Infected host as reservoir of inoculum:

The infected host serving as reservoir of active inoculum is grouped into

a) Seed: Seed may be externally or internally infected by plant pathogens during the course of development and maturation in fruit or pod. Most seed borne pathogens survive as long as seed remains viable.

Ex 1: The pathogen of loose smut of wheat, Ustilago nuda tritici, enters the stigma and style and infects the young seed, in which it survives as mycelium.

Ex 2: Pseudomonas syringae pv. tomato has been shown to survive in dried tomato seed for 20 years.

b) Collateral hosts / Alternative hosts (wild hosts of same families): Collateral hosts are those which are susceptible to the plant pathogens of crop plants and provide adequate facilities for their growth and reproduction of these pathogens during off- season.

Ex: The fungal pathogen for blast disease of rice, Pyricularia grisea (Teleomorph: Magnaporthe grisea) can infect the grass weeds like Brachiaria mutica, Dinebra retroflexa,  etc., and survive during off-season of rice crop. As soon as a fresh rice crop is raised, the conidia (inoculum) liberated from the weed host disseminated by wind infects the fresh rice crop.

c) Alternate hosts (Wild hosts of other families):When a pathogen has very wide host range (as Sclerotium rolfsii, Rhizoctonia solani, Fusarium moniliforme) and is tolerant to wide range of weather conditions the alternate hosts become very important source of survival of the pathogen.

For example in temperate regions the alternate host of Puccinia graminis tritici (black or stem rust pathogen of wheat), the barberry bush (Berberis vulgaris) grows side by side with the cultivated host. In such areas this wild host belonging to a different family is important for survival of the fungus.

d) Self sown crops: Self sown crops, voluntary crops and early sown crops are reservoirs of many plant pathogens. Ex: Self sown rice plants harbour the pathogen (Rice tungro virus) as well as vector (Nephottetix virescens).

e) Ratoon crops: Sometimes ratoon crops also harbour the plant pathogens.

Ex: Sugarcane mosaic.

f) Survival by latent infection: Latent infection refers to the conditions in which the plant pathogens may survive for a long time in plant tissue without development of visual symptoms.

 Ex: Xylella fastidiosa, the causal agent of pierce’s disease of grapevine infect different weeds without developing visible symptoms.