Disease Resistance Breeding Programs Research Articles

In Vitro Collection for the Safe Storage of Grapevine Hybrids and Identification of the Presence of Plasmopara viticola Resistance Genes.

This paper focuses on the creation of an in vitro collection of grapevine hybrids from the breeding program of the Kazakh Scientific Research Institute of Fruit Growing and Viticulture and investigates the presence of Plasmopara viticola resistance mediated by Rpv3 and Rpv12 loci. We looked at the optimization of in vitro establishment using either shoots taken directly from field-grown plants or from budwood cuttings forced indoors. We further screened for the presence of endophyte contamination in the initiated explants and optimized the multiplication stage. Finally, the presence of the resistance loci against P. viticola was studied. The shoots initiated from the field-sourced explants were the more effective method of providing plant sources for in vitro initiation once all plant accessions met the goal of in vitro establishment. The concentration of phytohormones and the acidity of the culture medium have a great effect on the multiplication rate and the quality of in vitro stock cultures. Out of 17 grapevine accessions, 16 showed the presence of single or combined resistance loci against P. viticola. The grapevine accessions identified as carrying Rpv3 and Rpv12 alleles represent important genetic resources for disease resistance breeding programs. These accessions may further contribute to the creation of new elite cultivars of economic interest.

Immunoglobulin-like receptors in chickens: identification, functional characterization, and renaming to cluster homolog of immunoglobulin-like receptors

The cluster homolog of immunoglobulin-like receptors (CHIRs), previously known as the "chicken homolog of immunogloublin-like receptors," represents is a large group of transmembrane glycoproteins that direct the immune response. However, the full repertoire of putatively activating, inhibitory, or dual function CHIRA, CHIRB, and CHIRAB on chickens' immune responses is poorly understood. Herein, the study objective was to determine the genes encoding CHIR proteins and predict their function by searching canonical protein structure. A bioinformatics pipeline based on previous work was employed to search for the CHIRs from the newly updated broiler and layer genomes. The categorization into CHIRA, CHIRB, and CHIRAB types was assigned through motif searches, multiple sequence alignment, and phylogeny. In total, 150 protein-encoding genes on Chromosome 31 were identified as CHIRs. Gene members of each functional group (CHIRA, CHIRB, CHIRAB) were classified in accordance with previously recognized proteins. The genes were renamed to "cluster homolog of immunoglobulin-like receptors" (CHIRs) to allow for the naming of orthologous genes in other avian species. Additionally, expression analysis of the classified CHIRs across various reinforces their importance as immune regulators and activation in inflammatory tissues. Furthermore, over 1,000 diverse and rare CHIRs variants associated with differential Marek's disease response (P < 0.05) emphasize the impact of CHIRs on shaping avian immune responses in diverse contexts. The practical applications of these findings encompass advancing immunology, improving poultry health management, optimizing breeding programs for disease resistance, and enhancing overall animal health through a deeper understanding of the roles and functions of CHIRA, CHIRB, and CHIRAB types in avian immune responses.

Validated Molecular Marker for Downy Mildew Disease Resistance Breeding of Sunflower: A Short Review

The oomycete pathogen Plasmopara halstedii responsible for sunflower downy mildew (DM), that is a significant and important disease that greatly affects the economy. As of now, there is no non-race-specific resistance for this disease and breeders are depended on race-specific resistance to control DM disease. On the other hand, using conventional breeding procedure introgression of the DM resistance genes is a long-term task due to the highly virulent and aggressive nature of the P. halstedii pathogen. Molecular markers that can be applied at the seedling stage, offers rapid response for selection with higher precision as well as a lower cost. There are currently 36 downy mildew resistance genes (R genes), designated as Pl (Pl1-Pl36, Plhra, and PlArg, in sunflowers, each with a unique linkage group (LGs). The availability of DM resistance genomic data of sunflower, related to Single Nucleotide Polymorphisms (SNP) based markers with mine allelic diversity maximize the opportunity of utilizing Marker assisted selection (MAS) techniques for downy mildew resistance breeding. This review highlights the available genetic marker and their utilization at MAS techniques for enhancing downy mildew disease resistant breeding program of sunflowers.

Identification of QTLs and critical genes related to sugarcane mosaic disease resistance.

