnerioides race 3 was also controlled by a single dominant gene, designated Rsg4–3. Six AFLP markers linked to Rsg4–3 were identified: E-ACA/M-CAG₁₂₀ (10.1 cM), E-AGC/M-CAT₈₀ (4.1 cM), E-ACA/M-CAT₁₅₀ (2.7 cM), E-AGC/M-CAT₁₅₀ (3.6 cM), E-AAC/M-CAA₃₀₀ (3.6 cM), and E-AGC/M-CAT₇₀ (5.1 cM). Segregation analysis of the E-AAC/M-CAA₃₀₀ and E-ACA/M-CAG₁₂₀ markers in recombinant inbred lines derived from IT84S-2049×524B determined that both are located within linkage group 1 of the cowpea genetic map. The identification of AFLP markers linked to Striga resistance provides a stepping stone for a marker-assisted selection program and the eventual cloning and characterization of the gene(s) encoding resistance to this noxious parasitic weed. Received: 24 April 2000 / Accepted: 21 August 2000     

A compact sunflower line produced after cross Helianthus annuus x Verbesina encelioides

Intergeneric cross was made between the cultivated sunflower inbred line HA89 and an accession of wild Verbesina encelioides tolerant to drought and high temperature. The line was a BC₂F₅ progeny. The most remarkable feature of the plants was their compact architecture due to short petiole length and also, rather specific bright-yellow inflorescences. Similar plant architecture did not exist in either the wild or the cultivated parent. For sunflower, it is considered as a favourable and potentially useful adaptive trait. The line was multi-branched of medium type branching and possessed good agronomic characteristics. The overall characteristics of HA-VERBENC line make it a useful plant material for research on wide hybridization.     

Genetic mapping and QTL analysis of horticultural traits in cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis> L.) using recombinant inbred lines

A set of 171 recombinant inbred lines (RIL) were developed from a narrow cross in cucumber (Cucumis sativus L.; 2n = 2x = 14) using the determinate (de), gynoecious (F), standard-sized leaf line G421 and the indeterminate, monoecious, little-leaf (ll) line H-19. A 131-point genetic map was constructed using these RILs and 216 F₂ individuals to include 14 SSRs, 24 SCARs, 27 AFLPs, 62 RAPDs, 1 SNP, and three economically important morphological [F (gynoecy), de (determinate habit), ll (little leaf)] markers. Seven linkage groups spanned 706 cM with a mean marker interval of 5.6 cM. The location of F and de was defined by genetic linkage and quantitative trait locus (QTL) analysis to be associated with SSR loci CSWCT28 and CSWCTT14 at 5.0 cM and 0.8 cM, respectively. RIL-based QTL analysis of the number of lateral branches in three environments revealed four location-independent factors that cumulatively explained 42% of the observed phenotypic variation. QTLs conditioning lateral branching (mlb1.1), fruit length/diameter ratio (ldr1.2) and sex expression (sex1.2) were associated with de. Sex expression was influenced by three genomic regions corresponding to F and de both on linkage Group 1, and a third locus (sex6.1) on linkage Group 6. QTLs conditioning the number of fruit per plant (fpl1.2), the number of lateral branches (mlb1.4) and fruit length/diameter ratio (ldr1.3) were associated with ll. The potential value of these marker-trait associations (i.e., yield components) for plant improvement is portended by the relatively high LOD scores (2.6 to 13.0) and associated R² values (1.5% to 32.4%) that are affiliated with comparatively few genetic factors (perhaps 3 to 10).Communicated by H.C. BeckerMention of trade name, proprietary product, or specific equipment does not constitute a guarantee or warranty by the USDA and does not imply its approval to the exclusion of other products that may be suitable     

Increasing Lysine Content of Waxy Maize through Introgression of Opaque-2 and Opaque-16 Genes Using Molecular Assisted and Biochemical Development

The low lysine content of waxy maize cannot meet the nutritional requirements of humans, livestock, or poultry. In the present study, the high-lysine genes o2 and o16 were backcrossed into wx lines using the maize high-lysine inbreds TAIXI19 (o2o2) and QCL3021 (o16o16) as donors and the waxy maize inbred line QCL5019 (wxwx) as a receptor. In the triple-cross F₁, backcross, and inbred generations, the SSR markers phi027 and phi112 within the wx and o2 genes and the SSR marker umc1121 linked to the o16 gene were used for foreground selection. Background selection of the whole-genome SSR markers was performed for the selected individuals. The grain lysine content was determined using the dye-binding lysine method. The waxiness of the grain was determined with the I₂-KI staining and dual-wavelength spectrophotometric analysis. The BC₂F₂ generation included 7 plants of genotype wxwxo2o2O16_, 19 plants of genotype wxwxo16o16O2_, and 3 plants of genotype wxwxo2o2o16o16. In these seeds, the average amylopectin content was 96.67%, 96.87%, and 96.62%, respectively, which is similar to that of QCL5019. The average lysine content was 0.555%, 0.380%, and 0.616%, respectively, representing increases of 75.1%, 19.9%, 94.3%, respectively, over QCL5019. The average genetic background recovery rate of the BC₂F₃ families was 95.3%, 94.3%, 94.2%, respectively. Among these 3 wxwxo2o2O16O16 families, 4 wxwxo2o2O16o16 families, and 3 wxwxo2o2o16o16 families, the longest imported parent donor fragment was 113.35 cM and the shortest fragment was 11.75 cM. No significant differences in lysine content were found between the BC₂F₄ seeds and the BC₂F₃ seeds in these 10 families. This allowed us to increase the lysine content of waxy corn and produce seeds with excellent nutritional characteristics suitable for human consumption, animal feed, and food processing. This may be of significance in the breeding of high-quality corn and in improvement of the nutrition of humans, livestock, and poultry.     

