A SNP mutation affects rhizomania-virus content of sugar beets grown on resistance-breaking soils

Rhizomania is one of the most devastating biotic stresses affecting sugar beet (Beta vulgaris L.). It is caused by Beet necrotic yellow vein virus (BNYVV) vectored by the plasmodiophorid Polymyxa betae K. The only means available to control the disease is the use of genetically resistant varieties. “Rizor” or “Holly” (Rz1) and WB42 (Rz2) have been the most widely used resistance sources in the commercial varieties. Recently, naturally occurring resistance-breaking (RB) rhizomania strains have been identified causing major concerns. The aim of this study was to identify SNP mutations that show associations with resistance to rhizomania in sugar beet plants grown under resistance-breaking (RB)-BNYVV soils. Rhizomania virus content was evaluated by indirect triple-antibody sandwich-ELISA within two F ₂ segregating populations respectively grown on an AYPR and IV-BNYVV strain infected soils. Bulked segregant analysis (BSA) was performed. The resistant and susceptible plants were genotyped with a 384-SNPs panel. Of the 384 SNPs, SNP249 was found to associate with the resistance both to the AYPR strain (R ² = 0.37; P = 0.0004) and to the IV-BNYVV (R ² = 0.09; P = 0.0074). Our results suggested that the SNP249 could be readily applicable for marker-assisted breeding of resistance to AYPR strain of rhizomania.     

Sources of resistance to <Emphasis Type="Italic">Phytophthora</Emphasis> root rot within the genus <Emphasis Type="Italic">Beta</Emphasis>

Phytophthora root rot caused by Phytophthora drechsleri Tucker is one of the most devastating sugar beet diseases in tropical areas. To identify genetic resources resistant to this disease, an aggressive isolate of P. drechsleri was selected. Then, a screening method was optimized based on the standard scoring scales of 1–9 (1: no symptoms, 9: complete plant death). Finally, 19 sugar beet lines, three cultivars, and 14 accessions of the wild species Beta vulgaris subsp. maritima, B. macrocarpa, B. procumbens, and B. webbiana were evaluated for resistance to the most aggressive isolate of P. drechsleri by using the optimized method (inoculum included 20 g of rice seed together with superficial wound creation). The isolates of P. drechsleri had significant variation in aggressiveness, and Kv10 was the most aggressive isolate on the susceptible variety Rasoul. The lines O.T.201-15, SP85303-0 (resistant check), and S2-24.P.107 had the lowest disease index with scores of 3.09, 3.13, and 3.27 respectively; they were categorized into the resistant group. The interaction between isolates and genotypes was not significant, which indicated the same response of each genotype to different isolates. Investigating the resistance of different generations of sugar beet revealed that progeny selection would be an effective method for increasing the resistance level of breeding materials to P. drechsleri. Among the wild species, the accession 9402 belonging to B. macrocarpa and the accession 7234 of B. vulgaris subsp. maritima had the lowest disease index (2.29 and 2.60, respectively) and were categorized into the resistant group.     

Efficiency of some molecular markers linked to rhizomania resistance gene (Rz 1 ) for marker assisted selection in sugar beet

Sugar beet (Beta vulgaris L.) is one of the two major products supplying sugar (sucroses) in the world. Rhizomania is one of the most destructive diseases of sugar beet world-wide. Holly is the major source of resistance to rhizomania. The objectives of this study were to identify the dominant homozygous genotypes resistant to rhizomania using ZN1 molecular marker, to field evaluate S₁ progenies of plants already proved to be containing the marker and also to determine the relationship of this and other SCAR (sequence characterized amplified region) markers with SNP1 (single nucleotide polymorphism) marker associated with the Rz ₁ gene. Molecular analysis was carried out on 27 O-type populations (consisting of 13 susceptible and 6 resistant genotypes). Field evaluation and scoring of the phenotypic traits including greenness, growth, uniformity and disease score of 12 O-type populations were carried out on a rhizomania-infested field. The percent agreement of coupling marker ZN1 and repulsion marker ZN8 with disease score was 0.91 and 0.93, respectively. Although all O-types had the Rz ₁ resistance gene but the phenotypic differences were observed due to the effect of different genetic backgrounds and modifier genes. Overall, the results showed that the selected markers can be used for marker-assisted selection (MAS) to reduce the time and cost of breeding programs and increase the efficiency of selection.     

