Biological control of Plasmodiophora brassicae in two important Brassica species

Maryam Khodashenas Rudsari, MSc

Disertační práce

Abstract:

Rapeseed (Brassica napus) and Chinese cabbage (B. rapa) are economically significant Brassica crops cultivated worldwide, but their production is often hampered by severe infections of Plasmodiophora brassicae, causing substantial economic losses. P. brassicae, the causative agent of clubroot, is a challenging pathogen to manage due to its long-lived resting spores, broad host range, and diverse pathotypes. Biocontrol strategies involving chitinolytic organisms, which produce chitinase, are gaining traction as environmentally friendly alternatives to chemical treatments. Chitinases play a crucial role in protecting plants against chitin-containing pathogens, and since chitin is a major component of P. brassicae resting spores and is critical during pathogenesis, chitinase-producing organisms such as Paenibacillus chitinolyticus, Trichoderma harzianum, and T. viride may suppress P. brassicae by targeting chitin at key stages of its life cycle. This study investigated whether endemic chitinolytic bacteria, including P. chitinolyticus, and fungi, including T. harzianum and T. viride, could effectively suppress clubroot. Greenhouse experiments were conducted in three phases. In the first phase, the biocontrol potential of P. chitinolyticus cell-free supernatant (CFS), T. harzianum, and T. viride on Chinese cabbage was evaluated. The second phase assessed the combined effects of the bacteria and fungi. Disease severity index was determined 35 days after inoculation with P. brassicae. Results revealed that applying P. chitinolyticus, T. harzianum, and T. viride on the same day as pathogen inoculation reduced disease severity index in Chinese cabbage by 55%, 75%, and 86%, respectively. However, while combining P. chitinolyticus with either species of Trichoderma reduced clubroot severity, none of these combinations outperformed the individual applications of P. chitinolyticus, T. harzianum, or T. viride. In the final phase, additional experiments extended the assessment to include application timings at 5 and 14 days post-inoculation to identify the optimal timing of P. chitinolyticus CFS for controlling clubroot in both Chinese cabbage and rapeseed. The findings demonstrated that P. chitinolyticus CFS was most effective in the early stages of clubroot development, with diminishing suppressive effects in later stages. Notably, P. chitinolyticus CFS also improved shoot dry weight in both crops, highlighting its dual potential as a biofertilizer and bioprotectant in clubroot management. In conclusion, applying P. chitinolyticus on the day of P. brassicae inoculation or within nine days afterward significantly reduces disease severity and effectively suppresses clubroot. However, field trials are necessary to validate the efficacy of P. chitinolyticus CFS under real-world conditions.

Keywords

Biocontrol, Clubroot, cell free supernatant, Paenibacillus chitinolyticus, Chinese cabbage, Trichoderma

Jazyk práce: angličtina

Datum vytvoření / odevzdání či podání práce: 11. 2. 2025

Obhajoba závěrečné práce

• Vedoucí: doc. Ing. Miloslav Zouhar, Ph.D.
• Oponent: Jaroslav Salava, Ing., CSc., externi, Petr Baranyk, externi, Radovan Pokorný, Mgr., externi

Česká zemědělská univerzita v Praze

Fakulta agrobiologie, potravinových a přírodních zdrojů

Doktorský studijní program:
Plant Protection