Lecture 10c: Plant-Pathogen Fungi and OOmycetes Flashcards
Root rot diseases
- if symptoms appear aboveground, the plants usually fail to recover
- Browning and softening of root tips, root lesions that vary in size and colour, yellowing and wilting of leaves, stunted plant growth, reduced yield and crop loss
Host and pathogen white root rot
Host: Avacado
Pathogen: Rosellinia necatrix
detected in Limpopo, MPU, KZN
Info about Rosellinia necatrix
- Soil-borne
- Necrotroph
Symptoms of white root rot of avocados
- above-ground: only noticeable once infection is established, Leaf yellowing, wilting and drying on the tree
*White, cottony mycelial growth: roots, soill surface, Underneath the bark at the crown
Sexual spore disease cycle of white root rot of avocados
- Easily found in infected tissue
- Sexual structures formed inside perithecium
- Perithecium takes a long time to develop and only under natural conditions
Asexual spore disease cyce of white root rot of avocados
- Clamidospores: Rarely found under natural conditions
- Conidiospores: Conidia originate at the ends of synnemata
penetrate avocado roots through
- Natural openings
- Wounds
- Direct penetration via a sclerotium
Epidemiology of white root rot of avocados
- Soil moister is the most important factor
- Mycelium growth requires good aeration
- mycelium growth is inhibited by light
- Organic material enhances mycelium growth
- Unlike most fungi, R.necatrix growth is not inhibited by high pH
Management of white root rot of avocados
- Physical control: soil solarisation, soil/root barriers to prevent mycelium spread, burning infected trees
- Resistant roots
- Chem control: Chloropicrin, fungicides, fluazinam
- Biological control: Mycoviruses, Trichoderma spp., Bacteria (Bacillus subtilis)
Phytophthora root of avocados H&P
Host: avocado
Pathogen: Phytophthora cinnamomi
Symptoms of phytophtora root rot of avocados
- Chlorosis, brown necrotic leaf tips and space foliage
- Infected feeder roots turn black and brittle
- Redis-brown crankers (not common in avos)
Phytophthora cinnamomi characteristics
- Soil-borne pathogen
- Hemi-biotroph
- Large host range
- First discovered in SA
Zoospore disease cycle of phytophthora root rot of avocados
Swim through water filled soil pores, atrracted by root exudates
Chalmydospore disease cycle of phytophthora root rot of avocados
Are thick-walled spores (asexual). Survival structures
Sporangia disease cycle of Phytophthora root rot of avocados
- Release zoospores in flooded or water-saturated soils
- Form on the surface of infected tissue