Hypersensitive reaction and P/HRGP accumulation is modulated by nitric oxide through hydrogen peroxide in pearl millet during Sclerospora graminicola infection

Priming of pearl millet seedlings with nitric oxide (NO) donors sodium nitroprusside (SNP) and S-nitrosoglutathione (SNOG) induced hypersensitive reactions (HR) and accumulation of Proline/Hydroxyproline-rich glycoprotein (P/HRGP) during infection by downy mildew pathogen Sclerospora graminicola. Such defense responses were specifically altered by concentration of NO donors resulting in the modulation of endogenous NO in seedling tissues. The stoichiometric interactions of NO and hydrogen peroxide (H₂O₂) when followed in relation to HR and P/HRGP accumulation, the degree of defense response varied with H₂O₂ level, the latter being largely influenced by NO concentration. Therefore, balancing NO and H₂O₂ is vital for optimum expression of defense responses for imparting disease resistance.     

Induction of β-1,3-glucanase in Seedlings of Pearl Millet in Response to Infection by Sclerospora graminicola

Differential resistance of pearl millet cultivars to downy mildew disease was correlated with the levels of -1,3-glucanase in their seeds. Higher activity of the enzyme in highly resistant cultivars and lower activity in the highly susceptible ones suggested the possible use of -1,3-glucanase as a biochemical marker for screening pearl millet cultivars for downy mildew disease. Inoculation of seedlings with the downy mildew pathogen Sclerospora graminicola resulted in increased enzyme levels in resistant cultivars. Mesocotyl and shoot regions of seedlings recorded higher levels of enzyme than the root. Isoelectric focusing revealed four basic isoforms with pI 9.6, 9.0, 8.9 and 8.2 and two acidic isoforms with pI 4.9 and 6.2 of -1,3-glucanase in pearl millet. The pI 9.6 isoform was a major isoform of the enzyme in the pearl millet seedlings with a probable developmental function. Isoforms pI 6.2 and pI 8.2 appeared to be involved in resistance and pI 4.9 isoform seemed to be involved in pathogenesis of pearl millet-downy mildew.     

Chitosan enhances disease resistance in pearl millet against downy mildew caused by Sclerospora graminicola and defence-related enzyme activation

BACKGROUND: The present study investigated the effect of chitosan seed priming on the induction of disease resistance in pearl millet against downy mildew disease caused by Sclerospora graminicola (Sacc.) Schroet. RESULTS: Pearl millet seeds were primed with chitosan at different concentrations: 0.5, 1.5, 2.5 and 3 g kg^?1 seed. Of the different concentrations, 2.5 g kg^?1 was found to be optimum, with enhanced seed germination of 99% and seedling vigour of 1782, whereas the untreated control recorded values of 87% and 1465 respectively. At optimum concentration, chitosan did not inhibit sporulation and release of zoospores from sporangia. Furthermore, pearl millet seedlings raised after seed treatment with chitosan showed an increased level of the defence‐related enzymes chitosanase and peroxidase as compared with the untreated pearl millet seedlings on downy mildew pathogen inoculation. The effect of chitosan in reducing downy mildew incidence was evaluated in both greenhouse and field conditions, in which respectively 79.08 and 75.8% disease protection was obtained. CONCLUSION: Chitosan was effective in protecting pearl millet plants against downy mildew under both greenhouse and field conditions by inducing resistance against the pathogen. Thus, chitosan formulation can be recommended for seed treatment in the management of downy mildew disease. Copyright © 2008 Society of Chemical Industry     

Screening pearl millet cultivars by ELISA for resistance to downy mildew disease

In an earlier study, we described identification of a protein from a virulent pathotype of Sclerospora graminicola , the binding reaction of which differentiated susceptible and resistant cultivars of pearl millet to downy mildew disease. This protein and corresponding antibody were used in an enzyme-linked immunosorbent assay (ELISA) to screen suspension cells of pearl millet cultivars for their resistance to the downy mildew pathogen. Screening results for 31 pearl millet cultivars correlated positively with the established field screening method.     

