Resistance Breeding Programs Research Articles

Stability and suitability of genotypes and environment to Ascochyta blight of chickpea.

Ascochyta blight (AB) is a major biotic constraint to chickpea production internationally. The disease caused by the phytopathogenic fungus Ascochyta rabiei is highly favored by prolonged spells of low temperature and high humidity. The disease scenario is expected to aggravate in the near future as a result of rapidly changing climatic conditions and the emergence of fungicide-resistant pathogen strains. Tapping into host-plant resistance is the most logical way to preempt such a crisis. Presently, high levels of stable resistance against AB are yet to be identified from the chickpea gene pool. The present study was aimed at facilitating this process through multi-environment testing of chickpea genotypes. Using the GGE biplot analysis method, we could identify three genotypes, viz., ICCV 16508, ICCV 16513, and ICCV 16516, from the International Ascochyta Blight Nursery, which showed consistent moderate resistance reactions across all the tested environments. Moreover, we were able to evaluate the test locations for their suitability to support AB screening trials. Ludhiana and Palampur locations were identified as the most ideal for continual screening in the future. Controlled environment screening at the ICRISAT location offered to reduce large plant populations to small meaningful sizes through initial screening under controlled environment conditions. This study will further improve the scope of phenotyping and sources of stable resistance to be utilized in future AB resistance breeding programs.

Genetics of downy mildew resistance in indigenous cucumber germplasm

Cucumber (Cucumis sativus L.) is a major Cucurbitaceous vegetable crop widely grown in tropical andsubtropical regions of the world. Downy mildew is the most damaging disease in cucumber worldwide causingsignificant yield loss. The wide diversity in terms of different economically important traits including severityto downy mildew infestation is available in Indian-originated germplasm. To investigate the genetic inheritanceof cucumber downy mildew disease resistance, one resistant genotype (DC-70) from India was crossed with acontrasting susceptible genotype (DC-773). The parents and their progenies were evaluated in both field andnet house conditions for downy mildew disease resistance. Field condition data were recorded 4-times from30 days until the plants die. The lower leaf surface was inoculated 20-25 days after sowing at the seedlingstage by spraying the inoculum. The proportion of infection was recorded 4-times from 8-days to 65-daysafter inoculation, and the per cent disease index and area under the disease progress curve (AUDPC) werecalculated from these proportions. Based on the PDI and AUDPC, it was established that resistance to downymildew in the genotype, DC-70 was controlled by a major gene. Additive-dominance model fits the segregationdata and the additive effect was significant. Finally, the downy mildew disease inheritance pattern indicatedthat it is controlled by a single recessive gene in DC-70, which can be successfully introgressed into desiredelite genotypes to facilitate the downy mildew resistance breeding programme.

Field Screening of Maize (Zea mays L.) Genotypes against Turcicum Leaf Blight (TLB) under Artificial Conditions

Background: There are a variety of critical problems facing tropical maize cultivation, such as disease infestation, insect/pest and weed problems. Foliar diseases in particular cause significant losses in agricultural yield. Leaf blight, known as northern leaf blight, is a disease of maize leaves caused by an overgrowth fungus. Therefore, it was necessary to develop sources of resistance to TLB and then a field experiment was conducted to study the performance of 64 (44 test crosses, 11 lines, 4 examiners and 5 assays) During Spring 2021-22 at the Agricultural College Farm, Babatla.
 Methods: Screening was carried under field conditions by adopting an artificial disease inoculation technique Disease score was recorded at tasseling, 20 DAT and maturity stages by using 1-9 scale.
 Results and Discussion: At maturity stage 12 crosses, seven lines and one check showed resistant reaction (R); 25 crosses, 4 inbreds, one check showed moderately resistant reaction (MR); 7 crosses, 3 inbreds and one check showed moderately susceptible reaction (MS) and one inbred, two checks showed susceptible reaction (S) under field screening. 
 Conclusion: The lines VL171488-2, VL18828, VL19705-8, VL18142, VL175869, SNL19582-22 and tester LM13 showed resistant disease reaction for TLB pathogen at phenotypic level. These lines can be used in future TLB resistance breeding programmes.

Comparative transcriptome-wide identification and differential expression of genes and lncRNAs in rice near-isogenic line (KW-Bph36-NIL) in response to BPH feeding.

