Indagini sull'eziologia del cancro corticale del noce da legno, sui fattori condizionanti e sulla resistenza genetica di Juglans
Author(s)
Ravaioli, Fulvio
Date Issued
February 27, 2009
Type
Doctoral Thesis
Abstract
This study has significantly contributed to clarify the ethiology of the bark canker, a serious emergent disease of the walnut for timber, to improve the knowledge on some predisposing factors and on the existence of Juglans species or cultivar resistant to it.
The ethiology of the disease has been investigated by isolations from diseased material coming from different zones and artificial inoculations in planta of the different pathogenic agents found, verifying the possible achievement of mutual antagonism or synergism and the ability of them to take asymptomatically place (endophytism) into the tissues of healthy plants.
The bacterium Brenneria nigrifluens and the fungi Botryosphaeria spp. (B. parva, B. dothidea e B. obtusa)and Fusarium solani, all agents of cortical necrosis, were always isolated from the advancement edge of the canker lesions. They have also been the only ones able to produce alterations on artificially inoculated young plants of walnut. With the evolution of the cankers, it would seem to increase the fungal incidence and to decrease that of the bacterium. The two fungi have also shown an endophytic habitus. Any mutual antagonism was observed among the three microorganisms, neither with other bark pathogens often aggregate to them, as Phomopsis juglandina and Paraconiothyrium brasilense.
It would seems therefore that the disease is evidence for a complex ethiology, in which probably B. nigrifluens triggers the lesions, on which suddenly Botryosphaeria spp. and Fusarium solani are installed (perhaps directly from the endophytic phase), extending and increasing the alterations and, in some case, replacing themselves with the bacterium.
The thickness of the plantings or however any circumstance that provoke elevated damp into the plantation seems to predispose the disease.
In experimental plantations struck by the disease, all the assorted cultivars of Juglans regia have unfortunately shown susceptibility to the disease, while Juglans nigra and the tested Juglans nigra x J. regia, NG23, hybrid resulted resistant.
The artificial inoculations of the three pathogens on a series of different species of Juglans have confirmed the susceptibility of Juglans regia and the good behaviour of J. nigra and its hybrids only approached by J. hindiis, of scarce practical interest. J. nigra represents therefore an interesting point of reference for a possible future genetic improvement of the walnut.
Additional information
Dottorato di ricerca in Protezione delle piante
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