Pearl Millet Downy Mildew Disease Research Articles

Elucidating the role of effector protein as biomarker for enhanced resistance against pearl millet downy mildew disease

A variety of secreted effectors are used by fungal pathogens to evade, disrupt, or modify crucial elements of transcription, defense signaling, and metabolic processes to induce resistance against biotic stress in host plant. Induced resistance is a crucial component of managing downy mildew disease in Pennisetum glaucum. However, the underlying mechanisms of effectors and their host targets in biotrophic fungal infections are mainly unknown. In the current study, the effector protein 35983_g from Sclerospora graminicola was treated against the Pennisetum glaucum callus and seedlings of resistant and susceptible variety to downy mildew and compared with the control. Hypersensitivity response (HR), protein-cell wall cross-linking, lignin deposition, hydrogen peroxide (H2O2), phenylalanine-ammonia lyase (PAL) and peroxidase (POX) were evaluated in the both the varieties of Pennisetum glaucum. Experimental data demonstrated that effector protein induced HR, boosted the activity of the enzymes PAL and POX. Additionally, a histochemical examination showed that downy mildew resistant variety treated with effector protein had thicker cell walls due to lignin deposition than untreated cultivar. The identified oomycetes effector protein in this study can be used as a biomarker in breeding programmes to screen pearl millet downy mildew resistant lines across the globe.

Genome-Wide Characterization of Effector Protein-Encoding Genes in Sclerospora graminicola and Its Validation in Response to Pearl Millet Downy Mildew Disease Stress.

Pearl millet [Pennisetum glaucum (L.) R. Br.] is the essential food crop for over ninety million people living in drier parts of India and South Africa. Pearl millet crop production is harshly hindered by numerous biotic stresses. Sclerospora graminicola causes downy mildew disease in pearl millet. Effectors are the proteins secreted by several fungi and bacteria that manipulate the host cell structure and function. This current study aims to identify genes encoding effector proteins from the S. graminicola genome and validate them through molecular techniques. In silico analyses were employed for candidate effector prediction. A total of 845 secretory transmembrane proteins were predicted, out of which 35 proteins carrying LxLFLAK (Leucine-any amino acid-Phenylalanine-Leucine-Alanine-Lysine) motif were crinkler, 52 RxLR (Arginine, any amino acid, Leucine, Arginine), and 17 RxLR-dEER putative effector proteins. Gene validation analysis of 17 RxLR-dEER effector protein-producing genes was carried out, of which 5genes were amplified on the gel. These novel gene sequences were submitted to NCBI. This study is the first report on the identification and characterization of effector genes in Sclerospora graminicola. This dataset will aid in the integration of effector classes that act independently, paving the way to investigate how pearl millet responds to effector protein interactions. These results will assist in identifying functional effector proteins involving the omic approach using newer bioinformatics tools to protect pearl millet plants against downy mildew stress. Considered together, the identified effector protein-encoding functional genes can be utilized in screening oomycetes downy mildew diseases in other crops across the globe.

Lipopolysaccharide-induced priming enhances NO-mediated activation of defense responses in pearl millet challenged with Sclerospora graminicola.

Lipopolysaccharide (LPS) elicitors isolated from Pseudomonas fluorescens UOM SAR 14 effectively induced systemic and durable resistance against pearl millet downy mildew disease caused by the oomycete Sclerospora graminicola. Rapid and increased callose deposition and H2O2 accumulation were evidenced in downy mildew susceptible seeds pre-treated with LPS (SLPS) in comparison with the control seedlings, which also correlated with expression of various other defense responses. Biochemical analysis of enzymes and quantitative real-time polymerase chain reaction data suggested that LPS protects pearl millet against downy mildew through the activation of plant defense mechanisms such as generation of nitric oxide (NO), increased expression, and activities of defense enzymes and proteins. Elevation of NO concentrations was shown to be essential for LPS-mediated defense manifestation in pearl millet and had an impact on the other downstream defense responses like enhanced activation of enzymes and pathogen-related (PR) proteins. Temporal expression analysis of defense enzymes and PR-proteins in SLPS seedlings challenged with the downy mildew pathogen revealed that the activity and expression of peroxidase, phenylalanine ammonia lyase, and the PR-proteins (PR-1 and PR-5) were significantly enhanced compared to untreated control. Higher gene expression and protein activities of hydroxyproline-rich glycoproteins (HRGPs) were observed in SLPS seedlings which were similar to that of the resistant check. Collectively, our results suggest that, in pearl millet-downy mildew interaction, LPS pre-treatment affects defense signaling through the central regulator NO which triggers the activities of PAL, POX, PR-1, PR-5, and HRGPs.

