PHENOLS, POLYPHENOL OXIDASE AND PEROXIDASE IN PEPPER PLANTS INFECTED BY VIRULENT AND AVIRULENT STRAINS OF VERTICILLIUM

Pepper plants («Quadrato d'Asti») uninoculated or inoculated with a virulent isolate (P1) and with two avirulent isolates (M1 and M2) of Verticillium, were analyzed periodically for polyphenols and for polyphenol oxidase (PPO) and peroxidase (PO) activity in a study of pathogenesis in Verticillium wilt of pepper. After the initial appearance of slight wilt symptoms, the plants inoculated with M1 and M2 recovered whereas those inoculated with P1 became markedly stunted and showed severe wilt by the 10-13th day after inoculation. The polyphenol content increased above that of the control in the leaves of all the inoculated plants. The increase was moderate and did not consistently change with time in the leaves of the plants inoculated with the avirulent isolates, it was much more consistent, with a peak at the onset of severe (0.5) disease symptoms, in the plants inoculated with P1. The phenol content increased also in the stems of the inoculated plants with minor differences among Isolates. Marked activation of the PPO and PO enzymes were induced by P1 in the leaves as well as in the stem, with maxima at the most advanced disease stage. M1 and M2 induced intermediate and more fluctuating enzymatic responses. The data obtained are not consistent with the assumption that the general resistance exhibited by pepper plants against the majority of Verticillium isolates from other hosts is related to a prompt increase in phenols and/or phenol oxidizing enzymes. Foglie e fusti di piante di peperone («Quadrato d'Asti») non inoculate o inoculate con un ceppo virulento (P囎) e con due ceppi avirulenti (M1 e M2) di Verticillium, furono sottoposte ad analisi periodica dei fenoli e delle attività PPO e PO nell'ambito di una più ampia indagine sulla patogenesi della verticilliosi del peperone. Dopo l'iniziale comparsa di leggeri sintomi iniziali di awizzimento, le piante inoculate con M1 e M2 si ripresero mentre quelle inoculate con P1 presentarono sintomi progressivi di awizzimento e di nanismo a partire dal 10°-13° giorno dopo rinoculazione. Il contenuto in polifenoli aumentò nelle foglie di tutte le piante inoculate. L'aumento fu modesto e non vario sensibilmente nel tempo nelle piante inoculate con i ceppi avirulenti; fu più marcato con un massimo alla comparsa di sintomi fogliari gravi (0,5), nelle piante inoculate con P1. Il contenuto in fenoli aumento anche nel fusto delle piante inoculate con minori differenze tra i diversi ceppi. P1 indusse una forte attivazione