Determining resistance to <Emphasis Type="Italic">Fusarium verticillioides</Emphasis> and fumonisin accumulation in African maize inbred lines resistant to <Emphasis Type="Italic">Aspergillus flavus</Emphasis> and aflatoxins

Fusarium verticillioides and Aspergillus flavus cause Fusarium ear rot (FER) and Aspergillus ear rot (AER) of maize, respectively. Both pathogens are of concern to producers as they reduce grain yield and affect quality. F. verticillioides and A. flavus also contaminate maize grain with the mycotoxins fumonisins and aflatoxins, respectively, which has been associated with mycotoxicosis in humans and animals. The occurrence of common resistance mechanisms to FER and AER has been reported. Hence, ten Kenyan inbred lines resistant to AER and aflatoxin accumulation were evaluated for resistance to FER, F. verticillioides colonisation and fumonisin accumulation; and compared to nine South African lines resistant to FER and fumonisin accumulation. Field trials were conducted at three localities in South Africa and two localities in Kenya. FER severity was determined by visual assessment, while F. verticillioides colonisation and fumonisin content were quantified by real-time PCR and liquid chromatography tandem mass spectrometry, respectively. Significant genotype x environment interactions was determined at each location (P ≤ 0.05). Kenyan inbred CML495 was most resistant to FER and F. verticillioides colonisation, and accumulated the lowest concentration of fumonisins across localities. It was, however, not significantly more resistant than Kenyan lines CML264 and CKL05015, and the South African line RO549 W, which also exhibited low FER severity (≤5%), fungal target DNA (≤0.025 ng μL^?1) and fumonisin levels (≤2.5 mg kg^?1). Inbred lines resistant to AER and aflatoxin accumulation appear to be promising sources of resistance to F. verticillioides and fumonisin contamination.     

Marker assisted backcrossing for introgression of Fusarium wilt resistance gene into melon

Fusarium wilt, caused by Fusarium oxysporum f. sp. melonis is a common vascular wilt fungal disease in melon across the world. The resistance gene to race 1 of this causal agent, Fom-2, has been previously cloned and its sequence is available. The objective of this research was the introgression of Fom-2 from one resistant (Isabelle) genotype into two susceptible cultivars (Garmak and Tile-torogh) via marker assisted backcrossing. First, the leucine-rich repeats (LRR) domain of Fom-2 from resistant and susceptible genotypes was sequenced to develop functional markers. A length of 1274 bp of the 3′ end of this gene was isolated, cloned and sequenced. The difference between resistant and susceptible genotypes in this region was 28 nucleotide substitutions. Two allele specific primer pairs, Fom2-R409 and Fom2-S253, were designed based on nucleotide substitutions to amplify resistant and susceptible alleles, respectively. For introgression of the gene, donor (Isabelle) and recurrent (Garmak and Tile-torogh) parents were crossed. Resistant plants in BC₁F₁ and BC₂F₁ generations were first detected using artificial pathogen inoculation and later the plants were genotyped by functional markers to validate their resistance. The resistant plants were also selected phenotypically in each generation for background genome recovery, which conduced to high similarity of BC₃ generation with the recurrent parents. It was proved the developed markers are more precise and efficient than inoculation trial and could be used as confident tools for screening of resistant melon genotypes to Fusarium wilt.     

Identification of QTLs for resistance to Fusarium wilt and Ascochyta blight in a recombinant inbred population of chickpea (<Emphasis Type="Italic">Cicer arietinum</Emphasis> L.)

Fusarium wilt (FW; caused by Fusarium oxysporum f. sp. ciceris) and Ascochyta blight (AB; caused by Ascochyta rabiei) are two major biotic stresses that cause significant yield losses in chickpea (Cicer arietinum L.). In order to identify the genomic regions responsible for resistance to FW and AB, 188 recombinant inbred lines derived from a cross JG 62 × ICCV 05530 were phenotyped for reaction to FW and AB under both controlled environment and field conditions. Significant variation in response to FW and AB was detected at all the locations. A genetic map comprising of 111 markers including 84 simple sequence repeats and 27 single nucleotide polymorphism (SNP) loci spanning 261.60 cM was constructed. Five quantitative trait loci (QTLs) were detected for resistance to FW with phenotypic variance explained from 6.63 to 31.55%. Of the five QTLs, three QTLs including a major QTL on CaLG02 and a minor QTL each on CaLG04 and CaLG06 were identified for resistance to race 1 of FW. For race 3, a major QTL each on CaLG02 and CaLG04 were identified. In the case of AB, one QTL for seedling resistance (SR) against ‘Hisar race’ and a minor QTL each for SR and adult plant resistance against isolate 8 of race 6 (3968) were identified. The QTLs and linked markers identified in this study can be utilized for enhancing the FW and AB resistance in elite cultivars using marker-assisted backcrossing.     