Brown planthopper (BPH) is the most devastating pest of rice in Asia, causing substantial yield losses and has become a challenging task to be controlled under field conditions. Although extensive measures have been taken over the past decades, which resulted in the evolution of new resistant BPH strains. Therefore, besides other possible approaches, equipping host plants with resistant genes is the most effective and environment-friendly technique for BPH control. Here, we systematically analyzed transcriptome changes in the susceptible rice variety Kangwenqingzhan (KW) and the resistant near-isogenic line (NIL) KW-Bph36-NIL, through RNA-seq, depicting the differential expression profiles of mRNAs and long non-coding RNAs (lncRNAs) in rice before and after BPH feeding. We observed a proportion of genes (1.48%) and (2.74%) were altered in KW and NIL, respectively, indicating different responses of rice strains against BPH feeding. Nevertheless, we characterized 384 differentially expressed long non-coding RNAs (DELs) that can be impacted by the two strains by alternatively changing the expression patterns of the respective coding genes, suggesting their certain involvement in response to BPH feeding. In BPH invasion, KW and NIL responded differently by modifying the synthesis, storage, and transformation of intracellular substances, adjusting the nutrient accumulation and utilization inside and outside the cells. In addition, NIL expressed stronger resistance by acutely up-regulating genes and other transcription factors related to stress resistance and plant immunity. Altogether, our study elaborates valuable insights into the genome-wide DEGs and DELs expression profiles of rice under BPH invasion by high throughput sequencing and further suggests that NILs can be utilized in BPH resistance breeding programs in developing high-resistance rice lines.

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.

In-depth understanding of the genetic control of stripe rust resistance (Puccinia striiformis f. sp. tritici) induced in wheat (Triticum aestivum L.) by Trichoderma asperellum T34.

Wheat stripe rust (Pst) causes severe yield losses worldwide. Due to the continuous appearance of new stripe rust races, resistance has been broken in most of the highly resistant genotypes in Egypt and worldwide. Therefore, looking for new ways to resist such a severe disease is urgently needed. Trichoderma asperellum strain T34 has been known as an effective bioagent against many crop diseases. It exists naturally in Egyptian fields. Therefore, in the recent study, the effectiveness of T34 was tested as a bioagent against wheat stripe rust. For this purpose, 198-spring wheat genotypes were tested for their resistance against two different Pst populations collected from the Egyptian fields. The highest aggressive Pst population was used to test the effectiveness of T34. Highly significant differences were found between T34 and stripe rust suggesting the effectiveness of T34 in stripe rust resistance. Genome-wide association study (GWAS) identified 48 gene models controlling the resistance under normal conditions and 46 gene models controlling T34-induced resistance. Out of these gene models, only one common gene model was found suggesting the presence of two different genetic systems controlling the resistance under each condition. The pathways of the biological processes were investigated under both conditions. This study provided depth understanding of genetic control, hence will accelerate the future of wheat breeding programs for stripe rust resistance.

Identification of leaf rust resistance loci in a geographically diverse panel of wheat using genome-wide association analysis.

Leaf rust, caused by Puccinia triticina (Pt) is among the most devastating diseases posing a significant threat to global wheat production. The continuously evolving virulent Pt races in North America calls for exploring new sources of leaf rust resistance. A diversity panel of 365 bread wheat accessions selected from a worldwide population of landraces and cultivars was evaluated at the seedling stage against four Pt races (TDBJQ, TBBGS, MNPSD and, TNBJS). A wide distribution of seedling responses against the four Pt races was observed. Majority of the genotypes displayed a susceptible response with only 28 (9.8%), 59 (13.5%), 45 (12.5%), and 29 (8.1%) wheat accessions exhibiting a highly resistant response to TDBJQ, TBBGS, MNPSD and, TNBJS, respectively. Further, we conducted a high-resolution multi-locus genome-wide association study (GWAS) using a set of 302,524 high-quality single nucleotide polymorphisms (SNPs). The GWAS analysis identified 27 marker-trait associations (MTAs) for leaf rust resistance on different wheat chromosomes of which 20 MTAs were found in the vicinity of known Lr genes, MTAs, or quantitative traits loci (QTLs) identified in previous studies. The remaining seven significant MTAs identified represent genomic regions that harbor potentially novel genes for leaf rust resistance. Furthermore, the candidate gene analysis for the significant MTAs identified various genes of interest that may be involved in disease resistance. The identified resistant lines and SNPs linked to the QTLs in this study will serve as valuable resources in wheat rust resistance breeding programs.

