Abstract
In the present study, Paenibacillus dendritiformis, Trichoderma harzianum, and Trichoderma asperellum were appraised as potential biocontrol agents that induce resistance in chilli (Capsicum annuum) against the devastating pathogen Colletotrichum truncatum, which causes anthracnose. Bright-field and scanning electron micrographs showed the hyphal degradation, lysis, and abnormal swelling in C. truncatum against P. dendritiformis in a dual plate assay. Under greenhouse conditions, chilli seeds pretreated with P. dendritiformis, T. asperellum, T. harzianum, and T. asperellum + T. harzianum by soil soak method inflicted an induced systemic resistance (ISR) in chilli against a C. truncatum-challenged condition. In chilli, the disease index percentage was significantly reduced in the T. asperellum + T. harzianum-treated seeds, followed by the T. harzianum-, T. asperellum-, and P. dendritiformis-treated seeds as compared to the untreated and challenged, respectively. Chilli seeds were primed with T. asperellum + T. harzianum (78.67%), which revealed maximum disease protection under the challenged condition, followed by T. harzianum (70%), T. asperellum (64%), and P. dendritiformis (56%) as compared to untreated and C. truncatum-challenged (6%) condition served as control. The seeds that were pretreated with biocontrol agents (BCAs) inflicted ISR against C. truncatum by enhancing the activity of defence-related enzymes (superoxide dismutase (SOD), peroxidase (POX), polyphenol oxidase (PPO), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and phenylalanine ammonia-lyase (PAL)), accumulating phenolic compounds, and increasing the relative chlorophyll content in chilli. Nitroblue tetrazolium (NBT) and 3,3′-Diaminobenzidine (DAB) stains were used to detect the accumulation of superoxide anion and hydrogen peroxide that appeared nearby the fungal infection sites. The accumulation of reactive oxygen species (O2− and H2O2) in the pathogen-inoculated leaves was a maximum of 48 hpi, followed by P. dendritiformis, T. asperellum, T. harzianum, and T. asperellum + T. harzianum treated tissue upon C. truncatum-challenged condition as compared to the control. Overall, our results showed the potential of T. harzianum, T. asperellum, and P. dendritiformis as biocontrol agents that prevent infection by C. truncatum and inflict an induced systemic resistance in chilli by enhancing the biosynthesis of phenolic compounds, defence and antioxidative enzymes, and reducing the lesion development and reactive oxygen species accumulation. This is the first report of induced systemic resistance against anthracnose in chilli obtained by application of T. harzianum, T. asperellum and P. dendritiformis, through seed priming.
Highlights
Chilli (Capsicum annuum L.), commonly known as “red pepper”, is an important fruit that is considered an essential spice in India and various other countries
The results revealed that the development of induced systemic resistance and reduction in fruit lesions was higher in T. asperellum + T. harzianum treated compared to independent-treated and C. truncatum-challenged samples
The results revealed that chilli fruits challenged with C. truncatum significantly enhanced the activities of superoxide dismutase, catalase, ascorbate peroxidase, and guaiacol peroxidase at 24 h and 48 h as compared to the untreated and unchallenged samples, but the maximum antioxidative enzyme activities were observed in the combination of T. asperellum + T. harzianum under C. truncatum-challenged condition
Summary
Chilli (Capsicum annuum L.), commonly known as “red pepper”, is an important fruit that is considered an essential spice in India and various other countries. Chilli peppers are a rich source of fibres, protein, vitamin A, C, and E, capsaicin, capsidiol, capsaicinoids, capsochrome, potassium, and folic acid. It is used in beverages and medicines [1,2]. In the last few years, the fruit yield suffered because of the attack of various diseases of biotic and abiotic natures Fungal diseases, such as anthracnose, damping-off, Fusarium wilt, collar rot, dry root rot, and stem rot, are considered the major cause behind these losses. Moore) alone caused 50% yield loss worldwide [7,8]
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