Polymorphisms of the <Emphasis Type="Italic">FT</Emphasis> gene as a tool to identify underground rhizome types of bamboos

The Flowering Locus T (FT)-like genes of angiosperms are highly conserved. The FT-encoded proteins include a phosphatidylethanolamine-binding domain that is involved in the control of the shoot apical meristem identity and flowering time. In the present study, FT genes were investigated in 20 bamboo species that are grouped into sympodial, mixed and scattered bamboos based on their morphology. All examined orthologous FT genes consisted of four exons and three introns. Their encoded protein sequences contained the critical amino acid residues Tyr85, Glu109, Leu128, Tyr134, Trp138, Arg139, Gln140 and Asn152, of which each possesses a biological function. The DNA sequences were rich in single nucleotide polymorphism (SNP) sites. The SNP frequency was 1 SNP/16.8 bp, and the nucleotide diversity (π) equaled 0.265. Some SNPs altered restriction enzyme sites or resulted in changes in amino acid contents. The correlation analysis showed that several SNPs were informative in relation to the underground rhizome types of bamboos. Therefore, FT polymorphisms could be used as a tool to identify the underground rhizome types of bamboos. The phylogenetic tree constructed based on the FT gene sequences showed that the obtained clustering was consistent with the underground rhizome types. The SNP markers developed in the present study will provide information on the genetic diversity of bamboos and they can aid taxonomic study as well.     

Genetic effect of <Emphasis Type="Italic">Striga</Emphasis> resistance in sorghum genotypes

Striga is an important parasitic weed causing substantial economic losses in cereal and legume crop production in sub-Saharan Africa. Integrated Striga management approaches such as a combined use of Striga resistant varieties and Fusarium oxysporum f.sp. strigae (FOS), a biocontrol agent of Striga, are an option to control the parasite and to boost sorghum productivity. Understanding host gene action influencing Striga resistance, with or without FOS treatment, is key to developing improved sorghum varieties with durable resistance and high yield. The objective of this study was to determine the gene action and inheritance of Striga resistance using genetically diverse populations of sorghum involving FOS treatment. Twelve sorghum parents selected for Striga resistance, FOS compatibility or superior agronomic performances were crossed using a bi-parental mating scheme. The selected male and female parents and their F₁ progenies, backcross derivatives and the F₂ segregants were field evaluated at three locations in Tanzania known for their severe Striga infestations using a lattice experimental design with two replications. The following data were collected and subjected to generation mean analysis (GMA): days-to-50% flowering (DFL), seed yield per plant (SYP) and number of Striga per plant (SN). GMA showed the preponderance of additive genetic action contributing to the total genetic variation in the evaluated sorghum populations. The additive genetic effect for DFL, SYP and SN, with and without FOS treatments, ranged from 72.02 to 86.65% and 41.49 to 95.44%, 75.62 to 91.42% and 71.83 to 91.89%, and 77.35 to 93.56% and 72.86 to 95.84%, in that order. The contribution of non-additive genetic effects was minimal and varied among generations. FOS application reduced DFL and SN and improved SYP in most of the tested sorghum populations. DFL of sorghum populations was reduced by a mean of 8 days under FOS treatment compared to the untreated control in families such as 675 × 654, AS435 × AS426 and 1563 × AS436. FOS treatment improved SYP with a mean of 6.44 g plant^?1 in 3424 × 3993 and 3984 × 672. The numbers of Striga plants were reduced with a mean of 16 plants due to FOS treatment in the crosses of 675 × 654, 1563 × AS436, 4567 × AS424, and 3984 × 672. The study demonstrated that additive genes were predominantly responsible for the inheritance of Striga resistance in sorghum. Pure line cultivar development targeting reduced DFL, SN and high SYP in the selected populations may provide enhanced response to selection for integrated Striga management (ISM) programme.     

