Effective selection of soybean cultivars to wildfire disease pathogen Pseudomonas amygdali pv. tabaci

Wildfire, caused by Pseudomonas amygdali pv. tabaci is one of the most destructive bacterial diseases and was recognized as a disease of soybean in 1943. Wildfire has been seen a steady increase in the incidence and prevalence on some cultivars of soybean in Korea by climatic changes but there is little information on effective control measures for wildfire or soybean varieties showing complete resistance to the disease. In this study, the efficient and reliable screening method to evaluate soybean genotype for resistance to P. amygdali pv. tabaci in field had been developed. In order to determine the host resistance of the soybean cultivar against P. amygdali pv. tabaci, development of symptom by infiltration inoculation was evaluated. Significant differences between susceptible plants and resistant plants were observed through these assays. Based on these results, ‘Shinpaldal2’, ‘Daepung’ are resistant to wildfire compared to ‘Hwangeum’, ‘Taekwang’. The optimum temperature of this pathogen was between 20-25°C and when the pathogen was in the optimum temperature, the responses of susceptible or resistant cultivar were dramatically different. Prior to initiation of resistance breeding of soybean wildfire, it is imperative to set uniform resistance screening techniques. The obtained results can be effectively used to enhance the selection of wildfire resistance as well as directly applied in resistant soybean development. Resistant lines identified through this assay could be directly used in soybean breeding programs for wildfire resistance.     

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.     

Mapping QTLs for plant height and flowering time in a Chinese summer planting soybean RIL population

Soybean is a primary source of plant oil and protein and has a high nutritional value. Plant height (PH) and flowering time (FT) are two important agronomic traits in breeding programs for soybean. In this study, we mapped QTLs associated with PH and FT in three environments using a population with determinate growth including 236 recombinant inbred lines (NJZY-RIL) derived from a cross between two summer planting varieties, ZXD and NN1138-2. A high-density genetic map with 3255 SLAF-markers was constructed that spanned 2144.85 cM of the soybean genome with an average marker distance of 0.66 cM. Altogether, six QTLs controlling PH and eleven QTLs controlling FT were mapped using mixed-model-based composite interval mapping and composite interval mapping methods. qPH-1-1 and qFT-15-2 were two novel main effect QTLs identified in this study; qFT-6-2, qFT-15-2, qFT-16-1, qPH-1-1, qPH-15-1 and qPH-16-1 were consistently detected across environments and by the two mapping methods. Two pairs of QTLs, qFT-15-2 and qPH-15-1 as well as qFT-16-1 and qPH-16-1, which were located in the same marker interval on chromosomes 15 and 16, respectively, were found to have close linkage or pleiotropy. These results may increase our understanding of the genetic control of PH and FT in soybean and provide support for implementing marker-assisted selection in developing soybean cultivars with high yield and early maturity in summer planting regions.     

Allelic variation at the gliadin coding loci of improved Ethiopian durum wheat varieties

The objective of this study was to determine gliadin allele compositions of 20 improved Ethiopian durum wheat varieties using acid-polyacrylamide gel electrophoresis (A-PAGE). Each block of co-dominantly inherited polypeptides encoded by gliadin loci were identified and their genetic diversities were estimated using statistical analyses. A total of 30 electrophoretic blocks were identified at five major gliadin loci. In addition, four novel gliadin blocks were identified. Gli-B1 and Gli-A2 loci had higher numbers of gliadin alleles (nine and ten, respectively) compared to other loci. Alleles Gli-A1c on chromosome 1A, Gli-B1c on chromosome 1B, Gli-A2a, and Gli-A2o on chromosome 6A, and Gli-B2h on chromosome 6B had maximal frequencies in their corresponding loci. Varieties were classified into three main clusters and one singleton based on genetic distances of detected gliadin alleles. These results indicate that Ethiopian durum wheat varieties are genetically diverse with unique allele compositions at gliadin-coding loci.     

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.     

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.     

