# Assessment of the susceptibility to Erwinia amylovora of 90 varieties or selections of Pear

Bernard Thibault, P. Lecomte, Léonce Hermann, André Belouin

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Bernard Thibault, P. Lecomte, Léonce Hermann, André Belouin. Assessment of the susceptibility to Erwinia amylovora of 90 varieties or selections of Pear. Acta Horticulturae, 1987, 217, pp.305-309. hal-01601312

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<figure><img src="image_1.png" /></figure>

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ASSESSMENT OF THE SUSCEPTIBILITY TO Erwinia amylovora OF 90
VARIETIES OR SELECTIONS OF PEAR

B. Thibault*, P. Lecomte**, L. Hermann*, A. Belouin*

* Station d'Arboriculture Fruitière

**Station de Pathologie Végétale et de Phytobactériologie

Institut National de la Recherche Agronomique

Centre de Recherches d'Angers

Beaucouzé - 49000 Angers

France

Abstract

A collection of 70 varieties of Pear and 20 U.S. or Canadian Selections was artificially inoculated on shoots in the experimental orchard of Dax.

Two inoculations were carried out, one in 1984 (12 to 40 shoots by genotype) and one in 1985 (24 shoots).

The results are presented in diagrams where the severity is in absciss and the frequency in ordinate.

Some genotypes as 'Kieffer' or 'HW 605' show a high frequency but a somewhat low severity. On the other hand 'Beurré Hardy' shows a low frequency but a high severity.

An other point is the stability of the classification for the varieties with a low or a high susceptibility and the variability for the varieties with medium susceptibility. The responses were generally more severe in 1985 than in 1984.

A collection of 70 varieties of Pear and 20 U.S. or Canadian Selections was planted in the experimental orchard in Dax (South-West of France) where climatic conditions are very favourable for the bacteria. 3 replications of 3 trees were planted (see the list below).

When the trees were four year old they were artificially inoculated by needle prick and syringe just below the top of at least 30 cm long shoots. In 1984 12 to 40 shoots were inoculated by genotype and in 1985 24 shoots (strain 2045 ; density 10⁸).

The results take in consideration three criteria :

- The Frequency (or Infectivity) : the ratio between the number of shoots with blight and the total number of inoculated shoots.

- The Severity : the mean of percentages of extended lesion to the total length of the shoot for all blighted shoots.

- The Index of susceptibility : the product between Frequency and Severity.

On diagrams we put the Severity in absciss and the Frequency in ordinate and it is possible to draw the curves of iso-index.

A) A variety is classed as very few susceptible if Severity is less or equal to 50, Frequency less or equal to 65 and Index less or equal to 10.
B) It is classed as few susceptible if Severity is less or equal to 50, Frequency less or equal to 65 and Index between 10 and 20.

These two classes may be joined

C) It is classed as moderately susceptible if Severity is greater than 50, Frequency greater than 65 but Index lower than 40.

D) It is classed as highly susceptible if Index is between 40 and 60.

E) It is classed as very highly susceptible if Index is between 60 and 100 (Fig. 1).

We can note the specific behaviour of some varieties as 'Kieffer' which is in the class C in 84 and 85 with a high Frequency and a low Severity. On the other hand 'Beurré Hardy' shows for both years a low Frequency but a high Severity (the same for 'HW 604').

The responses to the inoculations in 85 were more severe than in 84. The average of Frequencies goes from 44 in 84 to 66 in 85 and the average of Severity from 37 to 57. Particularly on 21 varieties which had not reacted to the inoculation in 84 only 2 : *Pyrus ussuriensis* and U S 309 did not react in 85.

22 varieties classed in A or B in 84 were in the same classes in 85

18 varieties classed in D or E in 84 were in the same classes in 85

So there is a good correlation between the years for the varieties showing a low or very low susceptibility and for the varieties showing a high or very high susceptibility.

