Lowest Disease Severity Index Research Articles

SALINITY, VERTICILLIUM WILT TOLERANCE AND GENETIC DIVERSITY ANALYSIS OF UPLAND COTTON GENOTYPES

Cotton is one of the most economically important crops. Screening and selection salt-tolerant cotton genotypes using DNA molecular markers not only introduces tolerant cultivars valuable for hybridization and breeding programs, but also identifies DNA regions implicated in the salinity tolerance mechanism. Screening and selection of cotton genotypes resistant to salinity stress and Verticillium wilt disease using DNA molecular markers not only introduces tolerant cultivars valuable for hybridization and breeding programs, but also identifies DNA regions implicated in the tolerance mechanism. The lowest Disease Severity Index was recorded in AP-317 (0.37) and Tashkent-2 (0.32) varieties. A total of 63 bands were generated based on 12 ISSR primers, 50 of which were polymorphic. The highest PIC value was recorded for UBC841 (0.466). AP-317 of Azerbaijan origin and Kirqizistan-174 of Kyrgyzstan origin were the most distant (0.358) genotypes and at the same time showed high resistance to Verticillium wilt. The obtained results showed that ISSR markers were an effective tool for determining genetic variation and identification of cotton cultivars.

Evaluation of Amisulbrom Products for the Management of Clubroot of Canola (Brassica napus).

Clubroot, caused by Plasmodiophora brassicae, is an important disease of canola (Brassica napus). Amisulbrom, a quinone inside inhibitor (QiI), was evaluated for its effectiveness in clubroot management in Alberta, Canada. Resting spores of P. brassicae were treated in vitro with 0, 0.01, 0.1, 1, and 10% (w/v) amisulbrom to determine its effect on spore germination and viability. Amisulbrom inhibited resting spore germination by up to 79% and reduced viable spores by 31% relative to the control. Applications of a liquid solution (AL1000, 1000 g active ingredient (ai) ha-1) and granular formulations (AF700, 700 g ai ha-1; AF1000, 1000 g ai ha-1; AF1500, 1500 g ai ha-1) of amisulbrom were tested on the canola cultivars '45H31' (clubroot-susceptible) and 'CS2000' (moderately resistant) under greenhouse conditions and in field experiments in 2019 and 2020. In the greenhouse, the treatments were evaluated at inoculum concentrations of 1 × 105 or 1 × 107 resting spores g-1 soil. A trend of decreasing clubroot severity with an increasing amisulbrom rate was observed. At the lower spore concentration, treatment with AF1500 resulted in a clubroot disease severity index (DSI) <20% for both cultivars, while the lowest DSI under both low and high spore concentrations was obtained with AL1000. The field results indicated a significant reduction in DSI, with varied effects of rates and liquid vs. granular formulations. The greatest reductions (up to 58.3%) in DSI were obtained with AF1500 and AL1000 in 2020. These findings suggest that amisulbrom holds promise as part of an integrated clubroot management approach.

Integration of Soybean (Glycine max) Resistance Levels to Sclerotinia Stem Rot into Predictive Sclerotinia sclerotiorum Apothecial Models.

Sclerotinia stem rot (SSR) is a major disease of soybean across the Upper Midwest region of the United States. Management of this disease has relied on fungicide applications, but due to the environmental conditions necessary for SSR to develop, many of these applications are unnecessary. To mitigate this, predictive models have been developed using localized weather data for predicting the formation of Sclerotinia sclerotiorum apothecia, the inoculum source of SSR, and these models were integrated into a decision support system called Sporecaster. However, these models do not account for the soybean resistance levels to SSR. In this study, fungicide trials were performed across seven site-years in Wisconsin between 2020 and 2022 examining fungicide applications applied at one of three action thresholds (low, moderate, and high) following Sporecaster recommendations in combination with four soybean varieties representing three SSR resistance levels (susceptible, moderately resistant, and resistant). From these trials, the low and moderate action thresholds resulted in similarly low disease severity index (DIX) levels comparable to the standard across all varieties. However, the low action threshold was most accurate for predicting SSR development in the susceptible variety, and the high action threshold was most accurate for predicting SSR development for the three resistant varieties. Both the susceptible soybean and a moderately resistant line yielded similarly high results. Additionally, the use of all fungicide applications led to similar partial profits at grain sale prices of either $0.44 or $0.55 kg-1. Overall, this study uncovered relationships between soybean resistance levels to SSR and Sporecaster, allowing for improved recommendations for fungicide applications.

