Introgression Of Resistance Genes Research Articles

Immunogenic breeding program. Stage I-phytopathological screening of the grape gene pool

At the present stage of science development it is necessary to develop and implement the grape breeding programs for immunity basing on the international level of knowledge about the genetics of immunity to pathogens that cause culture diseases. The extensive material on genes of grape resistance to Plasmopara viticola and Erysiphe necator (Uncinula necator), which cause mildew and oidium diseases, has been collected thanks to the MAS technology. There is an evidence of necessity to pyramidize genes of resistance to these pathogens in one progeny genome for consistent field resistance to the complex of these pathogens. However, even at present, the issue of study the transfer of specific genes of resistance from parents to the progeny, their combining ability in one genome, and gene expression during pathogenesis remains relevant. This publication discusses the formation of grape breeding program in the FSBSI Institute Magarach of the RAS on introgression of resistance genes of the species Vitis rotundifolia (Muscadinia rotundifolia), and also presents the results of phytopathological screening of populations resulting from crossing with this species.

Identification of Field Tolerance and Resistance to Mal Secco Disease in a Citrus Germplasm Collection in Sicily

Mal secco is a tracheomycotic disease caused by the fungus Plenodomus tracheiphilus (Petri) Gruyter, Aveskamp, and Verkley that has caused severe damage and loss of yield in the citrus industry in the Mediterranean area, for 100 years. While the disease can affect different cultivated citrus species, lemon (C. × limon var. limon (L.) Burm. f.) and citron are the most susceptible. The identification of resistant or field-tolerant clones and hybrids is a major goal for lemon growers and breeders. To identify sources of resistance or tolerance to the disease, we performed a phenotypic survey on a lemon and lemon-like open-field germplasm planted at CREA (Research Centre for Olive, Fruit and Citrus Crops), Italy, in an area with high pathogen pressure. Phenotyping was performed visually, four times, for three consecutive years, on a total of 50 accessions, with two or three replicate trees per accession. Moreover, molecular screening based on real-time PCR was performed, for two consecutive years, on twigs, young leaves, and mature leaves of all plants, to detect the pathogen in the absence of clear symptoms. The accessions were categorized into seven groups based on the presence of visual symptoms, real-time PCR pathogen detection, and canopy volume. The results revealed sources of tolerance in lemon and citron hybrids. The molecular screening identified P. tracheiphilus in all lemon clones, with mean Ct values ranging from 17 to 39. The screening also identified P. tracheiphilus in clones without clear symptoms, indicating their ability to tolerate the disease. Moreover, a strong negative correlation was found between the Ct values in twigs and symptom severity (r = −0.72). This indicates that the DNA from twigs is the most appropriate for use in performing reliable phenotyping of mal secco susceptibility in adult plants. An autotetraploid lemon (Doppio Lentini) seems to be immune to the disease, under natural pressure, since P. tracheiphilus was not detected by real-time PCR and visual screening. Overall, the data obtained are a valuable resource for identifying both the most tolerant lemon varieties suitable for areas with high pathogen pressure and the best breeding parents for the introgression of resistance genes into lemon genotypes.

Cold-tolerant introgression line construction and low-temperature stress response analysis for bell pepper

ABSTRACT We aimed to screen cold-tolerant introgression lines (ILs) of bell pepper and investigate stress responses of these bell peppers under low temperature. Seedlings of cold-resistant wild-type bell pepper CA157, cultivated bell pepper CA52, and their ILs were evaluated for their tolerance to low temperature. Electrical conductivity measurement was performed on ILs and two parents. Then, contents of physiological and biochemical indexes including malondialdehyde (MDA), proline, and soluble sugar content were examined. Moreover, the superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POD) activities were further investigated. Finally, the chlorophyll fluorescence (PSII) parameters in all pant leaves were examined. A total of 22 IL plants showed better resistance than their recurrent parent CA52. CL122 was one of the most outstanding plants in ILs that had similar performance with wild bell pepper CA157. Cold resistance analysis based on physiological and biochemical indexes showed that factors such as electrical conductivity, MDA, and PSII were closely related to cold resistance among CA157, CA52, and CL122 under low-temperature stress. In conclusion, ILs constructed in the current study might be used for cold resistance gene introgression between wild and cultured species. Moreover, CL122 might be a novel bridge material for understanding low-temperature response in bell pepper. Furthermore, electrical conductivity, MDA, and PSII might be used to identify the low-temperature resistance of bell pepper plants in a period of obvious differentiation.

