Predicting favorable conditions for early leaf spot of peanut using output from the Weather Research and Forecasting (WRF) model

Engineered green nanoparticles interact with Nigrospora oryzae isolated from infected leaves of Arachis hypogaea

Oilseed crop diseases are a major concern around the world, particularly in India. The synthetic fungicides not only kill the pathogen, but they also harm the host plant and beneficial microbes and on continuous usage, they decrease the soil fertility. To overcome this problem, green nanotechnology has been a greater alternative with promising benefits. The green synthesized nanoparticles from the extract of various plant parts are an effective remedy for killing the pathogens without affecting the host plants and the environment. Hence, in our study silver nanoparticles were synthesized from Fennel seed (Foeniculum vulgare) extract. The synthesis of nanoparticles was confirmed using UV-vis, Fourier transform infrared, dynamic light scattering, zeta potential, and scanning electron microscopic analysis. The in vitro antifungal study was carried out and revealed that the nanoparticles had high efficacy against the isolated phytopathogen Nigrospora oryzae which causes tikka disease in Arachis hypogaea plants. Hence, F. vulgare seed nanoparticles can be used as an effective alternative to synthetic fungicides without causing any deleterious effect on soil microflora or the environment.

Association of differentially expressed R-gene candidates with leaf spot resistance in peanut (Arachis hypogaea L.)

Early leaf spot (ELS) and late leaf spot (LLS) are major fungal diseases of peanut that can severely reduce yield and quality. Development of acceptable genetic resistance has been difficult due to a strong environmental component and many major and minor QTLs. Resistance genes (R-genes) are an important component of plant immune system and have been identified in peanut. Association of specific R-genes to leaf spot resistance will provide molecular targets for marker-assisted breeding strategies. In this study, advanced breeding lines from different pedigrees were evaluated for leaf spot resistance and 76 candidate R-genes expression study was applied to susceptible and resistant lines. Thirty-six R-genes were differentially expressed and significantly correlated with resistant lines, of which a majority are receptor like kinases (RLKs) and receptor like proteins (RLPs) that sense the presence of pathogen at the cell surface and initiate protection response. The largest group was receptor-like cytoplasmic kinases (RLCKs) VII that are involved in pattern-triggered kinase signaling resulting in the production reactive oxygen species (ROS). Four R-genes were homologous to TMV resistant protein N which has shown to confer resistance against tobacco mosaic virus (TMV). When mapped to peanut genomes, 36 R-genes were represented in most chromosomes except for A09 and B09. Low levels of gene-expression in resistant lines suggest expression is tightly controlled to balance the cost of R-gene expression to plant productively. Identification and association of R-genes involved in leaf spot resistance will facilitate genetic selection of leaf spot resistant lines with good agronomic traits.

Identification of expressed R-genes associated with leaf spot diseases in cultivated peanut

Peanut (Arachis hypogaea L.) is an important food and oilseed crop worldwide. Yield and quality can be significantly reduced by foliar fungal diseases, such as early and late leaf spot diseases. Acceptable levels of leaf spot resistance in cultivated peanut have been elusive due to environmental interactions and the proper combination of QTLs in any particular peanut genotype. Resistance gene analogs, as potential resistance (R)-genes, have unique roles in the recognition and activation of disease resistance responses. Novel R-genes can be identified by searches for conserved domains such as nucleotide binding site, leucine rich repeat, receptor like kinase, and receptor like protein from expressed genes or through genomic sequences. Expressed R-genes represent necessary plant signals in a disease response. The goals of this research are to identify expressed R-genes from cultivated peanuts that are naturally infected by early and late spot pathogens, compare these to the closest diploid progenitors, and evaluate specific gene expression in cultivated peanuts. Putative peanut R-genes (381) were available from a public database (NCBI). Primers were designed and PCR products were sequenced. A total of 214 sequences were produced which matched to proteins with the corresponding R-gene motifs. These R-genes were mapped to the genome sequences of Arachis duranensis and Arachis ipaensis, which are the closest diploid progenitors for tetraploid cultivated peanut, A. hypogaea. Identification and association of specific gene-expression will elucidate potential disease resistance mechanism in peanut and may facilitate the selection of breeding lines with high levels of leaf spot resistance.

Gene cluster conservation provides insight into cercosporin biosynthesis and extends production to the genus Colletotrichum

Species in the fungal genus Cercospora cause diseases in many important crops worldwide. Their success as pathogens is largely due to the secretion of cercosporin during infection. We report that the cercosporin toxin biosynthesis (CTB) gene cluster is ancient and was horizontally transferred to diverse fungal plant pathogens. Because our analyses revealed genes adjacent to the established CTB cluster with similar evolutionary trajectories, we evaluated their role in Cercospora beticola to show that four are necessary for cercosporin biosynthesis. Lastly, we confirmed that the apple pathogen Colletotrichum fioriniae produces cercosporin, the first case outside the family Mycosphaerellaceae. Other Colletotrichum plant pathogens also harbor the CTB cluster, which points to a wider role that this toxin may play in virulence.

Species in the genus Cercospora cause economically devastating diseases in sugar beet, maize, rice, soy bean, and other major food crops. Here, we sequenced the genome of the sugar beet pathogen Cercospora beticola and found it encodes 63 putative secondary metabolite gene clusters, including the cercosporin toxin biosynthesis (CTB) cluster. We show that the CTB gene cluster has experienced multiple duplications and horizontal transfers across a spectrum of plant pathogenic fungi, including the wide-host range Colletotrichum genus as well as the rice pathogen Magnaporthe oryzae. Although cercosporin biosynthesis has been thought to rely on an eight-gene CTB cluster, our phylogenomic analysis revealed gene collinearity adjacent to the established cluster in all CTB cluster-harboring species. We demonstrate that the CTB cluster is larger than previously recognized and includes cercosporin facilitator protein, previously shown to be involved with cercosporin autoresistance, and four additional genes required for cercosporin biosynthesis, including the final pathway enzymes that install the unusual cercosporin methylenedioxy bridge. Lastly, we demonstrate production of cercosporin by Colletotrichum fioriniae, the first known cercosporin producer within this agriculturally important genus. Thus, our results provide insight into the intricate evolution and biology of a toxin critical to agriculture and broaden the production of cercosporin to another fungal genus containing many plant pathogens of important crops worldwide.

Draft Genome Sequence of Cercospora arachidicola, Causal Agent of Early Leaf Spot in Peanuts

Cercospora arachidicola, causal agent of early leaf spot, is an economically important peanut pathogen. Lack of genetic information about this fungus prevents understanding the role that potentially diverse genotypes may have in peanut breeding programs. Here, we report for the first time a draft genome sequence of C. arachidicola.