More Information about tomato breeding lines from the CDR project C21-008 can be found at the following URL site: www.plantpath.wisc.edu/GeminivirusResistantTomatoes/CDR/GT.htm
Objective: Evaluation of germplasm for resistance to begomoviruses
At the beginning of the current CDR project (C21-008), several breeding lines were selected, with assistance from F. Vidavski, Hebrew University of Jerusalem (Tables 1 and 2). It was decided that, since resistance to geminiviruses already seemed to have been fixed in these breeding lines, it would be desirable to introduce resistance to other pathogens. Basic resistances to pathogens and other characters related to fruit quality, such as fruit size and firmness, are essential for release to the growers. The begomovirus resistant breeding lines were further evaluated and crossed to susceptible cultivars carrying other traits of interest (Table 3).
Table 1. Performance of parental lines (September, 2001 to February, 2002) and breeding lines which were selected.
Table 2. Performance of twelve resistant breeding lines compared to susceptible line GC6 (April to September, 2002).
Table 3. Cultivars susceptible to begomoviruses but carrying resistance to other pathogens and other characters of interest.
Some hybrids were produced by crosses between resistant and susceptible lines (Table 4; R X S, H1-H3 and H6-H9) and others by crosses among resistant lines (R X R; H4 y H5). One of the most popular cultivars in the area, the hybrid Marina (Sakata Seed Co.; H13), was used as a control.
Table 4. Performance of R X S and R X R hybrids (September/2001 to February, 2002).
The hybrids resulting from crosses to the susceptible cultivars (Table 3) were evaluated during the later part of 2002 (Table 5).
Table 5. Performance of R X S hybrids (April to September, 2002).
Additional hybrids were made by crosses among some of the resistant lines (Table 6).
Table 6. Performance of R X R hybrids (April to September, 2002).
After the International seminar on breeding of vegetable crops for resistance to whitefly transmitted geminiviruses, which was held in Antigua Guatemala in January, 2003, we were approached the manager of a seedling producing company, Mr. Richard Rotter, called Pilones de Antigua. Mr. Richard Rotter was interested in starting a vegetable seed company (tomatoes and peppers) and wanted to know if we would be willing to share our germplasm with him. Some begomovirus resistant lines were transferred to him in March, after the cycle of selection, these lines were Gh13, Gc9 (Table 2) and Th47-1 (a line selected from an early cross between a selection from Favi 9 and Lignon, a Cuban cultivar). Additionally, two other lines 31-4 (derived from a cross between Gper11 X Gh) and 36-4 (from a cross Gh1 X Gh2). These lines were crossed to produce hybrids Llanero 10, Llanero 11, Llanero 12 and Maya Garden. Additionally, based on previous results (Table 4), F. Vidavsky prepared seed of the H7 hybrid (Gh3 X susceptible line from his program), now called Llanero 7. The term Llanero, meaning plainsman, refers to the area in Sanarate where our trials are located, which is known by the locals as Los Llanos or the plains. The hybrid called Maya Garden was produced crossing two lines with high resistance and good flavor, irrespective of shape or firmness, with the idea planting it in home or school gardens for domestic consumption. These hybrids were first planted by Pilones de Antigua, at different locations, in early 2004 and at least some are being considered for commercial release, even though the shape of their fruit is round and the level of firmness is not as high as required in most market situations. Tables 8 and 9 show the performance of some of the breeding lines and hybrids in Sanarate during the last trial that has been conducted (December/2003 to April/2004). In view of the promising results that were observed in the Llanero hybrids, the owners of Pilones de Antigua decided to go ahead with the initiative of the seed company, and this has just recently been formed under the name Gentropic Seeds.
Table 7. Symptom severity and partial yield of begomovirus resistant breeding lines (December/2003 to April/2004).
Table 8. Symptom severity and partial yield of begomovirus resistant hybrids (December/2003 to April/2004).
From all of these hybrids, individual plants carrying desirable traits have been selected for several cycles. The most important criteria for selection have been resistance to begomoviruses along with fruit shape, fruit size, firmness and yield. The preferred fruit type for the Guatemalan market is a plum shape (the so called Roma type), with high firmness. A system for evaluating plants in the field was developed. There have been three cycles of selection up to now; March, 2003, September, 2003 and March, 2004. Along with the Guatemalan team, D. Maxwell has participated in all three evaluations, tomato breeders J Scott and F. Vidavski participated in the second and third evaluations respectively. As a result of these cycles of selection a wide array of resistant germplasm has been developed.
After the second cycle of selection (September, 2003), several of these lines were considered to be far enough along the selection process to participate in the formation of a new set of hybrids. These lines possessed the desired characters of fruit shape and firmness and could hopefully give origin to hybrids which could soon be released to the growers. The lines were given to Gentropic Seeds and approximately sixty hybrids (denominated XA hybrids) were produced and will be transplanted for evaluation in Sanarate and other locations in early July, 2004. After the third cycle of selection (March, 2004), several additional breeding lines with the desired qualities became available (Table 9). Several of these lines were again given to Gentropic Seeds for crossing and approximately 300 new XA hybrids are being produced at the present time. It must be stressed that Gentropic Seeds has agreed to pay the corresponding royalty fees for the use of these lines and that all the costs related to the crossing of the lines for the production of hybrids and the evaluation of these hybrids are being covered by the company. It would be highly desirable to introduce resistance to bacterial wilt into the elite begomovirus resistant lines.
Table 9. Lines selected in March 2004 with an overall rating above 80. Combinations of some of these lines are being used in the formation of around 300 hybrids to be evaluated at the end of 2004.