Sources Of Genetic Resistance Research Articles

Identification of new genetic sources of resistance to bacterial blight race 18 in diploid Asiatic cotton and resistance transfer to tetraploid Upland cotton (Gossypium hirsutum)

Identification of new genetic sources of resistance to bacterial blight race 18 in diploid Asiatic cotton and resistance transfer to tetraploid Upland cotton (Gossypium hirsutum)

Phytoparasitic Nematodes of Musa spp. with Emphasis on Sources of Genetic Resistance: A Systematic Review.

Bananas are a staple food that considerably contributes to both food security and income generation, especially in countries of Africa, Asia, and Central and South America. The banana plant (Musa spp.) is affected by various pathogens, of main concern being the plant-parasitic nematodes associated with the rhizosphere, the most important of which are Radopholus similis (burrowing nematode), Helicotylenchus sp. (spiral nematode), Pratylenchus sp. (root lesion nematode), and Meloidogyne sp. (gall nematode). Infected plants reduce their ability to absorb water and nutrients, which can lead to delayed flowering, fewer bunches, and lower fruit mass. Obtaining nematode-resistant banana cultivars through genetic improvement is an effective and sustainable option compared with chemical control with nematicides. Here, we provide the first systematic review of existing banana sources of resistance to nematodes to aid the management and control of nematodes in banana and plantain crops. Articles selected from different databases were evaluated, and searches were conducted using pre-established inclusion and exclusion criteria. We found 69 studies dealing with genetic improvement for nematode resistance in banana cultivation. Our findings revealed that sources of resistance are currently under investigation to combat the diseases caused by different nematode species in banana plants.

Registration of the “Woodies” multi–rust‐resistant barley germplasm

AbstractSelection for resistance to plant diseases is a continuous effort on the part of plant breeders. Sources of genetic resistance are often limited, despite considerable discovery efforts. Stem rust and stripe rust are two diseases of particular importance in barley (Hordeum vulgare L.) production. The present work aims to develop and deploy genotypes with resistance to these diseases that can be used in future breeding efforts. The Woodies, Woody‐1 (DH160733; Reg. no. GP‐218, PI 704479) and Woody‐2 (DH160754; Reg. no. GP‐219, PI 704480), are two doubled‐haploid genotypes produced via F1 anther culture named in honor of the late Lynn “Woody” Gallagher. These two‐row spring habit barley germplasm accessions were released by the Oregon Agricultural Experiment Station in 2023. These genotypes have demonstrated resistance to both stem and stripe rust at the seedling and adult plant stage in trials conducted between 2018 and 2023. The genetic basis of this resistance appears to be a novel quantitative trait locus conferring resistance to both diseases on chromosome 5H that is different from the known rpg4/Rpg5 complex for stem rust resistance found on the same chromosome. Seed can be requested from the Oregon State University Barley Breeding Program or from the NLGRP Germplasm repository.

Non-destructive SPE-UPLC-based Quantification of Aflatoxins and Stilbenoid Phytoalexins in Single Peanut (Arachis spp.) Seeds.

Aflatoxins are highly carcinogenic secondary metabolites of some fungal species, particularly Aspergillus flavus. Aflatoxins often contaminate economically important agricultural commodities, including peanuts, posing a high risk to human and animal health. Due to the narrow genetic base, peanut cultivars demonstrate limited resistance to fungal pathogens. Therefore, numerous wild peanut species with tolerance to Aspergillus have received substantial consideration by scientists as sources of disease resistance. Exploring plant germplasm for resistance to aflatoxins is difficult since aflatoxin accumulation does not follow a normal distribution, which dictates the need for the analyses of thousands of single peanut seeds. Sufficiently hydrated peanut (Arachis spp.) seeds, when infected by Aspergillus species, are capable of producing biologically active stilbenes(stilbenoids) that are considered defensive phytoalexins. Peanut stilbenes inhibit fungal development and aflatoxin production. Therefore, it is crucial to analyze the same seeds for peanut stilbenoids to explain the nature of seed resistance/susceptibility to the Aspergillus invasion. None of the published methods offer single-seed analyses for aflatoxins and/or stilbene phytoalexins. We attempted to fulfill the demand for such a method that is environment-friendly, uses inexpensive consumables, and is sensitive and selective. In addition, the method is non-destructive since it uses only half of the seed and leaves the other half containing the embryonic axis intact. Such a technique allows germination and growth of the peanut plant to full maturity from the same seed used for the aflatoxin and stilbenoid analysis. The integrated part of this method, the manual challenging of the seeds with Aspergillus, is a limiting step that requires more time and labor compared to other steps in the method. The method has been used for the exploration of wild Arachis germplasm to identify species resistant to Aspergillus and to determine and characterize novel sources of genetic resistance to this fungal pathogen.

