Downy Mildew Disease Resistance Research Articles

QTL mapping of downy mildew resistance in foxtail millet by SLAF‑seq and BSR-seq analysis.

Key message Three major QTLs for resistance to downy mildew were located within an 0.78 Mb interval on chromosome 8 in foxtail millet. Downy mildew, a disease caused by Sclerospora graminicola, is a serious problem that jeopardizes the yield and quality of foxtail millet. Breeding resistant varieties represents one of the most economical and effective solutions, yet there is a lack of molecular markers related to the resistance. Here, a mapping population comprising of 158 F6:7 recombinant inbred lines (RILs) was constructed from the crossing of G1 and JG21. Based on the specific locus amplified fragment sequencing results, a high-density linkage map of foxtail millet with 1031 bin markers, spanning 1041.66 cM was constructed. Based on the high-density linkage map and the phenotype data in four environments, a total of nine quantitative trait loci (QTL) associated with resistance to downy mildew were identified. Further BSR-seq confirmed the genomic regions containing the potential candidate genes related to downy mildew resistance. Interestingly, a 0.78-Mb interval between C8M257 and C8M268 on chromosome 8 was highlighted because of its presence in three major QTL, qDM8_1, qDM8_2, and qDM8_4, which contains 10 NBS-LRR genes. Haplotype analysis in RILs and natural population suggest that 9 SNP loci on Seita8G.199800, Seita8G.195900, Seita8G.198300, and Seita.8G199300 genes were significantly correlated with disease resistance. Furthermore, we found that those genes were taxon-specific by collinearity analysis of pearl millet and foxtail millet genomes. The identification of these new resistance QTL and the prediction of resistance genes against downy mildew will be useful in breeding for resistant varieties and the study of genetic mechanisms of downy mildew disease resistance in foxtail millet.

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

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

Genetics of downy mildew resistance in indigenous cucumber germplasm

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

Line × Tester Analysis for Estimation Combining ability of some New Yellow Maize Inbred Lines for Grain Yield and Downy Mildew Resistance

A line×tester analysis was performed at Sakha Research Station; during summer 2017, using twenty new yellow maize inbred lines and two testers; inbred line Sk-4 and single cross SC180. The resulting 40 F1 crosses in addition to four check hybrids were evaluated in two trails during summer 2018. The first trail; for yield and other traits, was performed at Sakha and Sids Agricultural Research Stations. The second trial; for downy mildew disease resistance, was carried out under two levels of nitrogen fertilization in the disease nursery at Sakha Station. Significantly differences were detected between the two locations for the most studied traits and between the two nitrogen levels for downy mildew resistance. Significant of differences were observed among lines, testers and their interaction for all studied traits, except among testers for downy mildew resistance and line×tester interaction for plant height, ear height and downy mildew resistance. The non-additive gene effects were predominant in the inheritance of grain yield, ear length, ear diameter and downy mildew resistance. For general combining ability effects, the best general combiners were Sk5013/71 for grain yield and downy mildew resistance. While, the best tester was Sk-4 for grain yield and most traits. The desirable hybrids for specific combining ability effects were Sk5002/62×Sk-4, Sk5005/66×Sk-4 and Sk5021/74×SC180 for grain yield and Sk5004/65×SC180 for downy mildew resistance. Single cross Sk5013/71×Sk4, also three-way crosses Sk5010/69×SC180 and Sk5013/71×SC180 were superior for grain yield and high resistance to downy mildew resistance. These crosses could be use in maize breeding program.

Elicitation of Novel Trichogenic-Lipid Nanoemulsion Signaling Resistance Against Pearl Millet Downy Mildew Disease.

