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Kubilay Kurtulus Bastas, Aysen Akay, and Salih Maden

The first outbreak of fire blight incited by Erwinia amylovora (Burr.) Winslow et al. occurred on pome fruits in Turkey in 1985, and it is now one of the most serious diseases of pear, apple, quince, and loquat (Oktem and Benlioglu, 1988). In this study, experiments were conducted in Konya Province to evaluate the efficacy of Glomus intraradices Schenck & Smith vesicular–arbuscular mycorrhiza (VAM) and bactericides for control of the shoot blight phase of fire blight and control of shoot growth on the different apple cultivars (Gala, Red Elstar, Pinova, Jonagored) on M9 rootstock in 2002 to 2003. Streptomycin provided 84.38% to 95.24% and 85.28% to 89.97% disease control in 2002 and 2003, respectively. Copper complex was not so effective against shoot blight phase of the disease, and it reduced disease by 16.18% to 27.75% and 14.48% to 19.06% in 2002 and 2003, respectively. Results of VAM application were encouraging, indicating a reduction of fire blight by Glomus intraradices of between 9.7% and 50.5% in 2002 and between 23.9% and 48.4% in 2003, respectively.

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Joseph J. Rothleutner, Ryan N. Contreras, Virginia O. Stockwell, and James S. Owen

characteristics. Although Cotoneaster generally is robust and easy to cultivate, many taxa are susceptible to the bacterial disease fire blight caused by Erwinia amylovora . Disease susceptibility limits the potential of the genus in landscape applications. For

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Kubilay Kurtulus Bastas and Fikrettin Sahin

adaptation studies ( Barut, 2000 ). Fire blight, caused by the bacterium Erwinia amylovora (Burr.) Winslow et al., is a disease that affects many Rosaceous species with apple ( Malus sp.) and pear ( Pyrus sp.) being of the greatest economic significance

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Nicole L. Russo, Terence L. Robinson, Gennaro Fazio, and Herb S. Aldwinckle

is their susceptibility to rootstock blight, a discrete fire blight infection of the rootstock. Fire blight, incited by the bacterium Erwinia amylovora [(Burr.) Winslow et al.], is a common bacterial disease of rosaceous plants ( Vanneste and Eden

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Henry K. Ngugi and James R. Schupp

for blossom thinning of fruit trees ( Schupp et al., 2008 ). Several extensive trials were conducted in commercial peach orchards, but as a result of concerns about fire blight, only one preliminary trial was conducted on apple at the Penn State Fruit

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Kristin E. Neill, Ryan N. Contreras, Virginia O. Stockwell, and Hsuan Chen

foundation plants, as hedges, in parking lots, or in a mass planting along roadsides. Although cotoneasters often are attractive and utilitarian for landscaping, most available cultivars are susceptible to the bacterial plant disease fire blight caused by

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P.G. Braun, P.D. Hildebrand, and A.R. Jamieson

Twenty-five cultivars of red raspberry (Rubus idaeus L.) and one purple raspberry (R. occidentalis L. × R. idaeus L.) were evaluated for their resistance to fire blight caused by Erwinia amylovora (Burr.) Winslow et al. Actively growing raspberry cane tips were wound inoculated with three isolates of the pathogen and disease development was assessed over 17 days. Three methods of evaluating resistance were used: area under the disease progress curve (AUDPC), a weighted AUDPC called the area under the disease severity curve (AUDSC), and lesion length. A wide range of resistance levels was observed, but no cultivars were symptomless. Primocane-fruiting cultivars tended to be more resistant than floricane-fruiting ones. Of the three E. amylovora isolates used in this study, one was significantly more virulent than the other two, but no cultivar × isolate interaction was detected.

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T. Jones, J. Strang, G. Brown, and P. Wolfe

Kentucky is one of seven states in the southeast evaluating 13 Asian pear cultivars for suitability to the region. The cultivars were planted on a (20′ × 10′) spacing in 1989 at three separate locations. Data on time of bloom, tree growth, fire blight susceptibility and fruit quality and yield were collected. This study demonstrates the variability seen in Asian pear cultivars in response to site. There was a significant site by cultivar interaction for fire blight. The Princeton site had significantly more fire blight than either Lexington or Quicksand. Four cultivars, Niitaka, Shin Li, Shinko and Shinseiki had low fire blight ratings which were not significantly different between the three sites. Asian pear growth rates were significantly different between the three sites, but cultivar growth rates were not. Tree growth rate showed a significant negative correlation to fire blight rating. That is infected trees did not grow much. Initial findings show Shinko, Shinseiki and Niitaka to have some tolerance to fire blight spread and to produce good yields of attractive fruit. However, Niitaka had a very tough skin with a tendency towards fruit cracking. The cultivar Shin Li which also had fire blight tolerance did not produce fruit or flowers.

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W.C. Johnson, H.S. Aldwinckle, J.L. Norelli, and H.T. Holleran

A primary focus of the apple rootstock breeding and evaluation program at USDA-ARS/Cornell Univ. has been to develop screening protocols to identify genotypes resistant to the fire blight bacterium (Erwinia amylovora). Direct inoculation is a simple technique, but does not represent the only mode by which rootstocks become infected in the orchard. Selection based on direct inoculation screens may, however, enrich the population for resistant genotypes. Large breeding populations from controlled crosses are shoot-tip inoculated with E. amylovora, and the fraction showing the highest levels of resistance are retained for further evaluations. These survivors are again screened through direct inoculation in the field, and the less-resistant genotypes are discarded. Following selection for other pathogen tolerance and horticultural characters, elite genotypes are multiplied through asexual propagation. Replicated tests using direct inoculation with multiple strains of E. amylovora are then used to estimate the level of fire blight resistance of elite genotypes. A final screen utilizes mature, grafted orchard trees to verify that the resistance of rootstock genotypes to fire blight is maintained under conditions simulating natural infection. Direct inoculation screening and selection have resulted in a high frequency of strong resistance to severe fire blight epidemics in recent orchard inoculation trials.

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D.C. Ferree, J.C. Schmid, and B.L. Bishop

Survival of replicated rootstock plantings of apple trees (Malus ×domestica) to fire blight (Erwinia amylovora) infection shows that a wide range of rootstock susceptibility exists. Trees on `Malling 26' (M.26), `Malling 9' (M.9), and `Mark' consistently had significant losses. Of the dwarfing rootstocks widely available commercially, `Budagovsky 9' (B.9) survived well with productive trees, but was not resistant to fire blight infection. The following experimental rootstocks had good survivability with many live productive trees in one or more trials: `Poland 2' (P.2), `Vineland 1' (V.1), `Malling 27 EMLA' (M.27 EMLA), `Budagovsky 491' (B.491), `Budagovsky 409' (B.409), `Vineland 7' (V.7), `Vineland 4' (V.4), and `Oregon Rootstock 1' (OAR1).