<Emphasis Type="Italic">LKF</Emphasis>, the locus regulating large grains in the rice cultivar ‘Fusayoshi’, is identical to the loci encoding a serine/threonine protein phosphatase with Kelch motif

The LKF locus, which regulates grain size in the rice cultivar ‘Fusayoshi’ showing large grain, has been mapped to the proximal part of the long arm of chromosome 3. An incomplete dominant allele, Lkf, caused large grain size of Fusayoshi. The structure and function of this locus, however, have not yet been determined. In a similar position to LKF on chromosome 3, two loci, Os03g0407400 (GS3) and LOC_Os03g44500, have been already reported as loci also regulating rice grain size. The objective of the present study was to determine the nucleotide sequences of both Os03g0407400 and LOC_Os03g44500 for different alleles at the LKF locus. Results showed that only one known single nucleotide polymorphism (SNP) in exon 10 of LOC_Os03g44500 was detected between a large-grain allele (Lkf) and a small-grain allele at the LKF locus, whereas no polymorphisms in Os03g0407400. This SNP, visualized using a dCAPS marker, clearly demonstrated nearly complete co-segregation with grain length in an F₂ population segregating the Lkf at LKF. Other large-grain mutant lines with large-grain alleles at the LKF locus, which originated from another cultivar ‘Gimbozu’, also showed the same SNP in exon 10 of LOC_Os03g44500. It was concluded from these results that LKF is identical to LOC_Os03g44500, and the detected SNP in exon 10, at least, which is included in Kelch-like repeat motif, could be essential for expression of the large-grain phenotype.     

Analysis of a major rice blast resistance gene in the rice restorer line Hanghui 1179

Rice blast, caused by the fungal pathogen Magnaporthe oryzae, is one of the most devastating diseases of rice (Oryza sativa) worldwide. Identification and utilization of resistance genes in rice breeding is considered to be an effective and economical method to control this disease. Hanghui 1179 (HH1179) is a new native rice restorer line developed in South China. The hybrids derived from HH1179 show broad-spectrum resistance against rice blast in South China, and a further understanding of the genetic resistance in HH1179 will provide useful information for breeding resistant cultivars. In the present study, we used bulked segregant analysis combined with specific-length amplified fragment sequencing to identify a dominant gene from HH1179 that provides resistance against the rice blast isolate GD13-14. Association analysis indicated that the resistance gene is located on chromosome 6 and we mapped the target gene to a 100.8 kb region (between markers InDel-8 and RM19818) that contains the Pi2/Pi9/Piz/Piz-t/Pi50 gene cluster. Candidate gene prediction and cDNA sequencing indicated that the target resistance gene in HH1179 is Pi2. Our findings will be valuable for resistance breeding with restorer line HH1179.     

Identification of novel quantitative trait loci associated with brown planthopper resistance in the rice landrace Salkathi

The brown planthopper (BPH) is a potent pest of rice in Asia and Southeast Asia. Host resistance has been found to be the most suitable alternative to manage the insect. But varietal resistance has been found to be short-lived. There has been a constant search for alternate resistance genes. We developed an F₈ recombinant inbred population for the BPH resistance gene in Salkathi, an indica landrace from Odisha, India. Phenotyping of RILs against the BPH population at Cuttack, Odisha showed continuous skewed variation with four peaks at 2.1–3.0, 4.1–5.0, 6.1–7.0 and 8.1–9.0 SES score, suggesting the involvement of quantitative loci for resistance to BPH in Salkathi. Mapping showed the presence of two QTLs on the short arm of chromosome 4. One QTL, with phenotype variance of 37.02% is located between the markers RM551 and RM335. The other QTL, with phenotype variance of 7.1% is located between markers RM335 and RM5633. The two QTLs have been designated as qBph4.3 and qBph4.4. QBph4.3 seems to be a novel QTL associated with BPH resistance. We have successfully transferred qBph4.3 and qBph4.4 into two elite rice cultivars, Pusa 44 and Samba Mahsuri. Fine mapping of the identified QTLs may lead to a successful transfer of QTLs into other elite germplasm backgrounds.     

