Search

Maydis leaf blight, caused by Bipolaris maydis, is a serious foliar disease of maize distributed widely throughout the world and causing significant yield losses. The study aimed to describe stages of the infection process of B. maydis on maize leaves. The adaxial surfaces of maize leaves were inoculated with a conidial suspension of B. maydis and leaf samples were collected from 24 to 120 hrs after inoculation (hai). At 24 hai, the germ tubes from the germinated conidia and fungal hyphae attempted to penetrate the leaf through the stomata. These results provide new insight into the infection process of B. maydis on maize leaves and may contribute to the development of more effective management of maydis leaf blight.

Rice sheath blight, caused by Rhizoctonia solani, is one of the increasing concerns in rice causing severe economic losses worldwide. Chemical control measures are already in practice for the manag...

Black pepper-associated endophytic Pseudomonas putida BP25 displayed volatile-mediated antagonism against rice blast fungus Magnaporthe oryzae 1637. The major chemical fraction identified in the volatiles of Pseudomonas putida BP25 was 2-methylpyrazine and 2-ethyl-3,6-dimethylpyrazine; both of them inhibited all developmental stages such as conidial germination, mycelial growth, and sporulation of M. oryzae. To validate the antifungal activity of 2-methylpyrazine and 2-ethyl-3,6-dimethylpyrazine on blast disease, in planta experiments were conducted on rice seeds and seedlings. Blast disease incidence and disease severity on volatile-treated seedlings were significantly reduced as compared to mock. Seedlings that emerged from volatile-exposed seeds were analyzed for expression of candidate defense gene, OsPAD4, OsEDS1, OsPDF2.2, OsPR3, and OsPR1.1 by quantitative real-time PCR (qPCR). Seedlings exposed to volatiles showed significant induction of the OsPAD4 gene with both 2-ethyl-3,6-dimethylpyrazine and 2-methylpyrazine. Direct antifungal activity of pyrazine coupled with its defense elicitation capability can be harnessed for rice seed disinfection to ensure healthy, vigorous, and disease-free transplants.

An investigation employing a detached leaf assay was performed to evaluate the biocontrol efficacy of silver nanoparticles (AgNPs) augmented Calothrix elenkinii against Alternaria alternata infection in tomato. A dose of 50 mg l− 1 AgNPs was selected, which was based on chlorophyll accumulation (as an index of C. elenkinii growth), microscopic observations and biocidal potential of AgNPs against A. alternata. Higher leaf chlorophyll accumulation and lower endoglucanase activity were recorded in in the AgNPs, C. elenkinii and AgNPs augmented C. elenkinii-treated leaves, compared to pathogen challenge alone. Further, microscopic examination showed that these treatments had an alleviating role towards the damaging effects of A. alternata infection on chloroplasts and leaf structure. PCR based amplification using Internal Transcribed Spacers (ITS)-specific primers revealed no band in the treated samples, illustrating the absence of A. alternata, and the biocontrol efficacy of the treatments. Application of AgNPs, C. elenkinii and AgNPs augmented C. elenkinii imparted a protective effect against A. alternata, by inhibiting the growth of the pathogen in tomato leaves and modulating the growth and enzymatic activities of the host. This method proved valuable for gaining insights into the interplay between cyanobacterium, nanoparticle and pathogen-challenged leaves, and illustrated that AgNPs augmented C. elenkinii has the potential to be scaled up as an effective biocontrol option.

Banded leaf and sheath blight disease caused by Rhizoctonia solani f. sp. sasakii is a major constraint of Kharif maize. Wide host range of pathogen, its ability to survive as sclerotia under adverse environmental conditions and lack of resistant sources are some of the bottlenecks in its management. To reduce our dependence on chemicals, experiment was conducted at five hot-spots in India viz., Ludhiana (PAU and Ladhowal), Delhi, Karnal and Pantnagar centres to study the effect of leaf stripping method on disease severity and yield parameters of present day maize hybrids of different maturity groups as well as speciality corn cultivars. Per cent disease control achieved with leaf stripping treatment in different cultivars varied from 16.66 to 54.76% being highest at PAU, Ludhiana centre and lowest at Pantnagar centre. Maximum percent increase in yield was observed at Delhi centre (28.37%) closely followed by PAU, Ludhiana centre (28.23%). Positive correlation (r) was observed between mean per cent disease control and mean percent increase in yield.

