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RESEARCHES ON THE EARLY WARNING OF INFECTIONS RISK WITH FIREBLIGHT ERWINIA AMYLOVORA AND BEHAVIOR OF SOME NEW APPLE CULTIVARS

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Author(s): Marin F.C | Sumedrea Mihaela | Călinescu Mirela | Sumedrea D., | Chitu E | Tănăsescu N

Journal: Scientific Papers of the Research Institute for Fruit Growing Pitesti, Romania
ISSN 1584-2231

Volume: XXVII;
Start page: 82;
Date: 2011;
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Keywords: apple cultivars | infection risk | artificial inoculation | shoots | fireblight

ABSTRACT
The paper presents the results regarding the early warning of the infections risk and the behavior of some new released and introduced apple cultivars and their vulnerability on fire blight (Erwinia amylovora). 20 apple cultivars, grafted on 6 rootstocks were assessed about their vulnerability and susceptibility on the infection with Erwinia amylovora on shoots. During 2009-2011, using common and specific software it was noticed that daily mean temperatures in May ranged between 14.8-19.9 ºC, but in June and July oscillated between 19.2-19.5 and 20.9-21.5 ºC. Also, daily mean air relative humidity ranged between 70.4-75.8% in May, 69.9-75.7% in June and 69.6-77.1% in July. The conditions were favorable for the apple blooming and shoots development, but for the pathogen as well. Investigations on the infections risks using the plants cells electric conductivity revealed that apple leaves and green fruits could be tolerant to first infections with Erwinia amylovora, as long as their juice or sap electric conductivity range between 190-250 mV, and their pH oscillate between 2.5-4.5. Artificial infections with Erwinia amylovora on growing shoot, sampled from some new apple cultivar-rootstock combinations, evidenced that the shoots collected from the cultivars ‘Initial /M9’, ‘Rustic /M9’, ‘Ariane /M9’, ‘Crimson Crisp /Pajam 1’ and ‘Golden Orange’ were not damaged, the disease attack frequency and severity being null 0%. Opposite, the attack higher frequency F% was noticed on the artificially infected shoots sampled from the cultivars ‘Dalinred/EMLA’, ‘Topaz /M9’ and ‘Topaz /T337’, and was between 5.88-9.78%. Among the artificially infected shoots, the most severely damaged (s=100%) were the ones sampled from the cultivars ‘Crimson Crisp /PI80’, ‘Dalinred /PI 80’, ‘Dalinred /T337’, ‘Dalinbel /EMLA’, ‘Goldrush /EMLA’ and ‘Topaz /M9’. All these aspects are very useful for schedule and precise execution of the preventive phytosanitary treatments against the fire blight, especially on the vulnerable cultivars.
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