Genetic Control Of Resistance Research Articles

Insights into the Key Genes in Cucumis melo and Cucurbita moschata ToLCNDV Resistance

Tomato leaf curl New Delhi virus (ToLCNDV, family Geminiviridae, genus Begomovirus) is a whitefly-transmitted virus that causes widespread damage in Cucurbitaceae and Solaneceae crops worldwide. The Spanish strain, ToLCNDV-ES, affects mainly cucurbit crops and has spread through the Mediterranean basin since its first detection in 2013 in the south of Spain. The control of the virus has been based on the adoption of measures to control the vector, which have not been sufficient to reduce production losses. Therefore, the identification of key genes for ToLCNDV resistance is essential for the development of resistant plants. Regarding genetic control of resistance in cucurbit crops, one major locus on chromosome 11 and two additional regions in chromosomes 12 and 2 of C. melo linked to ToLCNDV resistance have been described recently. Concerning C. moschata, a major QTL was also identified on chromosome 8 that resulted in synteny with a QTL on chromosome 11 of C. melo. In this work, we investigated the molecular basis of ToLCNDV resistance in contrasting accessions of C. melo and C. moschata by transcriptional characterization of 10 different candidate genes controlling host factors related to proviral or antiviral mechanisms. Two proviral factor genes, ARP4 in C. melo and SYTA in C. moschata, showed clear differences in expression levels when the susceptible and resistant accessions were compared. The knowledge of proviral factors associated with resistance could be used to screen an active mutagenesis TILLING platform. This is the case of C. pepo, in which no ToLCNDV resistance has been described to date. The relationship between the regulation of the genes ARP4 and SYTA, as well as the genome position of the described loci related to ToLCNDV resistance, is also discussed.

Genetic analysis of bacterial wilt resistance in eggplant (Solanum melongena L.)

Bacterial wilt triggered by Ralstonia solanacearum is one of the major devastating diseases causing significant yield reduction in eggplant. F1 hybrids (18 CARI-1 based F1 hybrids and 12 publicly available hybrids/varieties) were evaluated for bacterial wilt resistance, yield, and yield attributing traits. CARI-1 based F1 hybrids showed superiority in yields, however showed a varied level of resistance to bacterial wilt. Further, inheritance and gene action involved in resistance to Ralstonia solanacearum was studied. CARI-1 was crossed with two susceptible parents, Arka Neelachal Shyama and Pusa Purple Long to develop six generations for both the combinations. The genetic control of resistance to bacterial wilt was found to be polygenic in the case of the Arka Neelachal Shyama x CARI-1 derived population. While di-genic with complementary gene action in the case of Pusa Purple Long x CARI-1 F2 population, however deviation in expected ratios was observed in back cross populations. Generation mean analysis revealed the presence of epistasis. For Arka Neelachal Shyama x CARI-1 derived population, owing to the prevalence of additive × additive non-allelic interaction with a negative sign, delaying of selection to later generations, otherwise inter mating between the selected segregates accompanied by selfing for one or more generation(s) is advised for the aggregation of favorable alleles for enhancement of resistance. Similarly, for Pusa Purple Long x CARI-1 population, the simple selection can be efficient due to the prevalence of additive gene action. The inheritance details accumulated in this study would facilitate the introgression of bacterial wilt resistance into elite commercial genotypes.

Patterns of inheritance for cotyledon resistance against Sclerotinia sclerotiorum in Brassica napus

Sclerotinia rot, caused by the fungal pathogen Sclerotinia sclerotiorum, is a devastating disease on oilseed rape and mustard worldwide. While the focus to effectively control yield losses from Sclerotinia has been on locating stem resistance, resistance to leaf and to early (cotyledon) stage resistance to this pathogen are also important, both not only limiting additional plant damage, but also inoculum build up and spread onto stems. Three Brassica napus breeding populations developed in India, C2 (NC-8 × RQ-001-NCA-8 NC2-7), C5 (cv. Charlton × RQ-001-NCA-8 NC2-7) and C6 (cv. Charlton × NC4-5), were screened for cotyledon resistance (based on lesion diameter) under controlled environmental conditions to investigate the inheritance of disease resistance. Each population consisted of parents (P1 and P2), F1, F2, BC1P1 and BC2P2, except for population C5 which lacked BC1P1. Moderate broad sense heritability of 0.42, 0.31 and 0.49 for cotyledon resistance was found in populations C2, C5 and C6, respectively, and there was mostly non-additive genetic control of resistance. Analyses of generation means and variances indicated that the additive-dominance model was adequate to explain genetics of cotyledon resistance in population C2. There was heterosis for susceptibility (i.e., larger lesion diameter). The dominance × dominance digenic epistasis explained genetic control in population C6, with heterosis towards resistance (i.e., smaller lesion diameter). This information is critical for breeding for resistance to this important pathogen in Australia, India and elsewhere.