Differential induction of superoxide dismutase in downy mildew-resistant and -susceptible genotypes of pearl millet

Differential induction of superoxide dismutase (SOD) in downy mildew-resistant and -susceptible genotypes of pearl millet ( Pennisetum glaucum ) was observed on inoculation with Sclerospora graminicola . SOD activity was studied in resistant (IP18292) and susceptible (23B) pearl millet seedlings inoculated with S. graminicola . SOD activity increased by 2·3-fold in resistant seedlings upon inoculation. SOD activity was greatest in roots, with a specific activity of 3182 U per mg protein, after inoculation. SOD activity increased in all the resistant genotypes upon inoculation with S. graminicola . Native PAGE analysis showed four isozymes of SOD, three of which (SOD-1, -2 and -4) were Cu/Zn-SOD, whereas isozyme SOD-3 was Mn-SOD. This study also revealed increased intensity of all four isozymes of SOD in the resistant genotype upon inoculation. The involvement of SOD in pearl millet (host)–downy mildew pathogen interaction is discussed.     

Note: Proline — An inducer of resistance against pearl millet downy mildew disease caused by<Emphasis Type="Italic">Sclerospora graminicola</Emphasis>

In an attempt to find a suitable alternative to the otherwise perilous chemical control strategy of disease management, the amino acid proline was evaluated for its efficiency to elicit resistance in pearl millet (Pennisetum glaucum (L.) R. Br.) against downy mildew disease caused bySclerospora graminicola (Sacc.) Schroet both under greenhouse and field conditions. Proline treatment to seeds at 50 mM concentration for 3 h, significantly enhanced the seed germination and seedling vigor of pearl millet in comparison with the control. The same concentration and duration of seed treatment protected the pearl millet plants from downy mildew by offering 58% protection under greenhouse and 67% protection under field conditions. Studies revealed that 3 days were required for proline-treated plants to develop resistance, which was systemic and was sustained throughout the life of the plants. Apart from disease protection, proline was also found effective in enhancing vegetative and reproductive growth of the plants, as evidenced by the increase in height, fresh weight, leaf area, tillering capacity, 1000-seed weight and grain yield in comparison with the control plants. http://www.phytoparasitica.org posting Oct. 3, 2004.     

Unsaturated fatty acids from zoospores of <Emphasis Type="Italic">Sclerospora graminicola</Emphasis> induce resistance in pearl millet

Downy mildew of pearl millet, caused by Sclerospora graminicola, is a devastating disease, resulting in high economic losses in the semi-arid regions of the world. Recently, induction of host plant resistance using biotic and abiotic inducers are included among disease management practices as an eco-friendly approach. Unsaturated fatty acids are considered as a new generation of plant disease resistance inducers. In the present study, six unsaturated fatty acids, viz. docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), arachidonic acid (AA), linolenic acid, linoleic acid and oleic acid, all originally detected in the zoospores of S. graminicola,were applied to seeds of susceptible cultivars of pearl millet to examine their ability to protect against downy mildew under greenhouse and field conditions. In greenhouse experiments, EPA and AA induced a maximum of 78.6% and 76.5% protection, whereas linoleic acid, DHA and linolenic acid provided up to 66.3%, 61.2% and 24.5% protection, respectively. Oleic acid was not effective in protecting pearl millet (only 5.1% protection). A time interval of four days between treatment of seeds and challenge inoculation was required to obtain optimum protection. Plants raised from treated seeds and challenge inoculated at the tillering and inflorescence stages showed enhanced resistance, resulting in higher grain yield compared to untreated plants of the same cultivar. Chitinase activity was found to be higher in susceptible seedlings of pearl millet after treatment with the fatty acids and pathogen inoculation than in seedlings only inoculated with the pathogen. This indicates that host defence responses are activated and thus that induced resistance is involved in the protection observed. The role of unsaturated fatty acids as activators of resistance against downy mildew in pearl millet is discussed.     

