Evaluation Of Disease Resistance Research Articles

Characterization of novel wheat-Thinopyrum ponticum introgression lines derived from partial amphiploid AUS6770 for resistance to stripe rust

The wild decaploid species Thinopyrum ponticum (Podp.) Barkworth & D.R. Dewey is an important source of genes against biotic and abiotic stresses affecting wheat. The wheat–Th. ponticum partial amphiploid AUS6770 shows resistance to multiple diseases, including stripe rust, stem rust, and powdery mildew. Mitotic chromosomes of AUS6770 were characterized by non-denaturing-fluorescence in situ hybridization (ND-FISH), and the individual Th. ponticum chromosomes 1Ae to 7Ae were karyotypically distinguished by Oligo-FISH painting using bulked oligo pools based on wheat-barley collinear regions. A novel stripe rust resistant line A155, derived from AUS6770, was found to have 44 chromosomes, including a pair of 2Ae chromosomes and a pair of 6B-6Ae translocations. To detect plants with transfer of resistance genes from A155 to wheat chromosomes, 1770 plants were developed from F2–F5 progenies of A155 crossed with the susceptible wheat cultivar MY11 and characterized with ND-FISH using multiple probes. A high frequency of transmission of chromosome 2Ae was observed, and 31 types of 2Ae chromosomal aberrations were identified using ND-FISH. Ten chromosomal bins on the 2Ae chromosome were determined from the deletion and translocation lines based on genome-based PCR markers. In combination with the evaluation of disease resistance, the gene(s) for stripe rust resistance was located on the FL0.79–1.00 of 2AeS and covers the corresponding region of 0–58.26 Mb in the reference genome of Th. elongatum. The newly identified wheat-Th. ponticum 2Ae translocation lines can be exploited as potential germplasm in wheat breeding for stripe rust resistance

Response and disease resistance evaluation of sorghum seedlings under anthracnose stress

Sorghum is the world’s fifth-largest cereal crop, and anthracnose (Colletotrichum sublineola) is the main disease affecting sorghum. However, systematic research on the cellular structure, physiological and biochemical, and genes related to anthracnose resistance and disease resistance evaluation in sorghum is lacking in the field. Upon inoculation with anthracnose (C. sublineola) spores, disease-resistant sorghum (gz93) developed a relative lesion area (RLA) that was significantly smaller than that of the disease-susceptible sorghum (gz234). The leaf thickness, length and profile area of leaf mesophyll cells, upper and lower epidermal cells decreased in the lesion area, with a greater reduction observed in gz234 than in gz93. The damage caused by C. sublineola resulted in a greater decrease in the net photosynthetic rate (Pn) in gz234 than in gz93, with early-stage reduction due to stomatal limitation and late-stage reduction caused by lesions. Overall, the activities of superoxide dismutase (SOD) and catalase (CAT), the content of proline (Pro), abscisic acid (ABA), jasmonic acid (JA), salicylic acid (SA), and gibberellic acid (GA3), are higher in gz93 than in gz234 and may be positively correlated with disease resistance. While malondialdehyde (MDA) may be negatively correlated with disease resistance. Disease-resistant genes are significantly overexpressed in gz93, with significant expression changes in gz234, which is related to disease resistance in sorghum. Correlation analysis indicates that GA3, MDA, peroxidase (POD), and disease-resistance genes can serve as reference indicators for disease severity. The regression equation RLA = 0.029 + 8.02 × 10−6 JA–0.016 GA3 can predict and explain RLA. Principal component analysis (PCA), with the top 5 principal components for physiological and biochemical indicators and the top 2 principal components for disease-resistant genes, can explain 82.37% and 89.11% of their total variance, reducing the number of evaluation indicators. This study provides a basis for research on the mechanisms and breeding of sorghum with resistance to anthracnose.

