Abdul Mannan Akanda

Isolation and Identification of Plant Growth Promoting Rhizobacteria from Cucumber Rhizosphere and Their Effect on Plant Growth Promotion and Disease Suppression

Plant growth promoting rhizobacteria (PGPR) are the rhizosphere bacteria that may be utilized to augment plant growth and suppress plant diseases. The objectives of this study were to identify and characterize PGPR indigenous to cucumber rhizosphere in Bangladesh, and to evaluate their ability to suppress Phytophthora crown rot in cucumber. A total of 66 isolates were isolated, out of which 10 (PPB1, PPB2, PPB3, PPB4, PPB5, PPB8, PPB9, PPB10, PPB11, and PPB12) were selected based on their in vitro plant growth promoting attributes and antagonism of phytopathogens. Phylogenetic analysis of 16S rRNA sequences identified these isolates as new strains of Pseudomonas stutzeri, Bacillus subtilis, Stenotrophomonas maltophilia, and Bacillus amyloliquefaciens. The selected isolates produced high levels (26.78–51.28 μg mL-1) of indole-3-acetic acid, while significant acetylene reduction activities (1.79–4.9 μmole C2H4 mg-1 protein h-1) were observed in eight isolates. Cucumber plants grown from seeds that were treated with these PGPR strains displayed significantly higher levels of germination, seedling vigour, growth, and N content in root and shoot tissue compared to non-treated control plants. All selected isolates were able to successfully colonize the cucumber roots. Moreover, treating cucumber seeds with these isolates significantly suppressed Phytophthora crown rot caused by Phytophthora capsici, and characteristic morphological alterations in P. capsici hyphae that grew toward PGPR colonies were observed. Since these PGPR inoculants exhibited multiple traits beneficial to the host plants, they may be applied in the development of new, safe, and effective seed treatments as an alternative to chemical fungicides.

Chilli rhizosphere fungus Aspergillus spp. PPA1 promotes vegetative growth of cucumber (Cucumis sativus) plants upon root colonisation

A rhizosphere fungus was isolated from roots of chilli plants and identified as Aspergillus spp. PPA1. The fungus was tested for its ability to promote the growth of cucumber plants in a pot experiment. Cucumber seeds were sown in sterilised field soil amended with wheat grain inoculum (WGI) of PPA 1 at the rate of 0.5, 1 and 1.5% w/w, and plants were grown for 21 days in a net house. The treatment with PPA1 significantly increased shoot length, shoot fresh weight, shoot dry weight, root length, root fresh weight, root dry weight, plant length, leaf area and leaf chlorophyll content of cucumber plants compared to non-treated control. The growth promotion rate increased with the increasing concentration of inoculum of PPA1 applied to the soil. The fungus was re-isolated from the roots of cucumber plants at higher frequencies. These results suggest that Aspergillus spp. PPA1 is a root colonising plant-growth promoting fungus for cucumber.

Growth promotion effect of Fusarium spp. PPF1 from bermudagrass (Cynodon dactylon) rhizosphere on Indian spinach (Basella alba) seedlings are linked to root colonisation

A rhizosphere fungus was isolated from roots of bermudagrass (Cynodon dactylon) and identified as Fusarium spp. PPF1. A pot experiment was conducted to test its ability to promote the vegetative growth of Indian spinach seedlings (Basella alba). Indian spinach seeds were sown in sterilised field soil amended with wheat grain inoculum of PPF1 at the rate of 0.5 and 1.0% w/w, and plants were grown for 21 days in a net house. Significantly, higher germination percentage and vigour index were observed due to application of PPF1 in the potting soil. Treatment with PPF1 also significantly increased shoot length, shoot fresh weight, shoot dry weight, root length, root fresh weight, root dry weight, leaf area and leaf chlorophyll content of cucumber plants compared to non-treated control. The growth promotion rate increased with the increasing concentration of inoculum of PPF1 applied to the soil. The fungus was re-isolated from the roots of cucumber plants at higher frequencies, while a positive co-relation was found between the root colonisation ability and the plant growth enhancement by the isolate. These results suggest that growth promotion effect of Fusarium spp. PPF1 on Indian spinach (B. alba) are linked to root colonisation ability of the fungus.

New sources of resistance to Cucumber mosaic virus in Capsicum annuum

BackgroundCucumber mosaic virus (CMV) is the most serious virus disease affecting chilli (Capsicum annuum L.) worldwide and the absence of natural resistance makes management of CMV outbreaks difficult. The characterization of improved sources of resistance to CMV in chilli would facilitate the development of commercially acceptable chilli varieties with adequate levels of CMV resistance. A total of 30 chilli genotypes were evaluated for their reaction to CMV in field and artificial inoculated conditions during 2010-2011 and 2011-2012. Large differences were observed among genotypes for disease incidence, severity indexes, and yield losses. Based on observed data, genotype CA23 (Noakhali) was identified as resistant, while CA12 (Comilla-2) was categorized as moderately resistant to CMV both in natural and inoculated conditions. Enzyme-linked immunosorbent assay absorbance values of samples taken from CMV-infected leaves corresponded well with visible viral symptoms for these genotypes. The identified C. annuum CA23 and CA12 genotypes represent previously undescribed and potentially useful sources of CMV resistance.