Seed treatment with beta-aminobutyric acid protects Pennisetum glaucum systemically from Sclerospora graminicola

beta-Aminobutyric acid (BABA) treatment of pearl millet [Pennisetum glaucum (L) R Br] seeds influenced seedling vigour and protected the seedlings from downy mildew disease caused by the oomycetous biotropic fungus Sclerospora graminicola (Sacc) Schroet. Of the different concentrations of BABA tested, viz 25, 50, 75 and 100 mM, seeds treated with 50 mM for 6 h resulted in the maximum of 1428 seedling vigour and showed 23% disease incidence in comparison with the control which recorded a seedling vigour of 1260 and 98% disease incidence i.e. 75% protection from disease. Seeds treated with BABA when challenged for downy mildew disease using zoospores of S graminicola required 48 h after inducer treatment to develop maximum resistance. Durability of induced resistance was also tested in plants raised from seeds treated with the inducer and identified as resistant, by second challenge inoculation with the downy mildew pathogen at tillers and inflorescence axes. Reduced disease incidence of only 10 and 12% in these plants, compared with 71 and 76% disease in control plants inoculated at the tillers and inflorescence axes, respectively, suggested that resistance induced in seeds with BABA remained operative through vegetative and reproductive growth of pearl millet plants. Induction of resistance by seed treatment with BABA enhanced vegetative growth, viz height, fresh weight, leaf area and tillering, and reproductive growth, viz early flowering, number of productive ear heads and 1000 seed weight. Studies on induction of resistance in different cultivars of pearl millet with varying resistance reaction to downy mildew indicated that the protection offered by BABA is independent of the nature of cultivars used and not dependent on their constitutive resistance.     

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

BACKGROUND: 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. RESULTS: 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. CONCLUSION: 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. Copyright © 2009 Society of Chemical Industry     

Purification of an infection-related acidic peroxidase from pearl millet seedlings

Higher basal level of peroxidase activity was observed in highly resistant pearl millet cultivar IP 18292. Upon inoculation with downy mildew pathogen, Sclerospora graminicola, up to 60% increase in peroxidase activity was observed in highly resistant seedlings over the period of time. Iso-electric focusing analysis revealed that, two acidic isozymes of peroxidase with the pI of 5.9 and 5.1 present only in IP 18292 pearl millet seedlings. Upon inoculation with downy mildew pathogen, accumulation of these to isozymes was increased. These results indicated the possible involvement of acidic peroxidase in pearl millet defense. To study the nature of the acidic peroxidase which increases upon inoculation was purified from seedlings of highly resistant pearl millet cultivar using DEAE–Sepharose and Sephadex G-100 columns. The purified enzyme has a molecular weight of 21.8 kDa on SDS–PAGE and has a pI of 5.1. The optimum pH for maximum peroxidase activity was found to be at pH 7.0 and was resistant to high temperature (27–60 °C). The K_m for H₂O₂ and V_max of the enzyme reaction were 5.26 mM and 322.58 units, respectively. Purified peroxidase enzyme was found to be CaCl₂ dependent and both MgCl₂ and ZnCl₂ showed inhibitory effect on enzyme activity. Sodium azide and EDTA inhibited the enzyme and EGTA found to be specific inhibitor of peroxidase.     

The epidemiology, variability and control of the downy mildews of pearl millet and sorghum, with particular reference to Africa

Sorghum downy mildew ( Peronosclerospora sorghi ) infecting sorghum and maize, and pearl millet downy mildew ( Sclerospora graminicola ) infecting pearl millet can cause considerable yield loss in Africa. The last 15 years have witnessed an increase in knowledge of the biology, epidemiology and control of these two pathogens. Much information has been obtained on the effect of environmental factors on disease epidemiology, spore production and dispersal. Molecular techniques applied to study pathogenic variability have aided in defining relationships among these pathogens, although scope of the work is limited. Knowledge of the genetics and inheritance of resistance, and of resistance mechanisms, has also increased. This review presents the current state of knowledge of both downy mildew pathogens, with focus on their status on sorghum and pearl millet in Africa. Despite the advances in knowledge over the last 15 years, these downy mildews remain important constraints to sustainable crop production in the semi-arid regions of Africa. In some cases information obtained in Asia and the Americas can be extrapolated to Africa but care must be taken in ensuring its applicability. Priorities for future research relevant for Africa are proposed and discussed.     