The antifungal effect of propolis extract against cotton wild disease (Verticillium dahliae Kleb.)

The aim of this study is to investigate the antifungal activity of propolis against V. dahliae Kleb. under both in vitro and in vivo conditions. Firstly, the inhibitory effect of the propolis on mycelial growth in Potato Dextrose Agar (PDA) media containing its ethanol extract (PE) at various concentrations (0.003, 0.06, 0.125, 0.25, 0.5, and 1 ppm/mL) was investigated under in vitro conditions. Then to assess the effect of PE on non-defoliating (PHCVd3 isolate) and defoliating (PHCVd47 isolate) pathotypes of V. dahliae, the varieties Giza 45 (resistant), Carmen (tolerant), and Acala SJ2 (susceptible) treated with PEE (1 ppm/mL) were observed in the plant growth chamber up to the 4-6 leaf stage. The whole in vitro experiments were carried out with three replicates, and the studies in vivo experiment were with five replicates depending on a completely randomized parcels design. The most effective dose of PEE with1 ppm/mL dose resulted in 75.2% suppression against the PHCVd3 isolate, while the effect of the same dose against the PHCVd47 isolate was 74.4%. The lowest disease severity index (DSI) values against PHCVd3 and PHCVd47 isolates in cotton cultivars treated with PE were 1.34 and 1.64 in the Giza 45, respectively, and the highest DSI values were 3.80 and 3.90 in the Acala SJ2 cultivar in vivo experiment, respectively. The findings indicate that PE treatment has a promising effect against cotton wilt disease that could be combined with known plant protection strategies.

Identification of qBK2.1, a novel QTL controlling rice resistance against Fusarium fujikuroi

BackgroundBakanae disease caused by Fusarium fujikuroi is an increasing threat to rice production. The infected plants show symptoms such as elongation, slenderness, chlorosis, a large leaf angle, and even death. Bakanae disease is traditionally managed by seed treatment. However, fungicide-resistant F. fujikuroi isolates have emerged in several Asian areas, including Taiwan. This study aimed to identify new bakanae resistance quantitative trait loci (QTLs) and provide molecular markers to assist future breeding.ResultsA population of F2:9 recombinant inbred lines (RILs) was derived from the cross between an elite japonica Taiwanese cultivar ‘Taikeng 16 (TK16)’ and an indica variety ‘Budda’. ‘Budda’ was found highly resistant to all 24 representative isolates of the F. fujikuroi population in Taiwan. For the RIL population, 6,492 polymorphic single nucleotide polymorphisms (SNPs) spanning the rice genome were obtained by genotyping-by-sequencing (GBS) technique, and the disease severity index (DSI) was evaluated by inoculation with a highly virulent F. fujikuroi isolate Ff266. Trait-marker association analysis of 166 RILs identified two QTLs in ‘Budda’. qBK2.1 (21.97–30.15 Mb) is a novel and first bakanae resistance QTL identified on chromosome 2. qBK1.8 (5.24–8.66 Mb) partially overlaps with the previously reported qBK1.3 (4.65–8.41 Mb) on chromosome 1. The log of odds (LOD) scores of qBK1.8 and qBK2.1 were 4.75 and 6.13, accounting for 4.9% and 8.1% of the total phenotypic variation, respectively. 64 RILs carrying both qBK1.8 and qBK2.1 showed lower DSI (7%) than the lines carrying only qBK1.8 (15%), only qBK2.1 (13%), or none of the two QTLs (21%). For the future application of identified QTLs, 11 KBioscience competitive allele-specific PCR (KASP) markers and 3 insertion-deletion (InDel) markers were developed.ConclusionsCompared to other important rice diseases, knowledge of bakanae resistance has been insufficient, which limited the development and deployment of resistant cultivars. The discovery of qBK2.1 has provided a new source of bakanae resistance. The resistant RILs inheriting good plant type, good taste, and high yield characteristics from ‘TK16’ can be used as good resistance donors. Our newly developed markers targeting qBK2.1 and qBK1.8 can also serve as an important basis for future fine-mapping and resistance breeding.