Introgression of Genes for Resistance against Phytophthora infestans in Diploid Potato

Potato is playing an increasingly important role in food production. The development of new varieties is slow due to the genetic complexity of potato and the inefficient breeding process. Modern techniques, such as hybrid breeding and the introduction of new traits in specific, existing elite material, have not been reported in the development of new and improved potato varieties. This paper describes the first example of marker-assisted introgression of four different Phytophthora infestans resistance genes in selected highly homozygous, diploid potato lines. After two backcrosses and one selfing, the original line can be recovered with Phytophthora resistance, thus providing added value. After crossing two diploid lines, each with a different resistance gene, hybrids were obtained and tested for resistance to Phytophthora in small field trials. In these experiments, the hybrids with two resistance genes were more resistant than the plants with only one of the two resistance genes.

Association mapping of a locus that confers southern stem canker resistance in soybean and SNP marker development

BackgroundSouthern stem canker (SSC), caused by Diaporthe aspalathi (E. Jansen, Castl. & Crous), is an important soybean disease that has been responsible for severe losses in the past. The main strategy for controlling this fungus involves the introgression of resistance genes. Thus far, five main loci have been associated with resistance to SSC. However, there is a lack of information about useful allelic variation at these loci. In this work, a genome-wide association study (GWAS) was performed to identify allelic variation associated with resistance against Diaporthe aspalathi and to provide molecular markers that will be useful in breeding programs.ResultsWe characterized the response to SSC infection in a panel of 295 accessions from different regions of the world, including important Brazilian elite cultivars. Using a GBS approach, the panel was genotyped, and we identified marker loci associated with Diaporthe aspalathi resistance through GWAS. We identified 19 SNPs associated with southern stem canker resistance, all on chromosome 14. The peak SNP showed an extremely high degree of association (p-value = 6.35E-27) and explained a large amount of the observed phenotypic variance (R2 = 70%). This strongly suggests that a single major gene is responsible for resistance to D. aspalathi in most of the lines constituting this panel. In resequenced soybean materials, we identified other SNPs in the region identified through GWAS in the same LD block that clearly differentiate resistant and susceptible accessions. The peak SNP was selected and used to develop a cost-effective molecular marker assay, which was validated in a subset of the initial panel. In an accuracy test, this SNP assay demonstrated 98% selection efficiency.ConclusionsOur results suggest relevance of this locus to SSC resistance in soybean cultivars and accessions from different countries, and the SNP marker assay developed in this study can be directly applied in MAS studies in breeding programs to select materials that are resistant against this pathogen and support its introgression.

Genetic Variability of Passion Fruit Multispecific Hybrids and Their Respective Wild Parents Determined by Microsatellite Markers

The Passiflora genus comprises more than 500 species that are used for food, industrial, ornamental, and pharmaceutical purposes. The sour passion fruit (P. edulis Sims) has low genetic variability for disease resistance, and the use of wild species in the cross-breeding basis is a promising alternative for introgression of resistance genes. The objective of this study was to characterize multispecific hybrids and wild materials with potential to be used as parents in passion fruit genetic breeding programs, using microsatellite markers. Genomic DNA from 33 accessions was extracted and analyzed using 23 microsatellite markers, which were used to estimate the genetic dissimilarities among accessions. The genetic dissimilarity matrices were used to perform clustering analysis by dendrogram using the Unweighted Pair-Group Method as grouping criterion and by graphic dispersion based on multidimensional scale, using the principal coordinates method. Genetic distances between accessions ranged from 0.067 to 1.00. The markers indicated genetic variability among the studied accessions and also the efficiency of the recurrent genome recovery within the backcross program. The genetic structure among the accessions shows the clustering tendency between the wild accessions of P. hatschbachii and P. quadrifaria and the accessions obtained by crossing these species. The same occurred for P. incarnata and P. edulis accessions. The knowledge generated by the molecular characterization provides information on the diversity of accessions and contributes to the work of breeders in the selection of parents.

