Molecular diversity and fingerprints of Trichoderma associated with antagonistic potentials against Sclerotium rolfsii Sacc.

Journal of Plant Diseases and Protection - Antagonistic potentials of Trichoderma isolates were evaluated against the phytopathogen Sclerotium rolfsii causing stem rot in groundnut. The in vitro...     

Appraisal of RAPD and ISSR markers for genetic diversity analysis among cowpea (Vigna unguiculata L.) genotypes

The genetic variability and relationships among 11 cowpea genotypes representing two cultivars and nine elite genotypes were analyzed using 22 random amplified polymorphic DNA (RAPD) and nine inter-simple sequence repeat (ISSR) markers. ISSR markers were more efficient than RAPD assay with regards to polymorphism detection. But the average numbers of polymorphic loci per primer and resolution power were found to be higher for RAPD than for ISSR. Also, the total number of genotype specific marker loci, Nei’s genetic diversity, Shannon’s information index, total heterozygosity, and average heterozygosity were prominent in RAPD as compared to ISSR markers. The regression test between the two Nei’s genetic diversity indices showed low regression (0.3733) between ISSR and RAPD + ISSR-based similarities but maximum (0.9823) for RAPD and RAPD + ISSR-based similarities. The RAPD- and ISSR-generated cultivar- or genotype-specific unique DNA fingerprints able to identify the most diverse genotypes. A dendrogram constructed based on RAPD and ISSR combined data indicated a very clear pattern of clustering according to the groups (cultivars and elite genotypes). The results of principal coordinate analysis were comparable to the cluster analysis. Cluster analysis showed that most diverse genotypes (GP-125 — small size with good seed quality; GP-129, GP-90L — big size with poor seed quality) were separated from moderately diverse cultivars and genotypes. The genetic closeness among GP-129 and GP-90L, JCPL-42, and JCPL-107 could be explained by the high degree of commonness in these genotypes.     

Metabolic profiles of groundnut (<Emphasis Type="Italic">Arachis hypogaea</Emphasis> L.) genotypes differing in <Emphasis Type="Italic">Sclerotium rolfsii</Emphasis> reaction

A total of 60 compounds of known structure, comprising sugars, sugar alcohols, fatty acids, amino acids, organic acids, phenols and sterols were identified in stem extracts of groundnut using GC-MS. Sugars and fatty acids were predominant in stem extracts as compared to other metabolites. Distinguished metabolite patterns were observed in control and 96 h after infection (h.a.i.). Succinic acid, pentitol, scopolin, D-glucose and D-turanose, myo-inositol, fructose and mannitol were observed to be higher in control plants, whereas, D-ribopyranoside, thymol, pentadecanoic acid and octadecanoic acid increased at 24 hai than that of control. Interestingly, phenol related compounds such as phenol, hydroquinone, guaicol-.beta.-d-glucopyranoside, scopolin were also found lower in non-infected stems of TG37A. Moreover, tolerant genotypes (CS 319 and CS 19) had higher content of Thymol-.beta.-d-glucopyranoside, pentitol, D-glucose, D-turanose, scopolin and hydroquinone than that of moderately tolerant and susceptible genotypes. Sugar profiles using Ion chromatography revealed that glucose content decreased in moderately susceptible and susceptible genotype after S. rolfsii infection. Both constitutive and induced levels of cinnamic acid was observed higher in resistant genotypes than that of susceptible ones which was further supported by phenylalanine ammonia lyase activity. Thus, our study demonstrates the biological role of metabolites specifically sugars, phenolics and fatty acids in plant defense responses.     

Trichoderma viride induces phenolics in groundnut (Arachis hypogaea L.) seedlings challenged with rot pathogen (Aspergillus niger Van Tieghem)

The study showed significant differences in percent collar rot disease incidence in groundnut varieties grown in non-infested soil (T₁), challenged with pathogen – Aspergillus niger (T₂), and pathogen + Trichoderma viride 60 (T₃) treatments. Total phenols revealed a significantly higher content in tolerant varieties (J-11, GG-2) of groundnut compared with moderately susceptible (GAUG-10, GG-13) and susceptible (GG-20) varieties. The phenol content accumulated at a higher rate (193%) in GG-20, followed by GG-2 (146%) and J-11 (107%) varieties during disease development stages. HPLC analysis detected six major phenolics, viz., hydroquinone, gallic, chlorogenic, ferulic, salicylic and cinnamic acids. Among six peaks, hydroquinone was found highest in GG-2 at 3 days in T₃. Gallic and salicylic acids increased up to 9 days, while ferulic acid continued to induce up to 15 days in tolerant varieties (J-11, GG-2) of Trichoderma-treated (T₃) seedlings. A correlation study indicated that Trichoderma treatment induced five phenolics – except gallic acid – with a higher level of significance in a susceptible variety to reduce disease incidence compared with tolerant varieties. Results demonstrate the T. viride 60 mediated systemic induction of phenolics for biologic control and their probable role in protecting groundnut against A. niger infection.