Soil is a complex habitat where a large number of different micro organisms including fungal pathogens interacting with plants. These soil pathogens always depend on host to survive and reproduce.

They prefer to live within the soil and causing diseases in plants particularly tree seedlings.

Fungal pathogens

Common soil borne fungal pathogens and the diseases caused by them in tree seedlings are as follows.

Fusarium is a common soil fungal pathogen mainly cause root rots and wilt diseases in several tree seedlings in nursery. It reproduces very rapidly in the soil with adequate moisture.

Phytophthora causes root rot, crown rot and leaf blight in oak, poplar and eucalyptus seedlings. It is mostly found in contaminated soils and easily spreads through water.

Pythium is a fungal pathogen infects early stage of seedlings and causes damping off disease. Excessive moisture favours this pathogen to infect the seedlings.

Rhizoctoniat causes leaf blight in teak and damping off in most of the native tree species.

Verticillium fungi causes wilt disease at nursery stage in poplar, oak and shisham. Water stagnant in nurseries is one of the predisposing factors for the verticillium wilt disease.

Soil solarization

Soil solarization is the possible way to control or prevent these soil pathogens through raising of soil temperature.

Clean thin and transparent polythene sheet can be spread over the nursery soil. Solar energy will be trapped in this method and heats the soil This removes all the soil pathogens.

Soil fumigation with 4 per cent Formalin is also effective. The seed beds or nursery soils can be covered with thick polythene sheet and thereafter the Formalin solution sprayed on soil for fumigation. Overnight fumigation will give effective management of soil pathogens in nursery.

Preventive measures

— Right location with good drainage and appropriate sun light must be chosen before establishment of nursery.

— Injuries in seedlings should be avoided.

A.Karthikeyan & N. Krishnakumar, Institute of Forest Genetics and Tree Breeding, Coimbatore