Introgression of <Emphasis Type="Italic">Gossypium barbadense</Emphasis> L. into Upland cotton germplasm RMBUP-C4S1

Gossypium barbadense L. cotton has significantly better fiber quality than Upland cotton (G. hirsutum L.); however, yield and environmental adaptation of G. barbadense is not as wide as Upland. Most cotton in the world is planted to Upland cultivars. Many attempts have been made, over a considerable number of years, to introgress fiber quality alleles from G. barbadense into Upland. However, introgression barriers, primarily in the form of interspecific incompatibility, have limited these traditional approaches. The use of chromosome substitution lines (CSL) as a bridge should provide a more efficient way to introgress alleles from G. barbadense into Upland. We crossed 18 G. barbadense CSL to three cultivars and developed a random mated population. After five cycles of random mating followed by one generation of self-pollination to increase the seed supply, we grew the random mated population and used 139 G. barbadense chromosome specific SSR markers to assess a random sample of 96 plants for introgression. We recovered 121 of 139 marker loci among the 96 plants. The distribution of the G. barbadense alleles ranged from 10 to 28 alleles in each plant. Among the 96 plants we found individual plants with marker loci from 6 to 14 chromosomes or chromosome arms. Identity by descent showed little relatedness among plants and no population structure was indicated by a heat map. Using CSL we were able to develop a mostly Upland random mated population with considerable introgression of G. barbadense alleles which should be useful for breeding.     

Mapping and use of seed protein loci for marker-assisted selection of growth habit and photoperiod response in <Emphasis Type="Italic">Nuña</Emphasis> bean (<Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> L.)

The individual segregations of 14 seed protein loci named, SpA to SpM and Pha (phaseolin), were analyzed in a RIL population developed from the cross Xana × Cornell 49242. These seed protein loci were included in a genetic map previously developed in the same population. Protein loci, SpA, SpB, SpE, SpI, SpJ, and Pha, are organized in two different clusters, both located in linkage group (LG) 7; SpF, SpG, SpK, SpL, and SpM, form a single cluster in LG 4; SpC, is located in LG 3; and SpD, in LG 1. A close linkage was identified between the SpD seed protein locus, and the fin gene, controlling determinate growth habit. The usefulness of the SpD locus as a marker for the indirect selection of determinate growth habit and photoperiod insensitivity was checked in a F₂ population derived from the cross G12587 (an indeterminate and photoperiod sensitive nuña bean) × Sanilac (determinate and photoperiod insensitive) and in a set of Mesoamerican and Andean genotypes. Results indicate that SpD protein locus was useful to detect individuals having determinate growth habit and photoperiod insensitivity in the cross G12587 × Salinac although some recombinants were found. However, the linkage between the SpD locus and the genes controlling growth habit and photoperiod sensitivity should be checked before using the SpD locus for the indirect selection of these traits in different backgrounds.     

Chromosomal location of genes for resistance to powdery mildew in <Emphasis Type="Italic">Agropyron cristatum</Emphasis> and mapping of conserved orthologous set molecular markers

Agropyron cristatum exhibits resistance to Blumeria graminis f. sp. tritici. Disomic and ditelosomic chromosome addition lines of A. cristatum in ‘Chinese Spring’ wheat were utilized to determine which A. cristatum chromosomes carry resistance gene(s). Resistance is conferred by gene(s) on chromosome arms 2PL and 6PL. The availability of molecular markers capable of detecting these chromosome arms in a wheat background would be very useful for marker-assisted introgression of 2PL and 6PL chromatin into common wheat. With this aim, 170 wheat conserved orthologous set (COS) markers (92 and 78 from wheat homoeologous groups 2 and 6 respectively) were assessed for their utility in A. cristatum. A total of 116 (68.2%) COS markers successfully amplified product in A. cristatum and 46 (40.0%) of these markers were polymorphic between A. cristatum and common wheat. From marker loci mapping on wheat homoeologous group 2 chromosomes, 23 markers (34.9%) were polymorphic between A. cristatum and common wheat and from them 13 markers were assigned to chromosome arm 2PL and six markers were mapped to chromosome 4P of A. cristatum showing that this chromosome is related to wheat homoeologous group 2. From marker loci mapping on wheat homoeologous group 6 chromosomes, 23 (46.0%) markers were polymorphic between A. cristatum and common wheat and from them 17 markers were located on chromosome 6P, six of them were mapped to chromosome arm 6PS and five to chromosome arm 6PL, respectively. The specific COS markers allocated on the long arms of chromosomes 2P and 6P may have a role in marker-assisted screening in wheat breeding for powdery mildew disease resistance.     