QTL-seq reveals a major root-knot nematode resistance locus on chromosome 11 in rice (Oryza sativa L.)

The root-knot nematode Meloidogyne graminicola is a serious pest in rice affecting production in many rice growing areas. Natural host resistance is an attractive control strategy because the speed of the parasite’s life cycle and the broad host range it attacks make other control measures challenging. Although resistance has been found in the domesticated African rice Oryza glaberrima and the wild rice species O. longistaminata, the introgression of resistance genes to Asian rice O. sativa is challenging. Resistance due to a major gene in O. sativa would greatly aid breeding. Recently two accessions resistant to M. graminicola have been identified in a screen of 332 diverse O. sativa cultivars. In this study, these two resistant cultivars, LD 24 (an indica from Sri Lanka) and Khao Pahk Maw (an aus from Thailand), were crossed with a moderately susceptible cultivar, Vialone Nano (a temperate japonica from Italy). Approximately 175 F2 progeny of both populations were screened for susceptibility to M. graminicola infection. Between 20 and 23 individuals with highest and lowest galls per plants were pooled to make susceptible and resistant bulks which were sequenced to conduct bulked segregant analysis using the QTL-seq method. This revealed a nematode resistance locus from 23 Mbp to the bottom of rice chromosome 11 in both crosses suggesting a rare introgression of the same locus is responsible for resistance in both cultivars. While this information can be used in marker-assisted breeding, analysis of available SNP data revealed candidate loci and genes worthy of further investigation for gene identification.

Chromosome engineering-mediated introgression and molecular mapping of novel Aegilops speltoides-derived resistance genes for tan spot and Septoria nodorum blotch diseases in wheat.

We identified, mapped and introduced novel Aegilops speltoides-derived resistance genes for tan spot and SNB diseases into wheat, enhancing understanding and utilization of host resistance to both diseases in wheat. Tan spot and Septoria nodorum blotch (SNB) are two important fungal diseases of wheat. Resistance to these diseases is often observed as the lack of sensitivity to the necrotrophic effectors (NE) produced by the fungal pathogens and thus exhibits a recessive inheritance pattern. In this study, we identified novel genes for resistance to tan spot and SNB on Aegilops speltoides (2n = 2x = 14, genome SS) chromosome 2S. These genes confer dominant resistance in the wheat background, indicating a distinct NE-independent mechanism of resistance. Ae. speltoides chromosome 2S was engineered for resistance gene introgression and molecular mapping by inducing meiotic homoeologous recombination with wheat chromosome 2B. Twenty representative 2B-2S recombinants were evaluated for reaction to tan spot and SNB and were delineated by genomic in situ hybridization and high-throughput wheat 90K SNP assay. The resistance genes physically mapped to the sub-telomeric region (~ 8Mb) on the short arm of chromosome 2S and designated TsrAes1 for tan spot resistance and SnbAes1 for SNB resistance. In addition, we developed SNP-derived PCR markers closely linked to TsrAes1/SnbAes1 for marker-assisted selection in wheat breeding. TsrAes1 and SnbAes1 are the first set of NE-independent tan spot, and SNB resistance genes are identified from Ae. speltoides. The 2SS-2BS·2BL recombinants with minimal amounts of Ae. speltoides chromatin containing TsrAes1/SnbAes1 were produced for germplasm development, making the wild species-derived resistance genes usable in wheat breeding. This will strengthen and diversify resistance of wheat to tan spot and SNB and facilitate understanding of resistance to these two diseases.

