Plant Disease Research

Soil borne diseases are of serious concern in the production of disease free healthy apple nursery plants. Large numbers of seedlings/grafted plants are destroyed resulting in huge losses to the nursery producer and upsetting the planting targets. Most of these diseases have been partially controlled by soil-applied pesticides including formaldehyde, carbedazim, aureofungin, copper sulphate, metalaxyl etc. Dematophora necatrix Hartig (Rosellinia necatrix Prill.), and Sclerotium rolfsii causes root rot diseases in apple nurseries. In the present study an integrated disease management strategy involving non-chemical approaches control measures like soil solarization, biocontrol and the extracts/plant products of locally available medicinal plants were evaluated both in vitro and in vivo. The soil solarization studied carried out over the years revealed that solarization for 10 weeks resulted in increase in soil temperature by 7–10^oC at soil depths ranging from 10-30cm, thereby reducing the survival of propagules of Dematophora necatrix (31.66%) and Sclerotium rolfsii (46.66%) and reducing disease incidence. The plant products found inhibitory to Dematophora necatrix under in vitro and amended to pot mixture (soil:sand:vermicompost) resulted in increase in fungal population in caster (40.23X10⁴) followed by wild marigold (33.75x10⁴). Bacterial population was also maximum in caster (207.64x10⁵) followed by lantana (144.27x10⁵) whereas actinomycetes were maximum in garlic (31.96 x 10³) followed by caster. Experiments conducted at six locations in different blocks of district Shimla, Mandi and Kullu districts, where the disease is of regular occurrence revealed that soil heating by burning stubbles or soil solarization followed by application of Trichoderma viride at the time of transplanting and subsequent soil amendments with garlic/Vitex leaves have been found to be the best in comparison to control and other treatments.