Molecular genetic analysis of natural introgression to enhance chestnut blight resistance of Castanea henryi var. omeiensis

Castanea species have enormous potential for broad applications in the biomedical sciences and chemical wood industries. Due to the occurrence of fungal diseases, especially chestnut blight, the survival status of Castanea plants is seriously threatened. Castanea plants in China have natural tolerance to chestnut blight. This study investigated the genetic diversity and chestnut blight resistance of Castanea plants in China and searched for germplasm with high tolerance resistance. Cluster and population structure analysis revealed that wild Castanea plants in China could be divided into three groups with significant interspecific boundary, C. henryi var. omeiensis is located between C. mollissima and C. henryi var. henryi. The ABBA-BBAA test showed that significant gene introgression occurred between C. mollissima and C. henryi in Mount Emei, supporting the conclusion that C. henryi var. omeiensis as a natural hybrid resource. The results of disease resistance evaluation showed that the tolerance of wild C. mollissima to chestnut blight was the highest and significantly higher than that of wild C. henryi and C. seguinii. In particular, there is a strong association between disease tolerance in C. henryi var. omeiensis and the level of genetic introgression from C. mollissima. Then, the rIBD fragments of C. henryi var. omeiensis derived from C. mollissima were analyzed to reveal the source of disease resistance using whole genome resequencing data. A total of 203 rIBD segments containing 435 genes were identified. Finally, 41 candidate genes for chestnut blight resistance were selected through multiple omics. In conclusion, this study investigated a type of interspecific disease-resistant hybrid resources, identified a set of candidate genes for chestnut blight resistance, and provided new strategies for disease-resistant breeding of chestnut resources in the future.

Physical mapping of a new powdery mildew resistance locus from Thinopyrum ponticum chromosome 4AgS.

Thinopyrum ponticum (Podp.) Barkworth and D.R. Dewey is a decaploid species that has served as an important genetic resource for improving wheat for the better part of a century. The wheat-Th. ponticum 4Ag (4D) disomic substitution line Blue 58, which was obtained following the distant hybridization between Th. ponticum and common wheat, has been stably resistant to powdery mildew under field conditions for more than 40 years. The transfer of 4Ag into the susceptible wheat cultivar Xiaoyan 81 resulted in powdery mildew resistance, indicating the alien chromosome includes the resistance locus. Irradiated Blue 58 pollen were used for the pollination of the recurrent parent Xiaoyan 81, which led to the development of four stable wheat-Th. ponticum 4Ag translocation lines with diverse alien chromosomal segments. The assessment of powdery mildew resistance showed that translocation line L1 was susceptible, but the other three translocation lines (WTT139, WTT146, and WTT323) were highly resistant. The alignment of 81 specific-locus amplified fragments to the Th. elongatum genome revealed that 4Ag originated from a group 4 chromosome. The corresponding physical positions of every 4Ag-derived fragment were determined according to a cytogenetic analysis, the amplification of specific markers, and a sequence alignment. Considering the results of the evaluation of disease resistance, the Pm locus was mapped to the 3.79-97.12 Mb region of the short arm of chromosome 4Ag. Because of its durability, this newly identified Pm locus from a group 4 chromosome of Th. ponticum may be important for breeding wheat varieties with broad-spectrum disease resistance.

Genome-wide association study revealed genetic loci for resistance to fusarium wilt in tomato germplasm

Tomato Fusarium wilt caused by Fusarium oxysporum f.sp. lycopersici (Fol) constrains tomato production worldwide. Three hundred forty tomato accessions were evaluated for Fusarium wilt resistance and single nucleotide polymorphisms (SNPs) associated with resistance. The disease resistance evaluation revealed that 15, 13, and 15 accessions were identified as Fusarium wilt resistant in Test 1, 2, and Mean data, respectively, with the disease severity index (DSI) ranging from 0-16.7%. A genome-wide association study (GWAS) identified SNPs associated with resistance. Eighteen common SNPs were detected in at least two tests and located on chromosomes 4, 6, 7, 9, and 12. Six unique significant SNPs were found in either Test 1 or 2, located on chromosomes 2, 4, and 7. Candidate genes associated with Fusarium wilt resistance were identified. Notably, two genes encoding leucine-rich repeat-like protein and disease-resistance protein were predicted from the two unique SNPs, solDsnp10606 and solDsnp6266, respectively.