Inheritance of Striga hermonthica adaptive traits in an early‐maturing white maize inbred line containing resistance genes from Zea diploperennis

AbstractStriga hermonthica can cause as high as 100% yield loss in maize depending on soil fertility level, type of genotype, severity of infestation and climatic conditions. Understanding the mode of inheritance of Striga resistance in maize is crucial for introgression of resistance genes into tropical germplasm and deployment of resistant varieties. This study examined the mode of inheritance of resistance to Striga in early‐maturing inbred line, TZdEI 352 containing resistance genes from Zea diploperennis. Six generations, P1, P2, F1, F2, BC1P1 and BC1P2 derived from a cross between resistant line, TZdEI 352 and susceptible line, TZdEI 425 were screened under artificial Striga infestation at Mokwa and Abuja, Nigeria, 2015. Additive‐dominance model was adequate in describing observed variations in the number of emerged Striga plants among the population; hence, digenic epistatic model was adopted for Striga damage. Dominance effects were higher than the additive effects for the number of emerged Striga plants at both locations signifying that non‐additive gene action conditioned inheritance of Striga resistance. Inbred TZdEI 352 could serve as invaluable parent for hybrid development in Striga endemic agro‐ecologies of sub‐Saharan Africa.

Combinations of Independent Dominant Loci Conferring Clubroot Resistance in All Four Turnip Accessions (Brassica rapa) From the European Clubroot Differential Set

Clubroot disease is devastating to Brassica crop production when susceptible cultivars are planted in infected fields. European turnips are the most resistant sources and their resistance genes have been introduced into other crops such oilseed rape (Brassica napus L.), Chinese cabbage and other Brassica vegetables. The European clubroot differential (ECD) set contains four turnip accessions (ECD1–4). These ECD turnips exhibited high levels of resistance to clubroot when they were tested under controlled environmental conditions with Canadian field isolates. Gene mapping of the clubroot resistance genes in ECD1–4 were performed and three independent dominant resistance loci were identified. Two resistance loci were mapped on chromosome A03 and the third on chromosome A08. Each ECD turnip accession contained two of these three resistance loci. Some resistance loci were homozygous in ECD accessions while others showed heterozygosity based on the segregation of clubroot resistance in 20 BC1 families derived from ECD1 to 4. Molecular markers were developed linked to each clubroot resistance loci for the resistance gene introgression in different germplasm.

Generation of interspecific hybrids for introgression of mungbean yellow mosaic virus resistance in Vigna radiata (L.) Wilczek

Vigna radiata genotypes viz., SML 668 and SML 832 and V. mungo genotypes viz., Mash 114 and Mash 218 were crossed in all possible combinations during summer 2015 to generate F1 hybrids. Interspecific hybridization was attempted by using V. radiata genotypes as female parent. Pod set percentage varied from 5.5 percent (SML 832 x Mash 218) to 24.1 percent (SML 832 x Mash 114). The germination percentage ranged from 14.29 to 30.56. Maximum pollen fertility was observed in cross SML 668 x Mash 114 (28.36 percent) followed by SML 668 x Mash 218 (27.03 percent), SML 832 x Mash 218 (24.32 percent) and minimum in SML 832 x Mash 114 (22.59 percent).The purity of hybrids were tested through microsatellite markers. For parental polymorphism, microsatellite markers were selected from related Vigna species such as Vigna unguiculata, Vigna radiata and Vigna mungo. Out of 84 markers used, 46 were polymorphic i.e 54.76 per cent polymorphism between parents. These polymorphic markers were used for confirmation of hybrids produced from different crosses. All the F1 plants gave resistant reaction to Mungbean yellow mosaic virus (MYMV) indicating the introgression of resistance gene(s) from V. mungo to V. radiata.

Recovery of Valencia Groundnut (Arachis hypogaea L.) Traits in Early Segregating and Promising Late Leaf Spot Resistant Populations