Mapping Quantitative Trait Loci for Type II Fusarium Head Blight Resistance in Two Wheat Recombinant Inbred Line Populations Derived from Yangmai 4 and Yangmai 5.

Fusarium head blight (FHB) is a destructive wheat disease worldwide and significantly affects grain yield and quality in wheat. To understand the genetic basis underlying type II FHB resistance in two elite wheat cultivars Yangmai 4 (YM4) and Yangmai 5 (YM5), quantitative trait loci (QTL) mapping was conducted in two recombinant inbred lines (RIL) populations derived from the crosses of YM4 and YM5 with susceptible cultivar Yanzhan 1 (YZ1), respectively. Survey with markers linked to Fhb1, Fhb2, Fhb4, and Fhb5 in landrace Wangshuibai indicated the non-existence of these known FHB resistance genes/QTL in YM4, YM5, and YZ1. One overlapped resistance QTL was identified in both RIL populations, namely QFhb.Y4.2D/QFhb.Y5.2D, with a large effect on FHB resistance. One novel resistance QTL QFhb.Y4.5A mapped on chromosome 5A was detected only in YM4/YZ1 population. The resistance alleles of both QFhb.Y4.2D/QFhb.Y5.2D and QFhb.Y4.5A did not increase the plant height and did not significantly affect the heading date and flowering date. Kompetitive Allele-Specific PCR markers for QFhb.Y4.2D/QFhb.Y5.2D and QFhb.Y4.5A had been developed to verify in an additional set of 244 geographically diverse cultivars/lines. Pyramiding of the two resistance alleles decreased the percentage of symptomatic spikelets by 51.77% relative to the cultivars/lines without these two resistance alleles. QFhb.Y4.2D/QFhb.Y5.2D and QFhb.Y4.5A were shown to be useful alternatives in FHB resistance breeding programs. The results will facilitate the marker-assisted selection for introgression of the favorable alleles for improving FHB resistance in breeding programs.

Prospecting quantitative trait loci for maydis leaf blight (MLB) resistance using a population of teosinte‐introgressed maize (Zea mays ssp. mays) and in silico identification of candidate MLB resistance genes

AbstractMaydis leaf blight (MLB) is an important fungal disease of maize causing yield losses of the magnitude of 38 to 46% worldwide. Present investigation aimed to identify stable and reliable MLB‐resistant QTLs and introgression maize lines to facilitate their utilization in future MLB resistance breeding programmes. For this purpose, 169 backcross inbred lines (BILs), derived using teosinte (Zea mays ssp. parviglumis) as one parent, were grown in randomized block design with two replications in two environments. The lines were phenotyped and genotyped to identify the resistant QTLs by single marker analysis (SMA) method. Also, twenty‐five most resistant and twenty‐five most susceptible lines were selected in order to mimic bidirectional selective genotyping to identify MLB‐resistant QTLs by trait‐based (SGTB) and marker‐based (SGMB) approach. Six and five MLB resistance QTLs were identified in S1 and S2, respectively, by SMA method, while twelve and eight MLB‐resistant QTLs were detected by SGTB and SGMB approach, respectively. A total of fifteen MLB resistance QTLs identified by either SMA, SGTB or SGMB co‐localized with forty‐two QTLs affecting eleven morphological traits in maize. Out of the MLB resistance QTLs detected in both S1 and S2 by SMA, two QTLs linked to marker umc2392 and umc1393 were stable. Four QTLs linked to marker umc1869, umc1720, umc1428 and umc1393 were detected by all three methods and were reliable. A total of 23 genes exhibiting response to fungal pathogens were identified by means of in silico analysis, and these may be validated further so as to be used in future maize improvement programmes.