Ribonucleases in the Seedlings of Pearl Millet and their Involvement in Resistance Against Downy Mildew Disease

Tissue homogenates of pearl millet seedlings (cultivars HB 3, 843 B, ICMP 451 and IP 18292), with varying degree of resistance to downy mildew disease were tested for ribonuclease (RNase) enzyme activity and the profile of major RNase isozymes by substrate based gel assay. Polyacrylamide gel electrophoresis (PAGE) of the four pearl millet homogenates revealed 15–20 isozymes, varying in size from 6.5 to 121.0kDa. Most of the RNases were highly active between pH 6 and 8 with maximum activity at pH 7. Tissue specific expression of RNase was observed with more activity in the root, i.e., 38.84, 59.61, 39.90 and 49.23 units in HB 3, 843 B, ICMP 451 and IP 18292, respectively than in shoot 11.54, 9.95, 9.46 and 9.49 units in HB 3, 843 B, ICMP 451 and IP 18292, respectively. Effect of metal ions on the RNase profile indicates Zn⁺⁺ at 2, 20 and 200M concentrations to be inhibitory. Ca⁺⁺ and Mg⁺⁺ at 1mM concentration enhanced the enzyme activity while at 10mM inhibition of enzyme activity was observed. Inoculation with the downy mildew pathogen Sclerospora graminicola reduced RNase activity by 4–13% in compatible interactions while in incompatible combinations, the enzyme activity increased by 10–27%. The significance of RNase in pearl millet-downy mildew interaction and its involvement of in systemic acquired resistance of pearl millet against the downy mildew pathogen are discussed.     

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.     

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.     

不同栽培模式下葡萄霜霉病菌遗传结构的时间动态分析

为明确不同栽培模式下葡萄霜霉病菌Plasmopara viticola的遗传结构、遗传多样性及遗传分化水平,于2014-2015年定期采集露地和避雨2种栽培模式下的葡萄霜霉病菌菌株,利用6对SSR引物对该病菌基因型、遗传多样性及遗传分化进行对比分析。结果表明,露地和避雨栽培模式下葡萄霜霉病菌群体的Nei’s基因多样性指数大于0.14,香农多样性指数大于0.31,2种栽培模式下群体具有丰富的遗传多样性,但避雨栽培模式可显著降低群体等位基因数和等位基因频率。露地栽培模式下该病菌群体的流行模式呈现中等水平无性繁殖,2年初侵染和再侵染对病害流行的贡献率分别约占26.1%和73.9%;避雨栽培模式下葡萄霜霉病菌群体的流行模式则呈现高等水平无性繁殖,初侵染和再侵染对病害流行的贡献率分别约占4.3%和95.7%。卵孢子的形成对于葡萄霜霉病菌种群遗传变异和有效越冬起着关键的作用。2014-2015年露地栽培模式下葡萄霜霉病菌群体的主效流行基因型对病害流行的贡献率分别为44.5%和51.8%;而其在避雨栽培模式下葡萄霜霉病菌群体的贡献率分别可达84.2%和87.1%。同一年份的露地和避雨栽培模式下葡萄霜霉病菌群体的主效基因型种类相同,2个群体间的等位基因频率呈现显著正相关性,且二者之间存在频繁的基因交流,推测避雨栽培模式下葡萄霜霉病的初侵染源自于避雨设施附近的露地栽培病株上再侵染形成的飞散传播孢子囊。     

The reliability of leaf bioassays for predicting disease resistance on fruit: a case study on grapevine resistance to downy and powdery mildew

This study was designed to assess the reliability of grapevine leaf bioassays for predicting disease resistance on fruit in the field. The efficacy of various grapevine quantitative trait loci (QTLs) for conferring resistance to downy and powdery mildew was evaluated in bioassays and in a 2‐year field experiment for downy mildew. The resistance genes studied were inherited from Muscadinia rotundifolia (Rpv1 and Run1) and from American Vitis species through cv. Regent (QTLRgP and QTLRgD). In bioassays, genotypes carrying Run1 blocked powdery mildew development at early stages. Genotypes combining Run1 with QTLRgP displayed no greater level of resistance. For downy mildew, genotypes carrying Rpv1 and/or QTLRgD were more resistant than the susceptible cv. Merlot, and showed a high level of leaf resistance in the field (<10% severity). Disease levels on bunches were much higher than those on leaves, with a high variability between Rpv1 genotypes (1–48%). A Bayesian decision theory framework predicted that an OIV‐452 threshold of 5 in leaf bioassays allowed accurate selection of grapevine genotypes (P = 0·83) with satisfactory disease severity on bunches. Therefore, this study validates that the use of early bioassays on leaves, as currently performed by grapevine breeders, ensures a satisfactory level of resistance to downy mildew of bunches in the field.     