Reproducible Quantitative Trait Loci for Resistance to Soft Rot Caused by Dickeya dianthicola Derived from the Wild Potato Solanum microdontum (PI 458355) Are Located on Chromosomes 1, 3, and 5.

The potato wild relative Solanum microdontum is a breeder-friendly source of genetic resistance to soft rot. Our objectives were to (i) identify loci associated with soft rot resistance in S. microdontum germplasm and (ii) develop bi-parental populations in a self-compatible S. tuberosum genetic background to recover segregating F2 progenies, construct a linkage map, and identify quantitative trait loci (QTLs). Under objective (i), tubers from 103 S. microdontum genotypes from the United States Potato Genebank were inoculated with a high virulence strain of Dickeya dianthicola, and lesion size was measured after a 24-h incubation period at 30°C. Association analysis using 3,490 polymorphic Infinium array SNP markers identified soft rot resistance loci on chromosomes 1, 2, 3, 5, 7, 8, 11, and 12. Under objective (ii), a resistant S. microdontum accession PI 458355 was crossed with a highly fertile, self-compatible, diploid S. tuberosum pollen parent (PI 654351) to generate segregating F2 populations. Composite interval mapping was conducted using a genetic linkage map with 970 GBS-based SNP markers. Reproducible QTLs were detected on chromosomes 1, 3, and 5, explaining 11, 13, and 23% of the phenotypic variation, respectively. Homozygous S. microdontum alleles at the QTL on chromosome 5 and heterozygous or homozygous S. microdontum alleles at QTLs on chromosomes 1 and 3 significantly decrease lesion size compared with the homozygous S. tuberosum parent. The germplasm created in these studies provides a resource for studying traits from S. microdontum, and we can use the advanced F2 selections for future potato improvement. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Evaluation of lettuce germplasm for resistance to impatiens necrotic spot virus

Recently, impatiens necrotic spot virus (INSV) has emerged as a major pathogen of lettuce in the Salinas Valley of California. The virus is a member of the genus Orthotospovirus, and under natural conditions, is transmitted by the tiny insect, western flower thrips. Due to the high efficiency of virus transmission, chemical management of thrips vectors is often ineffective in preventing the spread of the disease. Utilization of genetic resistance will be a critical component for managing the disease; however, little is known about genetic sources of resistance in lettuce. Here, we evaluated 189 lettuce lines under natural disease pressure in four field experiments to identify INSV resistant germplasm. The stability of resistance was also evaluated using different inoculation methods under controlled conditions. Our results showed a significant variation (p < 0.0001) among lettuce cultivars for both INSV severity and incidence. We identified INSV resistant germplasm that belongs to different horticultural types and leaf color, including a red-leaf cultivar ‘Eruption’ with a high degree of genetic stability. Moreover, we characterized several factors influencing thrips and host plant relationships, including horticultural type, leaf color, and polyphenol concentration. Overall, INSV resistant germplasm identified in this study provide valuable resources for breeding of INSV resistant lettuce cultivars.