Selection of resistant genotypes of Quince (Cydonia oblonga Mill.) to root and crown rot caused by the pathogen, Phytophthora cactorum, in the lab condition

Phytophthora root and crown rot is a common disease of different hortcrops in rosaceae family including pomefruits and stonefruits. In order to characterize reaction of different quince genotypes to Phytophthora, infected root and crown tissues of apple and quince trees in addition to some soil around them were collected from the orchards and cultured on semi-selective media. Four oomycete isolates out of 20 samples were recovered from which Phytophthora isolates were identified as P. cactorum, using physiological and morphological criteria. Disease resistance evaluation of quince genotypes to P. cactorum was implemented using excised twigs of 24 genotypes in glass bottles containing carrot agar media overlaid with a fresh layer of P. cactorum. The pathogenic isolate of P. cactorum selected from a pathogenicity test on unripe pear fruits. After two weeks of preservation of bottles in dark condition in 25 °C in growth chamber, the extent of necrosis was measured using a digital calipers then it was divided by length of twig to get the necrosis proportion. The genotypes showed a statistically significant different reaction to the pathogen at 1% level. Comparison of means using Duncan multiple range test indicated that the genotype ASP2 with 82% of necrosis proportion was the most susceptible one and PH2 (released as cultivar Behta), Unk and Khosro genotypes with 8, 10 and 13 percent necrosis of twigs were the most resistant genotypes, respectively.

Root rot a silent alfalfa killer in China: Distribution, fungal, and oomycete pathogens, impact of climatic factors and its management.

Alfalfa plays a significant role in the pasture ecosystems of China’s north, northeast, and northwest regions. It is an excellent forage for livestock, improves soil structure, prevents soil erosion, and has ecological benefits. Presently root rot is a significant threat to the alfalfa productivity because of the survival of the pathogens as soil-borne and because of lack of microbial competition in the impoverished nutrient-deficient soils and resistant cultivars. Furthermore, these regions’ extreme ecological and environmental conditions predispose alfalfa to root rot. Moisture and temperature, in particular, have a considerable impact on the severity of root rot. Pathogens such as Fusarium spp. and Rhizoctonia solani are predominant, frequently isolated, and of major concern. These pathogens work together as disease complexes, so finding a host genotype resistant to disease complexes is challenging. Approaches to root rot control in these regions include mostly fungicides treatments and cultural practices and very few reports on the usage of biological control agents. As seed treatment, fungicides such as carbendazim are frequently used to combat root rot; however, resistance to fungicides has arisen. However, breeding and transgenic approaches could be more efficient and sustainable long-term control strategies, especially if resistance to disease complexes may be identified. Yet, research in China is mainly limited to field investigation of root rot and disease resistance evaluation. In this review, we describe climatic conditions of pastoral regions and the role of alfalfa therein and challenges of root rot, the distribution of root rot in the world and China, and the impact of root rot pathogens on alfalfa in particular R. solani and Fusarium spp., effects of environmental factors on root rot and summarize to date disease management approach.

Phenotyping for QTL identification: A case study of resistance to Plasmopara viticola and Erysiphe necator in grapevine.

Vitis vinifera is the most widely cultivated grapevine species. It is highly susceptible to Plasmopara viticola and Erysiphe necator, the causal agents of downy mildew (DM) and powdery mildew (PM), respectively. Current strategies to control DM and PM mainly rely on agrochemical applications that are potentially harmful to humans and the environment. Breeding for resistance to DM and PM in wine grape cultivars by introgressing resistance loci from wild Vitis spp. is a complementary and more sustainable solution to manage these two diseases. During the last two decades, 33 loci of resistance to P. viticola (Rpv) and 15 loci of resistance to E. necator (Ren and Run) have been identified. Phenotyping is salient for QTL characterization and understanding the genetic basis of resistant traits. However, phenotyping remains a major bottleneck for research on Rpv and Ren/Run loci and disease resistance evaluation. A thorough analysis of the literature on phenotyping methods used for DM and PM resistance evaluation highlighted phenotyping performed in the vineyard, greenhouse or laboratory with major sources of variation, such as environmental conditions, plant material (organ physiology and age), pathogen inoculum (genetic and origin), pathogen inoculation (natural or controlled), and disease assessment method (date, frequency, and method of scoring). All these factors affect resistance assessment and the quality of phenotyping data. We argue that the use of new technologies for disease symptom assessment, and the production and adoption of standardized experimental guidelines should enhance the accuracy and reliability of phenotyping data. This should contribute to a better replicability of resistance evaluation outputs, facilitate QTL identification, and contribute to streamline disease resistance breeding programs.