Identification of BCMV resistant germplasm in mungbean (Vigna radiata) using serological and molecular diagnostics

Diverse germplasm of mungbean serves as a source of resistant gene, screening of germplasm for BCMV resistance will provide resistance source. So, in 2018–2019 a total of 65 diverse mungbean accessions along with susceptible and resistant checks were screened against BCMV under natural conditions in the field and artificial inoculation under controlled conditions. Transmission electron microscopy, per cent disease incidence, serological Direct antigen coating- Enzyme-linked immunosorbent assay (DAC-ELISA) and reverse transcription-polymerase chain reaction (RT-PCR) diagnostics were used to detect and identify the BCMV resistant accessions. The study revealed that a total of 29 accessions were found to be immune to BCMV infections. However, these accessions need to be further evaluated in BCMV disease hotspots and under multilocation trials. Therefore, in the present study, accessions that were immune to BCMV may serve as valuable donors for the BCMV resistant mungbean breeding programme.

Evaluation Soybean Cultivars for Reaction to Heterodera glycines Populations HG Types 7 and 1.3.4.7 in Northeast China.

Soybean cyst nematode Heterodera glycines (SCN) is a major threat to global soybean production. Effective management of this disease is dependent on the development of resistant cultivars. Two SCN HG Types, 7 and 1.3.4.7. were previously identified as prevalent H. glycines populations in Northeast China. In order to evaluate soybean cultivars resistant to local SCN populations, 110 domestic commercial soybeans from different regions of Northeast China were assessed in the greenhouse to determine their potential as novel sources of resistance. The results suggested that cultivars responded differently to the two HG types. Of the 110 soybean cultivars evaluated, 24 accessions were classified as resistant or moderately resistant to HG Type 7, and five cultivars were classified as resistant or moderately resistant to HG Type 1.3.4.7. Among the tested cultivars, Kangxian 12 and Qingdou 13 had resistance response to both HG types 7 and 1.3.4.7. Thus, these broad-based SCN cultivars will be the valuable materials in the SCN resistance breeding program.

RESISTANCE IN COMMON BEAN(PHASEOLUS VULGARIS L.) TO UROMYCES APPENDICULATUS IN BULGARIA

Common bean rust, caused by Uromycesappendiculatus, is one of the most devastating diseases in common bean. Breeding for resistant cultivars is the most effective and eco-friendly method for disease control. Although there is no targeted breeding program in Bulgaria to create resistant cultivars to the pathogen, periodic screening of the virulent diversity of U. appendiculatus and sources of resistance to the identified races/pathotypes is carried out. During the last twenty years, four investigations were made to estimate virulence diversity in pathogen population. Eleven U. appendiculatus races (20-0, 20-1, 20-2, 20-3, 20-19, 29-0, 29-1, 28-1, 52-3, 20-16 and 20-18) are identified, distributed in Rhodope mountains and North Bulgaria. Chronologically each of the studies was accompanied or followed by a screening for sources of resistance to the pathogen under field conditions. Еach study found different numbers of resistant accessions depending on the virulent potential of the population used. In three of the studies, cultivars that showed resistant phenotype under field conditions were screened against a set of races, distributed in the country in the same time, under greenhouse. Bulgarian cultivar ‘Beslet’ showed resistant reaction under field and greenhouse in all investigation. The resistance of the cultivar to races 20-1 and 20-19 is governed by a single dominant gene. This cultivar can be successfully used in a breeding program for race-specific resistance. Fifty accessions with race-nonspecific resistance, expressed by low disease intensity and resistant/susceptible infection type, are identified in two investigations under field conditions.

Odporność odmian regionalnych i tradycyjnych jęczmienia jarego na porażenie mączniakiem prawdziwym zbóż i traw (Blumeria graminis f. sp. hordei)

Fifty accessions stored in the form of seeds by the National Center for Plant Genetic Resources, IHAR – PIB were evaluated. Identifica¬tion of the presence of specific resistance genes was carried out by the phenotypic method using a set of 11 differential isolates at the seedling stage. Based on the obtained results, no known resistance genes were found for any of the accessions. However, three cultivars deserved special attention: the E 0942 and the cultivars Putza and Wieloryb z Podhorec. The traditional cultivar E 0942 was susceptible to one isolate. The regional cultivar Putza was susceptible to 2 isolates and resistant to 6 isolates. The Wieloryb z Podhorec cultivar was susceptible to 2 isolates and moderately resistant to six isolates. The regional cultivars Wieloryb z Podhorec and Putza and the traditional cultivar E 0942 characterized in present studies may be a potential source of resistance to Bgh. These varieties may be used in integrated control of barley to control Bgh or as germplasm in barley resistance breeding programs.