Identification of new sources of resistance for pearl millet downy mildew disease under field conditions

AbstractPearl millet is an important cereal crop for smallholder farmers’ food security in Africa and India. However, its production has stagnated due to several factors such as downy mildew (DM). Thus, a study was conducted to identify new sources of resistance from pearl millet inbred lines derived from a collection of landraces originated from West and Central African countries. A set of 101 lines, including 99 inbred lines from West and Central Africa along with a 7042S and SOSAT C 88 as susceptible and resistant checks, respectively, were evaluated under field conditions with infector rows in Bambey and Nioro research stations during the rainy season of 2016. Data on DM incidence and severity, plant height, flowering time, panicle length and productive tillers were recorded. The results showed highly significant differences among lines for all observed traits. Among the tested lines, 55 including SOSAT C 88 were resistant, 16 moderately resistant and 30 including 7042S were susceptible to the disease. Out of the 55 resistant lines, 20 were disease free. Hierarchical ascendant cluster analysis grouped the lines into three clusters with the DM parameters and plant height as the most discriminant factors. Cluster II contains the susceptible lines, while cluster III comprises the moderately resistant lines. The lines which belongs to cluster I were characterized by their resistance to the disease. Further use of these available new sources of resistance will be very useful for improvement of pearl millet for DM resistance and other agronomic traits.

Systemic protection against pearl millet downy mildew disease induced by cell wall glucan elicitors from Trichoderma hamatum UOM 13

Abstract The obligate oomycete Sclerospora graminicola (Sacc.) Schroet, is the incitant of downy mildew disease, which is the main constraint in pearl millet production worldwide. Different elicitors from Trichoderma hamatum UOM 13, e.g. mycelial extract and cell wall glucans, were assessed for their resistance elicitation efficiency and the possible underlying mechanisms. Both mycelial extract and cell wall glucans of T. hamatum UOM 13 positively influenced seed quality parameters of pearl millet, significantly enhanced seed germination and seedling vigor in comparison to the untreated control. Seed priming with cell wall glucan elicitors of T. hamatum UOM 13 suppressed downy mildew on susceptible pearl millet seedlings under greenhouse conditions by induction of systemic host resistance. Of the different elicitor delivery methods tested, transplant root dip was more effective than seed treatment and foliar spray. A combination of transplant root dip + seed treatment + foliar spray was significantly more effective than the single delivery methods. The induced resistance corresponded to up regulation of genes of important defense proteins upon pathogen inoculation. Transcripts of genes of defense enzymes glucanase, phenylalanine ammonia lyase, peroxidase and polyphenoloxidase were significantly increased due to the T. hamatum UOM elicitor effect. Expression of hydroxyproline-rich glycoprotein genes, known to play an important role in cell wall cross-linking, were also up regulated in response to T. hamatum UOM cell wall glucan treatment. This study emphasizes the role of T. hamatum UOM as a potential elicitor of downy mildew resistance in pearl millet and presents novel insights into the involvement of important defense proteins mediating such as resistance trigger.