Mosaic viral diseases affect sugarcane productivity worldwide. Mining disease resistance-associated molecular markers or genes is a key component of disease resistance breeding programs. In the present study, 285 F1 progeny were produced from a cross between Yuetang 93-159, a moderately resistant variety, and ROC22, a highly susceptible variety. The mosaic disease symptoms of these progenies, with ROC22 as the control, were surveyed by natural infection under 11 different environmental conditions in the field and by artificial infections with a mixed sugarcane mosaic virus (SCMV) and sorghum mosaic virus (SrMV) inoculum. Analysis of consolidated survey data enabled the identification of 29 immune, 55 highly resistant, 70 moderately resistant, 62 susceptible, and 40 highly susceptible progenies. The disease response data and a high-quality SNP genetic map were used in quantitative trait locus (QTL) mapping. The results showed that the correlation coefficients (0.26~0.91) between mosaic disease resistance and test environments were significant (p< 0.001), and that mosaic disease resistance was a highly heritable quantitative trait (H2 = 0.85). Seven mosaic resistance QTLs were located to the SNP genetic map, each QTL accounted for 3.57% ~ 17.10% of the phenotypic variation explained (PVE). Furthermore, 110 pathogen response genes and 69 transcription factors were identified in the QTLs interval. The expression levels of nine genes (Soffic.07G0015370-1P, Soffic.09G0015410-2T, Soffic.09G0016460-1T, Soffic.09G0016460-1P, Soffic.09G0017080-3C, Soffic.09G0018730-3P, Soffic.09G0018730-3C, Soffic.09G0019920-3C and Soffic.03G0019710-2C) were significantly different between resistant and susceptible progenies, indicating their key roles in sugarcane resistance to SCMV and SrMV infection. The seven QTLs and nine genes can provide a certain scientific reference to help sugarcane breeders develop varieties resistant to mosaic diseases.

Evaluation of Indian Mustard Genotypes for White Rust Resistance Using BjuWRR1Gene and Their Phenotypic Performance

The present investigation was carried out to identify the potential donors of resistant gene(s)/the source of white rust disease in B. juncea using 30 genotypes, including locally adapted accessions and advanced breeding lines. Out of 30 genotypes, ten lines viz. Bio-YSR, CAULC-1, CAULC-2, CAULC-3, CAULC-4, CAURM-2, CAULR-7, CAURM-4, CAURM 4-1, and CAURM 4-2 exhibited a lower PDI value (lesser than mean 10.83) with a superior agronomic performance related with the disease. The evaluation of these ten genotypes for the presence of the BjuWRR1 gene using a gene-based marker depicted the presence of the functional allele of the BjuWRR1 gene in the five genotypes viz., Bio-YSR, CAULC-1, CAULC-3, CAURM 4-1 and CAURM 4-2. When compared with the sequenced amplicon of these genotypes, it is found to be identical with that of an east European Brassica juncea line, Donskaja-IV, the completely resistant genotype against various isolates of Albugo candida. The findings from the present study suggested that besides Bio-YSR, the local lines of Manipur CAULC-1 (Local Yella of Potshangbam) and CAULC-3 (Local Yella of Kakching Lamjao) can be used as the potential white rust resistance sources/donors in disease resistance breeding programmes for the development of elite B. juncea cultivars in the future. In addition to the local lines, two improved advanced lines, viz. CAURM 4-1 and CAURM 4-2, obtained from a hybridization programme, may be further evaluated for releasing resistant varieties against white rust.

Occurrence of Colletotrichum musicola causing anthracnose on Manihot esculenta.