Nanoemulsion was formulated from membrane lipids of Trichoderma spp. with the non-ionic surfactant Tween 80 by the ultrasonic emulsification method. Nanoemulsion with a droplet diameter of 5 to 51 nm was obtained. The possible effects of membrane lipid nanoemulsion on pearl millet (PM) seed growth parameters and elicitation of downy mildew (DM) disease resistance in PM was analyzed to develop an eco-friendly disease management strategy. Seed priming with nanoemulsion illustrates significant protection and elevated levels of early defense gene expression. Lipid profiling of Trichoderma spp. reveals the presence of oleic acid as a major fatty acid molecule. The prominent molecule in the purified lipid fraction of T. brevicompactum (UP-91) responsible for the elicitation of induction of systemic resistance in PM host against DM pathogen was predicted as (E)-N-(1, 3-dihydroxyoctadec-4-en-2yl) acetamide. The results suggest that protection offered by the novel nanoemulsion formulation is systemic in nature and durable and offers a newer sustainable approach to manage biotrophic oomycetous pathogen.

QTL mapping for sorghum downy mildew disease resistance in maize (Zea mays L.) in recombinant inbred line population of UMI79 X UMI936 (w)

Sorghum downy mildew (SDM) caused by the Oomycete, Peronosclerospora sorghi ((Weston and Uppal) C. G. Shaw) is a major impediment to maize production and productivity. Identifying genomic regions (QTLs), contributing to SDM resistance will aid in a marker-assisted resistant breeding program. In the present study, QTLs have been mapped for SDM resistance using 158 recombinant inbred lines (RILs) derived from the cross between SDM-susceptible (UMI79) and resistant (UMI936 (w)) inbred lines. Phenotyping for SDM reaction was conducted in three environments under artificial epiphytotic conditions. Inclusive composite interval mapping with simple sequence repeat (SSR) markers resulted in the identification of three putative QTLs, one with major-effect (PVE = 17.1 %) on chromosome three and other two with minor effects on chromosome six (PVE = 2.3) and seven (PVE = 3.4). Inclusive composite interval mapping detected one QTL for the all the three environments, all co-localizing near the same marker, bnlg420 on chromosome 3.

Diversity in Melon (Cucumis melo L.) Landraces of Karnataka State of Southern India for Downy and Powdery Mildew Disease Resistance

We present here the report on evaluation of melon landraces from the Karnataka state of India for resistance to downy mildew (Pseudoperonospora cubensis) and powdery mildew (Podosphaera xanthii), the major diseases of melon as well as other cucurbits. Thirty four melon landraces collected from different agro-climatic regions of the state were evaluated for resistance against downy mildew under natural epiphytotic conditions and powdery mildew under artificial conditions. Percent disease index (PDI) was calculated for each entry and based on that accessions were categorised as resistant, moderately resistant and susceptible. A very wide variation was observed among the accessions for resistance to both the diseases. Based on PDI, out of 34 accessions, COHB04, COHB37, COHB38, COHB41 and COHB43 were resistant to downy mildew. Ten genotypes were moderately resistant, fifteen were susceptible and four lines including susceptible check were highly susceptible to disease. Three landraces, COHB12, COHB38 and COHB40 were resistant to powdery mildew disease. Two genotypes were moderately resistant and rest of the lines were susceptible to disease. COHB38, an unexplored and uncultivated genotype was resistant to both the diseases. The highly resistant genotype COHB38 identified within the accessions tested offers an additional source for the development of downy and powdery mildew resistant melon cultivars.

QTLs and candidate genes for downy mildew resistance conferred by interspecific grape (V. vinifera L. × V. amurensis Rupr.) crossing

Considering the economic importance of grape (Vitis spp.), breeding for downy mildew (P. viticola) resistance has made great progress in the last two decades. However, the genetic and genomic information of resistance against grape downy mildew remain largely unknown. In this study, we described the quantitative trait loci (QTL) and candidate genes for downy mildew resistance in susceptible V. vinifera cv. ‘Red Globe’ and V. amurensis Rupr. cv. ‘Shuangyou’. Two novel QTLs for downy mildew resistance were mapped on linkage group (LG) 15, which have been named Rpv25 and Rpv26, respectively. Candidate gene analysis found that three cysteine-rich receptor protein kinase (CRK) near to two N genes in the Rpv25 locus, and a gene encoding LRR (leucine-rich repeat)-RLK (receptor-like protein kinases) family protein in Rpv26 locus may be associated to downy mildew resistance in current climatic conditions. The results of the present study provide useful information for grape downy mildew disease resistance breeding.