Elicitation of resistance and associated defense responses in Trichoderma hamatum induced protection against pearl millet downy mildew pathogen

Endophytic Trichoderma hamatum UoM 13 isolated from pearl millet roots was evaluated for its efficiency to suppress downy mildew disease. Under laboratory conditions, T. hamatum seed treatment significantly enhanced pearl millet seed germination and seedling vigor. T. hamatum seed treatment resulted in systemic and durable immunity against pearl millet downy mildew disease under greenhouse and field conditions. T. hamatum treated seedlings responded to downy mildew infection with high lignification and callose deposition. Analysis of defense enzymes showed that T. hamatum treatment significantly enhanced the activities of glucanase, peroxidase, phenylalanine ammonia-lyase, and polyphenol oxidase in comparison to untreated control. RT-PCR analysis revealed differentially expressed transcripts of the defense enzymes and PR-proteins in treated, untreated, and checks, wherein PR-1, PR-5, and cell wall defense HRGPs were significantly over expressed in treated seedlings as against their lower expression in controls. T. hamatum treatment significantly stimulated endogenous salicylic acid (SA) levels and significantly upregulated important SA biosynthesis gene isochorismate synthase. The results indicated that T. hamatum UoM13 treatment induces resistance corresponding to significant over expression of endogenous SA, important defense enzymes, PR-proteins, and HRGPs, suggesting that SA biosynthetic pathway is involved in pearl millet for mounting systemic immunity against downy mildew pathogen.

Isolation and evaluation of proteolytic actinomycete isolates as novel inducers of pearl millet downy mildew disease protection.

Native endophytic actinomycetes isolated from pearl millet roots were examined for their efficacy to protect pearl millet against downy mildew. Nineteen of 39 isolates were found to be proteolytic, of which 7 strains could directly suppress the sporangium formation of Sclerospora graminicola, the pearl millet downy mildew pathogen. Thus, mycelial suspensions containing either spores or cell-free extract of these 7 isolates were used for seed-coating and -soaking treatments to test for their induction of downy mildew resistance. Results indicated that seed-coating overall provided better protection to downy mildew than seed-soaking. In both treatments, the tested isolates demonstrated differential abilities in downy mildew disease protection, with Streptomyces griseus SJ_UOM-07-09 and Streptosporangium roseum SJ_UOM-18-09 showing the highest protection rates. Additionally, the levels of disease protection conferred by the actinomycetes were just slightly lower than that of the systemic fungicide Apron, suggesting their effectiveness. Further studies revealed that the more rapid root colonization by SJ_UOM-18-09 resulted in faster and higher induced resistance in comparison with SJ_UOM-07-09 under greenhouse conditions, indicating that SJ_UOM-18-09 was superior than SJ_UOM-07-09 in inducing resistance. Results from this study provide comprehensive information on biocontrol functions of SJ_UOM- 18-09 with great potential to control downy mildew disease in pearl millet.

Partially purified ns-LTPs from plant source promote growth and induce downy mildew disease resistance in pearl millet

Partially purified non-specific Lipid Transfer Proteins (ns-LTPs) of plant source were treated to pearl millet seeds at different concentrations for six hours. Among the tested, rice ns-LTP (100 μg/ml) showed a maximum seed germination of 94% and 1385 seedling vigour followed by maize and wheat. The treated seeds also enhanced growth parameters when compared to control plants. The maximum downy mildew disease protection of 56% was offered by rice ns-LTP (100 μg/ml) followed by maize and wheat which offered 52% and 47% protection, respectively. The ns-LTPs of maize and rice required minimum of three days after challenge inoculation to build up maximum resistance to downy mildew. The present investigation suggests that the ns-LTPs from plant source can be used as inducers in managing pearl millet downy mildew disease and also for plant growth promotion.

Elicitation of resistance in pearl millet by oligosaccharides of Trichoderma spp. against downy mildew disease

In this study, we made an attempt to develop an ecofriendly management strategy against pearl millet (PM) downy mildew (DM) disease through seed priming with cell wall oligosaccharide of Trichoderma spp. Oligosaccharide treatment with mannitol significantly enhanced the seedling vigor when compared with the other controls. Significant reduction in DM disease was recorded in seeds treated with oligosaccharides extracted from Trichoderma virens and its efficacy was further increased when treated along with mannitol. At the biochemical level, increased activity of defense-related enzymes such as peroxidase and lipoxygenase was recorded followed by accumulation of signaling molecule Jasmonic acid in seedlings raised from seed treated with oligosaccharide (with or without mannitol) from T. virens. Under field conditions, oligosaccharide with mannitol provided a significant protection against the DM disease over other treatments. The possible utilization of oligosaccharide in inducing the systemic resistance against DM disease in PM is discussed.

