Unleashing Bacillus species as versatile antagonists: Harnessing the biocontrol potentials of the plant growth-promoting rhizobacteria to combat Macrophomina phaseolina infection in Gloriosa superba.

Charcoal rot caused by Macrophomina phaseolina is one of the most devastating diseases that cause severe yield loss in Gloriosa superba cultivation. Plant growth-promoting rhizobacteria (PGPR) are extensively harnessed as biocontrol agents due to their effectiveness in combating a wide array of plant pathogens through a multifaceted approach. The present study delved into the mechanisms underlying its ability to inhibit root rot pathogen and its capacity to promote plant growth in G. superba, commonly known as glory lily. PGPR isolated from the rhizosphere of glory lily were subjected to in vitro assessments using the dual plate technique. The isolated Bacillus subtilis BGS-10 and B. velezensis BGS-21 showed higher mycelial inhibition (61%) against M. phaseolina. These strains also promote plant growth by producing indole-3-acetic acid, siderophore, ammonia, amylase, cellulase, pectinase, xylanase, and lipase chemicals. Genome screening of BGS-10 and BGS-21 revealed the presence of antimicrobial peptide genes such as Iturin (ituD gene), surfactin (srfA and sfp genes) along with the mycolytic enzyme ß-1,3-glucanase. Further, the presence of secondary metabolites in the bacterial secretome was identified through gas chromatography-mass spectrometry (GC/MS) analysis. Notably, pyrrolo[1,2-a] pyrazine-1,4-dione, hexahydro-3-(2-methylpropyl), 9 H-pyrido[3,4-b] indole and L-leucyl-D-leucine exhibited the highest docking score against enzymes responsible for pathogen growth and plant cell wall degradation. Under glasshouse conditions, tuber treatment and soil application of talc-based formulation of B. subtilis BGS-10 and B. velezensis BGS-21 suppress the root rot incidence with a minimal disease incidence of 27.78% over untreated control. Concurrently, there was a notable induction of defense-related enzymes, including peroxidase (PO), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL), in glory lily. Therefore, it can be concluded that plant growth-promoting Bacillus strains play a significant role in fortifying the plant's defense mechanisms against the root rot pathogen.

First Report of Clonostachys rosea as a Mycoparasite on Sclerotinia sclerotiorum Causing Head Rot of Cabbage in India.

Clonostachys rosea, an ascomycetous, omnipresent, cellulose-decaying soil fungus, has been reported to be a well-known mycoparasitic biological control agent. In this study, we isolated C. rosea, a mycoparasitic fungus for the first time in India from sclerotia of the notorious plant pathogen Sclerotinia sclerotiorum, causing head rot disease in cabbage. A total of five mycoparasitic fungi were isolated from the sclerotial bodies of S. sclerotiorum (TNAU-CR 01, 02, 03, 04 and 05). All the isolates were tested under morpho-molecular characterization. Among them, TNAU-CR 02 showed the greatest mycelial inhibition of 79.63% over the control. Similarly, the SEM imaging of effective C. rosea isolates indicated the presence of numerous conidia destroying the outer cortex layers of sclerotia. Metabolite fingerprinting of C. rosea TNAU-CR 02 identified 18 chemical compounds using GC-MS analysis. The crude antibiotics of C. rosea TNAU-CR 02 were verified for their antifungal activity against S. sclerotiorum and the results revealed 97.17% mycelial inhibition compared with the control. Similarly, foliar application of TNAU-CR 02 at 5 mL/litre on 30, 45 and 60 days after transplanting showed the lowest disease incidence of 15.1 PDI compared to the control. This discovery expands our understanding of the biology and the dissemination of C. rosea, providing a way for the exploitation of C. rosea against cabbage head rot pathogens.