Abstract
Aloe vera (L.) Burm.f. is a highly important and extensively cultivated medicinal plant and that is also extensively used in the cosmetic industry. It has been frequently reported to suffer from Alternaria leaf spot disease in various parts of the world. Various fungicides used to combat this disease, have deleterious effects on the environment and on pharmacologically important constituents of Aloe vera. To avoid the harmful effects of fungicides an ecofriendly approach has been adopted here. A weekly survey was conducted during 2013–2015 in and around North 24 Parganas (West Bengal) to obtain the percentage of disease index (PDI). For biological control of the disease, screening of the antagonistic efficacy of biocontrol agents was carried out through the in vitro dual-culture-plate method and scanning electron microscopy (SEM) was used to study the mechanism. The in vitro effects of fungicides on the radial growth of the pathogen were evaluated through the poison food method and were compared with potent antagonistic fungi. Field application of potent antagonistic fungi was conducted through the dip-and-spray method. The results showed that, the PDI peaked during the hot and humid conditions of May to September (76.57%–98.57%) but decreased during the winter, December-January (35.71–46.66%). Trichoderma asperellum exerted the greatest inhibition of the radial growth of A. brassicae acting through non volatile (70.39%) and volatile metabolites (72.17%). A SEM study confirmed the hyperparasitic nature of T. asperellum through hyphal coiling-T. asperellum was similar to 2% blitox-50 (73.92%) and better than 2% bavistin (59.77%) (in vitro). In agricultural field trials (2013–15), Trichoderma application restricted the disease to the smallest area (PDI 24.00–29.33%) in comparison to untreated plots (73.33%). In conclusion, saplings treated with the dip method (108 spores / mL) and sprayed 4 times with a spore suspension of biocontrol agents such as T. asperellum, T. viride and T. harzianum, standardized at a rate of 2.5 L / plot (36 sq ft) (108 spores/ mL) are suggested for the ecofriendly management of this epidemic leaf spot disease of Aloe vera in agricultural fields.
Highlights
Aloe vera (L.) Burm.f. (Aloe barbadensis) belongs to the family Aloeaceae and is an extensively cultivated medicinal plant worldwide, ranging from tropical to temperate regions
Seed priming of tomato with plant growth promoting rhizobacteria (PGPR) such as Pseudomonas aeruginosa, P. putida, Bacillus subtilis, B.cereus, Azotobacter chroococcum are reported to increase seed germination, seedling vigor, fruit size, chlorophyll content, IAA production, and rhizospheric phosphate solubilization, which in turn improve plant health and growth
These PGPR strains induce plants’ defences through upregulation of defenserelated enzymes such asperoxidise, polyphenol oxidase, glucanase and chitinase along with the production of hydrogen cyanide (HCN), siderophore which act as the inducers against Alternaria-derived early blight disease in tomato and / or other plant disease resistance involving Systemic Acquired Resistance (SAR) / Induced Systemic Resistance (ISR) mechanisms[14]
Summary
Aloe vera (L.) Burm.f. (Aloe barbadensis) belongs to the family Aloeaceae and is an extensively cultivated medicinal plant worldwide, ranging from tropical to temperate regions. Seed priming of tomato with plant growth promoting rhizobacteria (PGPR) such as Pseudomonas aeruginosa, P. putida, Bacillus subtilis, B.cereus, Azotobacter chroococcum are reported to increase seed germination, seedling vigor, fruit size, chlorophyll content, IAA production, and rhizospheric phosphate solubilization, which in turn improve plant health and growth. These PGPR strains induce plants’ defences through upregulation of defenserelated enzymes such asperoxidise, polyphenol oxidase, glucanase and chitinase along with the production of HCN, siderophore which act as the inducers against Alternaria-derived early blight disease in tomato and / or other plant disease resistance involving Systemic Acquired Resistance (SAR) / Induced Systemic Resistance (ISR) mechanisms[14]. Formulations from T. viride, T. harzianum, and T. virens have been frequently used as soil applications that, alone or in combination, provided maximum efficacy against diseases of cereals, vegetables, pulses, spices and fruits [19,20,18]
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