Chlorophyll Fluorescence Imaging as a Tool for Evaluating Disease Resistance of Common Bean Lines in the Western Amazon Region of Colombia.

The evaluation of disease resistance is considered an important aspect of phenotyping for crop improvement. Identification of advanced lines of the common bean with disease resistance contributes to improved grain yields. This study aimed to determine the response of the photosynthetic apparatus to natural pathogen infection by using chlorophyll (Chla) fluorescence parameters and their relationship to the agronomic performance of 59 common bean lines and comparing the photosynthetic responses of naturally infected vs. healthy leaves. The study was conducted over two seasons under acid soil and high temperature conditions in the western Amazon region of Colombia. A disease susceptibility index (DSI) was developed and validated using chlorophyll a (Chla) fluorescence as a tool to identify Mesoamerican and Andean lines of common bean (Phaseolus vulgaris L.) that are resistant to pathogens. A negative effect on the functional status of the photosynthetic apparatus was found with the presence of pathogen infection, a situation that allowed the identification of four typologies based on the DSI values ((i) moderately resistant; (ii) moderately susceptible; (iii) susceptible; and (iv) highly susceptible). Moderately resistant lines, five of them from the Mesoamerican gene pool (ALB 350, SMC 200, BFS 10, SER 16, SMN 27) and one from the Andean gene pool (DAB 295), allocated a higher proportion of energy to photochemical processes, which increased the rate of electron transfer resulting in a lower sensitivity to disease stress. This photosynthetic response was associated with lower values of DSI, which translated into an increase in the accumulation of dry matter accumulation in different plant organs (leaves, stem, pods and roots). Thus, DSI values based on chlorophyll fluorescence response to pathogen infection could serve as a phenotyping tool for evaluating advanced common bean lines. Six common bean lines (ALB 350, BFS 10, DAB 295, SER 16, SMC 200 and SMN 27) were identified as less sensitive to disease stress under field conditions in the western Amazon region of Colombia, and these could serve as useful parents for improving the common bean for multiple stress resistance.

First Report of Phytophthora parsiana Causing Crown and Root Rot on Guayule in the United States.

