Metabolic profiling for dissection of late leaf spot disease resistance mechanism in groundnut

Late leaf spot (LLS) caused by fungi Passalora personata is generally more destructive and difficult to control than early leaf spot. The aim of this study was to decipher biochemical defense mechanism in groundnut genotypes against P. personata by identifying resistance specific biomarkers and metabolic pathways induced during host-pathogen interaction. Metabolomics of non-infected and infected leaves of moderately resistant (GPBD4 and ICGV86590), resistant (KDG128 and RHRG06083) and susceptible (GG20, JL24 and TMV2) genotypes was carried out at 5 days after infection (65 days after sowing). Non-targeted metabolite analysis using GC-MS revealed total 77 metabolites including carbohydrates, sugar alcohols, amino acids, fatty acids, polyamines, phenolics, terpenes and sterols. Variable importance in projection (VIP) measure of partial least squares-discriminant analysis (PLS-DA) showed that resistant and moderately resistant genotypes possessed higher intensities of ribonic acid, cinnamic acid, malic acid, squalene, xylulose, galactose, fructose, glucose, β-amyrin and hydroquinone while susceptible genotypes had higher amount of gluconic acid 2-methoxime, ribo-hexose-3-ulose and gluconic acid. Heat map analysis showed that resistant genotypes had higher intensities of β-amyrin, hydroquinone in non-infected and malic acid, squalene, putrescine and 2,3,4-trihydroxybutyric acid in infected leaves. Dendrogram analysis further separated resistant genotypes in the same cluster along with infected moderately resistant genotypes. The most significant pathways identified are: linoleic acid metabolism, flavone and flavonol biosynthesis, cutin, suberin and wax biosynthesis, pentose and glucuronate interconversions, starch and sucrose metabolism, stilbenoid biosynthesis and ascorbate and aldarate metabolism. Targeted metabolite analysis further confirmed that resistant genotypes possessed higher content of primary metabolites sucrose, glucose, fructose, malic acid and citric acid. Moreover, resistant genotypes possessed higher content of salicylic, coumaric, ferulic, cinnamic, gallic acid (phenolic acids) and kaempferol, quercetin and catechin (flavonols). Thus metabolites having higher accumulation in resistant genotypes can be used as biomarkers for screening of LSS resistant germplasm. These results unravel that higher amount of primary metabolites leads to stimulate the accumulation of more amounts of secondary metabolites such as phenolic acid, flavanols, stilbenes and terpenoids (squalene and β-amyrin) biosynthesis which are ultimately involved in defense mechanism against LLS pathogen.

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The online version contains supplementary material available at 10.1007/s12298-021-00985-5.

Distinguish metabolic profiles and defense enzymes in Alternaria leaf blight resistant and susceptible genotypes of groundnut

Alternaria leaf blight is major fungal disease of summer groundnut, causes significant loss of haulm and pod yield. Aims of this study were to understand the role of metabolites and phenylpropanoid related enzymes in Alternaria leaf blight resistance and to find out metabolic marker for disease resistance. Alternaria leaf blight resistant (GPBD4 and CS186) and susceptible genotypes (GG2 and TPG41) of groundnut were grown in pots during rabi-summer 2015. Groundnut plants were infected with Alternaria alternata (Fr.) Keissler at 40 days after sowing. 5 days after infection, upper second leaves were collected from both control and infected plants for analysis. A total of 67 metabolites comprising sugars, sugar alcohols, amino acids, organic acids, fatty acids, sterols and phenolic were identified using gas chromatography-mass spectrometry (non-targeted metabolomics). Constitutive levels of alpha-d-galactoside, d-mannitol, d-erythropentitol, glycine, and hexadecanoic acid were observed higher in resistant genotypes compared to susceptible genotypes. Moreover, arabinofuranose, cinnamic acid, 2-butendioic acid, and linoleic acid were observed only in resistant genotypes at both control and infected stage. In susceptible genotypes myo-inositol, glucose and fructose content was increased after infection with pathogen while decreased in resistant genotypes. Resistant genotypes had higher constitutive level of cinnamic and salicylic acid compared to susceptible genotypes. Non-infected leaves of resistant genotypes also had higher activities of phenylalanine ammonia lyase and tyrosine ammonia lyase activities. Our results suggest that metabolites specifically present in resistant genotypes impart defense mechanism against Alternaria pathogen and can be used as bio-marker for screening of germplasm.

Efficacy and insecticidal properties of some essential oils against Caryedon serratus (Oliver)-a storage pest of groundnut

During storage groundnut is attacked by number of stored grain pest and management of these insect pests particularly bruchid beetle, Caryedon serratus (Oliver) is of prime importance as they directly damage the pod and kernels. Hence, some essential oils were tested for their insecticidal and fungicidal properties. Highest total bruchid mortality was recorded with the application of neem oil and pongamia oil at 10% (v/w) concentration and lowest in eucalyptus oil at 5% (v/w). Number of eggs laid was recorded 2.3 in neem oil 10% (v/w) which was lowest and significantly superior over untreated control and was at par with castor oil 10% (v/w) which recorded 2.5 eggs per 100 g of groundnut pods. There was no adult emergence in the groundnut pods treated with castor oil, eucalyptus oil, neem oil and pongamia oil at 10% (v/w) concentration. Groundnut pods treated with castor oil, eucalyptus oil, neem oil and pongamia oil at 10% (v/w) and neem oil at 5% (v/w) concentrations recorded no damage to pods and kernels and also zero per cent weight loss. These oils effectively influenced groundnut bruchid establishment and reduce damage besides reduction in aflatoxin contamination.