Antifungal efficacy of Hyptis suaveolens and Rumex nepalensis extracts against Alternaria solani: An approach for bio-pesticides

Globally, early blight is one of the serious threats leading to significant reduction of potato yield. The use of plant extracts in the management of plant diseases is gaining global significance. Hence, the main objective of this study was to determine the antifungal activity of Rumex nepalensis and Hyptis suaveolens (L.) Poiteau extracts against the fungal pathogen (Alternaria solani) causing early blight in potato. The study employed experimental research method with completely randomized design wherein the plant extracts were tested against the pathogen through in vitro and in vivo studies. In the in vitro study, results from the poison food technique showed that the aqueous extracts of aerial parts of R.nepalensis (RnA) was the most efficient in reducing the diameter growth of the fungus than R.nepalensis roots (RnR) and H. suaveolens (HS). The efficacy of the extracts was in the decreasing order of RnA > RnR > HS at all concentrations (20%, 40% and 60%). The fungal biomass extraction showed similar trend with RnA having the highest Initial Activity on Biomass (IAB) followed by RnR and HS. Interestingly, the fungal biomass growth decreased with increase in concentration of all three extracts. In the in vivo technique, plants treated with RnA prior to infection exhibited better tolerance to the test pathogen. Comparatively, RnA showed less Disease Severity Index (DSI) than RnR and HS for both preventive and curative controls. Consequently, the percentage reduction of disease was recorded highest in RnA preventive control (71.43%) compared to other treatments. The preventive control showed lower DSI and higher reduction of disease compared to the curative control. Although all three extracts showed some degree of antifungal activity against Alternaria solani, RnA showed higher activity in both in vitro and in vivo treatments. Therefore, RnA extracts can be used as a potential bio-fungicide for the control of early blight in potato.

Thymol and eugenol nanoparticles elicit expression of Ralstonia solanacearum virulence and potato defense genes and are potential bactericides against potato bacterial wilt

Bacterial wilt disease caused by Ralstonia solanacearum impacts negatively on potato production. This study evaluated the effects of thymol and eugenol encapsulated in chitosan nanoparticles (TCNP and ECNP) on the virulence genes (PhcA, XpsR and HrpG) of R. solanacearum and their in vivo efficacy against bacterial wilt. Gene expression levels of virulence genes in the presence of TCNP (5.6 and 11.3 µg mL−1) and ECNP (11.3 and 22.5 µg mL−1) together with those of plant defense genes (chitinase and β-l,3-glucanase) were determined through RT-qPCR. All the virulence genes were downregulated when exposed to both TCNP and ECNP while glucanase and chitinase genes increased and peaked after 18 hours post inoculation. The lowest disease severity index (10.3%) was recorded with plants treated with 90 µg mL−1 ECNP. The results of this study show that both TCNP and ECNP have a potential to be used as bacterial wilt bactericides.

Induce defense response of DADS in eggplants during the biotrophic phase of Verticillium dahliae

PurposeVerticillium wilt is a destructive vascular disease in eggplants. The complex defensive mechanisms of eggplant against this disease are very limited.MethodsOur work examined the bioactive properties of garlic allelochemical diallyl disulfide (DADS) as potential biostimulants for defense against V. dahliae in eggplant seedlings. We, therefore, foliar sprayed DADS on eggplants to study the defense response during the early biotrophic phase of V. dahliae (a hemibiotroph).ResultsDADS application significantly increased root peroxidase (POD), phenylalanine-ammonia lyase (PAL) enzyme activity, and reduced H2O2 levels after 24 h of fungal inoculation. Salicylic acid (SA) in leaves and roots was significantly increased while, the jasmonic acid (JA), indole acetic acid (IAA), and abscisic acid (ABA) levels were decreased. The microscopic examinations of V. dahliae infection in roots displayed that the progression of infection was restricted in DADS-treated plants. Depositions of lignin and phenolic compounds such as ferulic acid, p-coumaric acid, and caffeic acid content were significantly higher in DADS-treated plants at 48 h post-inoculation. Similarly, the DADS application up-regulated pathogenesis-related (PR1, PR2, and PR5), mitogen-activated protein kinase (MPK1), and lipoxygenase (LOX) genes. Furthermore, DADS-treated plants exhibited a lower disease severity index (23.3% vs. 57.0% in controls), indicating successful defense against V. dahliae.ConclusionsOur findings concluded that the biological function of garlic allelochemical DADS has a prominent role in the higher defense resistance of eggplants during the early infection of V. dahliae.