Resistance to <Emphasis Type="Italic">Cucumber green mottle mosaic virus</Emphasis> in <Emphasis Type="Italic">Cucumis sativus</Emphasis>

Cucumber green mottle mosaic virus (CGMMV) is a severe threat for cucumber production worldwide. At present, there are no cultivars available in the market which show an effective resistance or tolerance to CGMMV infection, only wild Cucumis species were reported as resistant. Germplasm accessions of Cucumis sativus, as well as C. anguria and C. metuliferus, were mechanically infected with the European and Asian strains of CGMMV and screened for resistance, by scoring symptom severity, and conventional RT-PCR. The viral loads of both CGMMV strains were determined in a selected number of genotypes using quantitative RT-PCR. Severe symptoms were found following inoculation in C. metuliferus and in 44 C. sativus accessions, including C. sativus var. hardwickii. Ten C. sativus accessions, including C. sativus var. sikkimensis, showed intermediate symptoms and only 2 C. sativus accessions showed mild symptoms. C. anguria was resistant to both strains of CGMMV because no symptoms were expressed and the virus was not detected in systemic leaves. High amounts of virus were found in plants showing severe symptoms, whereas low viral amounts found in those with mild symptoms. In addition, the viral amounts detected in plants which showed intermediate symptoms at 23 and 33 dpi, were significantly higher in plants inoculated with the Asian CGMMV strain than those with the European strain. This difference was statistically significant. Also, the amounts of virus detected over time in plants did not change significantly. Finally, the two newly identified partially resistant C. sativus accessions may well be candidates for breeding programs and reduce the losses produced by CGMMV with resistant commercial cultivars.     

Development of high-density interspecific genetic maps for the identification of QTLs conferring resistance to <Emphasis Type="Italic">Valsa ceratosperma</Emphasis> in apple

Valsa canker (Valsa ceratosperma (Tode ex Fr.) Maire) is one of the most destructive fungal diseases of apple, especially in Eastern Asia. In this study, the first high density genetic linkage map of Malus asiatica × Malus domestica was constructed by 640 simple sequence repeats (SSRs) and 490 single nucleotide polymorphisms (SNPs), which spanned 1497.5 cM with an average marker interval of 1.33 cM per marker. Quantitative trait loci (QTLs) for apple’s resistance to V. ceratosperma isolates 03-8 and xc56 were identified using the linkage map. Lesion lengths were used as the phenotypic data for the QTL analysis, which were measured on 1-year-old shoots inoculated with conidia of the two isolates. One QTL for resistance to isolate 03-8 was mapped on LG 16, and one QTL for resistance to isolate xc56 was detected on LG 9. Our research not only promoted the further understanding of the genetic basis of apple’s resistance to Valsa canker but also provided two molecular markers that might be used in future marker-assisted selection for resistance in apple breeding programs.     

Identification of favorable alleles in the <Emphasis Type="Italic">non</Emphasis>-<Emphasis Type="Italic">yellow coloring 1</Emphasis> gene by association mapping in maize

Association mapping was conducted to explore favorable alleles of the chlorophyll-related non-yellow coloring 1 (NYC1) gene under light and dark using an association panel of 146 maize inbred lines. A total of 14 polymorphic sites were identified to be significantly associated with at least one of the chlorophyll-related traits at the seedling stage. Four single nucleotide polymorphisms (SNPs) (S320, S2951, S3901, and S3355) from the NYC1 gene were respectively strongly associated with chlorophyll b (chlb), the ratio of chlorophyll a to chlorophyll b (chl_ratio), chlorophyll a degradation (chla_deg), and total chlorophyll degradation (total_chl_deg). SNPs S320 (C/A) in exon 1, and S2951 (A/G) in intron 8 was related to chlb, with 6.01 and 8.89% of phenotypic variation under light treatment, respectively. Under dark treatment, SNP S3901 (C/T), located in 3′ untranslated region (3′UTR), was associated with chl_ratio, explaining 7.01% of the observed phenotypic variation, whereas SNP S3355 (C/G) in intron 9 explained 6.48 and 5.18% of phenotypic variations in chla_deg and total_chl_deg, respectively. Taken together, these results indicated that the NYC1 gene plays an important role in chlorophyll content and other related traits, and different sites act on chlorophyll metabolism under different light intensities in maize seedlings. Furthermore, these findings improve our understanding of the genetic basis of chlorophyll metabolism under different light conditions.     