Screening and characterization of highly responsive genes related to the blast disease caused by Pyricularia oryzae in rice (Oryza sativa)

Blast, caused by Pyricularia oryzae, has been regarded as one of the most critical diseases in rice plants (Oryza sativa). Seeking a list of candidate genes is a major step for resistance breeding programs. In this study, at least 24 RNA-Seq datasets related to blast disease infection in rice plants have been obtained from databases. Among them, four microarray datasets obtained from blast-infected leaf samples in Indica rice varieties, including GSE122258, GSE126961, GSE78266 and GSE39635 were selected for further in silico analysis. Particularly, a total of 216 differentially expressed genes in blast-treated leaves were obtained by exploring four microarray atlas. Among them, at least 32 blast-responsive genes that exhibited similar expression patterns were selected for further bioinformatics analysis. Particularly, these differentially expressed genes encode important transcription factors and enzyme families. By using Expasy and Yloc tools, the physic-chemical properties of these proteins, including lengths, molecular weights, iso-electric points and grand average of hydropathy were greatly variable and the majority of these blast-responsive gene-encoding proteins was localized in the cytoplasm and nucleus. To sum up, this current study has provided fundamental knowledge about potential candidate differentially expressed genes for further functional characterization of genes aiming to control blast resistance in rice.

Marker-assisted pyramiding of southern leaf blight resistance QTLs qSLB3.1 and qSLB8.1 in maize (Zea mays)

Southern leaf blight (SLB) is one of the major diseases that cause substantial yield losses in maize (Zea mays L.) worldwide. Stacking broad-spectrum resistance genes/QTLs into prevalent cultivars is the prerequisite for durable disease resistance breeding programme. Therefore, a study was carried at the research farm and molecular biology laboratory of School of Agricultural Biotechnology, Punjab Agricultural University, Ludhiana, Punjab during 2017–21 to introgress SLB resistance QTLs from two donors, viz. CM139 (qSLB3.1) and LM5 (qSLB8.1) into CM140 inbred using marker-assisted backcross breeding (MABB). Crosses were made between CM139 × CM140 and LM5 × CM140 to generate two separate F1s. Each F1 was backcrossed twice to generate BC2F1 progenies. Foreground selection was performed at each step using linked flanking markers to each QTL and also evaluated for SLB resistance. The selected heterozygous BC2F1 plants from each cross were inter-crossed to combine qSLB3.1 and qSLB8.1 in the same genetic background. The F2 population was also evaluated phenotypically for SLB resistance and other morphological traits. A total of 18 plants were obtained having both the QTLs with homozygous donor alleles. The F2 plants having both QTLs and singly in the homozygous state were advanced to generate F3 progenies. The pyramided lines exhibited 29% lesser disease severity than the lines with either QTL. The present results indicated that additive effects of the QTLs for SLB resistance played an important role among these lines. To our best knowledge, this is the first report for the pyramiding of QTLs associated with SLB resistance. The pyramided lines would serve as potential donors in maize breeding programs.

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.

Updates on cowpea viruses in Southwest Nigeria: distribution, prevalence and coinfection.

The online version contains supplementary material available at 10.1007/s42360-022-00576-8.

Identification of sources of resistance in cowpea lines to Macrophomina root rot disease in Northern Ghana