НАСЛЕДОВАНИЕ ЭФФЕКТИВНОЙ ЮВЕНИЛЬНОЙ УСТОЙЧИВОСТИ ШЕСТИ ОБРАЗЦОВ AEGILOPS SPELTOIDES TAUSCH К ЛИСТОВОЙ РЖАВЧИНЕ

Background. Leaf rust (causal agent: Puccinia triticina Erikss.) is a serious disease of bread wheat in all crop-growing regions. An environmentally safe and economically profitable method to protect plants is cultivation of resistant varieties. Their development requires searching for the forms carrying new genes of resistance. Despite the fact that more than 70 Lr genes have been described, only two (Lr39(41) and Lr47) are effective in the seedling stage over all the territory of the Russian Federation. Thus, expanding the set of effective leaf rust resistance genes is a high-priority task. An important source of such genes are wild relatives of Triticum aestivum L., including Aegilops L. species. Knowing genetic control of resistance in newly identified forms will help to avoid the transfer of the same alien resistance genes onto bread wheat. Materials and methods. Inheritance of effective juvenile leaf rust resistance was studied in 6 accessions of Ae. speltoides Tausch from the VIR collection. Crossings were carried out in the field of Pushkin and Pavlovsk Laboratories of VIR (St. Petersburg). Genetic control of resistance to the disease was analyzed in the following accessions of Ae. speltoides: k-1000 (Turkey), k-1015 (Afghanistan), k-1593 (Iraq), k-2279 (Iran), k-2753 and k-2819 (unknown origin). Results and conclusions. The analysis of segregation for seedling resistance to leaf rust in F 2 и F 3 from the crosses between the 6 studied accessions and the susceptible Ae. speltoides accession k-1596 showed that each of them possessed one dominant resistance gene. The absence of susceptible plants in hybrid populations from the crosses between resistant accessions testified to a tight linkage or, more likely, the identity of their genes associated with resistance. The identified resistance gene cannot be identical to Lr28, Lr35, Lr36 and Lr51, earlier introgressed into the T. aestivum genome from Ae. speltoides. Before the introgression of the newly identified gene, it is necessary to study its identity to Lr47 using the phytopathological test; the use of molecular markers for this purpose is little informative.

Molecular and phenotypic identification of B-genome introgression linked to Leptosphaeria maculans resistant gene Rlm6 in Brassica napus × B. juncea interspecific hybrids

Blackleg is a devastating disease in canola worldwide, except in China, caused by the fungal pathogen Leptosphaeria maculans. The B-genome Brassica species were reported to have a strong resistance to the blackleg pathogen L. maculans. Backcross (BC) generations, BC1F1 to BC4F1, were derived from a cross B. napus × B. juncea. Phenotype of L. maculans isolate J20 showed that 49% of BC1F1, 27% of BC2F1, 15% of BC3F1, and 10% of BC4F1 plants were resistant to the isolate J20. Offspring from the interspecific hybridization were also analysed for the presence of dominant type SCAR markers detecting loci linked to the B. juncea genome. The plants with B. juncea introgression had a decrease in the presence of SCAR markers ranging from 47% in BC1F1 to 30% in BC2F1 and further down to 18% in BC3F1 and 11% in BC4F1 with respect to the marker B5Rlm6_1. A similar trend of loci reduction was also observed for the marker B5-1520. In contrast, the progression of the B. napus genome correlated with an incremental increase in the presence of the two markers with the advancement of the generations. However, segregation of SCAR markers and phenotypes for the blackleg resistance in BC1F1 plants had an acceptable fit to a Mendelian ratio of resistant versus susceptible, supporting the assumption that the genetic control of resistance is governed by a single dominant gene. The BC generations developed in this study, which show introgression of the B. juncea genome linked to the L. maculans resistance gene Rlm6, would facilitate breeding a B. napus variety resistant to blackleg in the future.

