Artificial induction of the apple replant problem byPenicillium claviforme inoculation

Inoculation of apple seedling roots withPenicillium claviforme reduced plant growth and resulted in morphological changes of roots resembling those found in seedlings growing in ‘apple replant problem’ soil (apple-sick soil). The introduced fungus persisted in the rhizosphere throughout the 30-month test period. The numbers of colony-forming units (CFU) ofPenicillium claviforme, as well as the ‘total’ number of CFU of micromycetes, were higher in the rhizoplane of the inoculated seedling in comparison with uninoculated plants. The numbers of CFU of phytotoxic micromycetes in the rhizosphere soil of inoculated seedlings were also proportionally higher. Apple tree growth was also reduced when seedlings were inoculated with the flucrescent bacteriumPseudomonas putida; however, no morphological changes were observed in the roots. Both micro-organisms introduced into the apple seedling rhizosphere caused changes in the microbial community. Inoculation withPenicillium claviforme andPseudomonas putida caused a decrease in the number of mycolytic bacteria in the rhizoplane of apple seedlings.