Guayule (Parthenium argentatum A. Gray) is a perennial shrub plant (approximately 50 cm in height) cultivated in the southwestern United States. It produces natural low-allergenic latex, resins and high-energy biofuel feedstock. During August 2021, a crown and root rot disease was observed on 2-year-old plants of direct-seeded guayule cultivar 'Az 2' in research plots located in Pinal county, Arizona, where a record 36 cm of rainfall fell during monsoon season. Symptoms included yellowing of leaves, wilting, and plant death. Average disease incidence was 16%. Isolation from necrotic crown and root tissues on 10% clarified V8-PARP (Jeffers and Martin 1986) yielded Phytophthora-like colonies. Three isolates were subcultured on V8 agar and chlamydospores and hyphal swellings were abundant in 2-week-old cultures. All three isolates produced abundant noncaducous and nonpapillate sporangia ranging from 33 to 54 μm × 20 to 39 μm (average 45.5 × 28.5 μm, n = 20) in soil water extract solution. Isolates did not produce oospores after 2 weeks on carrot agar at 20°C in the dark. Isolates had optimum vegetative growth at 30 oC and grew well at 35 oC. There was no growth at 5 and 40 oC. Genomic DNA was extracted from the mycelia of three isolates using DNeasy Plant Pro Kit (Qiagen Inc., Valencia, CA) according to the manufacturer's instructions. The internal transcribed spacer (ITS) region of rDNA, mitochondrially encoded cytochrome c oxidase 1 (cox 1) gene, and beta-tubulin (β-tub) gene were amplified with primers ITS1/ITS4 (White et al., 1990), COXF4N/COXR4N and TUBUF2/TUBUR1 (Kroon et al., 2004) and the resulting 3 amplicons were sequenced (GenBank Accession No. OK438221, OK484426, and OK484427). A BLASTn search of 811-bp amplicon (OK438221) revealed 99% match (762/766) with ITS sequences MG865562 which was Phytophthora parsiana Ex-type CPHST BL 47 from Iran. BLAST analysis of the 867-bp amplicon (OK484427) showed 99% identity (866/867) with the COX 1 sequence of P. parsiana (KC733455) from Virginia. BLAST analysis of the 941-bp amplicon (OK484426) showed 99% identity (928/938) with the β-tub sequence of P. parsiana (AY659746). To fulfill Koch's postulates, pathogenicity tests were conducted twice on 2-week-old 'Az 2' guayule seedlings grown in 10 plants per 1.9-liter pot filled with a steam-disinfested potting mix. Pots were placed in a plastic container and watered three times a week by flooding, to create waterlogged conditions. Plants were maintained in a greenhouse with 12 h day/12 h night (15-28 oC) and fertilized weekly with a 20-20-20 fertilizer at 1mg/ml. Fifty plants in 5 pots were challenged with a P. parsiana isolate by drenching each pot with 50 ml of a 1×105 zoospore/ml suspension. Fifty plants in 5 pots, serving as a control, received each 50 ml of distilled water. Symptoms of wilting, root rot, and plant death were observed 1 week afterward in inoculated plants, whereas control plants remained asymptomatic. P. parsiana was reisolated from necrotic roots of inoculated plants but not from control plants. To our knowledge, this is the first report of crown and root rot in guayule caused by P. parsiana in Arizona. P. parsiana is a species known for causing root rot on woody plants such as pistachio in California (Fichtner et al., 2016) and Iran (Mostowfizadeh-Ghalamfarsa et al., 2008). Arizona is home of desert woody guayule plant. P. parsiana may represent a significant barrier to commercialization of guayule for rubber in low desert areas of Arizona. The origin, distribution, and virulence of the pathogen on Arizona guayule is currently unknown. Disease resistance evaluation may help identify resistance in guayule germplasm that are useful in breeding for resistant cultivars.

Comparative Analysis of Host Range, Ability to Infect Tomato Cultivars with Tm-22 Gene, and Real-Time Reverse Transcription PCR Detection of Tomato Brown Rugose Fruit Virus.

Tomato (Solanum lycopersicum L.) is one of the most important vegetables in the world. However, tomato is also susceptible to many viral diseases. Several tobamoviruses, including tomato mosaic virus (ToMV), tomato mottle mosaic virus (ToMMV), and tomato brown rugose fruit virus (ToBRFV), are highly contagious pathogens that could result in significant economic losses if not controlled effectively. Tobamoviruses have been managed relatively well with broad adaptation of tomato cultivars with resistance genes. However, emergence of ToBRFV was shown to break down resistance conferred by the common resistance genes, resulting in serious outbreaks in many countries in Asia, Europe, and North America. The objective of this study was to conduct a comparative analysis of biological properties, including host range and disease resistance of ToMV, ToMMV, and ToBRFV. Results showed that despite many similarities in the host range, there were some unique host plant responses for each of the three viruses. In a comparative evaluation of disease resistance using the same tomato cultivars with or without Tm-22 gene, there was a striking difference in responses from tomato plants with Tm-22 gene inoculated with ToBRFV, ToMV, or ToMMV. Whereas these test plants were resistant to ToMV or ToMMV infection, all test plants were susceptible to ToBRFV. Further, for ToBRFV detection, a sensitive and reliable multiplex real-time reverse transcription (RT)-PCR assay using TaqMan probe with an internal 18S rRNA control was also developed. With simple modifications to RNA extraction and seed soaking, real-time RT-PCR could consistently detect the virus in single infested seed in varied levels of contamination, suggesting its usefulness for seed health assay.