Arbuscular Mycorrhizal Fungi and Dry Raw Garlic Stalk Amendment Alleviate Continuous Monocropping Growth and Photosynthetic Declines in Eggplant by Bolstering Its Antioxidant System and Accumulation of Osmolytes and Secondary Metabolites.

Vegetable production under plastic sheds severely threatens regional eco-sustainability via anthropogenic activities (excessive use of agrochemicals, pesticides) and problems associated with replanting. Long-term successive cropping across growing seasons induces continuous cropping stress, whose effects manifest as diminished plant growth. Therefore, it is imperative that we develop environmentally sustainable approaches, such as replacing agrochemicals with vegetable waste like dry raw garlic stalk (DRGS) or use biofertilizers like arbuscular mycorrhizal fungi (AMF) (e.g., Diversispora epigaea). In this study, the influence of AMF on the growth, biochemical attributes, antioxidant defense system, phytohormones, accumulation of osmolytes, phenols, and mineral elements in eggplant grown on DRGS-amended soils under continuous monocropping (CMC) was studied. The results showed that inoculation with AMF or the DRGS amendment could improve the pigments’ content, photosynthesis, and antioxidant defense system; augmented phytohormones synthesis (except for ABA), and increased the leaves’ mineral nutrients. These parameters were enhanced most by the combined application of AMF and DRGS, which also increased the concentration of osmolytes, including proline, sugars, and free amino acids in eggplant when compared with the control. Furthermore, either AMF and DRGS alone, or in combination, ameliorated the induced stress from continuous cropping by reducing the incidence of Fusarium wilt and production of ROS (reactive oxygen species); lipid peroxidation underwent maximal reduction in plants grown under the combined treatments. The AMF, DRGS, and AMF + DRGS exhibited a lower disease severity index (33.46, 36.42, and 43.01%), respectively, over control. Hence, inoculation with AMF coupled with DRGS amendment alters the photosynthetic attributes in eggplant through the upregulation of its antioxidant system and greater accumulation of osmolytes, which led to the improved growth and yield of eggplant.

Antimicrobial Activity of Pinus wallachiana Leaf Extracts against Fusarium oxysporum f. sp. cubense and Analysis of Its Fractions by HPLC.

Fusarium wilt has ruined banana production and poses a major threat to its industry because of highly virulent Fusarium oxysporum f. sp. cubense (Foc) race 4. The present study focused on the efficacy of Pinus wallachiana leaf extracts and its organic fractions against Foc in in vitro and greenhouse experiments. The presence of polyphenols in the fractions was also investigated using high performance liquid chromatography (HPLC). The in vitro tests carried out for the leaf extract of P. wallachiana showed its inhibitory effect on the mycelial growth and, based on this evidence, further characterization of fractions were done. Complete mycelial inhibition and the highest zone of inhibition against Foc was observed for the n-butanol fraction in vitro, while the n-hexane and dichloromethane fractions showed lower disease severity index (DSI) in greenhouse experiments. The fractions were further analysed by HPLC using nine polyphenolic standards, namely quercitin, myrecitin, kaempferol, rutin, gallic acid, trans-ferulic acid, coumeric acid, epicatechin and catechin. The highest content of polyphenols, based on standards used, was quantified in the n-butanol fraction followed by the ethyl acetate fraction of the leaf extract. This is the first report of antimicrobial activity of Pinus wallachiana extracts against Foc to the best of our knowledge.

Targeted generation of Null Mutants in ZmGDIα confers resistance against maize rough dwarf disease without agronomic penalty.

Targeted generation of Null Mutants in ZmGDIα confers resistance against maize rough dwarf disease without agronomic penalty.

