Epidemiology of Leaf Spot of Olive Tree Caused by Spilocaea Oleagina in Southern Spain

Factors Affecting Infection and Disease Development on Olive Leaves Inoculated with Fusicladium oleagineum

“…Infection and scab development were similar witb detached leaves and intact plants, confirming a previous report that detacbed leaves could be used to study tbis disease (43). Tbe use of detacbed leaves rather tban plants saves space and time.…”

“…Although results of the present study agree with some field observations (4,9,36,43), it is often difficult to compare field studies on the effects of environmental conditions on disease development ' The incubation period iJP) tor each plant was calculated as IP = Z[(i, -n,-i) x ',]/W, where n, -n,_i is the number of affected leaves between two successive assessments, r, is the time in days from inoculation, and N is the total number of assessed leaves. Disease severity (S) was assessed at the end of experiment using a rating scale of 0 to 8 (0 = no lesions, 8 = 88-100% of leaf surface covered with scab lesions or latent infections), "Plants were classified into two categories: young (tender leaves, <6 months old) and old (tough leaves, >7 months old). "…”

“…Factors determining the change from latent infection to active scab lesion are not known, but leaf wetness seems essential, as suggested by the differences between plants that were incubated in a growth chamber (without wetness) and those incubated in a shadehouse (688 h wetness); latent infections were much less numerous in the wet environment. Field observations are also consistent with this hypothesis because scab lesions appear after long periods of wetness (4,24,28,43).…”

“…If rain is frequent and temperatures are mild during spring, and if scab lesions are abundant on old leaves, severe epidemics may occur. The great importance of spring infection for olive scab epidemics has been emphasized by others (35,38,43) based on the extreme susceptibility of young leaves that are not protected by fungicides (38). Spring infections usually remain latent until the next fall or winter, when environmental conditions allow the development of scab lesions (43).…”

“…Most of this work has been done in the field, and information on the precise effects of environmental variables on olive scab under controlled conditions is scarce and imprecise (32,45,48). Data on how environmental variables affect disease development are needed to develop a forecasting system and an integrated approach to olive scab control (43). Recently, López-Doncel et al (22) described a method for inoculating olive with F. oleagineum that should facilitate epidemiological studies.…”