We can note, classed in A or B for both years, 17 hybrids or varieties specially bred for their resistance by U S or Canadian breeders. This demonstrates the possibility to increase the resistance by breeding programs.

However 'H W 605' had not a good behaviour nor in 84 or 85. 'Sirrine' was quite susceptible in our conditions. 'Star' - 'H 6310/1096' - 'U S 66.147.24' and 'Illinois 61-161' were fairly susceptible mainly in 85.

Among old European varieties 'Alexandre Lucas' seems very few susceptible as already noted. 'Beurré Giffard' - 'Beurré Précoce Morettini' 'Beurré Hardy' seem to be the less susceptible ones.

One or two more years will be useful for an accurate classification and to point out the stability or the variability of the responses according to the year.
<figure><img src="image_2.png" /><figcaption>Fig. 1
CLASSIFICATION ACCORDING TO 3 CRITERIA ON SHOOTS</figcaption></figure>
LIST OF VARIETIES

<table><thead><tr><th rowspan="2"></th><th rowspan="2"></th><th colspan="3">1984</th><th colspan="3">1985</th></tr><tr><th>F</th><th>S</th><th>C</th><th>F</th><th>S</th><th>C</th></tr></thead><tbody><tr><td>1</td><td>ALEXANDRE LUCAS</td><td>0</td><td>0</td><td>A</td><td>4</td><td>10</td><td>A</td></tr><tr><td>2</td><td>BEURRE GIFFARD</td><td>0</td><td>0</td><td>A</td><td>50</td><td>45</td><td>C</td></tr><tr><td>3</td><td>HONEYSWEET</td><td>0</td><td>0</td><td>A</td><td>29</td><td>13</td><td>A</td></tr><tr><td>4</td><td>HW 609</td><td>0</td><td>0</td><td>A</td><td>33</td><td>40</td><td>B</td></tr><tr><td>5</td><td>III. 7-D-10</td><td>0</td><td>0</td><td>A</td><td>42</td><td>70</td><td>C</td></tr><tr><td>6</td><td>III. 13-B-83</td><td>0</td><td>0</td><td>A</td><td>8</td><td>10</td><td>A</td></tr><tr><td>7</td><td>LEGIPONT</td><td>0</td><td>0</td><td>A</td><td>71</td><td>80</td><td>D</td></tr><tr><td>8</td><td>MAC</td><td>0</td><td>0</td><td>A</td><td>29</td><td>27</td><td>A</td></tr><tr><td>9</td><td>MAGALLON</td><td>0</td><td>0</td><td>A</td><td>42</td><td>12</td><td>A</td></tr><tr><td>10</td><td>MAGNESS</td><td>0</td><td>0</td><td>A</td><td>17</td><td>30</td><td>A</td></tr><tr><td>11</td><td>MIKADO</td><td>0</td><td>0</td><td>A</td><td>42</td><td>20</td><td>A</td></tr><tr><td>12</td><td>MOONGLOW</td><td>0</td><td>0</td><td>A</td><td>25</td><td>17</td><td>A</td></tr><tr><td>13</td><td>PYRUS USSURIENSIS</td><td>0</td><td>0</td><td>A</td><td>0</td><td>0</td><td>A</td></tr><tr><td>14</td><td>RICHARD PETERS</td><td>0</td><td>0</td><td>A</td><td>12</td><td>10</td><td>A</td></tr><tr><td>15</td><td>U.S. 70.526.59</td><td>0</td><td>0</td><td>A</td><td>37</td><td>45</td><td>B</td></tr><tr><td>16</td><td>U.S. 