Identification of pathogen-specific novel sources of genetic resistance against ascochyta blight and their underlying genetic control

Global chickpea production is restricted by ascochyta blight caused by the necrotrophic fungi ascochyta rabiei. Developing locally adapted disease-resistant cultivars is an economically and environmentally sustainable approach to combat this disease. However, the lack of genetic variability in cultivated chickpeas and breeder-friendly markers poses a significant challenge to ascochyta blight-resistant breeding efforts in chickpeas. In this study, we screened the mini-core germplasm of Cicer reticulatum against a local pathotype of ascochyta rabiei. A modified mini-dome screening approach resulted in the identification of five accessions showing a high level of resistance. The mean disease score of resistant accessions ranged between 1.75±0.3 and 2.88±0.4 compared to susceptible accessions, where the mean disease score ranged between 3.59±0.62 and 8.86±0.14. Genome-wide association analysis revealed a strong association on chromosome 5, explaining ~58% of the phenotypic variance. The underlying region contained two candidate genes (Cr_14190.1_v2 and Cr_14189.1_v2), characterization of which showed the presence of a DNA binding domain (cl28899 &amp; cd18793) in Cr_14190.1_v2 and its orthologs in C. arietinum, whereas Cr_14190.1_v2 carried an additional N-terminal domain (cl31759). qPCR expression analysis in resistant and susceptible accessions revealed ~3 and ~110-fold higher transcript abundance for Cr_14189.1 and Cr_14190.1, respectively.

Occurrence of the &lt;i&gt;FBF&lt;/i&gt;7 fire blight resistance locus in accessions of apple wild species (&lt;i&gt;Malus&lt;/i&gt; Mill.)

Background. Fire blight (Erwinia amylovora (Burill) Winslow et al.) is a dangerous disease of fruit crops. In the Russian Federation, fire blight is one of the quarantine diseases. Apple resistance to fire blight is controlled polygenically. However, the data on the genotypes of Malus Mill. wild species and varieties in the context of individual resistance loci are scarce. The purpose of the research was studying the genetic collection of apple wild species according to the FBF7 fire blight resistance locus to identify promising sources of resistance to E. amylovora.Materials and methods. The materials of this study included 23 wild and two cultivated apple-tree species (50 accessions) from the genetic collection of the I.V. Michurin FSC. The FBF7 QTL for fire blight resistance was identified with the flanking SCAR-markers AE10-375 and GE-8019, and SSR-marker CH-F7-Fb1.Results and conclusion. The GE-8019 marker was identified in 50.0% of the apple accessions, AE10-375 in 76.0% of the accessions, and CH-F7-Fb1 in 30.0%. Inter- and intraspecific polymorphism of the Malus genus was revealed for the analyzed resistance locus, as well as for individual DNA markers linked to the FBF7 QTL. The GE-8019 and AE10-375 markers flanking the FBF7 QTL were found in 42.0% of the studied genotypes. Meanwhile, three diagnostic markers (GE-8019, AE10-375, and CH-F7-Fb1) were identified only in 7 accessions: M. × robusta var. persicifolia (Carr.) Rehd. (к-41279), M. × cerasifera var. hiemalis Spach. (к-2342) (Ser. Baccatae), M. sylvestris (L.) Mill. (k-73 and k-123), M. × spectabilis var. albi plena (Ait.) Borkh. (к-2416) (Ser. Malus), M. × sargentii (Rehd.) Langenf. (k-2428) (Ser. Toringonae), and M. coronaria (L.) Mill. (к-2336) (Ser. Coronariae). These forms are promising genetic sources of resistance to E. amylovora.

An emergent plant‐parasitic nematode in Brazil: Aphelenchoides besseyi. Current status and research perspectives

AbstractAphelenchoides besseyi is an emerging and yet overlooked plant parasite of many economically important crops, including cotton, soybean and common bean. It presents an economic risk to these crops in several countries, notably in Brazil. Although first reported infecting strawberries in the United States as early as 1942, it was only identified to be the causal agent of green stem and foliar retention (GSFR) disease in Brazil in 2017. Currently, there are no chemical nematicides registered in Brazil against A. besseyi, and no known sources of genetic resistance. Here, we review the biology of A. besseyi, its spread across Brazil, its relevance to the country's current and future agriculture and the limited control measures. We describe control measures that have been successfully used to manage infestations of other plant‐parasitic nematodes and could potentially be extended to use in the control of A. besseyi. We also review and discuss potential future control measures, such as RNA interference and genome editing, for the development of crops with enhanced resistance to A. besseyi.