Single and multiple phenotype QTL analyses of downy mildew resistance in interspecific grapevines

Key messageDowny mildew resistance across days post-inoculation, experiments, and years in two interspecific grapevine F1 families was investigated using linear mixed models and Bayesian networks, and five new QTL were identified.Breeding grapevines for downy mildew disease resistance has traditionally relied on qualitative gene resistance, which can be overcome by pathogen evolution. Analyzing two interspecific F1 families, both having ancestry derived from Vitis vinifera and wild North American Vitis species, across 2 years and multiple experiments, we found multiple loci associated with downy mildew sporulation and hypersensitive response in both families using a single phenotype model. The loci explained between 7 and 17% of the variance for either phenotype, suggesting a complex genetic architecture for these traits in the two families studied. For two loci, we used RNA-Seq to detect differentially transcribed genes and found that the candidate genes at these loci were likely not NBS-LRR genes. Additionally, using a multiple phenotype Bayesian network analysis, we found effects between the leaf trichome density, hypersensitive response, and sporulation phenotypes. Moderate–high heritabilities were found for all three phenotypes, suggesting that selection for downy mildew resistance is an achievable goal by breeding for either physical- or non-physical-based resistance mechanisms, with the combination of the two possibly providing durable resistance.

Enhancement of downy mildew disease resistance in pearl millet by the G_app7 bioactive compound produced by Ganoderma applanatum

Pearl millet (Pennisetum glaucum) stands sixth among the most important cereal crops grown in the semi-arid and arid regions of the world. The downy mildew disease caused by Sclerospora graminicola, an oomycete pathogen, has been recognized as a major biotic constraint in pearl millet production. On the other hand, basidiomycetes are known to produce a large number of antimicrobial metabolites, providing a good source of anti-oomycete agrochemicals. Here, we report the discovery and efficacy of a compound, named G_app7, purified from Ganoderma applanatum on inhibition of growth and development of S. graminicola, as well as the effects of seed treatment with G_app7 on protection of pearl millet from downy mildew. G_app7 consistently demonstrated remarkable effects against S. graminicola by recording significant inhibition of sporangium formation (41.4%), zoospore release (77.5%) and zoospore motility (91%). Analyses of G_app7 compound using two-dimensional nuclear magnetic resonance spectroscopy and liquid chromatography-mass spectrometry revealed its close resemblance to metominostrobin, a derivative of strobilurin group of fungicides. Furthermore, the G_app7 was shown to stably maintain the inhibitory effects at different temperatures between 25 and 80 °C. In addition, the anti-oomycete activity of G_app7 was fairly stable for a period of at least 12 months at 4 °C and was only completely lost after being autoclaved. Seed treatment with G_app7 resulted in a significant increase in disease protection (63%) under greenhouse conditions compared with water control. The identification and isolation of this novel and functional anti-oomycete compound from G. applanatum provide a considerable agrochemical importance for plant protection against downy mildew in an environmentally safe and economical manner.

QTL ANALYSIS OF PATHOGEN RESISTANCE FACTORS AND RIPENING TIME TRAITS IN A GENETIC MAP FROM GRAPEVINE BREEDING LINE GF.GA-47-42 CROSSED TO 'VILLARD BLANC'