Endophytic Bacillus spp. from medicinal plants inhibit mycelial growth of Sclerotinia sclerotiorum and promote plant growth

Abstract Plant growth-promoting bacteria that are also capable of suppressing plant pathogenic fungi play an important role in sustainable agriculture. There is a critical need for conducting research to discover, characterize and evaluate the efficacy of new strains of such bacteria in controlling highly aggressive plant pathogens. In this study, we isolated endophytic bacteria from medicinal plants of Bangladesh and evaluated their antagonistic capacity against an important phytopathogenic fungus Sclerotinia sclerotiorum. Growth-promoting effects of those isolates on cucumber and rice seedlings were also assessed. Among 16 morphologically distinct isolates, BDR-2, BRtL-2 and BCL-1 significantly inhibited the growth of S. sclerotiorum through induction of characteristic morphological alterations in hyphae and reduction of mycelial dry weight. When cucumber and rice seeds were treated with these endophytic bacteria, seven isolates (BCL-1, BDL-1, BRtL-2, BRtL-3, BDR-1, BDR-2 and BBoS-1) enhanced seed germination, seedling vigor, seedling growth and number of roots per plant at a varying level compared to untreated controls. All isolates produced high levels of indole-3-acetic acid (6 to 63 μg/mL) in vitro. Two most potential isolates, BDR-2 and BRtL-2, were identified as Bacillus amyloliquefaciens and B. subtilis, respectively, based on the 16S rRNA gene sequencing. These results suggest that endophytic Bacillus species from native medicinal plants have great potential for being used as natural plant growth promoter and biopesticides in sustainable crop production.

Characterization of Sclerotinia sclerotiorum , an Emerging Fungal Pathogen Causing Blight in Hyacinth Bean ( Lablab purpureus )

Stems and pods of hyacinth bean cultivated in a farmer’s field in Gazipur District, Bangladesh, were found rotted in nearly 5% hyacinth bean plants. A fungus having fluffy mycelium and large sclerotia was isolated from affected tissues. Combined results of morphological, molecular and pathological analyses identified the fungus as Sclerotinia sclerotiorum (Lib) de Bary. Inoculating the fungus on healthy hyacinth bean plants and pods reproduced the symptoms previously observed in the field. The three isolates obtained from naturally infected plants were cross inoculated in hyacinth bean, okra and African-American marigold and they were pathogenic to these hosts. The optimum temperature and pH for its growth were 20°C and pH 5.0, respectively. Sclerotial development was favored at pH 5.0. Sucrose and mannitol were the best carbon sources to support hyphal growth, while glucose was the most favourable for sclerotial development. The hyacinth bean genotypes, HB-82 (Rupban Sheem) and HB-102 were found highly resistant, while HB-94 (Ashina) was moderate resistant to the fungus. Finally, S. sclerotiorum was sensitive to Bavistin, Dithane M-45 and Rovral fungicides and Ca in the form of CaCl2. This observation could possibly aid in eliminating field loss in hyacinth bean caused by an emerging pathogenic fungus S. sclerotiorum.

First report of Sclerotinia sclerotiorum causing pod rot disease on okra in Bangladesh

Abstract Pods of okra (Abelmoschus esculentus L Moench) ‘BARI Dherosh-1ʹ cultivated in a farmer’s field in Gazipur District, Bangladesh, were found rotted in December 2014. A fungus having fluffy mycelium and large sclerotia was isolated from affected pods. Combined results of morphological, molecular and pathological analyses identified the fungus as Sclerotinia sclerotiorum (Lib) de Bary. Inoculating the fungus on healthy okra pods reproduced the symptoms previously observed in the field. This is the first report of S. sclerotiorum causing disease of okra in Bangladesh.

Medicinal Plant Extracts and Protein Kinase C Inhibitor Suppress Zoosporogenesis and Impair Motility of Phytophthora capsici Zoospores

Ansary M.W.R., Haque E., West H.M., Rahman M.M., Akanda A.M., Wang Y., Islam M. T. (2016): Medicinal plant extracts and protein kinase C inhibitor suppress zoosporogenesis and impair motility of Phytophthora capsici zoospores. Plant Protect. Sci., 52: 113–122. The effects of water and acetone extracts from 100 medicinal plants growing in Bangladesh, along with a selective inhibitor of protein kinase C (PKC), chelerythrine chloride, were tested on zoosporogenesis (release of zoospores from the sporangia) and motility of Phytophthora capsici zoospores. Among 10 active crude acetone extracts, those from Psidium guajava and Nigella sativa (100 μg/ml) suppressed zoosporogenesis relative to the control (100% zoospore release) to 60 and 40% released, respectively and inhibited motility of 100% of the zoospores within 60 min of treat ment. Chelerythrine chloride also suppressed zoosporogenesis (30% released) at 0.1 μg/ml and inhibited motility of 100% zoospores at 0.2 μg/ml within 60 minutes. Among water extracts of 100 medicinal plants, 56 impaired motility of zoospores in a dose- and time-dependent manner. Diluted (20-fold) water extracts of 10 plants including Ocinum gratissimum, Terminalia bohera , and Duranta plumeri inhibited motility and subsequently caused lysis of zoospores.