H. Sudini

Post-harvest management of aflatoxin contamination in groundnut

Aflatoxin contamination in groundnut by Aspergillus section Flavi is a major pre- and post-harvest problem causing kernel-quality loss. Post-harvest aflatoxin contamination is caused initially by infestation of aflatoxigenic strains at the pre-harvest stage, resulting in reduced kernel quality after harvest. Improper handling of pods and storage methods after harvest lead to high moisture and ambient temperatures, directly causing aflatoxin contamination. In this review, we report the extent of post-harvest contamination along the groundnut value chain in the Kolokani, Kayes, and Kita districts of Mali in West Africa. Groundnut kernels and paste samples were collected from retailers in selected markets from December 2010 to June 2011, and aflatoxin B1 (AFB1) content was estimated. Aflatoxin was significantly higher in groundnut paste than in kernels. Kolokani recorded the highest toxin levels in both kernels and groundnut paste compared with the other districts. Overall, AFB1 levels in kernels and paste i...

Efficacy of Bacillus subtilis MBI 600 Against Sheath Blight Caused by Rhizoctonia solani and on Growth and Yield of Rice

Rice sheath blight disease (ShB), caused by Rhizoctonia solani, gives rise to significant grain yield losses. The present study evaluated the efficacy of Integral®, the commercial liquid formulation of Bacillus subtilis strain MBI 600, against rice ShB and for plant growth promotion. In greenhouse studies, four log concentrations of Integral (from 2.2×106 to 2.2×109 cfu/mL) were used as seed treatment (ST). After 25 d, seedlings were dipped (SD) into Integral prior to transplanting. At 30 d after transplanting (DAT), leaf sheaths were inoculated with immature sclerotia of the pathogen. At 45 DAT, a foliar spray (FS) with Integral was applied to some treatments. The fungicide control was 50% carbendazim at 1.0 g/L, and a nontreated control was also included. Overall, there were 10 treatments, each with five replications. ShB severity was rated at 52 DAT, and seedling height and number of tillers per plant were rated at 60 DAT. In 2009, two field trials evaluated Integral at 2.2×108 and 2.2×109 cfu/mL. Integral was applied as ST, and seedlings were produced in a nursery bed. After 32 d, seedlings were treated with Integral as SD and transplanted into 10 m2 blocks. Foliar sprays were given at 45 and 60 DAT. There were seven treatments, each with eight replications arranged as a factorial randomized complete block design. At 20 DAT, the plots were broadcast inoculated with R. solani produced on rice grains. Seedling height before transplanting, ShB severity at 90 DAT, and grain yield at harvest were recorded. Integral at 2.2×109 cfu/mL provided significant increase of seedling heights over other treatments under greenhouse conditions. The Integral treatments of ST + SD + FS at 2.2×109 cfu/mL significantly suppressed ShB over other treatments. In field studies, Integral provided significant increase of seedling height in nursery, and number of tillers per plant, compared with the control. ShB severity was significantly suppressed with higher concentrations of Integral compared to lower concentrations. Grain yield were the highest at an Integral concentration of 2.2×109 cfu/mL. Overall, Integral significantly reduced ShB severity, enhanced seedling growth, number of tillers per plant and grain yield as ST + SD + FS at the concentration of 2.2×109 cfu/mL under the conditions evaluated.

Peanuts that keep aflatoxin at bay: a threshold that matters

Summary Aflatoxin contamination in peanuts poses major challenges for vulnerable populations of sub‐Saharan Africa and South Asia. Developing peanut varieties to combat preharvest Aspergillus flavus infection and resulting aflatoxin contamination has thus far remained a major challenge, confounded by highly complex peanut–Aspergilli pathosystem. Our study reports achieving a high level of resistance in peanut by overexpressing (OE) antifungal plant defensins MsDef1 and MtDef4.2, and through host‐induced gene silencing (HIGS) of aflM and aflP genes from the aflatoxin biosynthetic pathway. While the former improves genetic resistance to A. flavus infection, the latter inhibits aflatoxin production in the event of infection providing durable resistance against different Aspergillus flavus morphotypes and negligible aflatoxin content in several peanut events/lines well. A strong positive correlation was observed between aflatoxin accumulation and decline in transcription of the aflatoxin biosynthetic pathway genes in both OE‐Def and HIGS lines. Transcriptomic signatures in the resistant lines revealed key mechanisms such as regulation of aflatoxin synthesis, its packaging and export control, besides the role of reactive oxygen species‐scavenging enzymes that render enhanced protection in the OE and HIGS lines. This is the first study to demonstrate highly effective biotechnological strategies for successfully generating peanuts that are near‐immune to aflatoxin contamination, offering a panacea for serious food safety, health and trade issues in the semi‐arid regions.