Genome-wide SNP-based association mapping of resistance to <Emphasis Type="Italic">Phytophthora sojae</Emphasis> in soybean (<Emphasis Type="Italic">Glycine max</Emphasis> (L.) Merr.)

Phytophthora root rot (PRR) is among the most important soybean (Glycine max (L.) Merr.) diseases worldwide, and the host displays complex genetic resistance. A genome-wide association study was performed on 337 accessions from the Yangtze-Huai soybean breeding germplasm to identify resistance regions associated with PRR resistance using 60,862 high-quality single nucleotide polymorphisms markers. Twenty-six significant SNP-trait associations were detected on chromosomes 01 using a mixed linear model with the Q matrix and K matrix as covariates. In addition, twenty-six SNPs belonged to three adjacent haplotype blocks according to a linkage disequilibrium blocks analysis, and no previous studies have reported resistance loci in this 441 kb region. The real-time RT-PCR analysis of the possible candidate genes showed that two genes (Glyma01g32800 and Glyma01g32855) are likely involved in PRR resistance. Markers associated with resistance can contribute to marker-assisted selection in breeding programs. Analyses of candidate genes can lay a foundation for exploring the mechanism of P. sojae resistance.     

Development of RAPD and ISSR derived SCAR markers linked to <Emphasis Type="Italic">Xca1Bo</Emphasis> gene conferring resistance to black rot disease in cauliflower (<Emphasis Type="Italic">Brassica oleracea</Emphasis> var. <Emphasis Type="Italic">botrytis</Emphasis> L.)

Black rot caused by Xanthomonas campestris pv. campestris (Xcc) (Pam.) is the most devastating disease of cauliflower (Brassica oleracea var. botrytis L.; 2n = 2x = 18), taking a heavy toll of the crop. In this study, a random amplified polymorphic DNA (RAPD) and inter simple sequence repeat (ISSR) derived sequence characterized amplified region (SCAR) markers linked to the black rot resistance locus Xca1bo were developed and evaluated as a screening tool for resistance. The RAPD marker OPO-04₈₃₃ and ISSR marker ISSR-11₆₃₅ were identified as closely linked at 1.6 cM distance to the black rot resistance locus Xca1bo. Both the markers OPO-04₈₃₃ and ISSR-11₆₃₅ were cloned, sequenced and converted into SCAR markers and validated in 17 cauliflower breeding lines having different genetic backgrounds. These SCAR markers (ScOPO-04₈₃₃ and ScPKPS-11₆₃₅) amplified common locus and showed 100% accuracy in differentiating resistant and susceptible plants of cauliflower breeding lines. The SCAR markers ScOPO-04₈₃₃ and ScPKPS-11₆₃₅ are the first genetic markers found to be linked to the black rot resistance locus Xca1bo in cauliflower. These markers will be very useful in black rot resistance marker assisted breeding.     

