Banana (Musa spp.) is tremendously important for millions of cultivators and corporate growers, both for export and subsistence. The yield of commercial bananas across the world is staggeringly affected by Fusarium wilt (Panama disease) of bananas. It is a soil-borne disease whose causative agent is a hyphomycete i.e. Fusarium oxysporum f. sp. cubense 1–3. Obliteration of Gros Michel by Foc race 1 led to its substitution with resistant Cavendish cultivars that are now susceptible to Foc race 4 specifically Foc TR4 which gained an emplacement from South East Asia to Africa and recently entrenched in Latin America thereby jeopardizing intercontinental banana production 4–6. Management actions including crop rotation, flood fallowing, organic amendments, intercropping, molecular and biological control, etc have been applied to combat this disease but these measures provide short-term or little success under field conditions that advocate for continuous exploitation of pugnacious methodologies that are oppugnant to the calamitous disease 6–10.
Various research investigations of plant crude extracts revealed their inhibitory activities against phytopathogens that account for the presence of antimicrobial secondary metabolites as their compositional constituents. Additionally, these secondary metabolites e.g. terpenoids, alkaloids, tannins, saponins, phenylpropanoids, and flavanoids, etc are vital materials in the manufacture of sundry fungicides and pesticides 11–15. Secondary metabolites signify the adaptive potential of plants against biotic and abiotic stresses 16. Secondary metabolites structure, optimized through evolution, interferes with microbes molecular targets hence acting as a mechanism for plant defense 17. Phenolics are the profusely found secondary metabolites in plants18. Detection and identification of phenolics have now become an extensive research area because of the evidence that they have an indispensable role in the avoidance of the diseases that are linked to oxidative stress 19–21. The plant phenolic compounds are studied as vital sources of novel antibiotics, insecticides, natural drugs, and herbicides 22, 23. Continuous exploitation of botanicals from various plants and their different parts would be productive in discovering innovatory, environmentally safe antimicrobials that can vanquish the complications of multi-drug resistance and bioaccumulation of pesticides.
Being used as folk medicines, gymnosperm botanicals have also been extensively studied for their anti-inflammatory and antimicrobial potential in recent decades. The presence of diverse chemical constituents in these extracts is thought to be responsible for microbial growth inhibition 24–27. The P. wallachiana (commonly called Biar or Blue Pine) is a large cone-bearing evergreen tree belonging to family Pinaceae of gymnosperms with a height up to 35-50m and a diameter of 1-1.5m, having down-curved branches with a straight trunk. Leaves are long (15-20cm), slender, in fascicles of 5, flexible, the adaxial side having multiple bluish-white stomatal lines and abaxial side green 28, 29. It is one of the principal conifers mostly growing in the upper region of mountains associated with other gymnosperms and is regarded as an important medicinal plant 30. The majority of the research and pharmacognostic studies conducted on P. wallachiana strongly supported its antioxidant efficacies 31–34 and anticancerous potential of P. wallachiana needle extract 35. Antibacterial activity of P. wallachiana essential oil against tested bacterial strains 36 and antifungal efficacy of its essential oil against Fusarium verticillioides 37, antimicrobial activity of its hydroalcoholic extracts against tested bacterial strains and fungi 38, antibacterial activity against Acinetobacter baumannii 29 put forward its antimicrobial potential. Phytochemical studies reported antioxidant activity of P. wallachiana extracts that accounts for the presence of plentiful flavanoids and polyphenols in their phytochemical composition 32, 39. Phenolic compounds i.e. chlorogenic acid, catechins, ferulic acid, caffeic acid are well-known toxic compounds that are much faster concentrated in resistant varieties after their infection by the pathogen 40. Cell wall phenolics e.g. coumaric acid and trans ferulic acid play a crucial role during plant growth by defending it against stresses including infections and wounding etc 41. The antiviral potential of catechins and (-)-epicatechin gallate against the influenza virus had been noted. These polyphenols alter the membrane physical properties of the virus 42. The antimicrobial potential of polyphenols e.g. catechin, gallic acid, ferulic acid, p-coumaric acid, quercitin, and rutin against Xylella fastidiosa had also been described earlier 43. Similarly, antifungal activities of polyphenolics e.g. phenol, catechin, quercetin, ο-coumaric acid, gallic acid, pyrogallic acid, ρ-coumaric acid, ρ-hydroxy benzoic acid, protocatechuic, salicylic acid, coumarin, and cinnamic acid had been noted 44. Moreover, powerful antimicrobial activities by polyphenol compounds including kaempferol, gallic acid quercetin, and ellagic acid had been reported 45. Extracts abundant in antioxidants i.e. ascorbic acid, polyphenols, and flavonoids are a source of cell damage and leaking of biomolecules from the impaired microbial membranes. The present study was designed to investigate the antifungal potential of Pinus wallachiana botanicals against Foc and evaluating its various fractions for the presence of some important polyphenols that might be beneficial for combating Fusarium wilt problem.