Development of molecular markers linked to the Leptosphaeria maculans resistance gene Rlm6 and inheritance of SCAR and CAPS markers in Brassica napus × Brassica juncea interspecific hybrids

AbstractLeptosphaeria maculans causes blackleg disease on Brassica napus, an economically important oilseed crop. Brassica juncea has high resistance to blackleg and is a source for the development of resistant B. napus varieties. To transfer the Rlm6 resistance gene from B. juncea into B. napus, an interspecific cross between B. napus “Topas DH16516” and B. juncea “Forge” was produced, followed by the development of F2 and F3 generations. Sequence characterized amplified region (SCAR) and cleaved amplified polymorphic sequence (CAPS) markers linked to the L. maculans resistance gene Rlm6 were developed. Segregation of SCAR and CAPS markers linked to Rlm6 were confirmed by genotyping of F2 and F3 progeny. Segregation of CAPS markers and phenotypes for blackleg disease severity in F2 plants had a Mendelian ratio of 3:1 in resistant vs. susceptible plants, respectively, supporting the assumption that genetic control of resistance was by a single dominant gene. The molecular markers developed in this study, which show linkage with the L. maculans resistance gene Rlm6, would facilitate marker‐assisted backcross breeding in a variety development programme.

Моделювання природної еволюції видів роду Solanum L. cекції Petota Dumort. за фітофторостійкістю

<p>The article presents the theoretical substantiation and experimental data, confirming the natural evolution of potato species from the standpoint of the stability and effectiveness of genetic control of resistance to late blight. Resistant samples of wild potato species which were differ in the appearance of the trait were used as the initial material for research. Artificial infection of seedlings obtained from self-pollination of potato samples with the race of phytophthora (<em>Phytophtora infestans </em>(Mont.) De Bary) 1-11X, Y, Z (25-30 conidia in the view of the microscope, 120 x), which made it possible to identify various types of resistance to fungus. The evolutionary changes of the species, relating their response to the changing of phytopathological situation in their areas have been experimentally proven. The intraspecific variety of <em>S. demissum </em>Lindl and <em>S. stoloniferum </em>Schlechtd. samples by resistance to phytophthora, which manifested both among I1 and among I2, has been identified. Depending on the evolution of the samples, differences in the genetic control of resistance to the pathogen were found, which was manifested in the frequency of appearance of offspring with high resistance, hypersensitivity, high, medium and low field resistance, as well as complete damage of seedlings. In the species of <em>S. demissum</em> the sample was found, in its progeny the seedlings with extremely high resistance to the pathogen were not isolated, but in the case of the UK sample No 27-19 the part of such material was 94.2%. The lower level of genetic control in this species was characterized by the type of supersensitive resistance. Variation in the offspring samples by this type of resistance was observed in the range of 0-78.4%, and the splitting of seedlings with high field stability was even smaller and was within 0-45%. Similar data were obtained for the species of <em>S. stoloniferum</em>. A similar type of conjugate evolution of phytophthora resistance in the testing species has been experimentally proved. There were no differences in the manifestation of hypersensitive resistance or they were very insignificant. The maximum differences between species were 4% in the class with the offspring frequency of 81-100%. Based on the results of the phytophthora resistance evaluation of various samples of potato species in I2, it was assumed that under epiphytotic conditions in the area of species growth, samples with effective genetic control of the trait, i.e., with an extremely high degree of resistance, will be evolutionally promising. </p>

Sorghum [Sorghum bicolor (L.) Moench] breeding for resistance to leaf and stalk anthracnose, Colletotrichum sublineolum, and improved yield: Progress and prospects