Antixenosis and antibiosis mechanisms of resistance to pod borer, <Emphasis Type="Italic">Helicoverpa armigera</Emphasis> in wild relatives of chickpea, <Emphasis Type="Italic">Cicer arietinum</Emphasis>

The noctuid pod borer, Helicoverpa armigera is one of the most damaging pests of chickpea, Cicer arietinum. The levels of resistance to H. armigera in the cultivated chickpea are low to moderate, but the wild relatives of chickpea have exhibited high levels of resistance to this pest. To develop insect-resistant cultivars with durable resistance, it is important to understand the contribution of different components of resistance, and therefore, we studied antixenosis and antibiosis mechanisms of resistance to H. armigera in a diverse array of wild relatives of chickpea. The genotypes IG 70012, PI 599046, IG 70022, PI 599066, IG 70006, IG 70018 (C. bijugum), ICC 506EB, ICCL 86111 (cultivated chickpea), IG 72933, IG 72953 (C. reticulatum), IG 69979 (C. cuneatum) and IG 599076 (C. chrossanicum) exhibited non preference for oviposition by the females of H. armigera under multi-choice, dual-choice and no-choice cage conditions. Based on detached leaf assay, the genotypes IG 70012, IG 70022, IG 70018, IG 70006, PI 599046, PI 599066 (C. bijugum), IG 69979 (C. cuneatum), PI 568217, PI 599077 (C. judaicum) and ICCW 17148 (C. microphyllum) suffered significantly lower leaf damage, and lower larval weights indicating high levels of antibiosis than on the cultivated chickpea. Glandular and non-glandular trichomes showed negative correlation with oviposition, while the glandular trichomes showed a significant and negative correlation with leaf damage rating. Density of non-glandular trichomes was negatively correlated with larval survival. High performance liquid chromatography (HPLC) fingerprints of leaf surface exudates showed a negative correlation of oxalic acid with oviposition, but positive correlation with malic acid. Both oxalic acid and malic acid showed a significant negative correlation with larval survival. The wild relatives exhibiting low preference for oviposition and high levels of antibiosis can be used as sources of resistance to increase the levels and diversify the basis of resistance to H. armigera in cultivated chickpea.     

Mapping of new resistance (<Emphasis Type="Italic">Vr2</Emphasis>, <Emphasis Type="Italic">Rm1</Emphasis>) and ornamental (<Emphasis Type="Italic">Di2</Emphasis>, <Emphasis Type="Italic">pl</Emphasis>) Mendelian trait loci in peach

Peach powdery mildew is one of the major diseases of the peach. Various sources of resistance to PPM have thus been identified, including the single dominant locus Vr2 carried by the peach rootstock ‘Pamirskij 5’. To map Vr2, a linkage map based on microsatellite markers was constructed from the F₂ progeny (WP²) derived from the cross ‘Weeping Flower Peach’ × ‘Pamirskij 5’. Self-pollinations of the parents were also performed. Under greenhouse conditions, all progenies were scored after artificial inoculations in two classes of reactions to PPM (resistant/susceptible). In addition to Vr2, WP² segregated for three other traits from ‘Weeping Flower Peach’: Rm1 for green peach aphid resistance, Di2 for double-flower and pl for weeping-growth habit. With their genomic locations unknown or underdocumented, all were phenotyped as Mendelian characters and mapped: Vr2 mapped at the top of LG8, at 3.3 cM, close to the CPSCT018 marker; Rm1 mapped at the bottom of LG1, at a position of 116.5 cM, cosegregating with the UDAp-467 marker and in the same region as Rm2 from ‘Rubira’^®; Di2 mapped at 28.8 cM on LG6, close to the MA027a marker; and pl mapped at 44.1 cM on LG3 between the MA039a and SSRLG3_16m46 markers. Furthermore, this study revealed, for the first time, a pseudo-linkage between two traits of the peach: Vr2 and the Gr locus, which controls the red/green color of foliage. The present work therefore constitutes a significant preliminary step for implementing marker-assisted selection for the four major traits targeted in this study.     

