At the second stage, the three-way analysis of variance (ANOVA) based on a mixed model for means of ten trees was carried out for the means designed in an incomplete genotype-measurement time–year classification. At the first stage means of ten trees for each combination of genotype-measurement time–year were calculated. Statistical analysisĭata for fire blight infection recorded on ten trees (means of two shoots per tree) of each tested genotype across four measurement times and 3 years were analyzed using two-stage approach. The progression of symptoms was monitored for four consecutive weeks after the inoculation and evaluated according to the Gardner scale (Gardner et al. The level of infection was expressed as the percentage of the fire blight lesion lengths in relation to the overall shoot length. During 4 weeks of evaluation the following mean values were maintained: 27☌ (day), 21☌ (night) and 55% air humidity.Īfter inoculation the disease lesion length and the total length of the current season’s growth of the inoculated shoots were measured. In order to provide high humidity conditions after inoculation, plants were covered with plastic bags for 24 h. The strain was isolated from ‘Šampion’ apple cv in 1998 at the Research Institute of Pomology and Floriculture, Skierniewice, Poland. amylovora aggressive strain 691, containing 10 8 cfu ml −1. ( 2004), two youngest leaves of 50-cm-tall plants were clipped with scissors immersed in inoculum of the E. At the end of June 2007, 2008, and 2009, according to the method used by Bell et al. At the time of vegetation two shoots were developed from each scion. Grafted plants were grown in a greenhouse. The other objective of this study was to predict response of pear genotypes to pathogen infection across four measurement times.Įvery year (2007, 2008, and 2009) in winter time scions of each genotype were grafted on the potted seedlings of Pyrus caucasica in ten replicates. In each year of the replicated experiment all trees were of the same age. Since susceptibility of shoots is strongly influenced by their physiological state, three independent assessments for fire blight tests, with ten trees as replicates in each, were applied. Artificial inoculation of actively growing shoots with virulent strain of Erwinia amylovora provide an effective and reliable means for evaluating fire blight resistance Aldwinckle and Preczewski ( 1976). The aim of this study was to determine the level of fire blight resistance among different old cultivars and clones originating from breeding programs of several European countries using artificial inoculation. However, the susceptibility to blossom infection may be important in determining how readily infections are initiated in the orchard Aldwinckle and Norelli ( 1981). Blossom susceptibility of apple and pear cultivars received less attention than the susceptibility of vegetative tissues. Measurements of that type were shown to be strongly correlated with the field susceptibility of apple cultivars in several independent observations (Lespinasse and Aldwinckle 2000). The extent of lesion development on the shoot appeared to be most useful for that purpose. Susceptibility of pear or apple genotypes can be assessed through different methods of measurements after the inoculation of blossoms or shoots. Genetic diversity that exists within genus Pyrus has been used for this purpose (Bell and Janick 1977). Breeding of new cultivars resistant to fire blight is one of the most important goals to overcome the problem. communis are susceptible to this disease (van der Zwet et al. This disease can be especially problematic in regions where environmental conditions are favorable for the disease development, especially where springtime weather is warm and wet (van der Zwet and Keil 1979). A major factor that significantly limits the cultivation of European pear is fire blight caused by the bacterium Erwinia amylovora (Burrill) Winslow et al. 2001), only a small percentage of which are cultivated commercially (Bell et al. It encompasses approximately 5,000 cultivars (Monte-Corvo et al. The major edible species in Europe, North America, and temperate regions of the southern hemisphere is the European pear ( Pyrus communis L.), commercially cultivated for fruit production. The genus Pyrus, containing at least 22 species, is a highly diverse source of pome fruit cultivated throughout the temperate climate regions of the world.
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