62.574.13</td><td>0</td><td>0</td><td>A</td><td>46</td><td>24</td><td>B</td></tr><tr><td>17</td><td>U.S. 62.563.44</td><td>0</td><td>0</td><td>A</td><td>33</td><td>10</td><td>A</td></tr><tr><td>18</td><td>U.S. 56.112.148</td><td>0</td><td>0</td><td>A</td><td>12</td><td>17</td><td>A</td></tr><tr><td>19</td><td>U.S. 309</td><td>0</td><td>0</td><td>A</td><td>0</td><td>0</td><td>A</td></tr><tr><td>20</td><td>H.W. 601</td><td>0</td><td>0</td><td>A</td><td>4</td><td>30</td><td>A</td></tr><tr><td>21</td><td>HARROW DELIGHT</td><td>0</td><td>0</td><td>A</td><td>12</td><td>10</td><td>A</td></tr><tr><td>22</td><td>U.S. 65.003.23</td><td>8</td><td>10</td><td>A</td><td>63</td><td>18</td><td>B</td></tr><tr><td>23</td><td>ROI CHARLES DE WURT.</td><td>17</td><td>10</td><td>A</td><td>70</td><td>43</td><td>C</td></tr><tr><td>24</td><td>EWART</td><td>10</td><td>17</td><td>A</td><td>37</td><td>28</td><td>A</td></tr><tr><td>25</td><td>H.W. 600</td><td>25</td><td>10</td><td>A</td><td>54</td><td>50</td><td>C</td></tr><tr><td>26</td><td>U.S. 62.537.48</td><td>27</td><td>10</td><td>A</td><td>37</td><td>54</td><td>C</td></tr><tr><td>27</td><td>MAXINE</td><td>8</td><td>30</td><td>A</td><td>37</td><td>14</td><td>A</td></tr><tr><td>28</td><td>DOYENNE GRIS</td><td>8</td><td>30</td><td>A</td><td>79</td><td>86</td><td>E</td></tr><tr><td>29</td><td>H.W. 606</td><td>17</td><td>30</td><td>A</td><td>87</td><td>26</td><td>C</td></tr><tr><td>30</td><td>U.S. 65.016.12</td><td>30</td><td>23</td><td>A</td><td>75</td><td>31</td><td>C</td></tr><tr><td>31</td><td>III. 61.161</td><td>25</td><td>30</td><td>A</td><td>79</td><td>74</td><td>D</td></tr><tr><td>32</td><td>MICHIGAN 437</td><td>25</td><td>30</td><td>A</td><td>12</td><td>30</td><td>A</td></tr><tr><td>33</td><td>DAWN</td><td>42</td><td>14</td><td>A</td><td>71</td><td>79</td><td>D</td></tr><tr><td>34</td><td>ROMA</td><td>38</td><td>18</td><td>A</td><td>87</td><td>45</td><td>C</td></tr><tr><td>35</td><td>LOSCIOUS</td><td>9</td><td>50</td><td>A</td><td>50</td><td>66</td><td>C</td></tr><tr><td>36</td><td>B. PRECOCE MORETTINI</td><td>60</td><td>12</td><td>A</td><td>62</td><td>55</td><td>C</td></tr><tr><td>37</td><td>U.S. 66.147.24</td><td>50</td><td>18</td><td>A</td><td>100</td><td>54</td><td>D</td></tr><tr><td>38</td><td>CLARA FRIJS</td><td>8</td><td>70</td><td>C</td><td>50</td><td>90</td><td>D</td></tr><tr><td>39</td><td>CONFERENCE</td><td>33</td><td>30</td><td>A</td><td>79</td><td>62</td><td>D</td></tr><tr><td>40</td><td>H. 6310/1096</td><td>42</td><td>24</td><td>B</td><td>87</td><td>89</td><td>E</td></tr><tr><td>41</td><td>HARVEST QUEEN</td><td>50</td><td>20</td><td>A</td><td>71</td><td>34</td><td>C</td></tr><tr><td>42</td><td>H.W. 