Abstract

Resistance to both tomato yellow leaf curl geminivirus (TYLCV) in Israel and tomato mottle geminivirus (TMoV) in Florida have been reported in Lycopersicon chilense Dunal. Crosses of 12 L. chilense accessions onto tomato (L. esculentum Mill.) produced 597 fruit yielding 15 F1s from eight of the accesstions. Ten F1s were from true seed and five were obtained by embryo rescue. One accession (LA 1960) had fertile F1 and crossed readily,but this accession was discarded due to a lack of highly resistant F2 segregants. Five hundred and twenty-eight backcrosses (BCs) from seven accessions (LA 1932,LA 1938,LA 1959,LA 1963,LA 1968,LA 2779) resulted in approximately 2150 seed,but germination was only 2.4 percent,resulting in 43 BC1 plants. Thereafter,embryo rescue was used to obtain 512 BC plants with 58 to 117 BCs per accession. Seeding with two true leaves were inoculated with large numbers of viruliferous whiteflies in greenhouses. Plants remained in the greenhouses for about 3 weeks,after which those with few or no symptoms were transplanted to the field where whiteflies were allowed to thrive. Plants were rated for TMoV symptoms 64 days after transplanting on a 0-4 scale where 0 = no TMoV symptoms and 4 = symptoms over the entire plant and stunting. Interspecific F1s varied in disease severity,but generally were intermediate to parental lines. There were 27.4 percent of BC1s with ratings less than 3 indicating some resistance. Progeny from all susceptible BC1s (ratings>=3) tested were all susceptible. Subsequently seed was saved only from plants showing some resistance (<=2.5). All inbreds in 1994 traced to 35 BC1 plants (6.3 percent of the 555 BC1 plants). Disease screening and selection of resistance was repeated for three more seasons until the F1BC1S4 or F1BC2S3 resistance of some lines was obtained. Since 1990 approximately 37000 plants were screened for resistance . The most resistant lines obtained had low levels of disease symptoms on some plants under the inoculation system described. The most resistant lines were derived from L. chilense accessions LA 1932,LA 1938,LA 1961,LA 1968,and LA 2779. A trial in the Dominican Republic indicated some of the TMoV resistant lines were also highly resistant to TYLCV. All 12 lines tested for TYLCV were more resistant than susceptible varieties,nine were more resistant than TYLCV tolerant 'TY-20',while the other three were similar to 'TY-20'. The data suggest the introgressed resistances are not virus-specific and are controlled multigenically. Resistance to TYLCV from L. chilense accession LA 1969 has been introgressed in Israel and France and this work is briefly discussed. [AS]

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