Marker-assisted selection is an important tool of current grapevine breeding which aims to improve cultivars for more sustainable viticulture. Markers genetically linked to traits of interest are hence required. These can be identified by QTL (quantitative trait loci) analysis scanning genetic maps elaborated from controlled crosses for marker genotypes correlating with segregating phenotypes. Major traits of interest are resistances to pathogens like powdery and downy mildew (Erysiphe necator resp. Plasmopara viticola) of leaves and fruits. In addition, phenological traits have recently acquired special attention. Breeders wish to select grapes with a better defined ?window? of ripening time as ripening behavior affects both pathogen susceptibility and fruit quality. Ripening time needs to be considered within the context of the climate change debate. To identify genomic regions carrying loci affecting resistance traits and ripening time we constructed a genetic map using 151 individuals from the cross of grapevine breeding line Gf.GA-47-42 (?Bacchus? × ?Seyval?) with ?Villard blanc? (?Seibel 6468? × ?Subereux?). Both parental lines are resistant to powdery and downy mildew and vary considerably in ?veraison? time as an indicator of ripening. While Gf.GA-47-42 is rather early, ?Villard blanc? exhibits middle to late ?veraison? and this trait segregates clearly in the cross. Linkage/recombination analysis for map construction was based on more than 350 simple sequence repeat (SSR)-derived markers. Many of these loci were newly extracted from the Vitis reference genome sequence of PN40024 (http://www.genoscope.cns.fr/externe/GenomeBrowser/Vitis/). In addition, the mapping included 210 newly developed SNP (single nucleotide polymorphisms) markers. A subset of these was analyzed with two different techniques permitting to assess the reliability of SNP genotyping with both methods. The resulting map was scanned for QTL influencing powdery and downy mildew disease resistance and the time of ?veraison?. Several major QTL were identified.

Proteomic analysis of elicitation of downy mildew disease resistance in pearl millet by seed priming with β-aminobutyric acid and Pseudomonas fluorescens.

The study is based on the comparative proteomic analysis between BABA and P. fluorescens mediated resistance in pearl millet, in response to downy mildew causing biotroph - S. graminicola. To our knowledge, this article is the first to report on seedling proteome of pearl millet whose genome is not yet sequenced. In addition, the study also provides clue for the plausible antagonistic cross-talk that might exist between jasmonic acid signaling and salicylic acid signaling in SAR and ISR mediated resistance by BABA and P. fluorescens against the downy mildew pathogen. Furthermore, pearl millet seedling proteome being perturbed by pathogen inoculation was more apparent than that caused by elicitor treatment, as revealed by multivariate statistics like PCA. Analysis by gene enrichment tools further revealed that the glucose metabolism pathway was majorly being affected in our study. This could be attributed to the essential balance that is being maintained in energy diversion towards stress and normal physiological process due to the priming effect of the elicitors against biotic stress.

Non-specific lipid transfer proteins (ns-LTPs) from maize induce resistance in pearl millet against downy mildew disease

Non-specific Lipid Transfer Proteins were isolated and purified from maize seeds using combinations of ammonium sulphate precipitation and cat-ion exchange chromatography followed by HPLC. Two peptide segments were obtained by MALDI-TOF MS analysis, which were designated as ns-LTP M1 and ns-LTP M2. Both the ns-LTPs were treated to pearl millet seeds at different concentrations for 6 h. Among the concentrations tested, ns-LTP M1 (50 μg/ ml) showed a maximum seed germination of 94% and 1320 seedling vigor followed by ns-LTP M2. The maximum downy mildew disease protection of 62% was offered by ns-LTP M1 (50 μg/ ml) followed by ns-LTP M2 which offered 58% protection. Furthermore, peroxidase (POX) and lipoxigenase (LOX) enzymes related to plant resistance metabolism were also increased considerably after ns-LTP M1 treatment. POX activity was up to two folds when compared to susceptible control seedlings. Thus the present investigation suggests that the maize LTPs could enhance downy mildew disease resistance in pearl millet through the induction of defense mediated enzymes.

Development of SCAR marker associated with downy mildew disease resistance in pearl millet (Pennisetum glaucum L.).