PLANT GROWTH-PROMOTING ACTIVITIES OF BACILLUS SUBTILIS MBI 600 (INTEGRAL ® ) AND ITS COMPATIBILITY WITH COMMONLY USED FUNGICIDES IN RICE SHEATH BLIGHT MANAGEMENT

Sheath blight (ShB) of rice caused by Rhizoctonia solani is an economically important disease, causing significant yield losses. In this study, the growth promoting activities of commercial formulation of a bioagent, Bacillus subtilis MBI 600 (Integral®) and its compatibility with rice fungicides were evaluated. Integral was evaluated for growth promotion in rice on four cultivars (Cocodrie, Catahoula, Neptune, and Trenasse) under in vitro conditions. Treated rice seeds were incubated for 7 days, and the shoot and root lengths were measured. Rice cv. Cocodrie seeds were treated with strain MBI 600 at various concentrations and seeded in pots containing field soil in GH in a randomized complete block design. Germination and seedling lengths were measured at 7 and 15 days after sowing (DAS). The strain MBI 600 was found to produce siderophores. Seed treatment with Integral significantly increased shoot and root lengths at all concentrations in cvs. Cocodrie, Catahoula, and Trenasse under in vitro conditions. The shoot lengths ranged from 39 to 42 mm at a concentration of 2.20 x 109 cfu/ml in all CV’s. At 2.20 x 109 cfu/ml, the root lengths ranged from 47 to 69 mm. The shoot and root lengths of control seedlings were each up to 20 mm. Seed treatment with 2.20 x 108 and 2.20 x 109 cfu/ml significantly increased seedling emergence (81 to 89%) compared to 2.20 x 106 and 2.20 x 107 cfu/ml, and control (61%) under GH conditions. Similarly, seed treatment with 2.20 x 109 cfu/ml of MBI 600 resulted in the highest shoot and root lengths (335 and 166 mm respectively). Integral has good tolerance to hexaconazole, propiconazole, and validamycin; moderate tolerance to tricyclazole; and poor tolerance to benomyl and mancozeb at 1000 ppm. Integral showed compatibility to carbendazim and azoxystrobin up to 400 ppm. Overall, our results suggest that Integral produces siderophores, promoted rice seedling emergence and growth, and is compatible with rice fungicides.

Detection of aflatoxigenic Aspergillus strains by cultural and molecular methods: A critical review

Aflatoxin contamination of food and feed commodities, caused by Aspergillus section Flavi group of fungi, is a serious problem worldwide. Exposure through consumption of contaminated food and feed has deleterious effects on human and animal health. Therefore, aflatoxin contaminated products are a barrier to international trade of agricultural commodities. Not all fungi from Aspergillus section Flavi produce aflatoxins. Hence it is important to differentiate Aspergillus spp. into toxigenic and atoxigenic species to better understand their population structure in a specific environment. A range of methods are available today, including cultural, analytical and molecular methods, to identify the toxin producing ability of isolates from section Flavi. A comprehensive review of these methods would be of great use for researchers in developing nations where fully equipped aflatoxin detection laboratories are lacking. In this paper we critically reviewed the cultural and molecular methods of detecting aflatoxigenic Aspergillus species and their precision. Key words: Toxigenic Aspergillus, atoxigenic Aspergillus, cultural methods, PCR based methods.

Commercial Potential of Microbial Inoculants for Sheath Blight Management and Yield Enhancement of Rice

Sheath blight of rice is an economically significant disease worldwide. Use of plant growth-promoting rhizobacteria (PGPR), one type of microbial inoculants, for sheath blight management and yield enhancement of rice is gaining popularity in modern agriculture due to increasing concerns with the use of chemical fungicides. Among different microbial inoculants, PGPR are used for their growth-promoting activities and managing sheath blight in rice. However, the efficacy of experimental PGPR strains is typically not consistent under field conditions due to limited knowledge of their formulations, shelf life, delivery systems, compatibility with chemicals and agronomic practices, and the mode of action. In this chapter, a general review on scope and commercial potential of various PGPR for rice sheath blight management and yield enhancement is provided. Efficacy results obtained from tests with Integral®, a current commercial product, which contains the strain Bacillus subtilis MBI600, are presented as an example of the potential for PGPR in management strategies for sheath blight.