Comparative analysis of activities of vital defence enzymes during induction of resistance in pearl millet against downy mildew

Pearl millet [Pennisetum glaucum (L.) R. Br.] has the seventh largest annual production in the world giving it significant economic importance. Although generally well adapted to the growing conditions in arid and semi-arid regions, major constraints to yields are susceptibility to downy mildew disease caused by the oomycete Sclerospora graminicola (Sacc.) Schroet. Induction of resistance against downy mildew disease of pearl millet has been well established using various biotic and abiotic inducers. The present study demonstrated the comparative analysis of the involvement of the important defence enzymes like β-1,3-Glucanase, chitinase, phenylalanine ammonia-lyase (PAL), peroxidase (POX), polyphenol oxidase (PPO) and lipoxygenase (LOX) during induced systemic resistance (ISR) mediated by inducers like Benzo(1,2,3)-thiadiazole-7-carbothionic acid-S-methyl ester (BTH), Beta amino butyric acid (BABA), Chitosan and Cerebroside against pearl millet downy mildew disease. Native-PAGE showed six POX isozymes in all categories of uninoculated pearl millet seedlings and maximum intensity of bands was noticed in resistant seedlings. After inoculation in Cerebroside-treated seedlings, there were seven isoforms, POX-4 was not present in any other seedlings. Native-PAGE analysis showed the presence of five PPO isozymes in all categories of uninoculated pearl millet seedlings and after inoculation seven isoforms of PPO-7 were noticed, and the intensity of banding was more in resistant and Cerebroside-treated seedlings. The isoforms PPO-3 were present as an extra band after inoculation in all seedlings. Isoform PPO-7, though found in all seedlings, was very prominent in Chitosan- and Cerebroside-treated seedlings. β-1,3-Glucanase Native-PAGE analysis showed the presence of only one isozyme in all categories of uninoculated/inoculated pearl millet seedlings. Glu-1 isozyme was very prominent in all seedlings including resistant and susceptible seedlings. Among the induced resistant seedlings, highest intensity was observed in Cerebroside-treated seedlings. Native-PAGE analysis showed the presence of three LOX isozymes in all categories of uninoculated pearl millet seedlings, and the intensity of banding pattern was very low in BTH-treated seedlings. LOX-1 and LOX-2 were very prominent in resistant, Chitosan- and Cerebroside-treated seedlings. Upon inoculation, one extra band, LOX-3, was exclusively noticed in Cerebroside-treated seedlings. In inoculated seedlings, LOX-1, LOX-2 and LOX-4 were very prominent in Chitosan Cerebroside-treated seedlings compared to other seedlings.

Thionins (PR protein-13) mediate pearl millet downy mildew disease resistance

Thionins (PR protein-13) are a class of Cys-rich polypeptides of about 5 kDa, and have revealed their role of the defense in pearl millet to Sclerospora graminicola. The purified 5 kDa thionins show a pI of 8.2 and have anti-mildew activity tested on S. graminicola. The high level of transcript expression of thionins in resistant compared to susceptible cultivars was observed. Immunofluorescence studies have shown intense fluorescence in epidermal regions, confirming its involvement in arresting pathogen ingress and in vascular regions, confirming its systemic translocation during interaction. Epidermal peeling of resistant cultivars showed that thionin protein was present in higher quantities at the papillar region of the cell wall in seedlings.

Nitric oxide is involved in chitosan‐induced systemic resistance in pearl millet against downy mildew disease