Induction of resistance against downy mildew pathogen in pearl millet by a synthetic jasmonate analogon

The synthetic 1-oxo-indanoyl-l-isoleucine methyl ester (Ind-Ile-Me) represents a highly active mimic of octadecanoic phytohormones, which are involved in plant defenses against pathogens and pests. Seed treatments and foliar spray with Ind-Ile-Me were tested for induced resistance against downy mildew disease caused by the phytopathogenic oomycete Sclerospora graminicola in pearl millet (Pennisetum glaucum) under greenhouse and field conditions. Under greenhouse conditions, a 50% protection level was achieved after seed treatment. Seed treatment in combination with foliar spray resulted in 60% protection. The induction of resistance was correlated with the enhanced activities of defense-related proteins such as phenylalanine-ammonia-lyase, peroxidase, and enhanced level of hydroxyproline-rich glycoproteins. Under field conditions, a maximum protection of 62% was recorded upon seed treatment along with foliar spray. Hence, it infers that Ind-Ile-Me can be used as a valuable protection compound at least in downy mildew disease management.     

Influence of dosage,storage time and temperature on efficacy of metalaxyl-treated seed for the control of pearl millet downy mildew

Metalaxyl (Apron 35WS) as a seed treatment has been used extensively to control downy mildew (caused by Sclerospora graminicola) in pearl millet in India. However, the extent of disease control has varied across cultivars, years and locations. We investigated the effects of fungicide dosage, storage time and storage temperature of metalaxyl-treated seed on disease incidence in four pearl millet lines having varying levels of resistance. A linear relationship was found between fungicide dosage (0.5, 1.5 and 2 g a.i. kg⁻¹ seed) and reduction in disease incidence up to 40 days after emergence in all the lines. The normal fungicide dose (2 g a.i. kg⁻¹ seed) protected the crop for up to 20, 40 and 50 days after emergence in highly susceptible (7042S), moderately susceptible (4042R), and moderately resistant (ICMP 451) lines, respectively. However, the quarter and half the normal dosage of fungicide provided protection only up to 20 days after emergence in 7042R and 40 days after emergence in ICMP 451. Storage duration of metalaxyl-treated seed (2 g a.i. kg⁻¹) up to 9 months at 25 ± 2°C did not affect fungicide efficacy. Storage temperatures (5, 25 and 40°C) and duration (30, 60 and 90 days) of metalaxyl-treated seed (2 g a.i. kg⁻¹) showed differential effects in two pearl millet lines 7042S and 843B with downy mildew incidence being significantly lower in 7042S than in 843B. Metalaxyl-treated seed of 7042S and 843B stored at 40°C for different durations showed phytotoxic effects and it was more pronounced in 843B stored for 60 and 90 days where seed germination was inhibited in pot soil.     

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.     

Pre-inoculation with Hyaloperonospora parasitica reduces incubation period and increases severity of disease caused by Albugo candida in a Brassica juncea variety resistant to downy mildew

Studies were undertaken to determine any interaction of an asymptomatic isolate of Hyaloperonospora parasitica (downy mildew) with a virulent isolate of Albugo candida (white rust) and Brassica juncea. White rust symptoms appeared 4 days earlier and were significantly more severe when a variety of B. juncea resistant to downy mildew but highly susceptible to white rust was first inoculated with A. candida followed 10 days later with H. parasitica. DNA extractions of tissues indicated H. parasitica had colonized the asymptomatic plants systemically. These are the first reports of (a) the systemic colonization by H. parasitica in a host resistant to downy mildew, and (b) the increase in susceptibility of a Brassica to white rust disease from asymptomatic colonization by H. parasitica.