Summary of Field Evaluations of Tomato Germplasm in Sanarate Guatemala, April 2005

Evaluation team:  Luis Mejía and Rudi Teni, Universidad de San Carlos; Luis Rodriguez and Richard Rotter, Gentropic Seeds, S.A., Antigua, Guatemala; Douglas Maxwell, University of Wisconsin-Madison; Favi Vidavski and Hanokh Czosnek, Hebrew University of Jersualem, Rehovot, Israel; and Peter Hanson, Asian Vegetable Research and Development Center, Taiwan

Personnel visiting plots at Sanarate in April 05:

Evaluation team 

Goals:  
  

To evaluate the segregating  populations (>300 lines) from the diverse crosses of begomovirus-resistant lines by other germplasm with desirable characteristics of shape, size, firmness, disease resistance, etc.  Selection of advanced breeding lines (>F6). Also, many advanced breeding lines were only grown at Antigua, which has very low virus pressure and these lines were evaluated for horticultural characteristics.
   

To evaluate 270 hybrids with resistance to begomoviruses produced by Gentropic Seeds,S.A.

Past History:  Dr. Luis Mejia started a breeding program in 1998 for resistance to begomoviruses at a site in Eastern Guatemala near Sanarate.  This site was selected, as it has an extremely high whitefly population year around and inoculum for the tomato begomoviruses is always present.  Seven distinct bipartite begomoviruses have been identified in this site (Nakhla et al., pers. com.). Germplasm was collected from various breeding programs, which were focused on resistance to Tomato yellow leaf curl virus (TYLCV) in the Mediterranean region or Tomato leaf curl virus in Asia or on resistance to Tomato mottle virus and TYLCV in Florida.  In all cases, begomovirus resistance had been introgressed from wild tomato species.  From H. Laterrot, INRA, in France, three populations were obtained, and at least one of these populations had been field tested in Jordan.  The population with introgressions from L. pimpinellifolium and L. peruvianum (designed Pimpertylc J-13) was the most useful of these.  Other sources were i) hybrids (FAVI 9, FAVI 12, FAVI 13) with introgressions from L. hirsutum (Phytopathology 88:910-914) and line TY52  homozygous for  the Ty1 gene from L. chilense (Theor. Appl. Genet. 88:141-146) from H. Czosnek and F. Vidavski, the Hebrew University of Jerusalem, ii) two lines, TY198 and TY197, with introgressions from L. peruvianum from Moshe Lapidot and colleagues, Volcani Center (Plant Dis. 81:1425-1428; J. Amer. Soc. Hort. Sci. 123:1004-1006), iii) line H24 from P. Hanson, AVRDC, with introgressions from L. hirsutum (J. Amer. Soc. Hort. Sci. 125:15-20), and iv) several lines from J. Scott, University of Florida, with introgressions from L. chilense (J. Amer. Soc. Hort. Sci. 126:462-467).  In all cases, these lines or hybrids had moderate to high levels of viral resistance to begomoviruses.

   From the previous field trials, the following points were established:

• The TY52 (Ty1 gene resistance) and line H24 (Ty2 gene) were susceptible with very high virus pressure and these sources were not used in the breeding program.
• TY197 (peruvianum), TY198 (peruvianum), FAVI 9 (hirsutum), FAVI 12 (hirsutum) and lines from Scott (all chilense source of resistance, Gc9, Gc16, Gc172, Gc173) had high levels of begomovirus resistance and breeding lines were selected from these populations.
• The Pimpertylc J-13 population was moderately resistance and selections were from made from this population, eg, Gpim10.
• Combining different sources of resistance increased the level of resistance, eg, a line with hirsutum resistance x line with chilense resistance.
• At least seven begomoviruses are present at the field site.
• In the last couple years, a soil-borne pathogen identified by Jay Scott as Ralstonia solanacearum has caused consider losses in some of the breeding lines.  The FAVI 9, FAVI 12 and Scott lines have been most resistant to this problem.  Breeding lines from TY197 were very susceptible and those from TY198 were more resistant.
• F1 populations from crosses of lines with L. hirsutum-resistant (Vidavski and Czosnek hybrids as source of resistance) by susceptible lines are moderately resistant.
• F1 populations from crosses of lines with L. chilense-resistant (Scott lines as source of resistance) by susceptible lines are susceptible. Only in F2 populations are moderately resistant plants observed.  Excellent breeding lines with high resistance can be obtained by selecting resistant plants from each selfed generation.
• Advanced breeding lines selected from crosses with Scott's lines (chilense resistance) have generally had a higher level of resistance than advanced lines selected with crosses from Vidavski-Czosnek lines (hirsutum resistance).
• Ih902 breeding line (March 04) was segregating for green shoulder and resistance.