Screening of wild tomato species and interspecific hybrids for resistance/tolerance to Tomato brown rugose fruit virus (ToBRFV)

Tomato (Solanum spp.) is the second most-consumed vegetable after potato and grown all over the world. Tomato brown rugose fruit virus (ToBRFV) was first identified in 2014 on tomato plants, since then it has been reported in many countries. It is a significant threat to tomato production. This work aimed to identify the disease resistance source(s). To achieve this aim, a total of 44 tomato materials including 28 accessions of eight wild species, two accessions of Solanum arcanum Peralta, S. pennellii Correll, and S. sitiens I.M. Johnst., seven accessions of S. chilense (Dunal) Reiche, five accessions of S. pimpinellifolium L., four accessions of S. habrochaites S. Knapp & D.M. Spooner, three accessions of S. peruvianum L., one accession of S. chmielewskii (C.M. Rick et al.) D.M. Spooner et al. and S. huaylasense Peralta, 5 cultivated tomatoes (S. lycopersicum L.) and 11 interspecific F1 hybrids derived from S. habrochaites and S. pennellii were tested with ToBRFV isolates by using the biological testing method. Mechanical inoculation method was used for biological testing. ToBRFV was inoculated to 10 plants with 2-3 true leaves two replicates for each genotype. As a result, S. pimpinellifolium (LA1651), S. penellii (LA0716), and S. chilense (LA4117A, LA2747) were found tolerant to ToBRFV with the lowest disease severity index (DSI) with 19.6%, 28.3% and 35.0%, respectively. Also, molecular genetic analysis of the plant material by using molecular markers revealed that there was no interaction between other virus resistance genes (Tm-2 2 and Tm-1) and ToBRFV resistance. These wild tomato species identified in the present study are valuable genetic resources to develop new resistance cultivars for ToBRFV resistance in tomato breeding programs.

Bacillus cereus for Controlling Bacterial Heart Rot in Pineapple var. MD2.

Bacterial heart rot (BHR) disease caused by pathogenic bacteria, Dickeya zeae, is one of the destructive diseases of pineapple worldwide. This study explored the potential of Bacillus cereus against the BHR pathogen in vitro and in vivo. The BHR causal pathogen was isolated from symptomatic pineapple plants, demonstrating water-soaked and rotten basal tissues. Biological control agent (BCA) was isolated from asymptomatic pineapple leaves, later confirmed as B. cereus, and subsequently tested for the antagonistic activity against the BHR pathogen via disc diffusion assay and glasshouse trial. B. cereus showed the ability to inhibit the growth of BHR pathogen with 18.10 ± 0.36 mm of inhibition zone in diameter. The ability of B. cereus against the BHR pathogen was further confirmed via the glasshouse trial with five treatments. The results showed that treatments with B. cereus inoculation recorded lower disease severity index of 0.04 ± 0.01 than the positive control treatment with pathogen alone (0.53 ± 0.04). This finding indicated that B. cereus has a great potential as BCA against BHR disease in pineapple var. MD2, however, the effectiveness of this isolate needs to be further tested under actual field conditions.

Characterization and bioefficacy of green nanosilver particles derived from fungicide-tolerant Tricho-fusant for efficient biocontrol of stem rot (Sclerotium rolfsii Sacc.) in groundnut (Arachis hypogaea L.).

An efficient and eco-friendly bioefficacy of potent Tricho-fusant (Fu21) and its green nanosilver formulation against stem rot (Sclerotium rolfsii) in groundnut was established. Fu21 demonstrated higher in-vitro growth inhibition of pathogen with better fungicide tolerance than the parental strains. The green nanosilver particles were synthesized from the extracellular metabolites of Fu21 and characterized for shape (spherical, 59.34 nm in scanning electron microscope), purity (3.00 KeV, energy dispersive X-ray analysis), size (54.3 nm in particle size analyzer), and stability (53.7 mv, zeta). The field efficacy study exhibited that the seedling emergence was high in seeds treated with green nanosilver (minimum inhibitory concentration-[MIC] 20 µg Ag/ml), and a low disease severity index of stem rot during the crop growth was followed by the live antagonist (Fu21) in addition to seed treatment with a fungicide mix under pathogen infestation. The seed quality analysis of harvested pods revealed a high oil content with balanced fatty acid composition (3.10 oleic/linoleic acid ratio) in green nanosilver treatment under pathogen infestation. The residual analysis suggested that green nanosilver applied at the MIC level as seed treatment yielded similar effects as the control for silver residue in the harvested groundnut seeds. The green nanosilver at MIC has a high pod-yield under S. rolfsii infestation, demonstrating green chemistry and sustainability of the nanoproduct.

