EPWS 310 - PLANT PATHOLOGY
Contents of Lecture
Reading: pages 409 - 427
Serious diseases caused by Pythium and Phytophthora
These fungi are necrotrophs and range from root nibblers to outright root rots.
Pythium species tend to be root tip "nibblers" but may still account for serious yield losses.
Some Pythium species cause damping off and mild root rots usually of younger plants. They are bad in nurseries. Many Pythium species cause root defromation and may only be serious in root crops eg carrot and sugar beets (P. violae, P. ultimum and P. aphandermatum).
Pythium Disease Cycle Figure 11-18
Phytophthora species are very serious root rot in irrigated agriculture - zoospores.
There are several species which cause root rot of commercial crops and orchard trees. The initial above ground symptoms occur long after infection and colonization has progressed. The plants show wilting and general chlorosis and rapid necrosis and death of the whole plant or large parts of the plant.
Some Phytophthora root rots are very aggressive and can kill whole fields in a short time if condition are right. What are right conditions?
Older trees show decline and dieback rather than death. see next section
Chile root rot.
These fungi are able to infect most parts of the root system (cf. Pythium) and can grow along the root and up to the crown and stem. Control depends on resistance, good water management, rotation and careful chemical control (resistance).
Many Phytophthora species cause diseases of the lower stem of many woody hosts. such as nut trees, Citrus, avocado and forest trees. This causes decline dieback and death, P. cinnamomi, P. citrophthora (on citrus).
Injection of Phosphorous Acid (Fosetyl Al) and Metalaxyl have been very successful (because not in soil).
Many Phytophthora species have deciduous sporangia that are dispersed by wind eg P. infestans.
Rain splash and wind spreads sporangia and these diseases can be VERY serious.
See P. infestans.