English

Root rot is a destructive disease of Astragalus membranaceus var. mongholicus (AMM) and occurs frequently in recent years in the main cultivation regions in China. However, the progress of AMM resistance breeding is extremely slow due to the lack of resistance source and inefficiency of the conventional disease resistance evaluation method. This study aimed to provide information on the interaction between AMM and Fusarium solani, one of the predominant pathogens causing root rot and identify the resistance-related (RR) metabolites by using the nontargeted 1H nuclear magnetic resonance (NMR) metabolomics approach. Of the 24 metabolites examined, the concentration changes in sucrose, fructose, taurine and phenylalanine were negatively correlated with the root rot severity. The abundance of malic acid in F. solani-inoculated samples considerably decreased at 21 days post inoculation (dpi). The five metabolites were identified as RR metabolites, and only malic acid inhibited the fungal growth. These metabolites might serve as candidate biomarkers for discriminating the resistance levels of different AMM genotypes and establishing the high-throughput screening method of AMM breeding lines against root rot caused by F. solani. Results could assist in accelerating the resistance breeding program. The possible mechanisms of RR metabolites in plant defense against the pathogen were discussed. © 2021 Friends Science Publishers

Improving evaluation of potato resistance to Rhizoctonia solani infection by optimizing inoculum-based method combined with toxin-based assay

Rhizoctonia solani causes stem canker and significantly impacts potato production. Conventional assay to evaluate potato resistance using R. solani inoculum is time consuming. To establish an effective and fast assay, 20 potato cultivars/lines were examined using both R. solani AG2-1 as an inoculum and its derived toxin (RS toxin). In field trials of 2009 and 2010, wheat-bran-mediated inoculum of R. solani AG2-1 was incorporated at either 0, 2, 3, 4 or 5 g per seed piece in the soil before sowing in the furrow. Stem canker was evaluated sixty-five days after planting. Inoculation at 2, 3, or 4 g R. solani AG2-1 well distinguished resistance of potato cultivars/lines. For a quick assay of resistance screening, a toxin-based method was established by treating potato seedlings with RS toxin of R. solani AG2-1. RS toxin was prepared by heating R. solani AG2-1 culture. Potato seedlings were obtained through tissue culture and grown in Murashige and Skoog medium. Seedlings at the stage of 12 cm in height were transferred into agar amended with RS toxin and incubated for eight days. The level of inhibition caused by RS toxin was positively correlated with toxin concentration. By evaluating various potato cultivars/liens that have different sensitivities to toxin, the inhibition was from 33% to 100% on potato stems sections and from 32% to 148% on seedlings. The toxin-based evaluation was highly correlated with field data using pathogen inoculum (r = 0.731, P < 0.01). Inoculation with wheat bran-mediated R. solani AG2-1 of 2, 3 or 4 g per seed piece was effective in field evaluations. The toxin-based assay improved the efficiency of disease resistance evaluation. Both assays showed that none of the 20 potato cultivars/liens was completely resistant to R. solani AG2-1. However, cultivar ‘Desiree’ had the lowest level of disease, whereas ‘Atlantic’, ‘Favorita’, and ‘Shepody’ were the most susceptible cultivars.

Molecular marker assisted gene stacking for disease resistance and quality genes in the dwarf mutant of an elite common wheat cultivar Xiaoyan22

BackgroundDevelopment of wheat cultivars with multiple disease resistance and high quality are major objectives in modern wheat breeding programs. Gene stacking is an efficient approach to achieve this target. In this study, we pyramided yellow rust resistance gene (Yr26), powdery mildew resistance gene (ML91260) and high-molecular-weight glutenin subunits Dx5 + Dy10 into the dwarf mutant of an elite wheat cultivar, Xiaoyan22.ResultsSix pyramided wheat lines were obtained by molecular marker-assisted selection (MAS) and field evaluation of disease resistance. The desirable agronomic traits of pyramided lines, their identity with the original cultivar Xiaoyan22 except for plant height, tiller number and disease resistance, was achieved in this study. Meanwhile, the yield of pyramided lines is higher than Xiaoyan22 in the field test. In addition, analysis of flour quality indicated that the dough stability time of pyramided lines was longer than that of Xiaoyan22.ConclusionsSix pyramided wheat lines with two disease resistance and high quality were achieved in this study. It is feasible to improve multiple agronomic traits simultaneously by rational application of MAS.