604</td><td>25</td><td>43</td><td>B</td><td>37</td><td>72</td><td>C</td></tr><tr><td>43</td><td>STAR</td><td>27</td><td>43</td><td>B</td><td>92</td><td>57</td><td>D</td></tr><tr><td>44</td><td>PIERRE CORNEILLE</td><td>42</td><td>30</td><td>B</td><td>66</td><td>70</td><td>D</td></tr><tr><td>45</td><td>BEURRE HARDY</td><td>17</td><td>80</td><td>C</td><td>39</td><td>79</td><td>C</td></tr><tr><td>46</td><td>COSCIA</td><td>38</td><td>38</td><td>B</td><td>46</td><td>55</td><td>C</td></tr></tbody></table>
<table><thead><tr><th rowspan="2"></th><th rowspan="2"></th><th colspan="3">1984</th><th colspan="3">1985</th></tr><tr><th>F</th><th>S</th><th>C</th><th>F</th><th>S</th><th>C</th></tr></thead><tbody><tr><td>47</td><td>PRESIDENT HERON</td><td>38</td><td>42</td><td>B</td><td>92</td><td>87</td><td>E</td></tr><tr><td>48</td><td>BEURRE BOSC</td><td>36</td><td>50</td><td>B</td><td>71</td><td>89</td><td>E</td></tr><tr><td>49</td><td>KIEFFER</td><td>73</td><td>21</td><td>C</td><td>100</td><td>36</td><td>C</td></tr><tr><td>50</td><td>BEURRE CLAIRGEAU</td><td>91</td><td>15</td><td>C</td><td>-</td><td>-</td><td>-</td></tr><tr><td>51</td><td>ELDORADO</td><td>60</td><td>31</td><td>B</td><td>92</td><td>66</td><td>E</td></tr><tr><td>52</td><td>U.S. 58.301.80</td><td>-</td><td>-</td><td>-</td><td>33</td><td>30</td><td>A</td></tr><tr><td>53</td><td>CASTELL</td><td>83</td><td>22</td><td>C</td><td>100</td><td>87</td><td>E</td></tr><tr><td>54</td><td>BEURRE D'ANJOU</td><td>31</td><td>75</td><td>C</td><td>71</td><td>86</td><td>E</td></tr><tr><td>55</td><td>P.F.T.</td><td>61</td><td>42</td><td>C</td><td>50</td><td>45</td><td>C</td></tr><tr><td>-56</td><td>SIRRINE</td><td>77</td><td>32</td><td>C</td><td>100</td><td>88</td><td>E</td></tr><tr><td>57</td><td>SPADONA D'ESTATE</td><td>92</td><td>28</td><td>C</td><td>100</td><td>42</td><td>D</td></tr><tr><td>58</td><td>WILLIAMS (BARTLETT)</td><td>42</td><td>74</td><td>C</td><td>77</td><td>89</td><td>E</td></tr><tr><td>59</td><td>EPINE DU MAS</td><td>58</td><td>56</td><td>C</td><td>71</td><td>78</td><td>D</td></tr><tr><td>60</td><td>H.W. 605</td><td>75</td><td>41</td><td>C</td><td>100</td><td>65</td><td>E</td></tr><tr><td>61</td><td>DUCHESSE D'ANGOULEME</td><td>77</td><td>47</td><td>C</td><td>-</td><td>-</td><td>-</td></tr><tr><td>62</td><td>GENTIL BIANCA</td><td>100</td><td>22</td><td>C</td><td>75</td><td>33</td><td>D</td></tr><tr><td>63</td><td>BLANQUILLA</td><td>100</td><td>23</td><td>C</td><td>95</td><td>70</td><td>E</td></tr><tr><td>64</td><td>GENERAL LECLERC</td><td>100</td><td>26</td><td>C</td><td>94</td><td>73</td><td>E</td></tr><tr><td>65</td><td>Dr. J. GUYOT</td><td>100</td><td>30</td><td>C</td><td>96</td><td>62</td><td>D</td></tr><tr><td>66</td><td>BEURRE