In Uganda, there are no Valencia varieties that are resistant to leaf spot diseases. Introgression of resistance genes into elite lines is always associated with the transfer of undesirable traits from the donor parents. Knowledge of the degree of genetic relationship provides breeders with a more efficient way to identify populations of potential relevance for their plant improvement programs. The objective of this study was to determine the recovery of Valencia groundnut traits in the early segregating and promising late leaf spot (LLS) resistant populations. Four crosses between Valencia lines (P1) and donor lines (P2) were made. The populations that included F1, F2, BC1P1 and BC1P2, together with their parents (P1and P2) of each of the four crosses namely, Valencia C (P1) × ICGV-SM 02501 (P2), Valencia C (P1) × SGV-07009 (P2), NuMex-M3 (P1) × ICGV-SM 02501 (P2) and Redbeauty (P1) × ICGV-SM 03590 (P2) were evaluated. Cluster analysis revealed differences among the generations for the traits analysed with major and sub-clusters, implying that the generations of crosses formed a genetically diverse population that offers possible opportunity for selection. In the cross between NuMex-M3 X ICGV-SM 02501, the populations BC1P1 and F2, exhibited higher (80 %) recovery of the recurrent parental (NuMex-M3) traits. Similarly, the backcross population (BC1P1) to the susceptible elite variety of the Valencia C X ICGV-SM 02501 cross recovered approximately 75% of the recurrent parental traits Valencia C with lower LLS disease score. Such populations could result in higher gain in Valencia traits and LLS resistance when utilized the breeding program. For maximum gain in LLS resistance and recovery of Valencia traits, more selfing and backcrossing can be performed to fix the genes for LLS resistance as well those of Valencia characteristics. Keywords: cluster analysis; Arachis hypogaea; diverse populations

Analysis of differential transcript expression in chickpea during compatible and incompatible interactions with Fusarium oxysporum f. sp. ciceris Race 4.

The present study reports the transcriptome analysis of resistance (WR315) and susceptible (JG62) genotypes of chickpea in response to Fusarium oxysporum f. sp. ciceris (Foc)race 4 using the method of suppression subtractive hybridization. Altogether, 162 chickpea-expressed sequence tags (ESTs) were identified from two libraries and analyzed to catalog eight functional categories. These ESTs could be assembled into 18 contigs and 144 singletons with 10 contigs and 68 singletons from compatible and 8 contigs and 70 singletons from incompatible interaction. The largest category consisted of ESTs which encode for proteins related to hypothetical proteins (22.8%), followed by energy and metabolism (20.3%)-related genes, defense and cell rescue-related genes (17.9%) and signal transduction-related genes (16%). Among them, 17.1 and 18.7% were defense-related genes in compatible and incompatible interaction, respectively. These ESTs mainly includes various putative genes related to oxidative burst, pathogenesis and secondary metabolism. Induction of putative superoxide dismutase, metallothionein, 4-coumarate-CoA ligase, heat shock proteins and cysteine proteases indicated oxidative burst after infection. The ESTs belonged to various functional categories which were directly and indirectly associated with defense signaling pathways. Quantitative and semi-quantitative polymerase chain reaction exhibited differential expression of candidate genes and detected higher levels in incompatible interaction compared to compatible interaction. The present study revealed partial molecular mechanism associated with the resistance in chickpea against Foc, which is the key to design a strategy for incorporation of resistance via either biotechnological means or introgression of resistance genes.

Rewiring of the Fruit Metabolome in Tomato Breeding

Humans heavily rely on dozens of domesticated plant species that have been further improved through intensive breeding. To evaluate how breeding changed the tomato fruit metabolome, we have generated and analyzed a dataset encompassing genomes, transcriptomes, and metabolomes from hundreds of tomato genotypes. The combined results illustrate how breeding globally altered fruit metabolite content. Selection for alleles of genes associated with larger fruits altered metabolite profiles as a consequence of linkage with nearby genes. Selection of five major loci reduced the accumulation of anti-nutritional steroidal glycoalkaloids in ripened fruits, rendering the fruit more edible. Breeding for pink tomatoes modified the content of over 100 metabolites. The introgression of resistance genes from wild relatives in cultivars also resulted in major and unexpected metabolic changes. The study reveals a multi-omics view of the metabolic breeding history of tomato, as well as provides insights into metabolome-assisted breeding and plant biology.