Pearl Millet is an important crop coarse grain cereal crop in the semi arid tropics which is extremely susceptible to oomycete plant pathogen Sclerospora graminicola causing downy mildew (DM) disease. The aim of the current study is to breed resistance against downy mildew disease into high yielding cultivars of pearl millet. Hence, in the present work a sequence characterized amplified region (SCAR) marker was developed as a molecular screening tool to identify DM resistance source and presented here. Of the 27 inter simple sequence repeats (ISSR) decamer primers used to identify polymorphism amongst pearl millet genotypes ICMR-01007 (P1) and ICMR-01004 (P2) and their populations (F1 and F2), only one primer pair ISSR-22 produced polymorphic bands on ICMR-01004 producing 1.4 kb size. The PCR amplification of 1.4 kb band was found tightly linked to the resistant line of ICMR-01004 and also in F2 segregation population was in the ratio 3:1. This band was cloned, sequenced and candidate SCAR primer (SCAR ISSR 863 ) was designed. Segregant analysis of their F2 progeny revealed that the SCAR ISSR 863 marker was linked to downy mildew resistance linkage group (χ(2) 3:1 = 0.86, P = 0.22) with a genetic distance of 0.72 cM. This SCAR marker was further validated using diverse pearl millet lines of India and Africa. Results indicated that the SCAR ISSR 863 band was amplified in all the seven resistant lines and were absent in five susceptible lines. The confirmation of the ISSR-derived SCAR marker in different genetic backgrounds of pearl millet lines suggests that this marker can be exploited for DM resistance screening in pearl millet breeding programs.

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.

Cellulysin induces downy mildew disease resistance in pearl millet driven through defense response

The responses to cellulysin as an immune inducer in pearl millet that confers downy mildew resistance mediated through lipoxygenase (LOX), a jasmonate-dependent enzyme involved in defence signalling, are discussed in this paper. The susceptible pearl millet cultivar 7042S was treated with cellulysin at 10, 15, 20, 30 and 50 μg/ml concentrations. All tested concentrations showed enhanced seed germination and seedling vigour when compared with the untreated control. Maximum seed germination of 92 % and seedling vigour was obtained following 20 μg/ml cellulysin treatment. Significant (P < 0.05) downy mildew disease protection of 67 % and 71 % was observed when cellulysin was used at 20 μg/ml under greenhouse and field conditions, respectively. Further studies showed that the resistance induced by cellulysin treatment in pearl millet plant was systemic, required a minimum of 4 days to achieve maximum resistance development after pathogen inoculation seedling inoculation (five-day-old), and was sustained throughout the plant’s life. Plants raised from cellulysin-treated seeds and challenge inoculated at tillering (25-day-old) and inflorescence (45-day-old) showed persistence in resistance till the end of the crop period. A notable increase in LOX activity was observed in all the tested concentrations of cellulysin in plants inoculated with the pathogen at 24 h, compared to the control. However, a maximum 6-fold increase in LOX activity was noticed using a cellulysin concentration of 20 μg/ml 48 hours post inoculation. In contrast, glucanase (GLU) activity was high in control inoculated seedlings, but was low in cellulysin treated samples at all time intervals. The optimal cellulysin treatment (20 μg/ml) provided enhanced vegetative and reproductive parameters that resulted in higher yield compared to the untreated control.

Rhizosphere fungus Penicillium chrysogenum promotes growth and induces defence‐related genes and downy mildew disease resistance in pearl millet

