Microbes in Agriculture Flashcards
What do bacteria and fungi play beneficial roles in?
Bioremediation and phytoremediation, plant growth promotion, disease resistence, nitrogen fixing
Examples of pathogens (bad guys) in agriculture?
Fungi and oomycetes are important pathogens of crops throughout the world
-Phytophthora infestations (oomycete)
-Magnaportha oryzae (fungus)
What are oomycetes?
A distinct lineage of fungus-like eukaryotes that are related to organisms such as brown algae and diatoms
What is Phytophthora infestans?
The most destructive pathogen of potato and a model organism for the oomycete
-agent of the irish potato famine in mid 19th century
-management of this devastating pathogen is challenged by its remarkable speed of adaptation to control strategies such as genetically resistant cultivars
Phytophthora blight - phytophthora capsici
-Infected plants and fruit produce millions of asexual sporangia
-Each sporangium produces 20-40 swimming zoospores
-Pathogen spreads in water, splashing rain, irrigation
-Infeted plant dies, pathogen remains in debris
-If both mating types are present, oospores are produced
-Oospores can survive for years in soil and will infect roots or fruit when conditions are favourable
Example of a major fungal pathogen of rice?
Magnaportha oryzae
Magnaportha oryzae infection?
-Rice blast affects seedlings, causing a leaf spot disease
-In the field, the fungus sporulates profusely at nodes on the rice stem and rots the neck of the mature rice plant
-M.oryzae sporulates from lesions, and spores are dispersed by dewdrop splash
What can be used to look at Magnaportha oryzae?
Scanning micrograph
What does the dome-shaped appressorium do?
Generates enormous turgor of up to 8MPa to rupture the rice leafe cuticle
What initiates the Magnaportha oryzae fungal infection?
M.oryzae condida
Examples of bacterial plant pathogens?
Streptomyces scabies - gram pos
Xanthomonas oryzae - gram neg
What does streptomyces scabies do?
A gram pos actinomyces causing potato scab
What does Xanthomonas spp. do?
Bacterial plant pathogens that attack a wide range of host plants - look at diagram
-Bacterial blight and bacterial leaf streak of rice are caused by pathogenic variants of Xanthomonas oryzae
What was the beginnings of virology?
Tobacco mosaic virus
-RNA virus
Examples of good bacteria
Bacteria of the rhizobiaceae form symbiotic associations with leguminous plants - fix atmospheric N2
-Rhizobium
-Bradyrhizobium
-Sinorhizobium
-Mesorhizobium
How can rhizobacteria promote plant growth?
-The production of plant hormones such as IAA- indole acetic acid
-Increasing availability of nutrients to the plants (P,S,N, C- fixation(photosynthesis), decomposition)
-Restriction of the action of pathogens
What does Pseudomonas fluorescens F113 do?
Bacterial-oomycete interaction
Pseudomonas fluorescens F113 inhibits Pythium ultimum by production of 2,4-diacetyl phloroglucinol
What is pythium ultimum?
An oomycete, casual agent of early damping-off disease in sugar beet
What is Induced Systemic Resistance (ISR)?
Bacterial application to plant roots confers resistance to a range of pathogens subsequently applied to the leaves
-Fluorescent pseudomonads added to roots
-Fungi, oomycetes, bacteria - leaves resistant to these
Examples of direct PGP- plant growth promotion?
-N2 fixation
-Phosphate solubilization
-Iron production
-Auxin production
-ACC deaminase production
-Cytokine production
Examples of indirect PGP mechanisms?
-Antifungal metabolites production
-ISR responses
Neg PGP mechanisms
-Antibiotics
-HCN
-Lytic enzymes
