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Title: Pathogen Diversity and Biological Control of Verticillium Wilt of Tomato
Contributor(s): Al-Hamadani, Hazim Sabah Rahmah (author); Knox, Oliver  (supervisor)orcid ; Kristiansen, Paul  (supervisor)orcid 
Conferred Date: 2024-03-28
Copyright Date: 2021
Open Access: Yes
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Verticillium dahliae is an important soil-borne pathogen that attacks a wide range of hosts, resulting in economic crop losses worldwide. With mounting concerns over pesticide use within current consumer markets, there is a need to search for alternative control options. One such approach is the development of biocontrol agents. This was the purpose of this study, which explored the effect of biological control strategies for tomato Verticillium wilt caused by V. dahliae using antagonistic fungi, either alone or in combination with or without salicylic acid (SA).

Pathogenicity of four strains of V. dahliae included DAR 33757 from cotton, DAR 31890 from tomato, DAR 44537 from potato and DAR 81260 from olive, and these were assessed on the tomato Grosse Lisse cultivar. Among these strains, V. dahliae DAR31890 from tomato was significantly more virulent on tomato. Therefore, this strain was selected in all subsequent experiments. Potential antagonistic fungi were isolated from cotton roots and soil that adhered to the roots (rhizosphere soil) and evaluated as potential biocontrol agents (BCAs) against V. dahliae. The greatest suppression of fungal activity towards the pathogen was recorded by isolates 2 and 7, which were isolated from rhizosphere soil and subsequently identified as Trichoderma harzianum and an Aspergillus sp.

In vitro, these antagonists inhibited microsclerotia (MS) germination and mycelial growth of V. dahliae, reduced disease severity and promoted tomato plant growth in the glasshouse experiments. Thus, these two fungi were chosen as BCAs for further experiments in the next experiments. Hoagland nutrient solution plus tomato root exudates significantly stimulated MS germination compared to water agar only, and also increased the fungal weight of the pathogen and antagonistic fungi in liquid culture experiments. Of the root exudate compounds tested, amino acids, organic acids, and sugars significantly stimulated MS germination compared with the water agar treatments.

Dipping tomato seedling roots in spore suspensions of T. harzianum or Aspergillus sp. prior to inoculation of stems with V. dahliae significantly reduced disease severity and increased tomato growth parameters. The results also showed that soluble protein concentration was significantly increased in tomato leaves treated with BCAs.

SA at concentrations of 0.5, 1 and 2 mM affected mycelial growth of V. dahliae, T. harzianum and Aspergillus sp. Tomato seed germination and seedling vigour were enhanced at 0.5 mM concentration of SA and significantly reduced at 2 mM concentration.

The combination of SA and BCAs enhanced activities of these fungi against V. dahliae. The combination of SA and BCAs significantly reduced disease severity and enhanced shoot dry weight of tomato plants more than using either antagonists or SA alone.

Overall, this study provides insight into the efficacy of T. harzianum and Aspergillus sp. isolates for biological control of V. dahliae. Also, a combination of BCAs and SA can improve the consistency of biological control against plant pathogens more than using them individually.

Publication Type: Thesis Doctoral
Fields of Research (FoR) 2020: 300409 Crop and pasture protection (incl. pests, diseases and weeds)
300804 Horticultural crop protection (incl. pests, diseases and weeds)
310805 Plant pathology
Socio-Economic Objective (SEO) 2020: 180602 Control of pests, diseases and exotic species in terrestrial environments
260599 Horticultural crops not elsewhere classified
280101 Expanding knowledge in the agricultural, food and veterinary sciences
HERDC Category Description: T2 Thesis - Doctorate by Research
Appears in Collections:School of Environmental and Rural Science
Thesis Doctoral

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