Susceptible pearl millet seeds (cv 7042S) were treated with the plant growth promoting fungus Penicillium chrysogenum (PenC-JSB9) at 1 × 10(8) spores·ml(-1) to examine mRNA expression profiles of five defence responsive genes and test its ability to induce resistance to downy mildew caused by Sclerospora graminicola. PenC-JSB9 treatment at 1 × 10(8) CFU·ml(-1) for 6 h significantly enhanced seed germination (9.8- 89%), root length (4.08% to 5.1 cm), shoot length (18.9% to 7.77 cm) and reduced disease incidence (28%) in comparison with untreated controls. In planta colonisation of PenC-JSB9 showed that all three root segments (0-6 cm) and soil dilutions incubated on PDA produced extensive mycelial growth, however colonisation frequency of PenC-JSB9 was significantly higher in soil than in root segments. Spatiotemporal studies revealed that induction of resistance was triggered as early as 24 h and a minimum 2-3 days was optimal for total resistance to build up between inducer treatment and challenge inoculation in both experiments. In Northern blot analysis, transcript accumulation of resistant and PenC-JSB9 induced susceptible cultivars showed higher basal levels of defence gene expression than non-pretreated susceptible controls. Transcript accumulation in resistant seedlings challenge-inoculated with the pathogen showed maximum expression of CHS (3.5-fold increase) and Pr-1a (threefold increase) at 24 and 12 h, respectively. While PenC-JSB9 pretreated susceptible seedlings challenge-inoculated showed rapid and enhanced expression of LOX and POX at 48 h and for CHT at 24 h, whereas non-pretreated susceptible seedlings after pathogen inoculation showed weak expression of hybridised defence genes. Enhanced activation of defence genes by PenC-JSB9 suggests its role in elevated resistance against S. graminicola.

Thiamine seed treatment enhances LOX expression, promotes growth and induces downy mildew disease resistance in pearl millet

Seeds of pearl millet [Pennisetum glaucum (L). R.Br.] susceptible cv. 7042S were treated with thiamine at 5, 10, 15, 20 and 25 mM concentrations and growth promotion and downy mildew resistance were tested. Seed treatment with 20 mM thiamine resulted in 72 and 70 % disease protection under greenhouse and field conditions, respectively, and enhanced vegetative and reproductive growth parameters. Analysis of lipoxygenase (LOX) activity in inoculated pearl millet seedlings at different time intervals indicated that increased LOX activity was initiated at 3 h after inoculation (hai) and maximum activity was observed at 24 hai. Northern analysis showed that LOX mRNA transcript accumulation was higher in the resistant seedlings (cv. IP18292) than in susceptible seedlings. Thiamine seed treatment induces rapid LOX gene expression and results in significant disease protection against downy mildew disease.

Thiamine seed treatment enhances LOX expression, promotes growth and induces downy mildew disease resistance in pearl millet

Seeds of pearl millet [Pennisetum glaucum (L). R.Br.] susceptible cv. 7042S were treated with thiamine at 5, 10, 15, 20 and 25 mM concentrations and growth promotion and downy mildew resistance were tested. Seed treatment with 20 mM thiamine resulted in 72 and 70 % disease protection under greenhouse and field conditions, respectively, and enhanced vegetative and reproductive growth parameters. Analysis of lipoxygenase (LOX) activity in inoculated pearl millet seedlings at different time intervals indicated that increased LOX activity was initiated at 3 h after inoculation (hai) and maximum activity was observed at 24 hai. Northern analysis showed that LOX mRNA transcript accumulation was higher in the resistant seedlings (cv. IP18292) than in susceptible seedlings. Thiamine seed treatment induces rapid LOX gene expression and results in significant disease protection against downy mildew disease.

Biochemical events involved in downy mildew disease resistance in pearl millet in relation to H+-ATPase

Pearl millet (Pennisetum glaucum L. Br.) is the most important crop in India and Africa. Downy mildew disease of pearl millet caused by the oomycetous fungus Sclerospora graminicola (Sacc.) Schroet., is the major biological constraint in the production of pearl millet. Plasma membrane H+-ATPase is induced in resistant pearl millet against downy mildew pathogen. Sodium orthovanadate, an inhibitor of H+-ATPase, was used in this study to understand its effect on other known defence responses in pearl millet including H+-ATPase. Results suggest that vanadate down-regulates all defence responses tested, such as H+-ATPase (53 ± 5.0%), peroxidase (36 ± 5.6%), phenylalanine ammonia lyase (43 ± 4.5%), β-1,3 glucanase (25 ± 4.2%), lytic activity (32 ± 3.0%), hypersensitive response (57 ± 4.3%) and pathogen colonisation. These data indicate that the plasma membrane H+-ATPase may be a key step in the signaling pathway leading to defence activation in pearl millet against downy mildew disease.