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https://www.insipub.com/ajbas/691-705.pdf


Induction and Modulation of Resistance in Tomato Plants Against

Fusarium Wilt

Disease by Bioagent Fungi (Arbuscular Mycorrhiza) And/or Hormonal
Elicitors (Jasmonic Acid& Salicylic Acid):
1- Changes in Growth, Some Metabolic Activities

and Endogenous Hormones Related to Defence Mechanism

Abstract:

Biological control and hormonal inducers represents an interesting strategy to induced
disease resistance against pathogen especially when applied together. In the present study, tomato
plants infected by

Fusarium oxysporum were inoculated with arbuscular mycorrhizal (AM) fungi

and/ or sprayed 3 times with hormonal inducers (JA& SA). Plants were harvested at 14, 28 and 42
days after pathogen infection. Results showed that % of disease incidence in infected plants
gradually increased with increasing time of infection (86% at 42 days). Treatments with AM fungi,
JA and SA significantly reduced % of disease incidence. AM fungi plus JA had the highest effective
(92% efficiency). Growth rate (shoot and root) and % of mycorrhiza colonization markedly inhibited
in tomato plants in response to

Fusarium wilt disease as compared with healthy control. AM fungi,

JA and SA were more pronounced in increasing tomato growth especially when applied together.
SA- treated plants had low effect in mycorrhization as compared with JA- treated plants. Reduction
in total chlorophyll in infected leaves significantly decreased in plants treated with AM fungi and/ or
SA. Also, total soluble sugars, free amino acids and total soluble proteins increased in both leaves
and roots of AM and/ or JA& SA- treated plants as compared with infected control. Induction in
growth rate of these treatments was associated with increased in the contents of some inorganic
nutrients (N, P, K, Ca, Zn and Mn). Treatment of AM fungi plus JA had the highest N, P, Ca
contents, while high levels of K, Zn and Mn were recorded in AM fungi plus SA- treated plants.
Results revealed that induction in the uptake of nutrients could be responsible for increasing
susceptibility of tomato plants to

Fusarium wilt disease. On the other hand, infection with F.oxysporum markedly altered hormonal balance (IAA, GA , ABA, zeatin and zeatin- riboside) in leaves and roots of tomato plants. Thus, ABA was accumulated while levels of IAA, GA and cytokinins markedly reduced in infected plants. Actually, results revealed that increase in disease incidence and decrease in growth of Fusarium- tomato plants could be a morphological expression of the hormonal imbalance. The reverse was true in plants treated with AM fungi plus JA or SA, where levels of IAA, GA , zeatin and zeatin- riboside significantly increased in both leaves and roots. Finally, our results suggest that reduction in disease incidence, promotion in growth and metabolic activities in tomato plants inoculated with bioagent(AM fungi) and sprayed with elicitors(JA& SA) could be related to the synergistic and cooperative effect between them; which lead to the induction and regulation of disease resistance. Thus, two signal hormones could enhance the biological activity of AM fungi in tomato , potentially through interaction signalling pathways. AM fungi plus JA more effective than AM fungi plus SA.