Sorghum is one of the main staple food crops for millions of subsistence farmers in Africa. Biotic and abiotic challenges are the major production constraints of the crop. Amongst the sorghum biotic constraints, anthracnose is the major devastating disease causing up to 80% of yield reduction. The productivity and profitability of sorghum is limited by several biotic constraints, most notably anthracnose caused by the aggressive fungal pathogen Colletotrichum sublineolum. The most effective and environmentally responsible strategy to control anthracnose is through the incorporation of resistance genes. However, although several sources have been identified, the lack of information with regard to its genetic control of resistance has limited their adequate use in breeding programs. Additionally, the limitations of breeding regarding the leaf and stalk anthracnose resistance and also the need for evaluating materials for resistance and yield in different environments is of major importance. There is limited information about the combining ability, gene action and genetic effects and relationships between anthracnose resistance and grain yield which is required in devising appropriate strategies for developing resistant and high yielding sorghum varieties. This review provides theoretical basis of the progress and challenges for breeding sorghum for anthracnose resistance and improved yield.

Genetic analysis and gain from selection of thrips resistance in cotton

Host plant resistance, in integrated systems, could be a critical tool for reducing thrips damage to seedling cotton. Plant breeders, however, need information regarding the genetic nature of resistance for effective and efficient introgression into breeding material. Trials were conducted in 2011–2014 at the Texas A&M AgriLife Research and Extension Center at Lubbock to elucidate the genetic nature of thrips resistance and the gains to be expected from visual phenotypic selection. Another objective was to validate a visual rating system for assessing thrips feeding injury in seedling cotton. Broad sense heritability (H 2 ) ranged 41–67%, depending on the family. H 2 was higher in families with a day-neutral resistant parent than those with a photoperiodic resistant parent. Observed segregation ratios fit 3:1, 13:3, and 11:5 expected resistant/susceptible ratios, although nearly all of the phenotypic distributions exhibited closer fits to two-gene models. Additionally, the visual rating scale utilized in these evaluations exhibited a strong correlation (r s = 0.884) with directly-quantifiable leaf area reduction data. These results suggest that thrips resistance is a dominant trait, under a high level of genetic control. There also appears to be at least a second gene (Thr2) aiding in genetic control of resistance. Actual gain from selection ranged 2–21% per cycle of selection, depending on the selection intensity. Optimum selection intensity in these evaluations was 5%, resulting in an approximate 21% gain. These evaluations revealed that host plant thrips resistance varies widely in cotton and can be sufficiently captured and advanced by plant breeders using visual selection.

Diallel crosses for resistance to Macrophomina phaseolina and Thanatephorus cucumeris on cowpea.

This study aimed at identifying and selecting through partial diallel analysis, segregating populations of cowpea resistant to Macrophomina phaseolina and Thanatephorus cucumeris, based on the evaluation of general (GCA) and specific combining ability (SCA), involved in the genetic control of resistance. For this reason, 19 grouped cowpea genotypes, considering the resistance to these pathogens, were crossed in partial diallel scheme 14 x 5, during 2013 and 2014. The 70 F2 populations and the 19 parents were evaluated in a greenhouse as the reaction to pathogens, separately. The diallel analysis was performed according to the model of partial diallel proposed by Geraldi and Miranda Filho (1988). The additive effects predominated in the genetic control of the traits severity of charcoal rot (SEV) and area under the disease progress curve (AUDPC) to web blight, enabling the achievement of genetic gain with selection of resistant strains. Analyzing the effects of GCA, the parents BR 14-Mulato, BRS Tumucumaque and BRS Guariba, have a higher concentration of favorable alleles, highlighting, according to the values of SCA, the combinations BR 14-Mulato x MNC02-675F-4-10, BRS Tumucumaque x IT98K-1092-1, BRS Tumucumaque x MNC02-675F-4-10, BRS Tumucumaque x MNC02-675F-9-2, BRS Guariba x IT98K-1092-1, BRS Guariba x MNC02-675F-4-9, and BRS Guariba x MNC02-675F-4-10, as the most promising and indicated to obtain lines resistant to M. phaseolina and T. cucumeris in cowpea, simultaneously.

