Treatments with native Coleus forskohlii endophytes improve fitness and secondary metabolite production of some medicinal and aromatic plants.

Endophytes have been shown to play a crucial role in determining the fitness of host plant during their association, yet the cross-functional effect of endophytes of one plant on another plant remains largely uncharacterized. In this study, we attempt to analyze the effect of native endophytes of Coleus forskohlii (Phialemoniopsis cornearis (SF1), Macrophomina pseudophaseolina (SF2), and Fusarium redolens (RF1), isolated from stem and root parts) on plant growth and secondary metabolite enhancement in medicinal plant Andrographis paniculata, and aromatic plants Pelargonium graveolens and Artemisia pallens. Here, we report, endophytic treatments with SF2 (21%) and RF1 (9%) in A. paniculata resulted in significant enhancement of andrographolide along with plant primary productivity. Correspondingly, application of fungal endophytes RF1, SF1, and SF2 significantly improved the plant growth (11 to 40%), shoot weight (28 to 34%), oil content (44 to 58%), and oil yield (72 to 122%) in P. graveolens. Interestingly, treatment of A. pallens with three fungal endophytes resulted in significant enhancement of plant productivity and oil content (12 to 80%) and oil yield (32 to 139%). Subsequently, the endophyte treatments RF1 and SF1 enhanced davanone (13 to 22%) and ethyl cinnamate (11 to 22%) content. However, SF2 endophyte-treated plants did not show any improvement in ethyl cinnamate content but enhanced the content of davanone (10%), a signature component of davana essential oil. Overall, results depict cross-functional role of native endophytes of C. forskohlii and repurposing of functional endophytes for sustainable cultivation of economically important medicinal and aromatic crops.

Development of low-cost plant probiotic formulations of functional endophytes for sustainable cultivation of Coleus forskohlii.

Deployment of plant endophytes at field level is reported to make an impact on agricultural crop productivity; development and deployment of suitable crop specific plant probiotics in a suitable delivery matrix is a value-added task. In our study, we attempted to develop bioformulations of native, fungal endophytes of Coleus forskohlii to improve plant yield using two different carrier-based materials (talc and wheat bran). Initially, fungal endophytes (RF1, SF1, and SF2) were grown on sterilized wheat bran under solid state condition and their growth kinetics and pattern were analyzed by ergosterol content and scanning electron microscope, respectively. 10-day-grown fungal endophytic cultures were used for the development of two types of formulations (wheat bran and talc-based formulations) and tested for their efficacy on host plant, C. forskohlii under field conditions. Interestingly, application of wheat bran-based endophytic formulations significantly (p < 0.01) enhanced plant height (12-29%), number of branches (51-63%), root biomass (26-33%), photosynthetic pigments (32-101%), and forskolin content (35-56%) compared to talc-based formulations under field conditions. Shelf life of endophytes (RF1, SF1, and SF2) in both formulations revealed spore viability in wheat bran-based formulations for 6 months storage period as compared to talc-based formulations. Overall, the present investigation envisages developing plant probiotic bioformulations of functional endophytes of C. forskohlii to enhance root biomass and in planta forskolin content.

Functional Fungal Endophytes in Coleus forskohlii Regulate Labdane Diterpene Biosynthesis for Elevated Forskolin Accumulation in Roots.

Coleus forskohlii is a perennial medicinal shrub cultivated mainly for its forskolin content. The plant has been used since ancient times in ayurvedic traditional medicines for the treatment of hypertension, glaucoma, asthma, congestive heart failures, obesity, and cancer. Use of endophytic microorganisms presents a special interest for the development of value-added bioactive compounds through agriculture. Limited investigations have been undertaken on in planta enhancement of forskolin content using endophytic fungus in sustainable agriculture. Here we report specific roles of three fungal endophytes, Fusarium redolens (RF1), Phialemoniopsis cornearis (SF1), and Macrophomina pseudophaseolina (SF2), functionally acting as plant probiotic fungus, regulating secondary metabolite (forskolin) biosynthesis in C. forskohlii. The root endophyte, RF1, and shoot endophytes, SF1 and SF2, were found to enhance forskolin content by 52 to 88% in pot and 60 to 84% in field experiments as compared to uninoculated control plants. The three endophytes also enhanced total biomass owing to plant growth promoting properties. The expression of diterpene synthases (CfTPSs) like CfTPS1, CfTPS2, CfTPS3, and CfTPS4 were significantly upregulated in endophyte-treated C. forskohlii plants. Elevated expression of key diterpene synthases (CfTPS2) in the forskolin biosynthesis pathway, exclusively present in the root cork of C. forskohlii, was observed following SF2 endophyte treatment. Furthermore, endophyte treatments conferred a variety of antagonistic activity against nematode galls (80%) and plant pathogens like Fusarium oxysporum, Colletotricum gloeosporioides, and Sclerotium rolfsii. RF1 and SF1 fungal endophytes showed positive for IAA production; however, SF1 also indicated phosphate solubilization activity. Overall, the qualitative and quantitative improvement of in planta forskolin enhancement represents an area of high commercial interest, and hence, our work focused on novel insights for the application of three fungal endophytes for in planta enhancement of forskolin content for C. forskohlii cultivation by a sustainable approach.

