Different isolates of P. terrestris the causal organism of onion pink root rot, greatly differed in pathogenicity and secretion of the hydrolytic enzymes, polygalacturonase (PG), pectinomethylestrase (PME) and cellulose (Cx) in vitro and in vivo.
Positive correlation was obtained between the virulence of the pathogen isolates and the production of PG, PME, and PPO but not of Cx and PO˃ Hydrolytic enzymes were correlated positively with the susceptibility of the onion cultivars, while the reverse occurred with oxidative enzymes.
Production of onion transplants by active systemic fungicides was due to the inhibition or the regulation of the hydrolytic enzyme production. This may interpret the lower pink root rot infection obtained with the use of systemic fungicide. On the other hand, further accumulation of PPO and PO enzymes were synthesized in the root and bulb tissues of fungicidal treated transplants and transplanted in infested soil. This may cause accumulation of synthesized polyphenols and their oxidative products which play an important role in limiting the pathogen in plant tissues.