Cassava (Manihot esculenta) is one of the main food sources of energy in developing countries owing to its starch-rich roots (Pinweha et al., 2015). Anthracnose is considered the most destructive disease of the aerial part of this crop (Bragança et al., 2016; Liu et al., 2019), and it is caused by species such as Colletotrichum plurivorum, C. karstii, C. fructicola, C. siamense (Liu et al., 2019), and C. theobromicola (Oliveira et al, 2016). In 2019, leaves with irregular necrotic spots, typical symptoms of anthracnose, were collected in Pará, Brazil. Commercial sampled fields showed 20% of incidence of anthracnose. Colletotrichum strains were isolated and cultured on potato dextrose agar at 25 ºC with a 12-h light photoperiod from surface-disinfected (70% alcohol and 1% sodium hypochlorite) lesion transition area. Five of the obtained isolates exhibited brown colonies on the upper and lower surfaces. Conidia were hyaline, cylindrical and aseptate, 12.82-15.23 μm × 3.52-5.25 μm in size. These phenotypic characters were similar to those belonging to C. orchidearum sensu lato (Damm et al. 2019). Glyceraldehyde 3-phosphate dehydrogenase (GAPDH), β-tubulin (TUB2), chitin synthase 1(CHS-1), and histone HIS3 partial gene were amplified and sequenced for one representative isolate (UFT/Coll89). Sequences were deposited in GenBank [Accession numbers: MT396235 (GAPDH), MT800856 (TUB2), MT800870 (CHS-1), and MT856672 (HIS3)]. BLASTn searches of CHS-1 and HIS3 sequences showed 100% identity to C. musicola. Maximum Likelihood Phylogenetic analysis, including previously published sequences of closely related species, placed the isolate from Cassava in the C. musicola clade with 100% support, and confidently it assigned to this species. Pathogenicity was proven with inoculations by spraying a conidial suspension (106 conida mL-1) on 3-month-old cassava plants (three unwounded leaves per plant). The plants were placed in a humid chamber at 25 °C for 48h, and a 12-h photoperiod. The negative control was represented by plants inoculated with sterile distilled water. The experiment was repeated twice. The same symptoms observed in the field were reproduced only in inoculated leaves, from which the pathogen was reisolated lesions fulfilling Koch's postulates. No symptoms were observed on the negative control. To our knowledge, this is the first report of C. musicola joining a group of new and emergent species of Colletotrichum causing anthracnose in cassava producing regions around the world. The identification of this species causing cassava anthracnose is crucial to improve the disease control strategies and resistance breeding programs.

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.

Population Genetic Analyses of Phytophthora cinnamomi Reveals Three Lineages and Movement Between Natural Vegetation and Avocado Orchards in South Africa.

Phytophthora cinnamomi is the causal agent of root rot, canker, and dieback of thousands of plant species around the globe. This oomycete not only causes severe economic losses to forestry and agricultural industries, but also threatens the health of various plants in natural ecosystems. In this study, 380 isolates of P. cinnamomi from four avocado production areas and two regions of natural vegetation in South Africa were investigated using 15 microsatellite markers. These populations were found to have a low level of genetic diversity and consisted of isolates from three lineages. Shared genotypes were detected between isolates from avocado orchards and natural vegetation, indicating the movement of isolates between these areas. The population from the Western Cape natural vegetation had the highest level of genotypic diversity and number of unique alleles, indicating this could be the point of introduction of P. cinnamomi to South Africa. Index of association analysis suggested that five of six populations were under linkage disequilibrium, suggesting a clonal mode of reproduction, whereas genotypes sampled from a recently established avocado orchard in the Western Cape were derived from a randomly recombining population. This study provided novel insights on the genetic diversity and spread of P. cinnamomi in South Africa. It also reported on the predominance of triploidy in natural occurring populations and provided evidence for recombination of P. cinnamomi for the first time. The presence of two dominant genotypes in all avocado production areas in South Africa highlight the importance of considering them in disease management and resistance breeding programs.

Identification of the blast resistance genes in three elite restorer lines of hybrid rice

Hybrid rice has the advantage to pyramid multiple resistance (R) genes because a hybrid rice cultivar is developed from the cross of a sterile line with a restorer line that can harbor different R genes. Thus, knowing the R genes in an elite line will help the combination of different R genes into a hybrid rice cultivar. Here, we identified the blast R genes in Shu Hui 548 (SH548), Shu Hui 882 (SH882), and Wu Shan Si Miao (WSSM), three elite restorer lines of hybrid rice that showed resistance to the rice blast fungus in the disease nurseries. At controlled laboratory conditions, the three elite restorer lines exhibited resistance to more than 20 China Rice Blast strains that harbor different avirulence genes, indicating their broad-spectrum resistance to blast disease. Expression analyses detected the transcripts of multiple known blast R genes. Sequencing of the expressed R genes indicated that, besides Pid2, SH548 also contains Pi2 and Ptr, SH882 and WSSM also contain Pikm and Pi9-Type5, respectively. Pi9-Type5 is a novel functional allele of Pi9. Therefore, SH548, SH882, and WSSM can be exploited in combination with the sterile lines containing other R genes, and they can be used as blast resistance donors in disease-resistance breeding programs.