The nature and durability of resistance offered by chitosan and the involvement of nitric oxide (NO) in chitosan-induced defence reactions in pearl millet against downy mildew disease were investigated. It had previously been reported that chitosan seed priming protected pearl millet plants against downy mildew disease. Further elucidation of the mechanism of resistance showed that chitosan seed priming protects the plants systemically. A minimum 4 day time gap is required between the chitosan treatment and pathogen inoculation for maximum resistance development, and it was found to be durable. Chitosan seed priming elevated NO accumulation in pearl millet seedlings, beginning from 2 h post-inoculation, and it was found to be involved in the activation of early defence reactions such as hypersensitive reaction, callose deposition and PR-1 protein expression. Pretreatment with NO scavenger C-PTIO and nitric oxide synthase (NOS) inhibitor L-NAME before pathogen inoculation reduced the disease-protecting ability of chitosan, and defence reactions were also downregulated, which indicated a possible role for NO in chitosan-induced resistance. Protection offered by chitosan against pearl millet downy mildew disease is systemic in nature and durable. Chitosan-induced resistance is activated via NO signalling, as defence reactions induced by chitosan were downregulated under NO deficient conditions.

Seed priming with plant gum biopolymers enhances efficacy of metalaxyl 35 SD against pearl millet downy mildew

‘Priming’ the plant and seed induces a physiological state in which plants are able to activate defense responses. Plant-based exudates are excellent gum biopolymers which contain plant growth-regulating hormones with priming potential without any side effects. In this study, gum exudates of Acacia arabica, Moringa oleifera, Carica papaya and Azadirachta indica were evaluated for synergistic effects of seed priming with exuded gum biopolymer combined with metalaxyl (Apron 35 SD) on pearl millet seed quality, growth parameters, and resistance to Sclerospora graminicola. Seeds of 7042S were primed with gum biopolymers and metalaxyl 35 SD and evaluated under laboratory and greenhouse conditions. Seed germination and vigor were synergistically enhanced using gum biopolymers solution (1:2 w/v) with 3 g kg−1 metalaxyl 35 SD. A. arabica and A. indica gum biopolymers alone or with 3 g kg−1 of metalaxyl 35 SD resulted in seed germination of >91%. Seed priming with 6 g kg−1 of metalaxyl 35 SD gave 89% seed germination and was not significantly different from control. A similar trend in vigor was observed among treatments. Seed priming with gum biopolymers alone provided varied disease protection levels when compared with the control. A. arabica or A. indica gum with 3 g kg−1 of metalaxyl 35 SD was the superior treatment, offering significant 86% disease reduction while exhibiting a growth-promoting effect. Synergistic use of gum biopolymers and metalaxyl 35 SD by seed priming is highly effective in growth promotion and management of pearl millet downy mildew disease.

Integrated disease management of pearl millet downy mildew caused by Sclerospora graminicola

Field trials were conducted in infected sites at two locations: the Millet Breeding Station, TNAU, Coimbatore and at the Regional Research Station, Aruppukottai, to test the combination of promising treatments for the management of pearl millet downy mildew using the highly susceptible HB3 pearl millet. Pearl millet seeds were exposed to sporangial shed of Sclerospora graminicola and then sown. Incidence of downy mildew was recorded at 30, 45, 65 days after sowing (DAS) and the per cent disease was calculated. The yield of pearl millet was also recorded during the harvest and calculated as kg/ha. Seed treatment (ST) with Apron 2 g/kg + Ridomil 0.6% foliar spray (FS) 20 DAS was by far the most effective in reducing the incidence of pearl millet downy mildew disease to a minimum of 4.65% from a maximum of 66.09% in the control. Seed treatment with Pseudomonas fluorescens 10 g/kg (ST) ranks next (10.47%) followed by ST with Trichoderma viride at 4 g/kg (17.15%) and FS with the culture filtrate of Fusarium longipes (103 conidia/ml) 20 DAS (29.76%). The grain yield recorded 910 kg.ha in ST with T. viride, ST with Pseudomonas fluorescens (880 kg/ha).