Rapid identification of a major effect QTL conferring adult plant resistance to stripe rust in wheat cultivar Yaco“S”

Stripe rust is a devastating disease in common wheat (Triticum aestivum) worldwide. Growing cultivars with adult-plant resistance (APR) is an environmental friendly approach that provides long-term protection to wheat from this disease. Wheat cultivar Yaco“S” showed a high level of APR to stripe rust in the field from 2008 to 2014. The objective of this study was to detect the major quantitative trait loci (QTL) for APR to stripe rust in Yaco“S”. One hundred and eighty-four F_2:3 lines were developed from a cross between Yaco“S” and susceptible cultivar Mingxian169. Illumina 90K and 660K single nucleotide polymorphism (SNP) chips were implemented to bulked pools and their parents to identify SNPs associated with the major QTL. A high-density linkage map was constructed using simple sequence repeat (SSR) and SNP markers. Inclusive composite interval mapping detected a major effect QTL Qyryac.nwafu-2BS conferring stable resistance to stripe rust in all tested environments. Qyryac.nwafu-2BS were mapped to a 1.3 cm interval and explained 17.3–51.9% of the phenotypic variation. Compared with stripe rust resistance genes previously mapped to chromosome 2B, Qyryac.nwafu-2BS is likely a new APR gene to stripe rust. Combining SNP iSelect assay and kompetitive allele specific PCR technology, we found that the APR gene could be rapidly and accurately mapped and it is useful for improving stripe rust resistance in wheat breeding.     

Genetics of resistance in lettuce to races 1 and 2 of <Emphasis Type="Italic">Verticillium dahliae</Emphasis> from different host species

Race 1 resistance against Verticillium dahliae in lettuce was originally shown in the cultivar La Brillante to be conditioned by a single dominant gene (Verticillium resistance 1, Vr1). Multiple, morphologically diverse sources of germplasm have been identified as resistant to race 1. In this study, allelism tests indicated that resistance in these different lettuce cultivars is closely linked or allelic to the Vr1 gene. The Vr1 gene is defeated by race 2 isolates of V. dahliae. Only partial resistance to race 2 isolates is available in a few plant introductions (PIs). Greenhouse and field experiments conducted with these PIs demonstrated partial resistance to V. dahliae race 1 as well as race 2 isolates from lettuce. Cultivars resistant to race 1 and PIs with partial resistance to race 2 were challenged with several race 1 and 2 isolates originating from hosts other than lettuce. This indicated that cultivars resistant to race 1 and the breeding lines derived from them would also be resistant to race 1 isolates from other hosts; similarly, the partial resistance would be effective against race 1 and 2 isolates from hosts other than lettuce. Nevertheless, there were specific interactions that warrant further study. Although race 1 currently predominates in the major lettuce production area of the Salinas Valley, CA, breeding lettuce for resistance to V. dahliae should take both races into account.     

Identification of SNP for rice blast resistance gene <Emphasis Type="Italic">Pike</Emphasis> and development of the gene-specific markers

Rice blast disease caused by Magnaporthe oryzae is an important limiting factor to rice production in the world. Introgression of blast resistance genes into improved germplasm by marker-assisted selection has been considered as an effective and environmentally beneficial means to control this disease. Pike, a broad-spectrum blast resistance gene, was cloned by map-based strategy recently in our laboratory. Two adjacent CC-NBS-LRR genes (designated as Pike-1 and Pike-2) were required for Pike-mediated resistance. In the current study, sequence alignment of the SNP G1328C and the SNP-surrounding region let us find that the Pik DNA variants of the studied rice lines appear to be divided into G-, C-, T- and G’-types. Based on the four genotypes, a Pike-specific marker system consisting of three PCR-based markers CP-G1328C, CP-G1328T and CP-G1328G’ was developed and used to effectively differentiate G-type allele from each of the others. Using this marker system, we investigated distribution of the Pik DNA variants in a set of 326 rice varieties or breeding lines and found that there were 2, 130, 135 and 59 rice lines identified to carry G-, C-, T- and G’-type alleles, respectively. In addition, with sequence data of the SNP G1328C-containing genomic region derived from 56 rice lines, we constructed a phylogenetic tree with three major clades which just corresponded to the types of the Pik DNA variants described above.     