Identification of Elite Pigeonpea Genotypes against Fusarium Wilt and Sterility Mosaic Disease through AMMI and GGE Biplot Analysis

Background: Pigeonpea is an important legume crop in the world. The diseases Fusarium Wilt (FW) and Sterility Mosaic Disease (SMD) causes a complete yield loss i.e. up to 100% in susceptible pigeonpea genotypes. Amidst of these conditions the selection of stable resistant genotypes against these diseases under varying environmental conditions is the primary management choice for minimizing yield losses (Sharma et al., 2012; Bhaskar et al., 2016). Methods: Fifty pigeonpea genotypes were evaluated against Fusarium wilt and SMD in artificial epiphytotic conditions during four Kharif seasons i.e., 2017, 2018, 2019 and 2020. Additive main effects and multiplicative interaction (AMMI) analysis was used to decipher the interaction between genotype (G) and environment (E) for FW and SMD in pigeonpea. Result: Analysis revealed that in both the diseases IPCA1 and IPCA2 collectively contributed more than 80% interaction. AMMI biplots revealed that Kharif- 2019 shows positive effect to FW disease and negative effect to SMD. The AMMI model integration with GGE biplot, identified stable and resistant genotypes (1, 6, 7, 9, 11, 14, 20, 25, 21, 30, 33, 35, 42, 44, 46, 47, 48 and 49) to both FW and SMD based on their performance across diverse environments. These genotypes will be referred for pigeonpea FW and SMD disease resistance breeding programmes.

Outlook on disease resistant grapevine varieties

Breeding programs for disease resistance were developed from the 19th century on, in both the old (Europe) and new world as a way to promote sustainable viticulture. The main results of breeding, in terms of disease resistance and grape (and wine) quality are described, ranging from the first American hybrids to the most recent varieties. The activity of some representative breeders is discussed and the current situation in Italy is reported. Productive, legislative, and commercial aspects for wine production are considered, especially for European Union where the wine sector is strongly regulated. The perspectives of breeding for disease resistance are discussed, including the new breeding techniques (Nbt) like cis-genesis and genome editing. The importance to interact with the society to make acceptable these innovations is emphasized. While less acceptance problems are expected with table grapes, raisins or rootstocks, more concerns might arise with wine grapes. The role of science is to give the legislator tools to cope with sustainability and to educate the society (from the grape grower to the wine consumer) to a correct understanding. Innovations can be a real advantage only if they are accepted by all the actors of the wine chain.

Pathogenic Variability of the Jackfruit-Bronzing Bacterium Pantoea stewartii Subspecies stewartii Infection to Jackfruit Varieties and Its Pivotal Plant Hosts in Malaysia

Infection with Pantoea stewartii subspecies stewartii, which causes jackfruit-bronzing disease, is a huge problem faced by the jackfruit industry in Malaysia. This study was carried out to assess the disease ratings and aggressiveness performance of 28 Pantoea stewartii subspecies stewartii isolated from jackfruit-bronzing diseased jackfruits from four collection areas (Jenderam in Selangor State, Maran and Muadzam Shah in Pahang State, and Ipoh in Perak State) in Peninsular Malaysia, inoculated into jackfruit varieties (Tekam Yellow J33, Hong J34 and Subang Chap Boy J39), the sweetcorn variety, Mas Madu (two-week-old seedlings and nine-week-old seedlings), the cucumber variety, Rocky, and the pineapple variety, MD2. The results revealed that Pantoea stewartii subspecies stewartii produced symptoms upon all inoculations in the pathogenicity testing, thus fulfilling Koch’s postulates, except in the case of J39 and sweetcorn (two-week-old seedlings). No disease symptoms (disease rating 0) were observed in J39 and sweetcorn (two-week-old seedlings) within 14 days post-inoculation (14 dpi). The disease progression (based on disease ratings) proved that the jackfruit variety J39 was the most resistant, whereas J33 and J34 were susceptible to jackfruit-bronzing disease. The disease ratings of the 14-dpi period revealed a variability of disease progression among the 28 bacterial isolates, where the isolate JEN-14 had the fastest and highest disease ratings when inoculated into J33, J34, nine-week-old sweetcorn seedlings, cucumber, and pineapple. Likewise, the AUDPC value, based on disease rating, across the 28 isolates indicated that JEN-14 is the most aggressive and significant of the isolates (J33, J34, nine-week-old sweetcorn seedlings, cucumber, and cucumber pineapple inoculation; p &lt; 0.05). Even though isolates from Jenderam (other than JEN-14) and Maran had better disease ratings and the area under the disease progress curve (AUDPC) values than isolates from Muadzam Shah and Ipoh, no significant differences were found among the isolates (p &lt; 0.05). Based on our findings, we identified the isolate JEN-14 as the best potential candidate to assist in jackfruit-bronzing disease resistance breeding in the future. Last but not least, the methods, disease ratings, and variations of the aggressiveness profiles among the isolates from this study may be beneficial and significant by providing disease-rating references and appropriate screening approaches when selecting the most appropriately aggressive isolates for evaluating the defense response in the disease resistance breeding program.