The antimicrobial potential of cyanobacteria and metal nanoparticles has been explored for the control of phytopathogens, however, their interactions or synergy in a combined mode has not been studied. In the present investigation, the biocontrol potential of copper nanoparticles (CuNPs), cyanobacterium Calothrix elenkinii and copper nanoparticles augmented Calothrix elenkinii (CuNPs-Ce) were evaluated. Measures of disease severity indices, microbiological and physiological parameters in Fusarium solani infected tomato plants were evaluated, under greenhouse conditions. Application of C. elenkinii (Ce) and CuNPs alone showed 61–66% disease control efficacy, however, CuNPs-Ce showed higher efficacy of 76%. Similarly, augmentation enhanced the chitosanase activity by 10% and 7%, compared to CuNPs and C. elenkinii alone, respectively in pathogen challenged plants. Among the diseased plants, 1.3–1.6 fold increases in root length, root and shoot fresh weight were recorded in CuNPs-Ce treated plants, compared to control. The rhizosphere soil of diseased plants showed higher dehydrogenase activity, as compared to healthy plants. With the application of C. elenkinii, either alone, or augmented with CuNPs, the total PLFA content in soil increased significantly by 1.4–3.3 folds, compared to the control. However, it reduced in soils treated with chemical control Bavistin, reflecting its negative effects on soil microbial communities. The application of CuNPs or C. elenkinii alone or CuNPs-Ce not only reduced the disease severity, but also improved plant vigour. In future, efforts should focus towards exploiting the synergistic behavior of CuNPs-Ce as multifaceted biocontrol agents to control Fusarium root rot in tomato crop and minimize the dose for deployment effectively.

Maydis leaf blight (MLB) caused by Cochliobolus heterostrophus is one of the most important fungal diseases of maize. A study was conducted for phenotypical characterization of ten Indian maize inbred lines, which were grouped based on phenotyping and their morpho-physiological attributes against MLB disease. On the basis of phenotyping, they were categorized into five resistant inbreds viz., SC-7-2-1-2-6-1, SC24 (92)-2-3-2-1-1, DMSC-16-2, V-351-1-4 and HKI MBR-139-2, and five susceptible inbreds viz., CM-119, DMSC-28, HKI PC-8, HKI 1040-C2 and V341. The leaf hair density was high in resistant genotypes (249.79/microscopic field, at 100×) and significantly less in susceptible genotypes (99.33/microscopic field at 100×). Stomata count was found less (6.12/microscopic field, at 400×) in resistant genotypes as compared to susceptible genotypes (10.56/microscopic field at 400×). The rate of photosynthesis was high in uninoculated control plant than in the inoculated plants. Under inoculated conditions photosynthetic rate was significantly high in resistant lines than the susceptible inbred lines which were gradually reduced with the advancement of time. The transpiration rate of inoculated plants was also higher than the control plants at 5 days after inoculation (DAI), whereas it was decreased in both inoculated and control plants at 40 DAI. Elevated level of transpiration was detected in susceptible genotypes under inoculated condition. Upon inoculation stomatal conductance was decreased with the passage of time. However, there was a differential behavior in the stomatal conductance recorded in the tested maize inbred lines under control conditions.

Knowledge on the genetics of maydis leaf blight (MLB) is crucial to breed the resistant maize cultivars to combat disease epidemics as a sustainable and cost-effective approach. The present investigation was framed to understand the genetics of MLB resistance in subtropical maize. Two contrasting genotypes CM119 (susceptible) and SC-7-2-1-2-6-1 (resistant) were used to generate six genetic populations, namely P1, P2, F1, F2, BC1P1 and BC1P2, and evaluated in three target environments for MLB resistance under artificial epiphytotic condition. The CM119 and SC-7-2-1-2-6-1 showed susceptible and resistant reactions with mean disease reaction of 3.89-3.98 and 1.88-2.00, respectively. The derived generations, namely F1, F2, BC1P1 and BC1P2 showed mean disease reaction of 2.15-2.28, 2.44-2.51, 2.19-2.24 and 2.22-2.28, respectively in the test locations. The segregating generations (F2: 0.35-0.37; BC1P1: 0.24-0.29 and BC1P2: 0.17-0.20) showed variation for MLB disease resistance over the parental and first filial generations (P1: 0.11-0.17; P2: 0.08-0.13 and F1: 0.12-0.14). The genetic analysis of MLB resistance revealed the nonallelic interactions of duplicate epistasis type across the test locations. Among the gene interactions, dominance x dominance [l] effect was predominant over additive x additive [i] and additive x dominance [j] effects. The segregation analysis and the prediction of the number of major loci revealed at least two major genes associated with MLB tolerance in subtropical maize. Our investigation paved the foundation for the improvement of subtropical maize germplasm of MLB resistance.