Nitric oxide donor seed priming enhances defense responses and induces resistance against pearl millet downy mildew disease

Nitric oxide (NO) donors Nitroso- R-Salt, 2-Nitroso-1-Naphthol and Sodium Nitro Prusside (SNP) were evaluated for their effectiveness in protecting pearl millet [( Pennisetum glaucum L.) R. Br.] plants against downy mildew disease caused by Sclerospora graminicola [(Sacc). Schroet]. Optimization experiments with NO donors showed no adverse effect either on the host or pathogen. Aqueous SNP seed treatment with or without polyethylene glycol (PEG) priming was the most effective in inducing the host resistance against downy mildew both under greenhouse and field conditions. Potassium Ferrocyanide, a structural analog of NO donor lacking NO moiety failed to protect the pearl millet plants from downy mildew indicating a role for NO in induced host resistance. Spatio-temporal studies corroborated that the protection offered by NO donor treatment was systemic in nature and a minimum of 3-day time gap between the inducer treatment and subsequent pathogen inoculation was necessary for maximum resistance development. Disease protection ability of NO donors was also validated as durable in nature. Conversely, prior-treatment with NO scavenger 2-4-carboxyphenyl-4,4,5,5 tetrazoline-1-oxyl-3-oxide potassium salt (C-PTIO) rendered the pearl millet plants relatively susceptible for pathogen infection. Expression of primary defense responses like hypersensitive response, lignin deposition and defense related enzyme phenylalanine ammonialyase −EC 4.3.1.5 (PAL) were enhanced by NO donor treatments.

Activity of cyazofamid against Sclerospora graminicola, a downy mildew disease of pearl millet

The efficacy of cyazofamid was tested against pearl millet downy mildew disease caused by Sclerospora graminicola Schroet. Significant inhibition of sporangial sporulation, zoospore release and motility was observed at 0.3 mg mL(-1), and this concentration also provided good fungicidal activity under in vitro conditions. Under glasshouse conditions, none of the concentrations tested, either 0.01-2 mg mL(-1) as seed treatment or 1-10 mg mL(-1) by foliar application, was found to be phytotoxic. The effect of cyazofamid was tested by seed treatment alone, seed treatment followed by foliar application and foliar application alone. Seed treatment with cyazofamid offered only 19.7% disease control, but seed treatment followed by a single foliar application to diseased plants provided good control over disease, seed treatment with two foliar applications was significantly superior and foliar application alone showed a high level of activity, with 10 mg mL(-1) giving 97.9% disease control. Lack of systemic activity of cyazofamid was evident, root treatment giving disease levels on a par with the untreated control. The fungicide exhibited strong curative activity, but only moderate translaminar activity, with only marginal (34.8%) disease control after treatment of the adaxial leaf surface at 10 mg mL(-1). Loss of cyazofamid activity over time was very low, indicating stable residual and rainfastness activity. These results indicate that cyazofamid has a high potential to be an effective fungicide for the control of downy mildew disease of pearl millet.

DEVELOPMENTAL STAGE RESP ONSE OF PE ARL MILLET DOWNY MILDEW (SCLEROSPO RA GRAMINICOLA) TO FUNGICIDES

Inhibitory effect of 21 commercial and 6 experimental fungicides was assessed in model experiments against pearl millet downy mildew disease. Chemicals differed strongly by their anti-mildew activity, however neither the pathogen nor the host plant showed complete tolerance to any of compounds tested. Nevertheless, the plants outgrew depressant effect of compounds observed in germling stage and this activity did not significantly influence the yield. There was a significant correlation between yield performance and disease inhibitory effects assessed either in vitro or in vivo tests. The response of pathogen to investigated compounds varied during ontogeny, where zoosporangium formation was found to be the most sensitive ontogenetic event. When comparing responses of pathogen and host with fungicides by means of principal component analysis, the presence of two independent components has been demonstrated accounting for 86% of the total variation to which responses of host and pathogen contributed differently. The antisporulant activity of compounds evaluated on detached leaf segments and their positive effect on yield significantly correlated allowing to predict the expectable grain yield significantly (p>0.05). Beside acylanilides andoprim, drazoxolon and efosit offered efficacy on the level requested. Metalaxyl and tridemorph as well as andoprim and cymoxanil acted synergistically against S. graminicola.

Induction and accumulation of polyphenol oxidase activities as implicated in development of resistance against pearl millet downy mildew disease.