Expression Analysis of MaTGA8 Transcription Factor in Banana and Its Defence Functional Analysis by Overexpression in Arabidopsis.

TGA transcription factor is a member of the D subfamily of the basic region-leucine zippers (bZIP) family. It is a type of transcription factor that was first identified in plants and is the main regulator in plant development and physiological processes, including morphogenesis and seed formation in response to abiotic and biotic stress and maintaining plant growth. The present study examined the sequence of the MaTGA8 transcription factor, the sequence of which belonged to subfamily D of the bZIP and had multiple cis-acting elements such as the G-box, TCA-element, TGACG-element, and P-box. Quantitative real time polymerase chain reaction (qRT-PCR) analyses showed that MaTGA8 was significantly down-regulated by the soil-borne fungus Fusarium oxysporum f. sp. cubense race 4 (Foc TR4). Under the induction of salicylic acid (SA), MaTGA8 was down-regulated, while different members of the MaNPR1 family responded significantly differently. Among them, MaNPR11 and MaNPR3 showed an overall upward trend, and the expression level of MaNPR4, MaNPR8, and MaNPR13 was higher than other members. MaTGA8 is a nuclear-localized transcription factor through strong interaction with MaNPR11 or weaker interaction with MaNPR4, and it is implied that the MaPR gene can be activated. In addition, the MaTGA8 transgenic Arabidopsis has obvious disease resistance and higher chlorophyll content than the wild-type Arabidopsis with the infection of Foc TR4. These results indicate that MaTGA8 may enhance the resistance of bananas to Foc TR4 by interacting with MaNPR11 or MaNPR4. This study provides a basis for further research on the application of banana TGA transcription factors in Foc TR4 stress and disease resistance and molecular breeding programs.

The MLO1 powdery mildew susceptibility gene in Lathyrus species: The power of high-density linkage maps in comparative mapping and synteny analysis.

Powdery mildews are major diseases for a range of crops. The loss of function of specific Mildew Locus O (MLO) genes has long been associated with pre-haustorial plant resistance to powdery mildew and has proven to be durable in several species. Erysiphe pisi is the major causal agent of powdery mildew in pea (Pisum sativum L.) and in the closely related Lathyrus sativus L. and Lathyrus cicera L. PsMLO1 has been extensively studied in pea. However, no MLO gene family members have been isolated and characterized in Lathyrus species so far. In this study, MLO1 genes were isolated and characterized in L. sativus and L. cicera genotypes with varied levels of partial resistance against powdery mildew. Phylogenetic analyses confirmed that Lathyrus MLO1 belongs to Clade V, like all dicot MLO proteins associated with powdery mildew susceptibility. A L. sativus recombinant inbred line population (RIL) was genotyped by sequencing to develop a high-density L. sativus genetic linkage map. DNA sequence polymorphisms between the analyzed genotypes allowed the location of MLO1 in the newly developed L. sativus RIL genetic linkage map. Subsequent comparative mapping between L. sativus and L. cicera genetic maps and P. sativum, Lens culinaris Medik., and Medicago truncatula Gaertn. reference genomes revealed important aspects of the conservation of the MLO1 locus position and of the overall chromosomal rearrangements occurring during legume evolution, with relevance to legume disease resistance breeding programs.

Identification of novel sources for resistance against ascochyta blight and botrytis grey mould of chickpea

Ascochyta blight (Ab) and botrytis grey mould (bGM) are the major foliar diseases of chickpea that can cause severe yield losses. Thus, to identify stable sources, a set of 388 lines including 288 lines from Reference Set of chickpea and 100 advanced breeding lines were screened at PAU, Ludhiana for two years against Ab and bGM. One accession, ICC 1915, from the Reference Set and 24 advanced breeding lines were found resistant against Ab. None of the lines was found resistant against bGM, however, some lines were found moderately resistant. The identified lines can be used as sources of resistance in the disease resistance breeding programmes.