HaploCatcher: An R package for prediction of haplotypes.

Wheat (Triticum aestivum L.) is crucial to global food security but is often threatened by diseases, pests, and environmental stresses. Wheat-stem sawfly (Cephus cinctus Norton) poses a major threat to food security in the United States, and solid-stem varieties, which carry the stem-solidness locus (Sst1), are the main source of genetic resistance against sawfly. Marker-assisted selection uses molecular markers to identify lines possessing beneficial haplotypes, like that of the Sst1 locus. In this study, an R package titled "HaploCatcher" was developed to predict specific haplotypes of interest in genome-wide genotyped lines. A training population of 1056 lines genotyped for the Sst1 locus, known to confer stem solidness, and genome-wide markers was curated to make predictions of the Sst1 haplotypes for 292 lines from the Colorado State University wheat breeding program. Predicted Sst1 haplotypes were compared to marker-derived haplotypes. Our results indicated that the training set was substantially predictive, with kappa scores of 0.83 for k-nearest neighbors and 0.88 for random forest models. Forward validation on newly developed breeding lines demonstrated that a random forest model, trained on the total available training data, had comparable accuracy between forward and cross-validation. Estimated group means of lines classified by haplotypes from PCR-derived markers and predictive modeling did not significantly differ. The HaploCatcher package is freely available and may be utilized by breeding programs, using their own training populations, to predict haplotypes for whole-genome sequenced early generation material.

Molecular, phenotypic and histological analysis reveals a multi-tiered immune response and callose deposition in stone fruit rootstocks (Prunus spp.) against Pseudomonas syringae pv. syringae (Pss) infection

Bacterial canker, caused by Pseudomonas syringae pv syringae (Pss), is a serious disease of stone fruit orchards causing severe yield reductions and the death of entire trees. To analyze the response and to identify novel sources of Pss resistance in our rootstock breeding program, we used a novel, rapid and reliable leaf disk pathogenicity test to screen pre-breeding material constituted by interspecific hybrids of plum/peach/almond (‘AGAF’/‘ADAGAF’) or sweet cherry (‘PACIR’) species and commercial rootstocks with two Pss strains. Some ‘AGAF’/ ‘ADAGAF’ and all ‘PACIR’ rootstocks showed lower susceptibility than commercial rootstocks to Pss strains used. The reduced symptoms displayed by the ‘PACIR’ hybrids with Prunus lannesiana and P. incisa as genomic background suggest that these species could be novel sources of genetic resistance to Pss within the Cerasus subgenus. Histological and candidate gene expression analysis suggest a multi-tiered immune response of Prunus species to Pss attack with a higher callose deposition and activation of molecular mechanisms that would restrict the bacteria infection and help to maintain a better redox homeostasis and performance of ‘Marianna 2624′, a plum resistant genotype. Identification of Prunus species with resistance to Pss and the analysis of their immune response are the first step towards characterizing the underlying genetic mechanisms of resistance and introducing these traits into commercial germplasm.

Combined Omics Approaches Reveal Distinct Mechanisms of Resistance and/or Susceptibility in Sugar Beet Double Haploid Genotypes at Early Stages of Beet Curly Top Virus Infection.

