Biopriming chilli seeds with Trichoderma asperellum: A study on biopolymer compatibility with seed and biocontrol agent for disease suppression

Abstract

In this study, the biocontrol agent, Trichoderma asperellum, was bioprimed onto chilli seeds using several biopolymers (sodium alginate, carboxymethylcellulose, gum arabic, xanthan gum). T. asperellum showed >60 % growth inhibition towards Fusarium solani and Pythium ultimum, and is used subsequently for all tests. The compatibility of biopolymers to seed and T. asperellum, and the performance of the bioprimed seeds in tolerating disease is then assessed. Results showed that 1.5 % w:v sodium alginate (SA1.5) (imbibed for 1 h) has the highest compatibility with chilli seeds, with percentage of germination at 77.78 ± 4.44 %, seed vigour index at 320.79 ± 58.14 and germination rate at 1.27 ± 0.06. This treatment (SA1.5) also resulted in high coating efficacy, retaining 83.17 % of viable spores on chilli seeds and maintaining spore viability (4.08 ± 0.03 log spore/seed) after 24 h post-biopriming. SEM observations revealed high distribution of spores on chilli seeds with the use of SA1.5. With a treatment of just 102 spores/mL, the bioprimed seeds were able to suppress disease severity (DS) by F. solani in potted trials (27.33 ± 4.04 % DS). This is attributed to mycoparasitic properties of T. asperellum. Under F. solani infection, low proline level was recorded in bioprimed seedlings (0.94 ± 0.01 µmol/g fr. wt.) compared to non-bioprimed seedlings (5.05 ± 0.13 µmol/g fr. wt.), suggesting T. asperellum protected seedlings from pathogen. By contrast, the formulation of T. asperellum was less effective towards P. ultimum, as relatively high proline level (3.37 ± 0.05 µmol/g fr. wt.) and a lower total phenolic content (99.61 ± 4.29 mg GAE/100 g fr. wt.) were recorded. To conclude, our results revealed the compatibility of biopolymers, specifically sodium alginate with chilli seeds and T. asperellum, leading to enhanced efficacy in seed biopriming and seed tolerance to infection by F. solani.