Gene Pyramiding for Achieving Enhanced Resistance to Bacterial Blight, Blast, and Sheath Blight Diseases in Rice.

Bacterial blight, blast, and sheath blight are the commonest diseases causing substantial yield loss in rice around the world. Stacking of broad-spectrum resistance genes/QTLs into popular cultivars is becoming a major objective of any disease resistance breeding program. The varieties ASD 16 and ADT 43 are the two popular, high yielding, and widely grown rice cultivars of South India, which are susceptible to bacterial blight (BB), blast, and sheath blight diseases. The present study was carried out to improve the cultivars (ASD 16 and ADT 43) through introgression of bacterial blight (xa5, xa13, and Xa21), blast (Pi54), and sheath blight (qSBR7-1, qSBR11-1, and qSBR11-2) resistance genes/QTLs by MABB (marker-assisted backcross breeding). IRBB60 (xa5, xa13, and Xa21) and Tetep (Pi54; qSBR7-1, qSBR11-1, and qSBR11-2) were used as donors to introgress BB, blast, and sheath blight resistance into the recurrent parents (ASD 16 and ADT 43). Homozygous (BC3F3 generation), three-gene bacterial blight pyramided (xa5 + xa13 + Xa21) lines were developed, and these lines were crossed with Tetep to combine blast (Pi54) and sheath blight (qSBR7-1, qSBR11-1, and qSBR11-2) resistance. In BC3F3 generation, the improved pyramided lines carrying a total of seven genes/QTLs (xa5 + xa13 + Xa21 + Pi54 + qSBR7-1 + qSBR11-1 + qSBR11-2) were selected through molecular and phenotypic assay, and these were evaluated for resistance against bacterial blight, blast, and sheath blight pathogens under greenhouse conditions. We have selected nine lines in ASD 16 background and 15 lines in ADT 43 background, exhibiting a high degree of resistance to BB, blast, and sheath blight diseases and also possessing phenotypes of recurrent parents. The improved pyramided lines are expected to be used as improved varieties or used as a potential donor in breeding programs. The present study successfully introgressed Pi54, and qSBR QTLs (qSBR7-1, qSBR11-1, and qSBR11-2) from Tetep and major effective BB-resistant genes (xa5, xa13, and Xa21) from IRBB60 into the commercial varieties for durable resistance to multiple diseases.

Resistance assessment and biochemical responses of maize genotypes against Rhizoctonia solani f. sp. sasakii Exner causing Banded leaf and sheath blight disease

Maize (Zea mays L.) is a staple food in many parts of the world. In addition to being used as grain, animal feed, production of corn ethanol, starch, syrup etc., it has been widely consumed as a vegetable in the form of baby corn and sweet corn. Banded leaf and sheath blight (BLSB) is one of the major diseases affecting maize and is caused by Rhizoctonia solani f. sp. sasakii Exner. In the experiment forty six maize inbreds were screened for their reaction against the BLSB pathogen following artificial inoculation. Two inbred lines namely, EV1417 and CML-323 produced resistant and moderately resistant disease reaction respectively. Biochemical studies indicated the presence of a high level of pre-infectional barriers in the resistant line. Further, higher level of defense related enzymatic activities of peroxidase and poly phenol oxidase were detected in the resistant inbred line. After 48 h of inoculation, in comparison to highly susceptible EV1428, electrolyte leakage was found to be stabilized in EV1417 and CML-323. This study clearly establishes the presence of effective pre-infection barriers and induced biochemical defence mechanisms operating in the resistant inbred line. The identified resistant line EV1417 is further being used in BLSB disease resistance breeding programmes.