Sugar beet is susceptible to Beet curly top virus (BCTV), which significantly reduces yield and sugar production in the semi-arid growing regions worldwide. Sources of genetic resistance to BCTV is limited and control depends upon insecticide seed treatments with neonicotinoids. Through double haploid production and genetic selection, BCTV resistant breeding lines have been developed. Using BCTV resistant (R) [KDH13; Line 13 and KDH4-9; Line 4] and susceptible (S) [KDH19-17; Line 19] lines, beet leafhopper mediated natural infection, mRNA/sRNA sequencing, and metabolite analyses, potential mechanisms of resistance against the virus and vector were identified. At early infection stages (2- and 6-days post inoculation), examples of differentially expressed genes highly up-regulated in the 'R' lines (vs. 'S') included EL10Ac5g10437 (inhibitor of trypsin and hageman factor), EL10Ac6g14635 (jasmonate-induced protein), EL10Ac3g06016 (ribosome related), EL10Ac2g02812 (probable prolyl 4-hydroxylase 10), etc. Pathway enrichment analysis showed differentially expressed genes were predominantly involved with peroxisome, amino acids metabolism, fatty acid degradation, amino/nucleotide sugar metabolism, etc. Metabolite analysis revealed significantly higher amounts of specific isoflavonoid O-glycosides, flavonoid 8-C glycosides, triterpenoid, and iridoid-O-glycosides in the leaves of the 'R' lines (vs. 'S'). These data suggest that a combination of transcriptional regulation and production of putative antiviral metabolites might contribute to BCTV resistance. In addition, genome divergence among BCTV strains differentially affects the production of small non-coding RNAs (sncRNAs) and small peptides which may potentially affect pathogenicity and disease symptom development.

A Brief Overview of Bacteriocins and their Potential Applications against Phytopathogenic Bacteria

Gram-negative phytopathogens severely harm a number of economically significant crop plants. The effectivity of traditional approaches, such as the breeding and introduction of resistant cultivars, is limited by the lack of available sources of genetic resistance. Bacteriocins are small proteinaceous antibiotics produced by bacteria to kill closely related bacteria. Utilization of narrow-spectrum protein antibiotics as biocontrol agents is an effective strategy to shrink losses imposed due to specific bacterial phytopathogens. Several colicin-like bacteriocins have been found to be active against phytopathogenic bacteria. Bacteriocins frequently affect closely related bacterial strains, making them useful as targeted, low-side-effect, narrow-spectrum antibiotics. Even though using bacteriocins to control plant diseases is a promising strategy, minimal information is there regarding the abundance and functions of these chemicals against pathogenic bacteria and their natural enemies. This review is concerned with the efficient control of economically significant plant pathogenic bacteria using these potent and selective antimicrobial agents.

Molecular screening for Fusarium oxysporum resistance genes in chickpeas

Root rot and wilt (Fusarium oxysporum) are the most common pathogens among grain legumes, which cause yield losses of 10 to 40%. Wilt caused by Fusarium oxysporum f.sp. ciceris is a devastating disease in chickpea growing area. In this study, 50 chickpea genotypes were studied to identify genetic sources of resistance to the disease in 2021 and 2022 vegetative seasons. The studies were carried out against the natural background of the experimental field at the Saimasai Agrotechnopark site of the Kazakh National Agrarian Research University, and the studies were carried out against an artificial background at the experimental site of Agropark Ontustik LLP located in the village of Zhalpaksay, Almaty region, Karasai district. The resistance and susceptibility of the plants to F. oxysporum were determined four weeks after artificial inoculation. In field trials, 70% of the genotypes were resistant to wilt and the remaining 30% showed susceptibility to the disease with varying degrees. Molecular methods were used to identify genetic sources of resistance. In the molecular analysis, all 50 genotypes were screened using the primers CaSTMS2, TA200, TA194, TA72, TA46, TR29 and TR7, which are closely related markers to resistance genes. Marker selection can identify resistant genes when screening chickpea genotypes for this pathogen. As a result of screening, resistant chickpea genotypes have been identified that can be used in the breeding program to develop F. oxysporum resistant chickpea varieties.