Genetic control of resistance on Mangifera indica to Ceratocystis wilt

Ceratocystis wilt, caused by Ceratocystis fimbriata is one of the most serious limiting factors for mango production in Brazil. Despite efforts in the selection and the identification of mango cultivars resistant to Ceratocystis wilt, the genetic basis of the resistance remains unknown. Therefore, the objective of this study was to understand the inheritance of resistance to C. fimbriata by artificial inoculations of the pathogen in progenies of six commercial varieties of mango using “Tommy Atkins” as the male parent. The cultivars “Keitt”, “Palmer”, “Tommy Atkins” and “Van Dyke” were confirmed as moderately resistant, whereas “Coquinho”, “Espada” and “Haden” were susceptible. The results of the inoculation on the progenies of these cultivars revealed that the resistance in mango is polygenic with a prevalence of genes expressing the effects of dominance and epistasis. The genetic gain with the selection of the 10 more resistant plants was 46%, which indicated a 46% reduction in disease severity. In general, a low frequency of the alleles favorable to disease resistance was observed in the population studied, which suggests the need for the introduction of new sources of genetic materials carrying the genes responsible for resistance.

Tecnologia de duplo haploide na determinação da herança da resistência à podridão de colmo (Fusarium verticilioides) em linhagens de milho

RESUMO Foram utilizadas no trabalho quatro populações sintetizadas pelo cruzamento de duas linhagens homozigotas contrastantes quanto a resistência a F.verticilioides. Para a obtenção das linhagens haploides destas populações as mesmas foram cruzadas com indutor de haploidia, os haploides foram então duplicados e autofecundados, sendo as sementes colhidas fonte de origem das linhagens usadas no trabalho. Aos 70 dias após a semeadura as linhagens foram inoculadas com suspensão de esporos do patógeno F.verticilioides em concentração de 2 106esporos por mL e com 70 dias após a inoculação as espigas foram colhidas e pesadas e os colmos foram coletados, pesados e medidos em comprimento e diâmetro e seccionados longitudinalmente para avaliações dos sintomas, onde também foram medidos os comprimentos das lesões. Foram estimadas às variâncias fenotípica, ambiental, genotípica total e entre e dentro famílias, além da herdabilidade e da variância aditiva e de dominância. A variância devido a efeitos genéticos dominantes foram de maior magnitude, sendo que a herdabilidade no sentido restrito foi de 0,28. A distribuição de frequência observada podem indicar efeitos epistáticos envolvidos no controle genético da resistência a F.verticilioides. Os maiores ganhos esperados com a seleção foram alcançados com o emprego de seleção entre família e seleção massal.

Greenbug resistance in barley accessions from East and South Asia

Heterogeneous forms differing in level of expressing resistance to the Krasnodar greenbug population have been revealed as a result of studying 1358 barley accessions from East and South Asian countries. High resistance of 98 accessions is controlled by alleles not identical to alleles of the earlier identified Rsg1 gene. A difference in genetic control of resistance in barley landraces from China and North Korea was found.

Genetic Variation and Gains in Resistance of Strawberry to Colletotrichum gloeosporioides

Anthracnose crown rot is an important disease of strawberry primarily caused by Colletotrichum gloeosporioides in Florida and North Carolina. Information on the magnitude of additive and nonadditive genetic variation is required to define breeding strategies and to estimate potential genetic gains. However, little is known about the genetic control of resistance and its utility in breeding. Our objectives were to obtain estimates of heritabilities and of components of genetic variances, genotype-environment interactions, and gains for resistance, and to examine the effects of locations and transplant types on the estimates. An incomplete diallel mating design generated 42 full-sib families, which were propagated in plugs from seed (seedling tests) and as bare-root runner plants (clonal tests) of different genotypes of the same families. Both seedlings and clones were inoculated with C. gloeosporioides under field conditions in North Carolina and Florida during the 2010-11 season. Narrow-sense heritability (h(2)) and broad-sense heritability (H(2)) for both clones and seedlings were higher at the North Carolina location (h(2) = 0.34 to 0.62 and H(2) = 0.46 to 0.85) than at the Florida location (h(2) = 0.16 to 0.22 and H(2) = 0.37 to 0.46). Likewise, the seedling tests showed higher genetic control than the clonal tests at both locations. Estimates of dominance variance were approximately one-third of the additive variance at North Carolina and were even larger at Florida. Epistasis was negative at both locations and assumed zero for heritability (H(2)) calculations. Genotype-environment interactions were different by transplant type, suggesting rank changes across locations. 'Pelican' was the most resistant parent at both locations, followed by 'NCH09-68' at the NC location and 'Winter Dawn' at the Florida location. Selection and deployment of the most resistant clone within each of the five best families is estimated to produce average genetic gains of 53.0 and 73.7% at the North Carolina and Florida locations, respectively.