Whole genome analysis of the koa wilt pathogen (Fusarium oxysporum f. sp. koae) and the development of molecular tools for early detection and monitoring

BackgroundDevelopment and application of DNA-based methods to distinguish highly virulent isolates of Fusarium oxysporum f. sp. koae [Fo koae; cause of koa wilt disease on Acacia koa (koa)] will help disease management through early detection, enhanced monitoring, and improved disease resistance-breeding programs.ResultsThis study presents whole genome analyses of one highly virulent Fo koae isolate and one non-pathogenic F. oxysporum (Fo) isolate. These analyses allowed for the identification of putative lineage-specific DNA and predicted genes necessary for disease development on koa. Using putative chromosomes and predicted gene comparisons, Fo koae-exclusive, virulence genes were identified. The putative lineage-specific DNA included identified genes encoding products secreted in xylem (e. g., SIX1 and SIX6) that may be necessary for disease development on koa. Unique genes from Fo koae were used to develop pathogen-specific PCR primers. These diagnostic primers allowed target amplification in the characterized highly virulent Fo koae isolates but did not allow product amplification in low-virulence or non-pathogenic isolates of Fo. Thus, primers developed in this study will be useful for early detection and monitoring of highly virulent strains of Fo koae. Isolate verification is also important for disease resistance-breeding programs that require a diverse set of highly virulent Fo koae isolates for their disease-screening assays to develop disease-resistant koa.ConclusionsThese results provide the framework for understanding the pathogen genes necessary for koa wilt disease and the genetic variation of Fo koae populations across the Hawaiian Islands.

Mechanical sap transmission of Tomato leaf curl New Delhi virus infecting ridge gourd [Luffa acutangula (L.) Roxb.] in south India

Ridge gourd (Luffa acutangula L.) is an important cucurbitaceous crop cultivated throughout India. The crop is severely affected by yellow mosaic disease caused by Tomato Leaf Curl New Delhi Virus (ToLCNDV). The symptoms of ToLCNDV consists of yellow mosaic spots on young leaves, reduction in leaf area, leaf thickening flower abortion and severe stunting of the plants. High disease dissemination under epiphytotic conditions also affects the chemical control measures and leads to heavy crop losses. Identification of resistant sources is most important tool to reduce the economic loss and maximize quality and quantity of output. Efficient and simple screening procedures are very crucial in disease resistant breeding program. In this experiment, mechanical sap inoculation of ToLCNDV has been studied in twelve ridge gourd genotypes. All the inoculated plants developed characteristics ToLCNDV symptoms and severe infection after three-week post inoculation. In all the assays ToLCNDV transmission was confirmed by PCR amplification using virus specific primer followed by sequencing of random samples. Mechanical sap transmission is easy and simple screening method which will facilitate the development of ToLCNDV resistant breeding cultivars.

Genetic Diversity and Identification of Wilt and Root Rot Pathogens of Tomato in China.

Fungal wilt and root rot diseases affecting tomato have become prevalent in China in recent years and have caused considerable damage. In 2016 to 2018, symptoms of putative wilt and root rot diseases were observed in several locations in tomato cultivars with resistance to Fusarium oxysporum f. sp. lycopersici races 1 and 2. The objective of this study was to identify the causative agents of wilt and root rot of tomato in China and provide a basis for disease prevention and resistance breeding programs. Based on DNA sequence analyses of the internal transcribed spacer (ITS) region, 91 isolates from the roots of tomato plants showing symptoms of wilt and root rot were identified, including F. oxysporum (64 isolates), Fusarium solani (11 isolates), Fusarium proliferatum (2 isolates), Fusarium graminearum (2 isolates), Fusarium equiseti (1 isolate), Pythium aphanidermatum (6 isolates), Ascomycota sp. (2 isolates), and Plectosphaerella cucumerina (3 isolates). F. oxysporum accounted for 70.33% of the isolates obtained. In this case, using PCR-based methods for differentiation of F. oxysporum, we identified several formae speciales and races of F. oxysporum: 7 isolates were identified as F. oxysporum f. sp. lycopersici race 1, 2 isolates as F. oxysporum f. sp. lycopersici race 2, 35 isolates as F. oxysporum f. sp. lycopersici race 3, and 13 isolates as F. oxysporum f. sp. radicis-lycopersici. Pathogenicity tests revealed 55 isolates of tomato wilt and root rot pathogens to be virulent. This study demonstrated that F. oxysporum f. sp. lycopersici race 3 was the most widespread and highly virulent race among these tomato pathogens in China, followed by F. oxysporum f. sp. radicis-lycopersici. Therefore, the development of resistant varieties of tomato against F. oxysporum f. sp. lycopersici race 3 and F. oxysporum f. sp. radicis-lycopersici would aid efforts to develop effective disease management strategies.