Cucumber mosaic virus is widely distributed in Bulgaria causing serious losses to tomato production. Resistance to CMV has been found in the wild species Solanum lycopersicoides, L. peruvianum and L. pimpinellifolium (Nitanzy, 1975; Phills et al., 1977; Laterrot, 1979; Ciccarese et al., 1987). Stamova et al. (1990) tested tomato lines developed with the participation of L. chilense and selected plants which had no characteristic symptoms of MV. Up to the present no tomato cultivars resistant to the virus have been obtained.
The three-genome hybrid includes L. peruvianum var. humifusum, PI 127829 and L. chilense which are CMV resistant, however, some plants of L. peruvianum var. humifusum, were susceptible to the virus. The cultivated tomato (L. esculentum) line gf was CMV susceptible (Table 1).
Ten lines of the three-genome hybrid were tested in F6 developed by self pollination and selection for valuable economic and biological characters. Selection of lines highly resistant and resistant to bacterial wilt was made after artificial inoculation with Clavibacter michiganensis subs. michiganensis. All ten lines had the typical habit of the cultivated tomato, they were vigorous, with dense dark green leaves, had medium large, round firm fruits and were high yielding. After assessing CMV resistance in two of the parental forms we tested the lines presented in Table 1 for their resistance to the virus. The seedlings were mechanically inoculated with CMV at cotyledon and first true leaf stages. The symptomless plants were tested for presence of the virus after ELISA. All plants of lines LCH 162 and LCH 163 were symptomless and 75 and 50% of them respectively did not contain the virus. Individual plants of lines LCH 165, LCH 166, LCH 167 had mosaic symptoms and CMV was absent in all symptomless plants. In the remaining five lines both mosiac and symptomless plants with or without the virus were found . No lagging in development was observed in symptomless plants systemically inoculated with CMV as compared to tomatoes not inoculated with the virus. CMV concentration in the symptomless plants was from 100 to 1000 times lower than that in mosaic plants.
The most probable explanation for the presence of CMV resistance in F6 without any selection is the presence of genes for resistance in both parental lines. However, this does not exclude possible linkage of the genes for CMV and C.m. subs. michiganensis resistance. Kounovsky et al., (1985) reported linkage between Leveillula solanacearum f. sp. sapsici genes and the gene L1 (TMV) in pepper.
The new lines studied are distinguished by high economic qualities and could be used in breeding programs for complex resistance to CMV and C.m. subs. michiganensis.
Table 1. Resistance to tomato lines from the three genome hybrid L. esculentum-L.chilense-L. peruvianum var. humifusum to CMV.
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Mosaic No. Symptomless plants
Line Total _____________________________
N plants N %1 V+ V- %2
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L. esculentum 10 10 0 0.0 0 0 0.0
line-gf
L. peruvianum 16 7 9 55.5 0 5 100.0
var. humifusum
PI 127829 8 0 8 100.0 0 8 100.0
L. Chilense
LCH 161 10 1 9 90.0 4 5 55.6
LCH 162 8 0 8 100.0 2 6 75.0
LCH 163 8 0 8 100.0 4 4 50.0
LCH 164 14 6 8 57.2 5 3 37.5
LCH 165 6 2 4 66.7 0 4 100.0
LCH 166 6 1 5 83.4 0 5 100.0
LCH 167 8 1 7 87.5 0 7 100.0
LCH 168 10 1 9 90.0 2 7 77.8
LCH 169 13 5 8 53.9 3 5 62.5
LCH 170 13 6 7 53.9 4 5 42.9
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N - number; V+ - symptomless plant with virus; V- - symptomless plants free of
virus;1 - symptomless plants, % of all tested plants; 2 - plants free of virus, % of all symptomless plants.
Literature cited:
Ciccarese, F., M. Amenduni, M. Cirulli. 1987. Eucarpia tomato working group, Italy.
Kounovsky, J., Y. Todorova, E. Stoimenova. 1985. Capsicum News Letter, 4.
Laterrot, H. 1979. Station d'Amelioration des Plants Maraichers.
Nitanzy, F.E. 1975. Phytopathology Mediterrena, 14:16-20.
Phills, B.P., R. Prowwidenti, R.W. Robinson. TGC Reports, 27:18.
Stamova, L., D. Christova, M. Yordanov. 1990. Eucarpia tomato '90 working group, Spain.