New Sunflower Genotypes with Resistance to Drought, Main Pathogens and Broomrape (Orobanche cumana), Created at NARDI Fundulea

The development of human society in general depends and is conditioned by the presence of fresh water resources. Certainly, the main cause, which has led to the ascending curve of current needs and consumption, is determined by the demographic explosion and the rapid urbanization process. Therefore, industry and agriculture are among the biggest consumers of water. The real problem is not lack of resources but effective distribution and overall management it is. In the context of the aforementioned, at NARDI Fundulea was developed in 2010 a program to improve drought resistance and obtain new genotypes through introgression of resistance genes from Helianthus argophyllus species in cultivated specie (Helianthus annuus L.) (Project MAKIS, Financed by the World Bank). Helianthus argopyllus is the most interesting species with very pubescent leaves, moderate transpiration and good photosynthetic activity. These characters provide superior water use efficiency compared to cultivated species. For these reasons, it has been used in our research to achieve the above-mentioned goal. In this project, at NARDI Fundulea has successfully used interspecific immature embryo culture to obtain drought-resistant genotypes and shortening the breeding process by getting two to three generations/year. Starting with the BC6 generation of self-pollination, the resulted fertile lines (B, maintainer lines) were cross polinated with an androsterility source in order to produce the sterile analogues of these lines (all being B, maintenance, fertile) were performed. After 4-5 generations of sterile plant selection, sterile analogue lines for each of the new creations were obtained. After this, new sunflower hybrids were obtained using certain fertility restoration lines from the NARDI Fundulea collection. The new hybrids were tested in three very different locations and years in terms of rainfall and temperatures during sunflower vegetation (2014-2015-2016). Based on the results we can conclude that interspecific hybridization may be an additional technique in the breeding of the sunflower and can be successfully used to create new sources of genetic variability to improve germplasm for drought and pathogens resistance. The newly created genotypes have responded positively to testing under different climatic and soil conditions and can be included in the approval list for both classical and ecological culture conditions.

A Hypersensitivity-Like Response to Meloidogyne graminicola in Rice (Oryza sativa).

Meloidogyne graminicola is a major plant-parasitic nematode affecting rice cultivation in Asia. Resistance to this nematode was found in the African rice genotypes Oryza glaberrima and O. longistaminata; however, due to interspecific hybrid sterility, the introgression of resistance genes in the widely consumed O. sativa varieties remains challenging. Recently, resistance was found in O. sativa and, here, we report for the first time the histological and genetic characterization of the resistance to M. graminicola in Zhonghua 11, an O. sativa variety. Bright-light microscopy and fluorescence observations of the root tissue of this variety revealed that the root cells surrounding the nematode displayed a hypersensitivity-like reaction with necrotic cells at early stages of infection when nematodes are migrating in the root's mesoderm. An accumulation of presumably phenolic compounds in the nematodes' neighboring root cells was also observed. In addition, at a later stage of infection, not only were few feeding sites observed but also the giant cells were underdeveloped, underlining an incompatible interaction. Furthermore, we generated a hybrid O. sativa population by crossing Zhonghua 11 with the susceptible O. sativa variety IR64 in order to describe the genetic background of this resistance. Our data suggested that the resistance to M. graminicola infection was qualitative rather than quantitative and, therefore, major resistance genes must be involved in this infection process. The full characterization of the defense mechanism and the preliminary study of the genetic inheritance of novel sources of resistance to Meloidogyne spp. in rice constitute a major step toward their use in crop breeding.

Complex Interactions between Fungal Avirulence Genes and Their Corresponding Plant Resistance Genes and Consequences for Disease Resistance Management.

