Articles
INVESTIGATIONS ON OLIVE LEAF SPOT IN SARDINIA
Article number
586_166
Pages
769 – 772
Language
English
Abstract
Olive leaf spot, a disease induced by Spilocaea oleagina (Cast.) Hughes is widespread in Sardinia (Italy), where it is especially severe on cv.
Tondo Sassarese.
The most important effect of olive leaf spot attacks is premature defoliation which, in turn, has consequences on the plant’s vegetative activity and yield.
The relationship between early leaf shedding and plant behaviour with reference to flower production and fruit setting, was analyzed with a 5-year study (1994-98) conducted in a heavily infected area in the province of Sassari.
To this effect, homogenous groups of trees that were exposed to natural infections (referred to a “non protected trees”) or were treated with two spring treatment of a mixture of copper oxychloride and dodine (referred to as “protected trees”), were comparatively investigated.
The data collected were worked out statistically by the analysis of variance and Duncan’s test.
Whereas no significant differences were observed in defoliation rate between protected and non protected plants in summer, leaf shedding was significantly higher in non treated trees during autumn and winter.
The influence of early defoliation on flower bud differentiation was clear-cut, as the number of flower clusters was significantly lower (31%) in non protected plants, which had suffered heavy leaf dropping.
By contrast, buds from protected trees, that had retained leaves for longer periods, tended to differentiate into flower with a significantly higher frequency (81%).
A comparable effect was observed with reference to fruit production, which was significantly higher (28%) in protected plants, as compared with the prematurely defoliated non protected trees (8%). The detrimental effect of defoliation on flower production and fruit setting, which was dramatically shown by trees exposed to natural olive leaf spot attacks, was also evident in protected trees.
Also in these plants, fruit setting rate was higher (42%) in flower clusters originated from buds that had retained the leaf than in clusters from buds that had shed the leaf (13%).
In summary, the present investigation has experimentally shown the detrimental influence of premature defoliation on flower production and fruit setting regardless of whether or not defoliation is incited by fungal attacks.
In particular: (i) although in both protected and non protected trees buds that have suffered premature leaf shedding produce less flower clusters, this reduction is significantly higher in trees fully exposed to natural S. oleagina infections; (ii) flower clusters derived from buds that had retained the leaf yield a significantly higher fruit setting; (iii) controlling leaf spot chemically has a clear-cut beneficial effect on the crop, which is especially evident in the presence of heavy fungal attacks.
When infection is light and premature defoliation is also light, bearing of untreated plants can still be satisfactory.
Tondo Sassarese.
The most important effect of olive leaf spot attacks is premature defoliation which, in turn, has consequences on the plant’s vegetative activity and yield.
The relationship between early leaf shedding and plant behaviour with reference to flower production and fruit setting, was analyzed with a 5-year study (1994-98) conducted in a heavily infected area in the province of Sassari.
To this effect, homogenous groups of trees that were exposed to natural infections (referred to a “non protected trees”) or were treated with two spring treatment of a mixture of copper oxychloride and dodine (referred to as “protected trees”), were comparatively investigated.
The data collected were worked out statistically by the analysis of variance and Duncan’s test.
Whereas no significant differences were observed in defoliation rate between protected and non protected plants in summer, leaf shedding was significantly higher in non treated trees during autumn and winter.
The influence of early defoliation on flower bud differentiation was clear-cut, as the number of flower clusters was significantly lower (31%) in non protected plants, which had suffered heavy leaf dropping.
By contrast, buds from protected trees, that had retained leaves for longer periods, tended to differentiate into flower with a significantly higher frequency (81%).
A comparable effect was observed with reference to fruit production, which was significantly higher (28%) in protected plants, as compared with the prematurely defoliated non protected trees (8%). The detrimental effect of defoliation on flower production and fruit setting, which was dramatically shown by trees exposed to natural olive leaf spot attacks, was also evident in protected trees.
Also in these plants, fruit setting rate was higher (42%) in flower clusters originated from buds that had retained the leaf than in clusters from buds that had shed the leaf (13%).
In summary, the present investigation has experimentally shown the detrimental influence of premature defoliation on flower production and fruit setting regardless of whether or not defoliation is incited by fungal attacks.
In particular: (i) although in both protected and non protected trees buds that have suffered premature leaf shedding produce less flower clusters, this reduction is significantly higher in trees fully exposed to natural S. oleagina infections; (ii) flower clusters derived from buds that had retained the leaf yield a significantly higher fruit setting; (iii) controlling leaf spot chemically has a clear-cut beneficial effect on the crop, which is especially evident in the presence of heavy fungal attacks.
When infection is light and premature defoliation is also light, bearing of untreated plants can still be satisfactory.
Publication
Authors
M.P.M. Mungianu, L. Otgianu, G. Tolu, R. Garau, V.A. Prota, U. Prota
Keywords
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