In spite of modern crop protection measures, the overall crop losses due to pests and pathogens are huge. Rhizoctonia solani, Macrophomina phaseolina, Sclerotium rolfsii, and Fusarium oxysporum are...

The biocontrol efficacy of a cyanobacterium Calothrix elenkinii (Ce), silver nanoparticles (AgNPs) and their augmented complex (AgNPs-Ce) was evaluated. Foliar application of AgNPs-Ce reduced the disease severity by 47–58%, along with significant increases of 44–45%, 40–46% and 23–33% in leaf chlorophyll, carotenoid content, and polyphenol oxidase activity in the A. alternata infected tomato plants. A significant reduction in the pathogen load was recorded, both by plate counts and microscopic observations in the AgNPs, Ce and AgNPs-Ce treatments, while AgNPs-Ce also effectively reduced ergosterol content by 63–79%. Amplification using PCR-ITS primers revealed very faint bands or none in the AgNPs-Ce treated leaves, illustrating the inhibition of fungal growth. Significantly higher yield was recorded in the pathogen challenged plants receiving AgNPs-Ce, AgNPs, and Ce treatments. Higher expression of elicited antioxidant enzymes, along with enhanced plant growth attributes and lowered fungal load highlight the biocontrol potential of AgNPs-Ce treatment in A. alternata infected plants. This synergistic association can be explored as a promising biocontrol option against A. alternata challenged tomato plants under various agroclimatic conditions.

Anthracnose disease incited by Colletotrichum gloeosporioides reduces the yield and market-quality of mangoes worldwide. Previous studies have indicated the potential of diverse antimicrobial volatile organic compounds emitted by the endophytic Pseudomonas putida BP25 for plant disease suppression. In the present study, we have explored native-volatiles of Pseudomonas putida BP25 and a synthetic-volatile, 2-ethyl-5-methylpyrazine, earlier identified in volatilome of Pseudomonas putida BP25 for reducing anthracnose in mango cultivar, Amrapali. The bacterial volatile compounds displayed fungistatic effects on the mycelial growth of Colletotrichum gloeosporioides in vitro. In planta prophylactic fumigation of mangoes with native-volatiles or the bacterial origin synthetic 2-ethyl-5-methylpyrazine for 24 h at 25 °C showed a reduction of anthracnose severity (>76 % reduction over mock) on fruit. Additionally, physicochemical qualities such as total-soluble solids, total-phenols, total-proline, total-carotenoid, total-flavonoid, and fruit-firmness were increased in fumigated fruit as compared to untreated mangoes. Anthracnose suppression coupled with the fruit quality enhancement by bacterial volatiles and synthetic 2-ethyl-5-methylpyrazine presents a new opportunity for postharvest management of mango during the storage, transit, and trade.

Cyanobacteria are widely used as biofertilizers and their effectiveness is influenced by the type of carrier, which in turn, dictates the viability of the inocula being introduced for improving plant growth. Soil-less substrates were explored as carriers in the present investigation; the potential of perlite (P), cocopeat (C) and vermiculite (V), individually and in combinations (1:1) such as — perlite: cocopeat, perlite: vermiculite, cocopeat: vermiculite, and perlite: cocopeat: vermiculite (1:1:1.) was screened. Four agriculturally beneficial cyanobacterial cultures/biofilms — Calothrix elenkinii, Anabaena laxa, Anabaena torulosa-T . viride (An-Tr) and A. torulosa-Bacillus sp. (An-Bs) were characterised and shelf-life evaluated after augmenting them to such substrates. Time course analyses after 2, 10 and 20 weeks illustrated that chlorophyll, as an index of photosynthetic biomass and population counts of the bacterial/fungal partner of biofilms enhanced significantly. For their use as disease suppressive options, fungicidal activity against phytopathogenic fungi was tested and found to be enhanced with the period of incubation. P: C and C:V were identified as most promising, and augmentation with cyanobacteria/biofilms showed significant cyanobacterial colonisation in the substrate after 20 weeks, illustrating their extended shelf-life. PCR amplification using 16S cyanobacterial, bacterial and fungal ITS directed primers confirmed the utility of these substrates. Seed germination test with maize, radish and wheat seeds showed marginal increases as a result of augmentation, with no phytotoxicity, and these novel mixes need to be tested in pot and field experiments as inoculants.