Polyphenol oxidase (PPO) activity was analysed in seedlings of resistant and susceptible pearl millet [Pennisetum glaucum (L.) R.Br] cultivars with or without inoculation of the downy mildew pathogen Sclerospora graminicola (Sacc.) Schroet. Seedlings of resistant varieties had greater PPO activity than susceptible seedlings, and inoculated seedlings had significantly higher PPO levels than uninoculated seedlings. Temporal accumulation of PPO showed a maximum activity at 24 h post-inoculation in resistant seedlings, whereas in susceptible seedlings it peaked at 48 h. PPO activity was positively correlated with levels of downy mildew resistance in different pearl millet cultivars under field conditions. Native PAGE staining showed four isoforms of PPO, which were differentially induced in relation to the time of appearance and intensities in the uninoculated seedlings, whereas a fifth PPO isoform appeared after inoculation with S. graminicola. PPO activity was significantly higher in the shoot and leaves of pearl millet than in the root. Tissue printing analysis of the enzyme expression showed that the enzyme is predominantly expressed after pathogen inoculation and is localised in the epidermal and vascular regions. Temporal analysis of transcript accumulation showed that in resistant seedlings PPO mRNAs was expressed earlier and more abundantly than in susceptible seedlings. Our studies demonstrate, for the first time, that PPO is actively involved in plant defence and can be used as a marker of resistance to downy mildew infection in pearl millet.

Response of pearl millet downy mildew ( Sclerospora graminicola ) to diverse fungicides

The inhibitory effect of 15 commercial and five experimental fungicides was assessed both in greenhouse and field experiments against Sclerospora graminicola, the causative agent of pearl millet downy mildew disease. Chemicals differed in anti-mildew activity. However, neither the pathogen nor the host plant was completely tolerant to any compounds tested. The plants depressed by fungicides in the germling stage recovered until formation of inflorescence, so this activity did not significantly influence grain yield. There was a significant correlation between antisporulant activity of compounds evaluated on detached leaf segments and their positive effect on yield performance. All compounds increased the grain yield of downy mildewed pearl millet when applied in the maximum doses tolerated by pearl millet. However, analysis of the cost-return budget showed that disease control < 30% is uneconomic. Fungicides of the acylanilide series exhibited the highest protective effect (over 95%) and andoprim, drazoxolon and efosit were also effective.

Comparative efficacy of strobilurin fungicides against downy mildew disease of pearl millet

Three commercial formulations of strobilurins, viz., azoxystrobin, kresoxim-methyl, and trifloxystrobin were evaluated for their efficacy against pearl millet downy mildew disease caused by Sclerospora graminicola. In vitro studies revealed inhibition of S. graminicola sporulation, zoospore release, and zoospore motility at 0.1–2 μg ml −1 of all the three fungicides. The fungicides were evaluated for phytotoxic effects on seed quality parameters and for their effectiveness against downy mildew disease by treating pearl millet by: (1) seed dressing, (2) seed dressing followed by foliar spray, and (3) also by foliar spray alone. The highest non-phytotoxic concentrations of 5, 10, and 10 μg ml −1 for azoxystrobin, trifloxystrobin, and kresoxim-methyl, respectively, were selected for further studies. Under greenhouse conditions, these fungicides showed varying degrees of protection against downy mildew disease. Among the three fungicides, azoxystrobin proved to be the best by offering disease protection of 66%. Further, seed treatment along with foliar application of these fungicides to diseased plants showed enhanced protection against the disease to 93, 82, and 62% in treatments of azoxystrobin, kresoxim-methyl and trifloxystrobin respectively. Foliar spray alone provided significant increase in disease protection levels of 91, 79, and 59% in treatments of azoxystrobin, kresoxim-methyl, and trifloxystrobin, respectively. Disease curative activity of azoxystrobin was higher compared to trifloxystrobin and kresoxim-methyl. Tested fungicides showed weaker translaminar activity, as the disease inhibition was marginal when applied on adaxial leaf surface. Partial systemic activity of azoxystrobin was evident by root uptake, while trifloxystrobin and kresoxim-methyl showed lack of systemic action in pearl millet. A trend in protection against downy mildew disease similar to greenhouse results was evident in the field trials. Grain yield was significantly increased in all strobilurin fungicide treatments over control and maximum increase in yield of 1673 kg ha −1 was observed in combination treatments of seed treatment and foliar spray with azoxystrobin.