Genotyping new BXD recombinant inbred mouse strains and comparison of BXD and consensus maps

Nine additional BXD recombinant inbred (RI) strains have been developed from the F₂ cross of C57BL/6J and DBA/2J mouse strains. A tenth line stopped breeding in the F₁₂ generation. F₂₀ generation breeding pairs from the nine surviving strains and an F₁₂ pair from the extinct line were genotyped at 319 genetic markers (primarily microsatellites) spanning most of the genome. Where typing data were lacking, the established set of 26 BXD strains also were genotyped at these same loci. The availability of these additional nine strains enhances the value of the BXD RI set for analysis of complex phenotypic traits. The proportion of loci still segregating at the F₂₀ generation was found to closely approximate expectation, suggesting that selection favoring the retention of heterozygosity is not a strong factor. However, the number of crossovers between adjacent markers was frequently less than predicted from consensus map distances. A significant deficiency of recombinants was observed on Chrs 3, 4, 14, and X. On Chr 14, the estimated cumulative BXD map distance between the most proximal and distal markers was only 30.2 cM, compared with a distance of 60.0 cM in the consensus map. On the X Chr, the estimated and predicted cumulative distances were 38.8 and 69.5 cM, respectively. Over all chromosomes, the BXD RI map is 14.5% shorter than predicted from the consensus map. It is suggested that distances in some of the consensus maps are inflated. Alternatively, recombinant genotypes could be selected against during inbreeding owing to allelic interactions affecting fitness. The latter interpretation implies that relatively strong intrachromosomal epistasis is common. Received: 2 October 1998 / Accepted: 15 December 1998     

Okadaic acid causes breakdown of self-incompatibility in Brassica oleracea: evidence for the involvement of protein phosphatases in the incompatible response

Summary Detached pistils from inbred lines of Brassica oleracea L. var alboglabra were fed with okadaic acid (OA), an inhibitor of serine/threonine protein phosphatases, via the transpiration stream. Following self-pollination, pollen tubes were observed to have grown into or through the styles of pistils treated with OA, but not those of untreated controls. Treatment with 1 M OA was sufficient to completely overcome self-incompatibility (SI) in an inbred line homozygous for the S63 allele, though an OA concentration of 5 M was required to cause breakdown of SI in an inbred line homozygous for the S29 allele. At the higher concentration used, pollen tube growth was arrested before the pollen tubes reached the ovary, but this effect was also noted in cross-pollinated styles treated in the same manner. These data provide evidence for the involvement of type 1 and/or type 2A protein phosphatases in the Brassica SI signal transduction mechanism. Present address after November 1993: Department of Biology, Colorado State University, Fort Collins, Colorado, USA     

Genetic analysis of resistance to six virus diseases in a multiple virus-resistant maize inbred line

Key message

Novel and previously known resistance loci for six phylogenetically diverse viruses were tightly clustered on chromosomes 2, 3, 6 and 10 in the multiply virus-resistant maize inbred line, Oh1VI.

Abstract

Virus diseases in maize can cause severe yield reductions that threaten crop production and food supplies in some regions of the world. Genetic resistance to different viruses has been characterized in maize populations in diverse environments using different screening techniques, and resistance loci have been mapped to all maize chromosomes. The maize inbred line, Oh1VI, is resistant to at least ten viruses, including viruses in five different families. To determine the genes and inheritance mechanisms responsible for the multiple virus resistance in this line, F₁ hybrids, F₂ progeny and a recombinant inbred line (RIL) population derived from a cross of Oh1VI and the virus-susceptible inbred line Oh28 were evaluated. Progeny were screened for their responses to Maize dwarf mosaic virus, Sugarcane mosaic virus, Wheat streak mosaic virus, Maize chlorotic dwarf virus, Maize fine streak virus, and Maize mosaic virus. Depending on the virus, dominant, recessive, or additive gene effects were responsible for the resistance observed in F₁ plants. One to three gene models explained the observed segregation of resistance in the F₂ generation for all six viruses. Composite interval mapping in the RIL population identified 17 resistance QTLs associated with the six viruses. Of these, 15 were clustered in specific regions of chr. 2, 3, 6, and 10. It is unknown whether these QTL clusters contain single or multiple virus resistance genes, but the coupling phase linkage of genes conferring resistance to multiple virus diseases in this population could facilitate breeding efforts to develop multi-virus resistant crops.     

A complete genetic linkage map and QTL analyses for bast fibre quality traits, yield and yield components in jute (Corchorus olitorius L.)

We report the first complete microsatellite genetic map of jute (Corchorus olitorius L.; 2n = 2 × = 14) using an F₆ recombinant inbred population. Of the 403 microsatellite markers screened, 82 were mapped on the seven linkage groups (LGs) that covered a total genetic distance of 799.9 cM, with an average marker interval of 10.7 cM. LG5 had the longest and LG7 the shortest genetic lengths, whereas LG1 had the maximum and LG7 the minimum number of markers. Segregation distortion of microsatellite loci was high (61%), with the majority of them (76%) skewed towards the female parent. Genomewide non-parametric single-marker analysis in combination with multiple quantitative trait loci (QTL)-models (MQM) mapping detected 26 definitive QTLs for bast fibre quality, yield and yield-related traits. These were unevenly distributed on six LGs, as co-localized clusters, at genomic sectors marked by 15 microsatellite loci. LG1 was the QTL-richest map sector, with the densest co-localized clusters of QTLs governing fibre yield, yield-related traits and tensile strength. Expectedly, favorable QTLs were derived from the desirable parents, except for nearly all of those for fibre fineness, which might be due to the creation of new gene combinations. Our results will be a good starting point for further genome analyses in jute.