The evaluation of disease resistance of flax genotypes in relation to environmental factors

The evaluation of disease resistance of flax genotypes in relation to environmental factors

DIVERSITY OF THE PUMPKIN COLLECTION AND ITS HEREDITARY POTENTIAL. RESULTS AND PROSPECTS OF BREEDING PRACTICE

Background. Pumpkin is an important food, feed and medicinal crop. It is widely used by national cuisines in many countries and utilized as raw material for canning industry and in pharmacy to prepare drugs. The Kuban Experiment Station of VIR, where the collection of pumpkin genetic resources is maintained and regenerated for long-term storage in the genebank, conducts comprehensive research work to analyze the genetic diversity of pumpkin accessions and disclose the potential of its hereditary variation.Objective. The aim of this study was to screen various species from the global pumpkin collection and identify sources of traits valuable for breeders in order to develop promising cultivars and hybrids.Materials and methods. The pumpkin collection was studied and the breeding work was performed using the guidelines worked out by VIR’s scientists. The work included botanical description, study of variability and inheritance of traits, hybridization, inbreeding, mutagenesis, and different selection techniques (individual, group, individual/ family, and mass selection). In the first stages of the study, inbreeding was employed to select best plants from the collection in order to set up a trait-specific collection and incorporate its accessions into the hybridization process. Self-pollination was usedfor several years to obtain self-pollinated lines, sufficiently uniform in the selected trait. The hybrid progenies from crosses between parental forms were analyzed to throw light on the inheritance of major traits and their genetic control. The accessions were assessed for their earliness, productivity and quality. Evaluation of disease resistance was carried out in the field under natural infection pressure.Results and discussion. Targeted breeding efforts resulted in releasing cultivars of Cucurbita pepo L., C. maxima Duch. and C. moschata Duch. ex. Poir. having different maturation schedules and approved for cultivation in various regions of Russia: ‘Kustovaya oranzhevaya’, ‘Lechebnaya’, ‘Kustovaya zolotaya’, ‘Malyshka’, ‘Matreshka’, ‘Krasavitsa’, Zimnyaya sladkaya’, ‘Zhemchuzhina’, ‘Yantarnaya’ and ‘Mariya’. These cultivars are in demand among both agricultural producers and individual growers. New sources of valuable morphobiological and agronomic characters have been identified as useful for modern plant breeding trends: KL 625, ZhZM 692, L-180, L-193, KPL 168, KL 568 and KL 570. New bushy lines of C. maxima and C. moschata selected from cultivar and hybrid populations are now tested in an elite test nursery in order to submit the best of them to the State Variety Trials.

Evaluation of Disease Resistance of Rice Cultivar Developed in North Korea

Evaluation of Disease Resistance of Rice Cultivar Developed in North Korea

Development of a highly specific co-dominant marker for genotyping the Ph-3 (tomato late blight resistance) locus by comparing cultivated and wild ancestor species

