Coffee husk waste as a carrier for bioagents: development of Trichoderma-Bacillus consortia and their antimicrobials against soil borne Phytophthora cinnamomi Rands. in avocado

Abstract

In vitro studies identified Trichoderma harzianum T(MP)-7 and Bacillus amyloliquefaciens B(TI)-3 as effective biocontrol agents against Phytophthora cinnamomi PC(TKI)-10. The isolates were found compatible under in vitro conditions, and a bioformulation combining them in a 1:1 ratio was tested in different substrates. Among tested, coffee husk-based bioformulations supported the highest microbial populations, with initial counts of T. harzianum T(MP)-7 at 7.5 × 10¹² CFU/g and B. amyloliquefaciens B(TI)-3 at 6.8 × 10¹¹ CFU/g, which declined to 3.1 × 10⁷ and 3.8 × 10⁸ CFU/g, respectively, by day 120. In soil amended with coffee husk-based bioformulations, initial counts of T. harzianum T(MP)-7 (5.8 × 10⁷ CFU/g) and B. amyloliquefaciens B(TI)-3 (4.3 × 10⁷ CFU/g) declined to 2.4 × 10³ and 1.5 × 10³ CFU/g, respectively, over the same period. Coffee husk-based bioformulation significantly enhanced avocado seedling growth, achieving a 92 % germination rate, 14.00 cm root length, 52.43 cm shoot length, and an average of 16.33 leaves. GC-MS analysis identified multiple antifungal compounds, including azelaic acid, palmitic acid, stearic acid, squalene, caffeic acid, gallic acid, chlorogenic acid, and 3-hydroxybenzoic acid. Additionally, B. amyloliquefaciens B(TI)-3 harbored antifungal antibiotic-producing genes, successfully amplifying iturin D (800 bp), bacillomycin D (482 bp), iturin C (506 bp), bacillomycin A (344 bp), fengycin D (220 bp), mycosubtilin (482 bp), surfactin (675 bp), and β-glucanase (400 bp). Similarly, T. harzianum T(MP)-7 tested positive for chitinase (1700 bp) and β-1,3-glucanase (850 bp). Soil application of coffee husk-based bioformulation at 10 g/kg, alone or combined with arbuscular mycorrhizal fungi (AMF) and micronutrients significantly reduced P. cinnamomi disease severity. The combined treatment resulted in a mean disease severity index (DSI) of 16.00 %, representing a 64.71 % reduction over control, while coffee husk-based bioformulation alone reduced DSI to 21.31 % (53.87 % reduction). These findings highlight the potential of coffee husk-based bioformulations as a sustainable biocontrol strategy against P. cinnamomi, improving plant health and growth in avocado cultivation.