Pathogens In Plants

water or fertilizer. It is not unusual for plants with root rot to regenerate new roots to replace those killed by the pathogen, but the newly developed root system may only support the plant when adequate moisture is available. Such plants may not show above ground symptoms well enough to be culled in the nursery prior to sale. As several pathogens can produce the same symptoms, and two or more pathogens may be affecting the nursery crop, nurseries need access to a professional diagnostic laboratory. Accurate identification of pathogens is essential to allow the correct decision to be made regarding disease management (Anon.2016g).

7.1. Phytophthora spp.: Phytophthora spp. generally attacks roots, often entering at injury points (Gray and

Fusarium spp. : A large number of Fusarium spp. are present in soil, often occupying a saprophytic role from where susceptible host tissue may be attacked. Fusarium avenaceum, F. culmorum, F. oxysporum and F.solani are the more important species involved in diseases of seedlings and cuttings. These species are generally not host specific at the seedling stage and have a wide host range. Fusarium attack can result in seedling death. Fusarium species associated with plants can be pathogens, endophytes or saprophytes. They are widespread and can be a significant threat to production nurseries. They can cause damping-off, root and bulb rots, crown rots, stem and cutting rots, leaf spots and vascular wilts. Arguably the two most important species which impact nursery production are Fusarium oxysporum and Fusarium

Conidia and spores are normally dispersed by water splash although some are dispersed by air currents.

b) Species generally possess excellent saprophytic capabilities, and can survive for long periods as chlamydospores in host tissues, and as non-pathogenic parasites on alternative hosts.

c) Fusarium can be introduced into nurseries in a number of ways but most commonly with infected seed, corms or bulbs, cuttings and transplants. Seed coats can be contaminated with spores, or pieces of infected plant tissue, or there may be internal seed infection. Infected cuttings can be taken from apparently healthy plants.

7.4. Pseudomonas spp.: Wet and soft rot that affects any part of vegetable crops including heads, curds, edible roots, stems and