Inheritance of resistance to wheat yellow rust at adult plant stage

In order to investigate on inheritance and gene action for resistance to yellow rust, the resistant line C.B227 was crossed with the susceptible variety Avocet. Parents (P1 and P2) and the resulting F1, F2 and F3 generations were planted in a randomised complete block design with two replications in the field. The plants were inoculated with 70E0A+ pathotype of yellow rust in the research station of Gharakhil, Iran, and evaluated for resistance at adult plant stage. Disease severity and infection type of flag leaf were recorded for each single plant and final coefficient of infection was calculated. The results of weighted ANOVA indicated that the difference among the generations was significant (p < 0.01) for the trait final infection type. Generation mean analysis showed that dominant effect was more important than additive one. The degree of dominance indicated the presence of complete dominance. Additive, dominance and epistasic additive × additive [i] effects were important in genetic control of resistance. The results of generation variance analysis were consistent with generation mean analysis.

Genetic mapping of two genes conferring resistance to powdery mildew in common bean (Phaseolus vulgaris L.)

Powdery mildew (PM) is a serious disease in many legume species, including the common bean (Phaseolus vulgaris L.). This study investigated the genetic control behind resistance reaction to PM in the bean genotype, Cornell 49242. The results revealed evidence supporting a qualitative mode of inheritance for resistance and the involvement of two independent genes in the resistance reaction. The location of these resistance genes was investigated in a linkage genetic map developed for the XC RIL population. Contingency tests revealed significant associations for 28 loci out of a total of 329 mapped loci. Fifteen were isolated or formed groups with less than two loci. The thirteen remaining loci were located at three regions in linkage groups Pv04, Pv09, and Pv11. The involvement of Pv09 was discarded due to the observed segregation in the subpopulation obtained from the Xana genotype for the loci located in this region. In contrast, the two subpopulations obtained from the Xana genotype for the BM161 locus, linked to the Co-3/9 anthracnose resistance gene (Pv04), and from the Xana genotype for the SCAReoli locus, linked to the Co-2 anthracnose resistance gene (Pv11), exhibited monogenic segregations, suggesting that both regions were involved in the genetic control of resistance. A genetic dissection was carried out to verify the involvement of both regions in the reaction to PM. Two resistant recombinant lines were selected, according to their genotypes, for the block of loci included in the Co-2 and Co-3/9 regions, and they were crossed with the susceptible parent, Xana. Linkage analysis in the respective F2 populations supported the hypothesis that a dominant gene (Pm1) was located in the linkage group Pv11 and another gene (Pm2) was located in the linkage group Pv04. This is the first report showing the localization of resistance genes against powdery mildew in Phaseolus vulgaris and the results offer the opportunity to increase the efficiency of breeding programs by means of marker-assisted selection.

Genetic control of resistance to gray leaf spot of maize in tropical germplasm

The main goal of this study was to assess the nature and magnitude of gene effects for resistance to Cercospora leaf spot. A randomized block design with three replications was used. The data were obtained at the plant level by assessing the disease severity. The data were analyzed per experiment, using the average data per plot. A dominant-additive genetic model without epistasis was considered, with estimation of the components of means and variance. The genetic control of resistance to gray leaf spot is polygenic with predominance of the additive effects. Dominance was observed in a few small-effect loci and high heritability values.

