EFFECTS OF TEMPERATURE AND LEAF WETNESS DURATION ON THE INFECTION OF CELERY BY SEPTORIA-APIICOLA

The effect of temperature during various leaf wetness periods on the i nfection of celery (Apium graveolens) by Septoria apiicola was studied by inoculating plants with a suspension of 20,000 conidia per millili ter and incubating at five temperatures (10, 15, 20, 25, and 30 C) and for five wetness periods (12, 24, 48, 72, and 96 h). The number of le sions increased with temperature up to 25 C and then diminished. At ea ch temperature, lesions increased in number with increasing leaf wetne ss duration, except at 25 and 30 C at which fewer lesions appeared aft er 72 and 48 h of wetness, respectively. The highest number of lesions was recorded at 25 C for 72 h and the lowest at 10 and 30 C. The angu lar transformation of the proportion of the maximum number of lesions for each repetition was related to centered temperature and leaf wetne ss duration by a weighted least squares polynomial regression, (R(2)-a dj. [adjusted] = 74.8%). Cluster analysis was used to divide the respo nse surface into four disease-severity values. The shortest time inter val from inoculation to the appearance of first lesions occurred under optimal conditions of temperature and leaf wetness duration.