Conferring resistance to pre-harvest sprouting in durum wheat by a QTL identified in <Emphasis Type="Italic">Triticum spelta</Emphasis>

Pre-harvest sprouting (PHS) causes significant yield loss and degrade the end-use quality of wheat, especially in regions with prolonged wet weather during the harvesting season. Unfortunately, the gene pool of Triticum durum (tetraploid durum wheat) has narrow genetic base for PHS resistance. Therefore, finding out new genetic resources from other wheat species to develop PHS resistance in durum wheat is of importance. A major PHS resistance QTL, Qphs.sicau-3B.1, was mapped on chromosome 3BL in a recombinant inbred line population derived from ‘CSCR6’ (Triticum spelta), a PHS resistant hexaploid wheat and ‘Lang’, a PHS susceptible Australian hexaploid wheat cultivar. This QTL, Qphs.sicau-3B.1, is positioned between DArT marker wPt-3107 and wPt-6785. Two SCAR markers (Ph3B.1 and Ph3B.2) were developed to track this major QTL and were used to assay a BC₂F₈ tetraploid population derived from a cross between the durum wheat ‘Bellaroi’ (PHS susceptible) and ‘CSCR6’ (PHS resistant). Phenotypic assay and marker-assisted selection revealed five stable tetraploid lines were highly PHS resistant. This study has successfully established that PHS-resistance QTL from hexaploid wheat could be efficiently introgressed into tetraploid durum wheat. This tetraploid wheat germplasm could be useful in developing PHS resistant durum cultivars with higher yield and good end-use quality.     

Development and application of a molecular marker for TMV resistance based on <Emphasis Type="Italic">N</Emphasis> gene in tobacco (<Emphasis Type="Italic">Nicotiana tabacum</Emphasis>)

Tobacco mosaic virus (TMV) caused serious loss in yield and quality of tobacco every year. It is a long-term goal to improve the tobacco resistance against TMV by tobacco breeding. N gene was the firstly reported TMV-resistant gene, which showed resistance against all Tobamoviruses except the Ob stain and belonged to the toll-interleukin-1 receptor/nucleotide-binding site/leucine-rich repeat class of plant resistance (R) genes. At present, N gene had already been widely used in tobacco conventional breeding, but there is rare available molecular maker used in marker-assisted selection of TMV resistance. In this study, we designed a pair of primers that specific amplify N gene fragment based on the sequence of N gene intron III, named N-marker. Then, we identified TMV resistance by two selecting methods, PCR with N-marker and inoculated with the TMV-C strain. Results from the two method showed that (1) 13 varieties among 67 tobacco varieties displayed hypersensitive reaction when inoculated with the TMV-C strain, also contained N gene fragments screened by PCR with N-marker; (2) 105 strains of 200 BC1 strains showed resistance against TMV when inoculated with TMV-C strain, meanwhile, 103 of the 105 strains contained N gene fragment verified by PCR with N-marker. Therefore, the N-marker is reliable for high throughput screening of germplasm resources and tobacco breeding materials in selection of N-mediated TMV resistance. Our study not only developed a molecular marker for tobacco breeding, but also identified new germplasm resources that are resistant to TMV.     

Diploid and tetraploid progenitors of wheat are valuable sources of resistance to the root lesion nematode <Emphasis Type="Italic">Pratylenchus</Emphasis><Emphasis Type="Italic">thornei</Emphasis>

The root lesion nematode Pratylenchus thornei is widely distributed in Australian wheat (Triticum aestivum) producing regions and can reduce yield by more than 50%, costing the industry AU$50 M/year. Genetic resistance is the most effective form of management but no commercial cultivars are resistant (R) and the best parental lines are only moderately R. The wild relatives of wheat have evolved in P. thornei-infested soil for millennia and may have superior levels of resistance that can be transferred to commercial wheats. To evaluate this hypothesis, a collection of 251 accessions of wheat and related species was tested for resistance to P. thornei under controlled conditions in glasshouse pot experiments over two consecutive years. Diploid accessions were more R than tetraploid accessions which proved more R than hexaploid accessions. Of the diploid accessions, 11 (52%) Aegilops speltoides (S-[B]-genome), 10 (43%) Triticum monococcum (A ^m -genome) and 5 (24%) Triticum urartu (A ^u -genome) accessions were R. One tetraploid accession (Triticum dicoccoides) was R. This establishes for the first time that P. thornei resistance is located on the A-genome and confirms resistance on the B-genome. Since previous research has shown that the moderate levels of P. thornei resistance in hexaploid wheat are dose-dependent, additive and located on the B and D-genomes, it would seem efficient to target A-genome resistance for introduction to hexaploid lines through direct crossing, using durum wheat as a bridging species and/or through the development of amphiploids. This would allow resistances from each genome to be combined to generate a higher level of resistance than is currently available in hexaploid wheat.     

