Sources of resistance to powdery mildew caused by L. taurica are rather limited (Stamova, 1987). In order to enlarge the scope of genetic sources we tested 21 tomato lines from Costa Rica.
Plants with 4-5 leaves were inoculated with spore suspension of the fungus gathered from infected tomato leaves. The evaluation was made after 20 days using a scale for 0 to 4 (Table1). Nubmer 15 (type ceresiforme) collected personally by the first author didn't show any symptoms, the leaves remaining dark green without chlorotic flecks or mycelium on the under side. Genetic study of resistance and comparison with the gene for resistance in Laurica line are undertaken.
Low degree of damage showed number 8,9,17 and 7, all of them having one plant without symptoms.
Table 1. Reaction to tomato lines from Costa Rica to L. taurica
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Lines Number of leaves with rating Degree of damage
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0 1 2 3 4
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1 16 12 8 7 7 38.5
2 15 9 13 6 7 40.5
3 17 7 9 2 8 32.1
4 14 8 10 7 23 60.0
5 22 7 9 4 12 33.5
6 35 34 11 2 13 30.0
7 40 5 - 4 6 18.6
8 49 8 2 - - 10.1
9 29 13 1 2 6 13.9
10 33 18 - 1 2 24.1
11 14 12 11 7 16 53.7
12 18 13 12 7 7 34.2
13 25 14 8 5 8 28.7
14 28 11 4 5 3 22.5
15 76 - - - - 0.0
16 20 13 2 2 7 17.2
17 24 16 1 1 9 27.9
18 31 15 5 - 8 32.2
19 17 19 2 - 6 24.5
20 30 9 7 2 12 21.4
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Literature cited:Stamova, L. 1987 Breeding for dis. resistance in tomatoes. Dr. Sci. thesis