CAPIAUMONT</td><td>41</td><td>84</td><td>C</td><td>100</td><td>43</td><td>D</td></tr><tr><td>67</td><td>ABBE FETEL</td><td>50</td><td>77</td><td>C</td><td>100</td><td>81</td><td>E</td></tr><tr><td>68</td><td>COLOREE DE JUILLET</td><td>50</td><td>78</td><td>C</td><td>96</td><td>88</td><td>E</td></tr><tr><td>69</td><td>DELDAP</td><td>-</td><td>-</td><td>-</td><td>79</td><td>86</td><td>E</td></tr><tr><td>70</td><td>CLAPP'S FAVOURITE</td><td>54</td><td>73</td><td>C</td><td>75</td><td>90</td><td>E</td></tr><tr><td>71</td><td>BELLA DI GIUGNO</td><td>58</td><td>70</td><td>C</td><td>71</td><td>67</td><td>D</td></tr><tr><td>72</td><td>MORETTINI 64</td><td>83</td><td>56</td><td>D</td><td>100</td><td>90</td><td>E</td></tr><tr><td>73</td><td>DOYENNE D'HIVER</td><td>50</td><td>90</td><td>D</td><td>100</td><td>90</td><td>E</td></tr><tr><td>74</td><td>HIGHLAND</td><td>81</td><td>65</td><td>D</td><td>83</td><td>90</td><td>E</td></tr><tr><td>75</td><td>FORELLE</td><td>100</td><td>54</td><td>D</td><td>100</td><td>90</td><td>E</td></tr><tr><td>76</td><td>BONNE LOUISE</td><td>66</td><td>87</td><td>D</td><td>96</td><td>90</td><td>E</td></tr><tr><td>77</td><td>SUPERCOMICE DELBARD</td><td>77</td><td>84</td><td>E</td><td>100</td><td>90</td><td>E</td></tr><tr><td>78</td><td>PASSE CRASSANE</td><td>75</td><td>88</td><td>E</td><td>100</td><td>90</td><td>E</td></tr><tr><td>79</td><td>PACKHAM'S TRIUMPH</td><td>100</td><td>65</td><td>E</td><td>96</td><td>90</td><td>E</td></tr><tr><td>80</td><td>MADAME BALLET</td><td>100</td><td>74</td><td>E</td><td>100</td><td>90</td><td>E</td></tr><tr><td>81</td><td>TRIOMPHE DE VIENNE</td><td>86</td><td>87</td><td>E</td><td>96</td><td>90</td><td>E</td></tr><tr><td>82</td><td>DELWILMOR</td><td>92</td><td>81</td><td>E</td><td>100</td><td>83</td><td>E</td></tr><tr><td>83</td><td>BEURRE SUPERFIN</td><td>93</td><td>84</td><td>E</td><td>100</td><td>90</td><td>E</td></tr><tr><td>84</td><td>FIGUE D'ALENCON</td><td>100</td><td>81</td><td>E</td><td>96</td><td>89</td><td>E</td></tr><tr><td>85</td><td>PRECOCE DE TREVOUX</td><td>100</td><td>82</td><td>E</td><td>100</td><td>90</td><td>E</td></tr><tr><td>86</td><td>SOUTHWORTH</td><td>94</td><td>90</td><td>E</td><td>58</td><td>90</td><td>D</td></tr><tr><td>87</td><td>ALEXANDRINE DOUILLARD</td><td>96</td><td>86</td><td>E</td><td>-</td><td>-</td><td>-</td></tr><tr><td>88</td><td>LAXTON'S SUPERB</td><td>100</td><td>87</td><td>E</td><td>100</td><td>90</td><td>E</td></tr><tr><td>89</td><td>DOYENNE DU COMICE</td><td>100</td><td>87</td><td>E</td><td>98</td><td>90</td><td>E</td></tr></tbody></table>

F = Frequency

S = Severity

C = Classification