Inheritance of type IV glandular trichome density and its association with whitefly resistance from <Emphasis Type="Italic">Solanum galapagense</Emphasis> accession LA1401

Tomato is affected by a large number of arthropod pests, among which the whitefly (Bemisia tabaci) is considered to be one of the most destructive. Several accessions of the wild species of Solanum galapagense, including accession LA1401, are considered resistant to whitefly (B. tabaci). This resistance has been associated with the presence of type IV glandular trichomes on the leaf surface. Our research aimed to study the inheritance of type IV glandular trichome density and its association with resistance to whitefly (B. tabaci biotype B) in populations derived from the interspecific cross Solanum lycopersicum × S. galapagense ‘LA1401.’ High estimates for both broad-sense and narrow-sense heritabilities of type IV glandular trichome densities suggest that inheritance of this trait is not complex. Whitefly resistance was associated with high density of type IV glandular trichomes. F₂ (S. galapagense × S. lycopersicum) population plants selected for the highest densities of type IV glandular trichomes showed similar levels of resistance to those found in the donor of resistance LA1401.     

Heritability of the resistance to pepper huasteco yellow vein virus in wild genotypes of <Emphasis Type="Italic">Capsicum annuum</Emphasis>

Pepper huasteco yellow vein virus (PHYVV) is the main virus of pepper crop in Mexico. No resistant cultivars are available and resistance breeding is hampered by the lack of knowledge of heritability (h ²) of PHYVV resistance. This is a continuation of previous studies and the objectives were to analyze the h ² and the behavior of the resistant trait to PHYVV. Four resistant assays were done with three resistant wild lines (UAS12, UAS13 and UAS10) of Capsicum annuum in the S4, S5, S6 and S7 generation under greenhouse conditions. Plants from all tests were inoculated with PHYVV through Bemisia tabaci. Line UAS12 was the most resistant showing a significantly proportion of resistant plants, less disease symptoms and longer incubation time, followed by the lines UAS13 and UAS10 in all assays. Distribution of symptoms showed a bimodal tendency in all the trials, suggesting that two groups of genes are involved in this resistance trait. The lines UAS12, UAS13 and UAS10 showed the same pattern of response to selection with an average of h ² of 0.17, 0.06, 0.02 and 0.00 in the S4, S5, S6 and S7, respectively. These results indicate that all lines responded positively to the selection in the S4, S5 and S6, whereas in the S7 there was no response by the possible exhaustion of variation. Line UAS12 is the most promising genotype and the lines UAS13 and UAS10 are genetic resources that can be supplemented to breed the resistance of PHYVV. These results provides basic information for resistance breeding.     

Wild <Emphasis Type="Italic">Coffea arabica</Emphasis> resistant to <Emphasis Type="Italic">Meloidogyne paranaensis</Emphasis> and genetic parameters for resistance

Arabica coffee production is based on highly productive cultivars; however, these cultivars are susceptible to infestation by several biotic agents, including root-knot nematodes. Collections of wild Coffea arabica germplasm represent an important source of genetic variability for resistant cultivar development. In this study, 1046 plants derived from 71 wild coffee trees were evaluated with respect to Meloidogyne paranaensis resistance. In addition to information on plants reactions, we also evaluated the genetic parameters related to resistance. Progenies from the five most promising plants were also evaluated regarding resistance to M. incognita and M. exigua. The yield potential of selected plants was estimated through analysis of data for fruits harvested in 4 different years. Forty-seven plants were considered resistant based on reproduction factor values. The estimated heritability was high for all analyzed variables leading to substantial selection gain, mainly at the progeny mean level. On the basis of heritabilities and genetic correlations, we conclude that selection could be performed based on values of the gall and egg mass index. However, higher genetic gain could be obtained based on nematode count variables. A second experiment confirmed the reactions of the selected five plants to M. paranaensis, and multiple resistance was detected in three of them. The resistant accessions also have yield potential.