Epidemiology of Basil Downy Mildew.

Basil downy mildew (BDM) caused by the oomycete Peronospora belbahrii is a destructive disease of sweet basil (Ocimum basilicum) worldwide. It originated in Uganda in the 1930s and recently spread to Europe, the Middle East, Americas, and the Far East. Seed transmission may be responsible for its quick global spread. The pathogen attacks leaf blades, producing chlorotic lesions with ample dark asexual spores on the lower leaf surface. Oospores may form in the mesophyll of infected leaves. The asexual spores germinate on a wet leaf surface within 2 h and penetrate into the epidermis within 4 h. Spore germination and infection occur at a wide range of temperatures from 5 to 28.5°C. Infection intensity depends on the length of dew period, leaf temperature, and inoculum dose. The duration of latent period (from infection to sporulation) extends from 5 to 10 days, depending on temperature and light regime. The shortest is 5 days at 25°C under continuous light. Sporulation requires high humidity but not free leaf wetness. Sporulation occurs at 10 to 26°C. At the optimum temperature of 18°C, the process of sporulation requires 7.5 h at relative humidity ≥ 85%, with 3 h for sporophores emergence from stomata and 4.5 h for spore formation. Sporophores can emerge under light or darkness, but spore formation occurs in the dark only. Limited data are available on spore dispersal. Spores dispersed from sporulating plants contaminate healthy plants within 2 h of exposure. Settled spores may survive on leaf surface of healthy plants for prolonged periods, depending on temperature. Seed transmission of the disease occurs in Europe, but not in Israel or the United States. P. belbahrii in Israel also attacks species belonging to Rosemarinus, Nepeta, Agastache, Micromeria, and Salvia but not Plectranthus (coleus). A Peronospora species that infects coleus does not infect sweet basil. Control of BDM includes chemical, physical, and genetic means. The fungicide mefenoxam was highly effective in controlling the disease but resistant populations were quickly selected for in Israel and Europe rendering it ineffective. A new compound oxathiapiprolin (OSBP inhibitor) is highly effective. Nocturnal illumination of basil crops controls the disease by preventing sporulation. Daytime solar heating suppressed the disease effectively by reducing spore and mycelium viability. The most effective physical means is fanning. Nocturnal fanning prevents or limits dew deposition on leaf surfaces, and as a result, infection and sporulation diminish and epidemics are prevented. Genetic resistance occurs in wild basil and its transfer to sweet basil is under way.

Indole acetic acid production by fluorescent Pseudomonas spp. from the rhizosphere of Plectranthus amboinicus (Lour.) Spreng. and their variation in extragenic repetitive DNA sequences.

Fluorescent Pseudomonas (FP) is a heterogenous group of growth promoting rhizobacteria that regulate plant growth by releasing secondary metabolic compounds viz., indole acetic acid (IAA), siderophores, ammonia and hydrogen cyanide. In the present study, IAA producing FPs from the rhizosphere of Plectranthus amboinicus were characterized morphologically, biochemically and at the molecular level. Molecular identification of the isolates were carried out using Pseudomonas specific primers. The effect of varying time (24, 48, 72 and 96 h), Trp concentrations (100, 200, 300, 400 and 500 µg x ml(-1)), temperature (10, 26, 37 and 50 ± 2 degrees C) and pH (6, 7 and 8) on IAA production by 10 best isolates were studied. Results showed higher IAA production at 72 h incubation, at 300 µg x ml(-1) Trp concentration, temperature 26 ± 2 degrees C and pH 7. TLC with acidified ethyl acetate extract showed that the IAA produced has a similar Rf value to that of the standard IAA. Results of TLC were confirmed by HPLC analysis. Genetic diversity of the isolates was also studied using 40 RAPD and 4 Rep primers. Genetic diversity parameters such as dominance, Shannon index and Simpson index were calculated. Out of 40 RAPD primers tested, 9 (2 OP-D series and 7 OP-E series) were shortlisted for further analysis. Studies using RAPD, ERIC, BOX, REP and GTG5 primers revealed that isolates exhibit significant diversity in repetitive DNA sequences irrespective of the rhizosphere.