Horizontal and Vertical Resistance inVicia fabato Chocolate Spot Caused byBotrytis fabae

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Abstract
Of the 1,730 germ plasm lines tested for resistance to chocolate spot in Syria, 353 showed resistance in 1979 and 1980. Nineteen of these resistant lines were tested during two consecutive seasons in Syria, Egypt, England, and the Netherlands. Lines BPL 710, 1196, and 1179-1 were consistently resistant in all countries. Lines BPL 261, 266, 274, 470, 1055, 1058, 1278, 1390, 1543, 1544, 1547, 1548, and 1550 were resistant in Syria and Egypt but susceptible in England and the Netherlands. In tests repeated twice, BPL 710, 1196, and 1179-1 revealed no differential interaction, whereas BPL 1763, 1821, and ILB 1814 consistently revealed a significant differential interaction when inoculated with 12 isolates of Botrytis fabae from Syria. Therefore, BPL 710, 1196, and 1179-1 seemed to carry genes for a broad-based horizontal resistance compared with those for a narrow-based vertical resistance in BPL 1763, 1821, and ILB 1814. On the basis of their interactions with BPL 1763, 1821, and ILB 1814, the 12 isolates of the pathogen were classified into four groups representing races 1, 2, 3, and 4. These races seemed to be more common in England and the Netherlands than in Egypt and Syria.