Due to the importance of increasing soluble solids in processing tomatoes, the authors undertook a cursory survey of Lycopersicon species to assess them for solids content. Lycopersicon cheesmanii appeared to be the most promising, and the ease of intercrossing with L. esculentum made it theological choice for introgression of high soluble-solids genes into the cultivated tomato.
Soluble-solids data were collected for 30 L. cheesmanii accessions. Plants were grown in a greenhouse in Davis during the spring of 1982 and 1983. The following readings (Table 1), obtained using a temperature compensated B & L hand-held refractometer, represent averages for several samples per accession.
Table 1.
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Mean Mean
LA soluble solids race LA soluble solids race
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166 9.02 L. cheesmanii 317 12.40 f. minor
421 8.36 L. cheesmanii 436 12.41 f. minor
422 7.65 L. cheesmanii 438 12.10 f. minor
427 8.90 L. cheesmanii 483 15.93 f. minor
428 7.16 L. cheesmanii 526 14.68 f. minor
521 8.63 L. cheesmanii 527 13.20 f. minor
746 7.15 L. cheesmanii 528 13.07 f. minor
749 4.85 L. cheesmanii 747 14.73 f. minor
932 7.03 L. cheesmanii 748 13.71 f. minor
1039 10.62 L. cheesmanii 929 14.33 f. minor
1040 8.40 L. cheesmanii 1403 14.80 f. minor
1139 8.85 L. cheesmanii 1411 14.32 f. minor
1407 7.53 L. cheesmanii 1508 13.07 f. minor
1409 9.18 L. cheesmanii 1627 15.99 f. minor
1449 8.19 L. cheesmanii
1450 8.03 L. cheesmanii 490 7.00 VF36
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Very high soluble-solids readings were observed in nearly one-half of the
accessions tested. A curious pattern of low solids in L. cheesmanii and high
solids in the L. cheesmanii f. minor race was evident.Several high-solids accessions were selected for interspecific hybridization to L. esculentum. Two cultivars were chosen for this purpose: LA490 (VF36) was used as a recurrent parent which might prove useful to both processing and fresh market tomato breeders, and UC204B, which is a processing tomato cultivar.
The interspecific hybridization was relatively simple since there are no barriers to crossing. The F1 hybrids exhibited morphological characters intermediate between the two parents. Plants with the highest solids were selected and backcrossed to their respective recurrent parents.
Currently we are in the BC2 generation and are selecting strongly against the wild characters. Significant progress has been made in increasing solids content. BC1 plants selected in the field had solids readings in the range of 6.0 to 7.5%, while VF36 had a mean value of 5.5%. In addition, progress towards better horticultural characteristics has been good.
Further studies are underway to investigate the reason for differences in solids values between the L..cheesmanii and the minor race of L. cheesmanii.