Mapping QTL for resistance to eyespot of wheat in Aegilops longissima

Eyespot is an economically important disease of wheat caused by the soilborne fungi Oculimacula yallundae and O. acuformis. These pathogens infect and colonize the stem base, which results in lodging of diseased plants and reduced grain yield. Disease resistant cultivars are the most desirable control method, but resistance genes are limited in the wheat gene pool. Some accessions of the wheat wild relative Aegilops longissima are resistant to eyespot, but nothing is known about the genetic control of resistance. A recombinant inbred line population was developed from the cross PI 542196 (R) × PI 330486 (S) to map the resistance genes and better understand resistance in Ae. longissima. A genetic linkage map of the S(l) genome was constructed with 169 wheat microsatellite markers covering 1261.3 cM in 7 groups. F(5) lines (189) were tested for reaction to O. yallundae and four QTL were detected in chromosomes 1S(l), 3S(l), 5S(l), and 7S(l). These QTL explained 44 % of the total phenotypic variation in reaction to eyespot based on GUS scores and 63 % for visual disease ratings. These results demonstrate that genetic control of O. yallundae resistance in Ae. longissima is polygenic. This is the first report of multiple QTL conferring resistance to eyespot in Ae. longissima. Markers cfd6, wmc597, wmc415, and cfd2 are tightly linked to Q.Pch.wsu-1S ( l ), Q.Pch.wsu-3S ( l ), Q.Pch.wsu-5S ( l ), and Q.Pch.wsu-7S ( l ), respectively. These markers may be useful in marker-assisted selection for transferring resistance genes to wheat to increase the effectiveness of resistance and broaden the genetic diversity of eyespot resistance.

QTL associated with resistance to defoliation (Cylindrocladium pteridis) in Eucalyptus spp.

Leaf blight and defoliation caused by Cylindrocladium pteridis is one of the main leaf diseases found in Brazilian eucalypt plantations in warm and high rainfall regions. The inter and intraspecific variability in the intensity of defoliation indicate that your control can be achieved by planting resistant genotypes. In order to guide breeding programs and to predict the stability of resistance is essential to understand the genetic control of resistance in eucalypts to defoliation. Thus, the objectives of this paper were to map QTLs (Quantitative Trait Loci) associated with resistance to defoliation in a Eucalyptus urophylla x E. camaldulensis (EU11 x EC06) family and validate microsatellite markers linked to QTLs in four unrelated pedigrees involving different Eucalyptus species. Defoliation was evaluated on the branches of the lower third of the plants inoculated under controlled conditions. We identified five QTLs for resistance to defoliation (Rd), three on the map of the parental EU11, Rd-1 and Rd-2 located on linkage group (LG) 1 and Rd-4 located on LG6; and two QTLs located on the map of the parental EC06, present in LG2 (Rd-3) and LG8 (Rd-5). Markers linked to QTLRd-2 were validated in two unrelated families by simple linear regression analysis. This is the first genomic map of QTLs associated with resistance to defoliation caused by C. pteridis in Eucalyptus.

Rain Damage to Strawberries Grown in Southeast Queensland: Evaluation and Genetic Control

In Queensland, Australia, strawberries (Fragaria ×ananassa Duchesne) are grown in open fields and rainfall events can damage fruit. Cultivars that are resistant to rain damage may reduce losses and lower risk for the growers. However, little is known about the genetic control of resistance and in a subtropical climate, unpredictable rainfall events hamper evaluation. Rain damage was evaluated on seedling and clonal trials of one breeding population comprising 645 seedling genotypes and 94 clones and on a second clonal population comprising 46 clones from an earlier crossing to make preliminary estimates of heritability. The incidence of field damage from rainfall and damage after laboratory soaking was evaluated to determine if this soaking method could be used to evaluate resistance to rain damage. Narrow-sense heritability of resistance to rain damage calculated for seedlings was low (0.21 ± 0.15) and not significantly different from zero; however, broad-sense heritability estimates were moderate in both seedlings (0.49 ± 0.16) and clones (0.45 ± 0.08) from the first population and similar in clones (0.56 ± 0.21) from the second population. Immersion of fruit in deionized water produced symptoms consistent with rain damage in the field. Lengthening the duration of soaking of ‘Festival’ fruit in deionized water exponentially increased the proportion of damage to fruit ranging in ripeness from immature to ripe during the first 6-h period of soaking. When eight genotypes were evaluated, the proportion of sound fruit after soaking in deionized water in the laboratory for up to 5 h was linearly related (r2 = 0.90) to the proportion of sound fruit in the field after 89 mm of rain. The proportion of sound fruit of the breeding genotype ‘2008-208’ and ‘Festival’ under soaking (0.67, 0.60) and field (0.52, 0.43) evaluations, respectively, is about the same and these genotypes may be useful sources of resistance to rain damage.