Macrophomina root rot disease (MRRD) caused by Macrophomina phaseolina is an emerging threat to the profitable cowpea production in northern Ghana.Recommended control methods including the use of fungicides are ineffective and expensive for resource poor farmers whilst biocontrol options are not commercially available. An integrated method based on host plant resistance is considered the cheapest and most effective method of managing the disease. This study sought to confirm and characterize previously identified MRRD isolates from Northern Ghana using molecular technology, and to identify cowpea with potential sources of resistance to the MRRD. A PCR assay of ten isolates of the cowpea root rot pathogen revealed all isolates belonged to the species M. phaseolina, whilst a nucleotide BLAST of eight isolates showed 98% similarity with the sequences of Macrophomina isolates from other host available in GenBank. A sick pot method evaluation of 49 cowpea lines found 10 lines resistant to MRRD on a 1–9 disease severity scale (disease score, less than 5). A selection of eight resistant lines (Suvita 2, Abagbaala, IT97K573-1-1, IT93K-503-1-1, Hewale, AV2 3224, Nhyira and T2T4), and a susceptible check (Songotra) were evaluated against 10 isolates of M. phaseolina using a sick pot method. All the genotypes except for the susceptible check were resistant to MRRD. Thus, these genotypes could be used in cowpea MRRD resistance breeding programs.

Screening of short-day onions for resistance to Stemphylium leaf blight in the seed-to-bulb stage (stage I) and bulb-to-seed stage (stage II).

Stemphylium leaf blight, caused by Stemphylium vesicarium, is a very important fungal disease in onions since its epidemics are able to affect both the bulb yield and the seed quality. The aim of this study was to screen onion genotypes at stage I (seed to bulb) and further screen the identified resistant and susceptible genotypes at stage II (bulb to seed). One hundred and fifty-seven genotypes were screened against SLB under artificially inoculated field conditions. Results revealed a significant variation among the morphological and biochemical traits studied. Correlation studies revealed a significant and negative correlation between percent disease incidence (PDI), pseudostem width, neck thickness, and dry matter. Fifteen genotypes were identified as moderately resistant, and the rest were categorized as susceptible. Bulbs of the genotypes, identified as moderately resistant, were again screened for resistance in stage II. All the genotypes were categorized as moderately susceptible. Biochemical analysis revealed that total foliar phenol content, pyruvic acid, catalase, and peroxidase increased up to 20 days after inoculation (DAI) and thereafter declined. Protein content was highest in the initial stage and declined at 10, 20, and 30 DAI. The higher biochemical activity was observed in moderately resistant category genotypes compared with the susceptible ones. Correlation analysis showed a highly significant and negative correlation of PDI with total foliar phenol content (TFPC), pyruvic acid, catalase, peroxidase, and protein content. To conclude, it was observed that screening against SLB should be done at both the stages (stage I and Stage II) to identify resistant onion genotypes. Direction selection for genotypes with high dry matter, higher phenols, and enzymes may be an alternative pathway to select genotypes for a robust resistance breeding program.

Morpho-pathogenic and molecular diversity among Rhizoctonia bataticola isolates causing dry root rot of chickpea in Madhya Pradesh, India

Aim: The present study was conducted to identify the morphological, pathological and molecular variations in isolates of Rhizoctonia bataticola, causing dry root rot of chickpea collected from different parts of Madhya Pradesh, India. Methodology: The isolation, purification and identification of Rhizoctonia bataticola isolates was done from dry root rot infected chickpea plants, collected from 23 districts of Madhya Pradesh, India. Total 32 isolates of pathogen were obtained and further used for morphological, cultural, pathological and molecular characterization. The acquired data were subjected to DARwin5 software analysis for variability studies. The DNA isolates of the pathogen were also obtained and analysed to study molecular variability by RAPD analysis and the bands produced were subjected to PAST software for cluster analysis. Results: Thirty two isolates of R. bataticola with diverse origin showed a large variation in shape, size and initiation time of sclerotia. These isolates were pathogenic and grouped into three categories; highly virulent (59%), moderately virulent (25%) and less virulent (16%), under artificially inoculated conditions in sick soil method. The study of pathogenic variability revealed that ICC12441, ICC11332 and Pusa 212 were susceptible to all the isolates evaluated, whereas ICC12450, Pusa362, Pusa1103 showed moderate resistance against maximum isolates. Based on molecular characterization, the isolates were grouped into four clusters indicating that no two or more isolates were similar. Interpretation: The isolates of R. bataticola of chickpea from different agro-climatic zones of Madhya Pradesh, possess variability in their morphological and cultural characteristics, which not limited to geographical boundaries. The present study would be extremely useful for dry root rot management, as well as, in identifying donors for resistance breeding programmes. Key words: Chickpea, Diversity, Dry root rot, Pathogenicity, Rhizoctonia bataticola