During infection, pathogens secrete an arsenal of molecules, collectively called effectors, key elements of pathogenesis which modulate innate immunity of the plant and facilitate infection. Some of these effectors can be recognized directly or indirectly by resistance (R) proteins from the plant and are then called avirulence (AVR) proteins. This recognition usually triggers defense responses including the hypersensitive response and results in resistance of the plant. R—AVR gene interactions are frequently exploited in the field to control diseases. Recently, the availability of fungal genomes has accelerated the identification of AVR genes in plant pathogenic fungi, including in fungi infecting agronomically important crops. While single AVR genes recognized by their corresponding R gene were identified, more and more complex interactions between AVR and R genes are reported (e.g., AVR genes recognized by several R genes, R genes recognizing several AVR genes in distinct organisms, one AVR gene suppressing recognition of another AVR gene by its corresponding R gene, two cooperating R genes both necessary to recognize an AVR gene). These complex interactions were particularly reported in pathosystems showing a long co-evolution with their host plant but could also result from the way agronomic crops were obtained and improved (e.g., through interspecific hybridization or introgression of resistance genes from wild related species into cultivated crops). In this review, we describe some complex R—AVR interactions between plants and fungi that were recently reported and discuss their implications for AVR gene evolution and R gene management.

Genetic analysis of mechanisms associated with inheritance of resistance to sheath rot of rice

AbstractUnderstanding genetic mechanisms controlling inheritance of disease resistance traits is essential in breeding investigations targeting development of resistant genotypes. Using North Carolina design II, 32 F1 hybrids were generated by crossing eight susceptible to four resistant parents and submitted for field evaluation. The analysis of general and specific combining ability (GCA and SCA) indicated involvement of additive and non‐additive gene action controlling inheritance of horizontal resistance to sheath rot of rice. High GCA/SCA ratio and high heritability estimates revealed additive effects and were more predominant than none additive ones. The level of dominance indicated dominant genes was more important than recessive genes. Estimates of GCA and SCA analysis suggested that crop improvement programmes should be directed towards selection of superior parents or good combiners, emphasizing on GCA. As far as source of resistance is concerned, most promising genotypes were Cyicaro, Yunertian and Yunkeng. The predominance of additive genetic effects together with the relevance of dominant genes suggested possibilities of improving the resistance by introgression of resistance genes through recurrent selection coupled with phenotypic selection.

<b>Resistance to <i>Enneothrips flavens</i> Moulton and genetic parameters estimation in interspecific genotypes of peanut

Peanut is an oilseed crop of great importance for Brazilian agribusiness. A major factor affecting its production is pest incidence, mainly thrips. This study aimed to evaluate the potential for resistance to Enneothrips flavens in genotypes derived from the cross between IAC 503 and the amphidiploid (A. magna x A. cardenasii)4x and to estimate the genetic and phenotype parameters in these genotypes, allowing for better targeting in the selection. The experiments were conducted in a Federer augmented block design with additional checks in two generations (F3 and F4). Resistance to thrips was evaluated by its natural infestation and the symptoms of attacks by the insect. They were also evaluated using agronomic trait indicators of interspecific segregating with cultivated species. The results indicated that the selected progeny exhibited high resistance to thrips compared to commercial genotypes, and they had the amphidiploid as the insect resistance source. Some progenies selected as resistant also had good production traits, but with the degree of suitability to the A. hypogaea L. genotypes still low, the use of a backcross as an alternative for the introgression of resistance genes and the consequent recovery of adapted genotypes of superior recurring parents is suggested.

Post-transcriptional gene silencing and its implication to the asian soybean rust- a review article

Soybean is one of the most economically important crops in the world. Soybean yield is severely affected by biotic agents, especially by Asian Soybean Rust (ASR). The causal agent of ASR is Phakopsora pachyrhizi; a biotrophic fungus that belongs to Basidiomycota. Chemical control is the most effective control method for ASR, but it is costly. In the past, many soybean varieties resistant to ASR have been developed by introgression of resistance genes (R genes) to local varieties. Since P. pachyrhizi isolates are highly diverse, the resistant varieties are vulnerable to newly evolved pathogen isolates. Until now there is no variety that is resistant to all pathogen isolates. Therefore, there is a need to develop new strategies other than R genes. Identification of new candidate genes that are crucial for fungi in pathogenicity may lead to new options for P. pachyrhizi control. Many interesting genes have been identified but their study is impaired by the biotrophic nature of rust fungi. In this regard RNAi has emerged as a reverse genetic tool. The HIGS method (Host Induced Gene Silencing) is used to down regulate fungal candidate genes in planta. This is an indirect method where the silencing signal is formed in the plant but it mediates RNAi in the fungus.