טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentEfrat Bar
SubjectIdentification and Characterization of Microorganisms in
Apple Orchard Soils
DepartmentDepartment of Biology
Supervisors Full Professor Beja Oded
Dr. Doron Holland
Dr. Yael Laor
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Replant disease occurs when recently uprooted orchard is planted in the same spot with trees of the same species. The disease is manifested in slow growth of foliage and delayed fruit bearing. Alleviation of the replant symptoms by soil disinfection, or soil enrichment with compost, raised the assumption that this disease is primarily a biological phenomenon. Studies have demonstrated that the application of fungicides on Replanted soil led to increased growth of apple seedlings, reinforcing the hypothesis that fungi have a major role in the development of the disease.

We aim to find differences between soil fungi species in replant and virgin soils, and to characterize the effect of root residues on the dynamics of those fungi species in the soil. For the study, plots in Neve Ya’ar were planted with 5 trees each: Virgin plot, and Replanted plot.  

Fungi DNA from the different soil samples was amplified and the products were separated using Denaturing Gradient Gel Electrophoresis. Unique bands were found in the virgin and replanted soil and their involvement in the Replant phenomenon was suspected.

Sequencing and characterization the bands suggested that the fungi species found in the replant plot are pathogens of different plant species, while species found in virgin soil have known inhibitory effect against negatively affecting soil microorganisms. The effect of roots residues on soil fungi dynamics was investigated in an experiment containing four treatments. various treatments were tested for the presence of the unique fungi species found in the previous experiment. Despite the identification of different fungal species in virgin and replanted soils, assessing the impact of root residues on the fungi dynamics did not allow to conclude that these fungi indeed has a role in replant disease in this experiment.  However, higher mortality rate of apple seedlings, which were planted in pots containing root residues, suggesting that the presence of uprooted apple tree roots have an impact on the survival of the seedlings .

In conclusion, Differences between fungi population were found in the Virgin and in the Replant plots. The different species, may indicate that the Replant soil thrives with apple tree pathogenic fungi, and lacking fungi which inhibit the development of  plant pathogens fungi. We cannot extrapolate the universal involvement of these species in the Replant phenomenon. It is possible that the presence of microorganisms extracted founded on the apple tree root residues have an effect on the survival of apple seedlings.