Marker assisted selection (MAS) for developing powdery mildew resistant pea cultivars

In this contribution we review the state of the art for genetic resistance to powdery mildew, caused by Erysiphe pisi, in pea (Pisum sativum L.) and potential use of marker-assisted selection (MAS) for developing disease resistant cultivars. Powdery mildew is important in many production regions worldwide and reduces yield and crop quality when present in epidemic proportions. Although genetic resistance to powdery mildew is available (er1 and er2) and has been durable since its characterization in 1969, recently a new dominant gene (Er3) has been reported in Pisum fulvum, a wild relative of pea that is different from previously reported er1 and er2. The efficacy of these genes may be at risk from the point of view of new pathotypes and pathogens. Erysiphe trifolii has been reported that was not previously known as a pathogen of pea powdery mildew. A continued search for new and diverse resistant sources remains a priority in pea breeding and special emphasis should be paid to selection of resistance that will prolong durability of existing resistance genes. Marker assisted selection is a new emerging approach for target breeding that has been intensively employed especially in cereals and has recently got popularity among legume breeders. With the advancement of genomic research, especially related to quantitative traits loci, the MAS is potentially anticipated future technique for routine plant breeding that is scarce in legumes at present. In pea, various DNA markers have been reported linked to er1, er2 and Er3 at varying distances in different mapping populations that are currently being used in breeding programs. Currently MAS of single gene is the most powerful approach and successes have been witnessed. If single marker is not close enough to the gene of interest then two flanking markers are considerably utilized to improve the correct identification that is being successfully employed in MAS for powdery mildew resistance in pea.     

Karyotype analysis of eight wild <Emphasis Type="Italic">Tulipa</Emphasis> species native to China and the interspecific hybridization with tulip cultivars

The information of ploidy, karyotype and genetic relationship is useful for interspecific hybridization in ornamental plants. For Tulipa species native to China, very limited cytological information is available now. The objective of this study was to verify the chromosome number, karyotype and genetic relationship of the eight Tulipa species: T. edulis, T. schrenkii, T. iliensis, T. thianschanica, T. altaica, T. sinkiangensis, T. heterophylla and T. buhseana. And the interspecific crosses were made between T. altaica and ten tulip cultivars to obtain novel germplasm. The ovary-swelling, fruit-setting and bulblet formation rates were surveyed when different ploidy cultivars were used as female parents. This work confirmed that all eight species collected in China were diploid (2n?=?2x?=?24), among which chromosome numbers of T. thianschanica, T. sinkiangensis and T. heterophylla were firstly reported and the karyotypes of all any other species except for T. edulis were determined for the first time. The karyotypes of eight Tulipa species were classified as 3A, 4A or 3B. The results of interspecific hybridization showed significant difference when different ploidy cultivars were used as female parents. The highest fruit-setting rate was obtained when diploid cultivars were used as female parents crossed with diploid T. altaica, whereas the ovary swelling was observed in two out of four triploid cultivars as female parents, and no seeds were harvested when tetraploid cultivars were used as female parents. Our findings provided an effective means of cultivar improvement in tulip.     

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.     

The Híbrido de Timor germplasm: identification of molecular diversity and resistance sources to coffee berry disease and leaf rust

The main phytosanitary problems affecting global coffee production are the fungal diseases known as rust, caused by Hemileia vastatrix Berkeley and Broome, and coffee berry disease (CBD), induced by Colletotrichum kahawae Waller and Bridge. The main disease control strategy is the use of resistant coffee cultivars. Híbrido de Timor is the most important source of resistant varieties used in breeding programs worldwide. The objective of this work was to characterize the diversity and disease resistance of 152 HdT genotypes from the germplasm collection at the Universidade Federal de Viçosa (UFV). Accessions were phenotyped with H. vastatrix races II and XXXIII. Molecular analysis was carried out with 29 random microsatellite markers or single sequence repeats (SSRs), and two SSRs associated with the CBD resistance gene Ck-1. All accessions in the germplasm collection were resistant to H. vastatrix race II, and 141 were resistant to H. vastatrix race XXXIII. Based on the presence of markers, there were 106 accessions containing the CBD resistance gene Ck-1. In the diversity study, the 152 accessions clustered into 21 different groups. A unique molecular profile (fingerprint) was determined for each individual, using 52 alleles from 22 SSR markers. The HdT germplasm of UFV was highly diverse, and included 99 accessions with multiple disease resistance genes, including the CBD resistance gene Ck-1, and others conferring resistance to H. vastatrix races II and XXXIII.