Reproductive potential of the black bean aphid (Aphis fabae Scop.) on a range of faba bean (Vicia faba L.) accessions

AbstractThe black bean aphid is one of the main insect pests of faba bean, leading to yield losses in many countries. The aphid inflicts damage to faba bean through direct phloem feeding and indirectly by transmission of several viruses. Sources of genetic resistance or tolerance to the aphid have been hard to identify and to use in breeding because of the high environmental variability of the attack, the weak and partial nature of the resistance when found, and the low repeatability of experiments. A range of molecular genotyping tools is now available for identifying the genes underlying key traits in faba bean. Hence, we screened the responses of eight inbred lines (Columbo, Albus, Closed‐flower, Diana, Hedin/2, Icarus, ILB938/2, and Mélodie/2) of faba bean, derived from commercial cultivars and experimental germplasm, to aphid infestation in controlled (no‐choice‐test) and field (preference test) conditions. In the controlled environment, aphid performance was assessed by measuring fecundity and determining the intrinsic rate of natural increase (rm). In the field experiment, population growth was examined on Columbo, Closed‐flower, Hedin/2, and ILB938/2 during June and July. Each week, 10 plants in each plot, randomly chosen at the start, were screened for aphid colonization and number of plants attacked. For each plant, an index number was given reflecting the severity of aphid presence. Our results demonstrate a clear conformity between the results obtained from the indoor pot experiments and the field experiments. In both experiments, ILB938/2 showed partial resistance with significantly lower fecundity, rm, and field infestation when compared with the known susceptible line Columbo. The consistently strong performance of ILB938/2 against the black bean aphid suggests that it carries a factor or factors rendering it unconducive to aphid landing, feeding, and/or reproduction. Further investigation into the resistance mechanisms of ILB938/2 is planned.

Genetic sources of resistance bread winter wheat to leaf (brown) rust and their value in juvenile stage of growing

Actuality of the topic. With the growth of prices for fungicides, the ecological crisis of the biosphere, the absence of a wide range of donors, and with the constant variability of the pathogen, resistance of bread winter wheat plants is lost, therefore, it is important to search for new effective sources of resistance and involve them in breeding work for resistance to leaf rust. The purpose of the research is to compare genotypes of different ecological and geographical origin and to determine the best genetic sources of resistance to brown rust for their effective use in breeding. Methods. The experiment was carried out in laboratory conditions; Bread winter wheat samples were contaminated with leaf (brown) rust spores in the juvenile stage of growing. Research results. Among the four analyzed genetic sources of resistance of different ecological and geographical origins, the best were the representative genotypes from other breeding institutions of Ukraine. According to the average indicator of resistance, their average level of resistance was at the level of 6.5 points on a 9-point scale, and genotypes of Western European origin – 5.2 points, genotypes of selection from SGI–NCSS and CIMMYT-ICARDA - Turkey had the worst score – 4.6 and 3.4 points. Summary. The fact that bread winter wheat genotypes from other breeding institutions of Ukraine and Western European origin are the best can be explained by the formation of these genotypes in optimal conditions for the development of leaf (brown) rust, which served as a natural infectious background for selection for resistance to this trait. However, among genetic sources with low resistance, there are samples with increased resistance, which, in combination with other adaptive traits, can be successfully used in the selection of bread winter wheat for resistance to leaf (brown) rust for the south of Ukraine. Keywords: bread winter wheat, leaf (brown) rust, sources of resistance, genotypes-representatives, resistance

An international wheat diversity panel reveals novel sources of genetic resistance to tan spot in Australia

Key messageNovel sources of genetic resistance to tan spot in Australia have been discovered using one-step GWAS and genomic prediction models that accounts for additive and non-additive genetic variation.Tan spot is a foliar disease in wheat caused by the fungal pathogen Pyrenophora tritici-repentis (Ptr) and has been reported to generate up to 50% yield losses under favourable disease conditions. Although farming management practices are available to reduce disease, the most economically sustainable approach is establishing genetic resistance through plant breeding. To further understand the genetic basis for disease resistance, we conducted a phenotypic and genetic analysis study using an international diversity panel of 192 wheat lines from the Maize and Wheat Improvement Centre (CIMMYT), the International Centre for Agriculture in the Dry Areas (ICARDA) and Australian (AUS) wheat research programmes. The panel was evaluated using Australian Ptr isolates in 12 experiments conducted in three Australian locations over two years, with assessment for tan spot symptoms at various plant development stages. Phenotypic modelling indicated high heritability for nearly all tan spot traits with ICARDA lines displaying the greatest average resistance. We then conducted a one-step whole-genome analysis of each trait using a high-density SNP array, revealing a large number of highly significant QTL exhibiting a distinct lack of repeatability across the traits. To better summarise the genetic resistance of the lines, a one-step genomic prediction of each tan spot trait was conducted by combining the additive and non-additive predicted genetic effects of the lines. This revealed multiple CIMMYT lines with broad genetic resistance across the developmental stages of the plant which can be utilised in Australian wheat breeding programmes to improve tan spot disease resistance.