Evaluation of Trichoderma asperellum B1902 in Controlling Fusarium Wilt of Cavendish Banana Cultivar

Trichoderma species is one of the microorganisms with antagonistic properties as biological control agents. In the banana industry, Fusarium wilt disease caused by Fusarium oxysporum f. sp. cubense (Foc) has been practically managed using chemical pesticides that led to environmental disruptions, ineffective conditions and disease resistance. In preliminary study, T. asperellum gave better result compared to other species in inhibiting the growth of Foc in in vitro condition. Therefore, the aim of this study was to examine the effects of T. asperellum as a biological control of Fusarium wilt disease of banana. A total of 326 fungal isolates were isolated from soil samples obtained around Malaysia and identified as Trichoderma species based on phenotype characteristics. The species identity for the best candidates from dual culture test was confirmed based on internal transcribed spacers (ITS) and translation elongation factor 1 alpha (TEF-1α) sequence identity. In dual culture test, findings showed that three isolates with a high percentage inhibition of radial growth (PIRG) were observed in plates of T. asperellum isolates B1902 (84.85%), T2007 (77.78%) and C1667 (75.76%), which successfully inhibited the growth of F. oxysporum f. sp. cubense isolate 9888. Based on in vivo test, the best candidate was T. asperellum B1902 with lower disease severity index (DSI) value of 0.2 compared to the inoculated control with DSI of 3.6. As a conclusion, T. asperellum B1902 can be used as an alternative treatment in managing Fusarium wilt disease. Hence, future study should be focused on applying T. asperellum as a biocontrol agent in the field and controlling other plant diseases in the agricultural plantation.

Application of garlic allelochemicals improves growth and induces defense responses in eggplant (Solanum melongena) against Verticillium dahliae

Aqueous garlic extracts (AGE) and garlic allelochemical diallyl disulfide (DADS) have been recently reported to bear bioactive properties to stimulate plant growth and development and alter defense-related physiology. We, therefore, performed a bioassay to study these chemicals as possible biostimulants for defense against Verticillium dahliae in eggplant seedlings. AGE and DADS were applied as a foliar application to the eggplants and samples were collected before and after pathogen inoculation at various intervals to analyze the defense mechanism. The obtained data revealed that with the application of AGE and DADS, the seedlings showed responses including activation of antioxidant enzymes, an abundance of chlorophyll contents, alteration of photosynthesis system, and accumulation of plant hormones compared to the control plants. Furthermore, the microscopic analysis of the AGE or DADS treated plants showed high variability in pathogen density within the root crown at 28 days post-inoculation. The low abundance of reactive oxygen species was noticed in AGE or DADS treated plants, which indicates that the plants were able to successfully encounter pathogen attacks. The AGE and DADS treated plants exhibited a lower disease severity index (32.4% and 24.8% vs 87.1% in controls), indicating successful defense against Verticillium infection. Our results were therefore among the first to address the biostimulatory effects of AGE or DADS to induce resistance in eggplant seedlings against V. dahliae and may be used to establish preparation for garlic-derived bioactive compounds to improve growth and defense responses of eggplants under-protected horticultural situations such as glasshouse or plastic tunnels system.

A Field Evaluation of Jalapeño and Non-Jalapeño Chile Pepper Resistance to Phytophthora Blight Caused by Phytophthora capsici

Phytophthora capsici is a destructive soilborne pathogen, which causes Phytophthora blight in many vegetable crops including chile pepper (Capsicum sp.). Our research was aimed at evaluating the resistance of jalapeño cultivars in field conditions and identifying the factors associated with reduction of Phytophthora blight caused by P. capsici. Six jalapeño (NuMex Orange Spice, NuMex Pumpkin Spice, NuMex Jalmundo, TAM Jalapeño, Early Jalapeño, and NuMex Vaquero) and two non-jalapeño (CM-334 and NM 6-4) cultivars were inoculated with P. capsici at the fruiting stage. Disease severity index (DSI), disease incidence (DI), and area under the disease progress curve (AUDPC) for each cultivar were measured. The most susceptible jalapeño cultivars with the highest DSI, DI, and AUDPC were NuMex Orange Spice, NuMex Jalmundo, and NuMex Pumpkin Spice, whereas the least susceptible jalapeño cultivars were Early Jalapeño, TAM Jalapeño, and NuMex Vaquero, with the lowest DSI, DI, and AUDPC. The identified jalapeños with reduced susceptibility to Phytophthora blight can be planted in infested fields, combined with other control methods, which may help in soil disinfestation by reducing the inoculum level in soil over time.