Late blight is a devastating disease for tomato especially in areas with high humidity and low temperature caused by Phytophthora infestans. A late blight resistance gene, Ph-3, has been widely used in tomato breeding program as it confers incomplete dominant resistance to a wide range of P. infestans isolates of tomato. This gene was derived from a wild ancestor species of cultivated tomato, Solanum pimpinellifolium accession L3708, and located in a resistance (R) gene cluster. Although this gene was cloned a few years ago, and some markers have been developed and used, the effectiveness of these markers was not evaluated with a diverse cultivars panel. Based on the comparative analysis of the Ph-3 locus sequences from L3708, cultivar Heinz1706 and S. pimpinellifolium accession LA1589, we developed a robust co-dominant PCR-based marker Ph-3-GLR/S for the Ph-3 locus. We performed a comparison about efficiency and accuracy of Ph-3-GLR/S with two cleaved amplified polymorphic sequence (CAPS) markers Ph3.gsm/HincII and TG328 developed previously. Ph-3-GLR/S exhibited robust co-dominant patterns compared to Ph3.gsm/HincII. For certain accessions, TG328 and Ph-3-GLR/S yielded the contrast genotyping result. To clarify this discrepancy, disease resistance evaluation by detached leaf inoculation supported the consistency between Ph-3-GLR/S genotyping and resistance phonotype, showing Ph-3-GLR/S was more accurate than TG328. All these findings indicated that our marker Ph-3-GLR/S could serve as a highly specific and robust co-dominant marker for marker-assisted selection of Ph-3.

Evaluation of Malus gene bank resources with German strains of Marssonina coronaria using a greenhouse-based screening method

Marssonina coronaria is considered a threat to organic apple production in Central Europe. Since the application of fungicides is limited in organic production, breeding for resistance seems to be a promising strategy to manage the disease in the future. In this study, an artificial inoculation method similar to procedures used in apple scab greenhouse screenings was developed using German strains of the pathogen M. coronaria for evaluating 110 Malus domestica cultivars. The strains were morphologically and molecularly characterized and confirmed as M. coronaria. Symptom development was significantly influenced by incubation method, conidia concentration and point of inoculation, but not by leaf position and different water types used for inoculation. The success of inoculation and spread of the fungus on infected leaves were confirmed by conventional PCR. Moreover, there was a difference in development of disease symptoms between inoculations with conidia from in vitro grown strains (in vitro inoculum) and conidia from diseased leaves from the orchard (field inoculum) in a time dependent manner. These differences which were first found with the susceptible cultivar ‘Topaz’ after artificial inoculation with in vitro and field inoculum were confirmed on 20 more apple cultivars inoculated with different in vitro grown strains. In summary, all tested cultivars, including 21 which are scab-resistant, developed symptoms of this disease. Results from three years of investigation indicate a decrease in virulence of M. coronaria strains, when cultivated on artificial culture (growth)-media. Hence field inoculum is recommended for artificial greenhouse screenings for the evaluation of disease resistance in Malus genetic resources.

Evaluation of disease resistance and tolerance to elevated temperature stress of the selected tissue-cultured Kappaphycus alvarezii Doty 1985 under optimized laboratory conditions.

Information on the abiotic stress tolerance and ice-ice disease resistance properties of tissue-cultured Kappaphycus alvarezii is scarce and can pose a big hurdle to a wider use of tissue-cultured seaweed in the industry. Here, we reported on a study of seaweed-associated bacteria diversity in farmed and tissue-cultured K. alvarezii, and ice-ice disease resistance and elevated growth temperature tolerance of tissue-cultured K. alvarezii in laboratory conditions. A total of 40 endophytic seaweed-associated bacteria strains were isolated from 4 types of K. alvarezii samples based on their colony morphologies, Gram staining properties and 16S rRNA gene sequences. Bacteria strains isolated were found to belong to Alteromonas sp., Aestuariibacter sp., Idiomarina sp., Jejuia sp., Halomonas sp., Primorskyibacter sp., Pseudoalteromonas sp., Ruegeria sp., Terasakiella sp., Thalassospira sp. and Vibrio sp. Vibrio alginolyticus strain ABI-TU15 isolated in this study showed agar-degrading property when analyzed using agar depression assay. Disease resistance assay was performed by infecting healthy K. alvarezii with 105cells/mL Vibrio sp. ABI-TU15. Severe ice-ice disease symptoms were detected in farmed seaweeds compared to the tissue-cultured K. alvarezii. Besides disease resistance, tissue-cultured K. alvarezii showed better tolerance to the elevated growth temperatures of 30 and 35°C. In conclusion, our overall data suggests that tissue-cultured K. alvarezii exhibited better growth performance than farmed seaweeds when exposed to elevated growth temperature and ice-ice disease-causing agent.