Indirect Plant Growth Promotion in Grain Legumes: Role of Actinobacteria

Grain legumes (beans, pulses, and oilseeds) are protein-rich crops and to a larger extent diversify farming systems. These crops are often confronted by a number of biotic and abiotic stresses in the natural environment resulting in a significant reduction in their productivity. Management options employed to counter such stresses include cultural and agronomical practices apart from the use of chemicals. Among others, biological control using beneficial microbes is environmentally safe and sustainable solution to minimize the deleterious effects of biotic and abiotic stresses in grain legumes. Microbes are known to exhibit a number of mechanisms conferring resistance to plants. Many such useful organisms, termed plant growth-promoting microbes (PGPM), have been studied extensively for their role in agriculture. Among the microbes studied, plant growth-promoting Actinobacteria (PGPA) have been gaining popularity. These microbes are a group of important free-living, spore-forming organisms exploited for their role in producing many agriculturally important substances. These microbes have shown the ability to both suppress pathogen inoculums employing one or more mechanisms of antagonism (hyperparasitism and the production of lytic enzymes, antibiotics, and siderophores) and also resist abiotic stresses (drought, salinity, heavy metals, heat, etc.) by lowering the levels of ethylene by producing 1-aminocyclopropane-1-carboxylate (ACC) deaminase. It is not only important to identify such microbes but also to extrapolate these findings and achieve similar results under field conditions. This chapter focuses on the common mechanisms reported for Actinobacteria majorly streptomycetes and to a lesser extent by non-streptomycetes in protecting the crop plants particularly grain legumes. We believe it also helps to encourage further investigations especially with the lesser explored non-streptomycetes.

Ultrastructural studies on the interaction between Bacillus subtilis MBI 600 (Integral ® ) and the rice sheath blight pathogen, Rhizoctonia solani

The present study evaluated interactions of the biological control agent Bacillus subtilisstrain MBI 600 (Integral®) and Rhizoctonia solani, the rice sheath blight pathogen, through scanning electron microscopy (SEM). Ultrastructural effects related to antibiosis were studied by dual culture of B. subtilis (MBI 600) and R. solani on potato dextrose agar (PDA) plates. Hyphal growth near the inhibition zone was processed. To study the effects of hyperparasitism on fungal ultrastructure, Integral was sprayed on R. solani mycelia and observations were made three days later. Interactions of B. subtilis (MBI 600) and R.solani in planta were determined by spraying detached rice leaves with B. subtilis (MBI 600) and then inoculating with sclerotia of R. solani. In addition, sclerotia were dipped in Integral for 24 h, and cut sections were then observed. Overall the results indicate that B. subtilis (MBI 600) caused loss of structural integrity, shriveling, abnormal coiling, and lysis of the R. solani hyphae due to antibiosis and hyperparasitism in dual culture assays. On rice leaves, B. subtilis (MBI 600) also caused abnormal coiling, shriveling, and break down of hyphae. Sclerotia of R. solani dipped in Integral resulted in colonization of B. subtilis(MBI 600), maceration, and fragmentation of inner walls. Our results suggest that B. subtilis (MBI 600) from the product Integral was highly effective in suppressing R. solani.

Aspergillus flavus infection triggered immune responses and host-pathogen cross-talks in groundnut during in-vitro seed colonization.

Aflatoxin contamination, caused by fungal pathogen Aspergillus flavus, is a major quality and health problem delimiting the trade and consumption of groundnut (Arachis hypogaea L.) worldwide. RNA-seq approach was deployed to understand the host-pathogen interaction by identifying differentially expressed genes (DEGs) for resistance to in-vitro seed colonization (IVSC) at four critical stages after inoculation in J 11 (resistant) and JL 24 (susceptible) genotypes of groundnut. About 1,344.04 million sequencing reads have been generated from sixteen libraries representing four stages in control and infected conditions. About 64% and 67% of quality filtered reads (1,148.09 million) were mapped onto A (A. duranensis) and B (A. ipaёnsis) subgenomes of groundnut respectively. About 101 million unaligned reads each from J 11 and JL 24 were used to map onto A. flavus genome. As a result, 4,445 DEGs including defense-related genes like senescence-associated proteins, resveratrol synthase, 9s-lipoxygenase, pathogenesis-related proteins were identified. In A. flavus, about 578 DEGs coding for growth and development of fungus, aflatoxin biosynthesis, binding, transport, and signaling were identified in compatible interaction. Besides identifying candidate genes for IVSC resistance in groundnut, the study identified the genes involved in host-pathogen cross-talks and markers that can be used in breeding resistant varieties.

Pathogenic and Molecular Variability of Aspergillus niger Isolates Causing Collar Rot Disease in Groundnut

Pathogenic variability studies of 26 isolates of collar rot pathogen (Aspergillus niger) of groundnut collected from different districts of Telangana and Andhra Pradesh states were conducted under greenhouse conditions by using two groundnut cultivars TMV-2 and JL-24. The mean seedling mortality ranged from 29.7 per cent (MBNRAn-1 (Palkapally)) to 94.4 per cent (ATPAn-1 (Jogannapet)). All the isolates of A. niger showed differential reaction with regard to seedling mortality on JL-24 and TMV-2 cultivars. Similarly genetic relatedness among eight virulent isolates (two isolates from each district) of A. niger from groundnut was assessed by using RAPD analysis. The similarity index values among the A. niger isolates varied from 0.571 (between WGL An-2 and CHT An-3) to 0.229 (between MBNR An-3 and WGL An-2).