Identifying inbred lines with resistance to endemic diseases in exotic maize germplasm

AbstractMal de Rio Cuarto (MRC) and common rust (CR), caused by Mal de Rio Cuarto virus (MRCV) and Puccinia sorghi, respectively, are endemic diseases affecting maize (Zea mays L.) production in Argentina. Exotic maize germplasm is an important source of resistance to these diseases. The aim of this work was to identify maize lines that exhibit MRC and CR resistance. A multienvironment trial was performed to phenotypically assess a diverse panel of inbred lines from the International Maize and Wheat Improvement Center (CIMMYT). The maize lines were evaluated using a disease severity index (DSI) for MRC and CR in the central area of Argentina. A multitrait mixed linear model (MLM) was used to identify the lines with the best performance for both diseases and estimate genetic parameters. No correlation of resistance between MRC and CR was found among the tested lines. Additionally, best linear unbiased predictions (BLUPs) of genotypic effects were used as response variable to perform a genome‐wide association study (GWAS). The GWAS revealed promising alleles for maize breeding, two associated with MRC and three with CR. Lines with lower DSI for MRC and CR were identified as novel materials for incorporating resistance to the local germplasm.

Screening US peanut mini-core accessions for resistance to Sclerotinia blight caused by Sclerotinia sclerotiorum

Sclerotinia blight is a destructive disease of peanut caused by Sclerotinia sclerotiorum (Lib.) de Bary and Sclerotinia minor Jagger. Crop management practices are routinely used to control Sclerotinia blight, however, development of resistant cultivars together with crop management practices may provide a lasting solution to control the disease in peanut fields. In this study, 95 accessions of United States’ peanut mini-core collection were evaluated using detached leaflet and whole plant inoculation methods under greenhouse conditions. The area of detached leaflet infected was scored using a scale from 0 (no disease) to 4 (76%–100% leaflet area infected). Whole plants were evaluated based on disease severity index (DSI) from 0% (no disease) to 100% (entire plants infected). In the detached leaflet inoculation method, accessions PI-268586, PI-268696, PI-356004, PI-372305, and PI-429420 had the lowest average disease score of 2.7. In the whole plant inoculation method, accessions PI-200441, PI-259658, PI-319770, PI-323268, and PI-337293 had the lowest DSI from 86% to 90%. The two inoculation methods resulted in different set of accessions with the lowest disease level. These results may reflect differences in disease pressure between the two screening methods.

Nitric oxide improves tolerance to Fusarium oxysporum f. sp. cubense Tropical Race 4 in banana

Nitric Oxide (NO) is one of the most studied signalling molecules as it is an important modulator that interact with other molecules during plant defence mechanism against pathogen attack. The predominant regulatory mode of action of NO is protein S-nitrosylation - the covalent binding of NO moiety to the sulfhydryl group of cysteine residue to form S-nitrosothiol (SNO). In this study, we examined the potential role of NO in modulating the interaction of banana- Fusarium oxysporum f. sp. cubense Tropical Race 4. We demonstrated that pre-treatment of banana seedlings with NO donor S-nitrosoglutathione (GSNO) managed to delay Fusarium wilt symptom development, corresponding to a low disease severity index (DSI) whereas pre-treatment with NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) increased the DSI. GSNO treatment increased the SNO level from 57.6 μM mgˉ1 during the early stage of infection to 97 μM mgˉ1 in Foc TR4-challenged banana roots. Biotin switch assay also showed that the banana proteins are S-nitrosylated following inoculation with FocTR4. The findings of this study suggested that NO can improve the tolerance of banana to Foc TR4 through S-nitrosylation, as a molecular mechanism underlying the interaction between the FocTR4 and banana.