Evaluation of Malus Germplasm Identifies Genetic Sources of Powdery Mildew and Frogeye Leaf Spot Resistance for Apple Breeding.

Apple is an important fruit crop of temperate regions. The narrow genetic base of commercially cultivated apples has resulted in its vulnerability to a large number of fungal, bacterial, and viral pathogens. Apple breeders are always seeking new sources of resistance within the cross-compatible Malus species that can be deployed into elite genetic backgrounds. We have evaluated resistance to two major fungal diseases of apples: powdery mildew and frogeye leaf spot, using a germplasm collection of 174 Malus accessions to identify novel sources of genetic resistance. In 2020 and 2021, we evaluated these accessions for the incidence and severity of powdery mildew and frogeye leaf spot diseases at Cornell AgriTech, Geneva, New York, in a partially managed orchard. The severity and incidence of powdery mildew and frogeye leaf spot, as well as weather parameters were recorded in June, July, and August. Total incidence of powdery mildew and frogeye leaf spot infections increased from 33 to 38%, and 56 to 97% in 2020 and 2021, respectively. Our analysis showed that relative humidity and precipitation correlate with powdery mildew and frogeye leaf spot susceptibility. The predictor variables with highest impact to the variability of powdery mildew were accessions and relative humidity in May. A total of 65 Malus accessions were found to be resistant to powdery mildew, and only one accession showed moderate resistance to frogeye leaf spot. Several of these accessions belong to Malus hybrid species and domesticated apples and can therefore be potential sources of novel resistance alleles for apple breeding.

Exploration of Sources of Genetic Resistance in Maize Genotypes Against Stem Borer (Chilopartellus (Swinhoe))

Fourteen different maize genotypes were screened for their relative resistance to maize stem borer Chilopartellus (Swinhoe) under glass house condition at National Maize Research Program, Rampur, Chitwan during two consecutive years 2018 and 2019. The design of the experiment was completely randomized design having 2 replications. The unit plot size was one row of one meter length with 50 cm row to row and 20 cm plant to plant spacing. Two second instar larva of C. partellus (Swinhoe) per plant were released two times, first at 8th leaves (vegetative) and second at 12th leaves (Before tasseling) stages. Insect damage parameters (IDPs) viz. dead heart percentage, damage % at vegetative and foliar stage, foliar injury rating (1-9) at vegetative and before tasseling stage, tunnel length (cm), exit hole number and yield per plot were recorded to study the germplasm susceptibility level. The result revealed that IDPs and yield varied significantly among the tested genotypes. Over the years, IDPs like dead heart percentage (5.17%), percent damage atpre-tasseling stage (10.6%), foliar injury level (2.25), tunnel length (10.15 cm) and exit holes (2.32) were found lower with high yield (2235 g/plot) in RML-95/ RML-96 followed by RML- 86/RML-96. Two pipeline maize hybrids RML-95/RML-96 and RML-86/RML- 96 with least damaged by maize stem borer in both years will be useful for maize stem borer resistance source.&#x0D; Bangladesh J. Agril. Res. 45(3): 293-301, September 2020

Identification of Genetic Sources of Resistance to the Seed-Born Leaf Stripe Disease of Barley (Pyneophera graminea Ito &amp; Kurib)

Identification of Genetic Sources of Resistance to the Seed-Born Leaf Stripe Disease of Barley (Pyneophera graminea Ito & Kurib)