Post-flowering stalk rot (PFSR) complex caused by Fusarium verticillioides (Sacc.) and Macrophomina phaseolina (Tassi) Goid, is among the important constraints that limits the productivity of maize ( Zea mays L.). The absence of high levels of stable resistant sources to the pathogens has necessitated the continued search and identification of new sources of resistance. The principal goal of this work was once to identify new sources of resistance to PFSR and validate their stability across multi-environments by multi-year testing. A set of 80 elite inbred lines screened in the field against PFSR for three consecutive years at four hotspots in India (Hyderabad, Ludhiana, New Delhi and Udaipur) under artificially created disease epiphytotics. The scores on the scale of 1 to 9 based on the disease reaction were recorded by splitting the stems of each plant. Significant (p=

Leaf rot of cauliflower caused by Choanephora cucurbitarum is reported for the first time in India. Koch’s postulates were fulfilled for the first time for this fungus-host association demonstrating that C. cucurbitarum, known to be the pathogen behind soft rot on numerous hosts is also a pathogen of cauliflower.

A study was undertaken to evaluate the decline of the residues of pyridalyl in tomatoes grown in two different cultivation systems: open field (conventional cultivation) and net house (pot experiment). Field experiment was conducted with commercial (10 EC) and nanoformulation of pyridalyl on tomato crop. Tomato plants were subjected to pesticide spray, when fruits were close to ripeness. Fruit samples were taken periodically and cleaned up using QuEChERS methodology, and the residue of pyridalyl was analyzed by ultrahigh-performance liquid chromatography (UHPLC). It dissipated in tomato fruit following the first-order kinetics. In field, average initial deposit of pyridalyl in tomato was observed to be 0.222 and 0.371 μg g(-1) at recommended and double the recommended application rate, respectively, using nanoformulation while it was 0.223 and 0.393 μg g(-1) on using commercial formulation, respectively. The half-life (t1/2) value of nanopyridalyl in tomato fruit was 2.8 and 3.2 days while for commercial formulation, it was 2.5 and 2.6 days for recommended and double the recommended dose, respectively. In India, maximum residue limit (MRL) on tomato has not been fixed for pyridalyl but its residues were always below European MRLs (5 μg g(-1)) on tomato at both application rates. The results of terminal residue showed that pyridalyl residues were below the available MRL. Low residues in tomatoes suggested that this pesticide is safe to use under the recommended dosage. No statistical differences were observed between the cultivation systems in relation to the residue levels of pyridalyl.

Two highly resistant genotypes of wheat viz. HD 29 and DWL 5023 and one highly susceptible genotype WL 711 against Karnal bunt (KB) disease were studied for their difference in morphological features, growth para­meters and isozyme patterns. It revealed that both the resistant geno­types were bearing higher number of spikelets with short internodes in the spike as compared to the susceptible genotype. In contrast WL 711 had significantly higher number of stomata in sheaths, flag leaf base, booted glumes and rachis. The hair count was significantly high on the glumes and rachis of HD 29 and DWL 5023 than on WL 711. HD 29 possessed significantly narrow glume opening distance between lemma and palea followed by DWL 5023 and WL 711. Moreover, the period between ear emergence and anthesis was short in HD 29 followed by DWL 5023 and WL 711. Out of the twelve isozyme systems performed using seeds and seedlings of the genotypes, majority of them gave rise to comparatively higher number of bands in HD 29 and DWL 5...

The effects of the highly aggressive isolate KB-2 of the Karnal bunt pathogen (Neovossia indica) on phenol metabolism, peroxidase (POX) and its isoenzymes were studied in wheat. Two resistant genotypes, HD 29 of bread wheat (Triticum aestivum) and DWL 5023 of durum wheat (T. durum), and one susceptible bread wheat, WL 711, were used. In the bread wheats, total phenols reached a maximum 2 days after inoculation (d.a.i.). In the resistant durum line, total phenols did not change significantly for 6 d.a.i., but declined significantly at 10 d.a.i. Three phenolic compounds, caffeic acid, l-tyrosine and hydroquinone, were detected using thin-layer chromatography. The first two were detected at all times at and after inoculation, but hydroquinone was detected only in the resistant wheats at 6 d.a.i. The activity of POX was highest at 2 d.a.i. in the two resistant wheats, but increased more slowly to a peak at 6 d.a.i. in the susceptible wheat. The number of isoenzymes of POX detected by polyacrylamide gel electrophoresis (PAGE) changed after inoculation with KB-2. The maximum number of isoenzymes occurred at 2 d.a.i. in the two resistant wheats and at 6 d.a.i. in the susceptible wheat. Although the isoenzymes detected in seedlings were not identical to those detected in seeds, the PAGE banding patterns of seeds and seedlings were the same for the two resistant wheats. The potential use of the additional band at a relative mobility of 0·42 in seeds and 0·28 in seedlings as markers for Karnal bunt resistance is discussed.