Kunal Mandal

A novel pathovar of Xanthomonas axonopodis causes gumming of Guggal (Commiphora wightii)

Guggal (Commiphora wightii (Arnott) Bhandari comb. nov.) is a small tree which is tapped for medicinally important oleo–gum–resin. Naturally infected plant oozes oleo–gum–resin from its trunk and primary branches. However, in either case, the plant dies slowly after oozing. A bacterium was established to be responsible for these phenomena. Four isolates of this bacterium were characterised by biochemical tests, Biolog GN2 microplate reaction, rDNA sequencing, which suggested that the pathogen belonged to the genus Xanthomonas. However, phylogenetic analysis based on chaperone protein (dnaK) gene, TonB–dependent receptor (fyuA) gene, DNA gyrase B (gyrB) gene and RNA polymerase sigma factor (rpoD) gene sequences placed it as a member of X. axonopodis 9.2 rep–PCR/DNA–DNA homology cluster close to X. perforans, X. alfalfae and X. euvesicatoria. Further elucidation of phylogenetic position of the test strains was achieved from a gyrB based tree considering sequences from 71 representative strains. Test strains were confirmed to be members of X. axonopodis. These had very narrow infectivity limited to Commiphora spp. Hence, we propose a novel pathovar, X. axonopodis pv. commiphoreae pv. nov. as the cause of gum oozing in guggal. Pathotype is DXA 01 = CFBP 7580 = LMG 26789.

Scientific analysis of indigenous techniques for guggal (Commiphora wightii) tapping in India

Guggal, a threatened species that is endemic to western India, is tapped to extract medicinally important oleo-gum-resin (guggul). However, the plant dies after gum exudation. The indigenous tapping techniques used by local people were examined in Gujarat, India to discover the scientific basis behind these techniques: selection of gum inducer, season of tapping, and plant parts to be tapped. First, the presence of Xanthomonas axonopodis pv. commiphorae (Xac) in the gum suspension used for tapping was established. This bacterium induces gum oozing from the tapped plants and later, causes them to die off. The population of Xac in gum was found to decrease with the age of the gum. With that, fresh gum increased the tapping success. Second, local people preferred tapping during the warm season, which we validated by determining that Xac growth was best at 30 °C. Tapping during September (mean temperature 25.7–30 °C) clearly favoured growth of the pathogen and yielded maximum guggul. Multiple tapping on a mature tree ensured maximum gum extraction before its death. Finally, application of indigenous technology under natural plant stands by the local people ensured availability of this important raw drug for consumption. Our study established that the age-old traditional methods have a strong scientific basis. However, it is imperative to formulate strategies based on contemporary scientific understanding to protect this natural resource before it becomes extinct.

In planta detection of Macrophomina phaseolina from jute (Corchorus olitorius) by a sodium acetate-based direct PCR method

Macrophomina phaseolina (Tassi) Goid. is the most important pathogen of jute and primarily causes seedling blight, leaf spot and stem rot. The pathogen was detected from field samples by a simple method of direct PCR (dPCR) which obviates the steps of DNA extraction. The leaf bits were treated with a lysis buffer at 65°C for 25 min, whereas the stem pieces were initially incubated at 65°C for 5 min followed by incubation at 60°C for 25 min and the lysate was used as PCR template. Based on the type of tissue, the composition and concentration of lysis buffer systems were optimized. For leaf samples the optimized buffer system composed of 20 mmol l-1 tris (hydroxymethyl aminomethane (Tris)-Cl (pH 8.0), 1.5 mmol l-1 ethylene diamine tetra acetate (EDTA) (pH 8.0), 1.4 mol l-1 sodium acetate and 200 μg/ml proteinase K. Further, 3% PVP (w/v) and β-mercaptoethanol (1% w/v) were added into the buffer. In case of stem samples, PVP was not applied and higher concentrations were used for other components. M. phaseolina could be detected from both leaf and stem samples generating amplicon of 350 bp. This is the first report of detecting M. phaseolina by a direct PCR method without DNA extraction.

First report of downy mildew on Lepidium sativum in India

Downy mildew caused by Hyaloperonospora parasitica on different members of Brassicaceae has been reported from different parts of the world. In India, the pathogen is recorded for the first time on Lepidium sativum. Proper management strategies need to be formulated against this disease as incidence is increasing.

First report of hog-plum (Spondias pinnata) leaf spot disease

Hog–plum is a tree species with edible fruits. The plant is naturally distributed in the tropical areas of the Indian subcontinent. Our effort to introduce it in the semi–arid conditions of western India failed as the plants developed severe shot–hole type leaf spot symptoms. Association of a fungus with the disease was detected and its pathogenicity was established. The pathogen was identified to the genus level (Colletotrichum) based on the morphological and molecular markers.

Induction of male and female sterility in isabgol (Plantago ovata) due to floral infection of downy mildew (Pernospora plantaginis)

Downy mildew (Peronospora plantaginis) caused two different types of infection in the floral parts of isabgol (Plantago ovata). Systemic infection resulted in long spikes bearing weak and sterile florets, which later turned black due to saprophytic growth. Localised infection produced various symptoms ranging between normal flower opening and failure to bloom. Different parts of infected flowers such as sepal, petal, filament and anther were reduced in size compared to healthy flowers. However, gynoecium was elongated in localised infection. P. plantaginis induced gradual sterility of isabgol flowers. Androecium was affected more than the gynoecium was. Pollen number, pollen viability and germination reduced drastically due to localised infection. On the contrary, there were no significant differences between healthy and locally infected flowers in terms of stigma receptivity. In systemically infected spikes, bud development was arrested leading to sterility. When localised disease severity was high, secondary systemic infection caused similar symptoms. Microscopic observations showed presence of the pathogen in different parts of the flowers. Downy mildew adversely affected seed yield and quality; producing seeds, which were smaller and lighter than the healthy ones and later, became black. Seed yield was reduced by as much as 73.45 percent. Husk content per unit seed mass increased relatively as the total surface area of infected seeds increased.

First report of sweet wormwood leaf blight disease in India

Artemisia annua is an important drug plant yielding antimalarial compounds. It was found to be infected by Alternaria alternata in India. The pathogen reduces active leaf area and is also known to produce mycotoxins. Hence, the disease demands serious attention to ensure the availability of a safe drug.

First report of downy mildew onLepidium sativum in India

Downy mildew caused byHyaloperonospora parasitica on different members of Brassicaceae has been reported from different parts of the world. In India, the pathogen is recorded for the first time onLepidium sativum. Proper management strategies need to be formulated against this disease as incidence is increasing.