Information about trial:

After last trail, which ended in October 04, the field was fallow until early January 05 when a susceptible tomato hybrid was transplanted in various locations througt the field. Approximately two weeks later, the one month old seedlings, which were produced at Pilones de Antigua, were transplanted. No insecticides were used in the field plots. Commerical cultivars, (Silverado and Sheriff), were planted throughout the plot area. In all cases these commerical hybrids had DSI of 4 at 85 days after transplanting and essential no yield. In most cases the plants for the commercial hybrids were dead at the time of the evaluation of the hybrids and breeding lines.

This area of Guatemala is normally very dry and has a few rains during the rainy season (May to October). Wilt plants were detected in late February and PCR tests confirmed that these plants were infected with Ralstonia solanacearum. Also, there appears to be another soil-borne pathogen, which is killing some lines and not other lines.

Few tomatoes are planted in the valley where are field trial is located because they usually have 100% incidence and growers are switching to other crops, eg cucumbers.

Naming lines: Breeding lines will start with letter "G" for Guatemala followed by a number (number for F1) and lower case letter indicating source of resistance, such as "h" for hirsutum, "c" for chilense, "p" for peruvianum, "pim" for pimpinellifolium and "u" for unknown (eiiter h, c or hc). For example, Gh13 (hirsutum resistance) and Gc9 (chilense resistance) are two breeding lines.  Other selections will have a number followed by the lower case letter and then a series of numbers indicating the generation, such as Gh24-1-1-1 (hirsutum resistance, F5 seeds, collected from this plant).  

Scoring plants: (see Selection Criteria)

Plants were scored for DSI, stage, fruit shape, firmness, color of fruit, yield, vigor, and overall. Other characteristics considered were green shoulder, jointless, determinate (T=1), semi-determinate (T=8), indeterminate (T=3).

Conclusions from April 2005 field evaluation at Sanarate (high virus pressure):

            221 populations (breeding lines, two blocks) and 270 XA hybrids (two blocks) were evaluated at about 85 days after transplanting.  Most plants had mature fruit.  The begomovirus pressure was very high as susceptible cultivars had been planted about 2 weeks before the test lines. DSI for commercial cultivar, Silverado, was 4 (scale: 0 no symptoms; 4 severe leaf symptoms and plants stunted). There were over 300 susceptible control plants and each plant had a DSI > 4 or were dead.

              Shape, size, and firmness were major criteria for selection of the plants for future testing.  A firm fruit with a saladette shape (roma shape) of about 120 g is the most desirable fruit type for Guatemala.  Silverado, Marina, Toro, and Elios are popular tomato cultivars for the major markets in Guatemala.  Round tomatoes are available in the up scale grocery stores and the Sheriff-type is sold to San Salvador. 

• Resistant hybrids (Gentropic Seeds, S.A.):   270 hybrids were evaluate in two locations: no virus pressure (Antigua) and high virus pressure (Sanarate). These hybrids were made from F4, F5, F6, and F7 parents. In some their was considerable segregation and others were nearly uniform for plant type. From the 270 hybrids, about 44 were selected for future studies at Sanarate. Seed was collected from these 44 selections. At least one of these hybrids was very promising for production of XC populations (consideration for multiple site testing before commercialization). All hybrids were evaluated and given scores of 1, 2 or 3. Value of 1 hybrids should be advanced to XB and evaluted at two or more locations, 2 and 3 value hybrids should be created again as new XA's with more advanced parental lines and these would be evaluated at locations with and without high virus pressure.

• Outstanding breeding lines: Gu143-1-1-1-b

               Bacterial wilt was detected in late February 2005 and caused considerable problems in certain areas of the field. Because of this problem, many of the XA hybrids have been planted in a commercial field in Salama in March 2005.

Conclusions from April 2005 field evaluation at Antigua (low virus pressure):

     About 80 of the best breeding lines from October 2005 evaluation were planted at Antigua, where there is very low begomovirus pressure. This plot is at about 1500 m and temperatures are rarely above 26 C. The major lesson from these plot is that some lines which had high yield at Sanarate (hot, near 35 C, 890 m) did not yield well in the next generation at Antigua. The question is this climate or inbreeding depression. This is not known, so some of the low yielding lines will be planted at Sanarate (hot) for evaluation in October 05.           

Progress: 

               LINES: Selection continued on all lines from October 2004. About 230 plants were selected and seeds saved from these plants. An idea of the range of lines with different characteristics can be obtained by reviewing the lines for March 04. Future efforts will concentrate on developed of super elite breeding lines with known resistance genes and on development of breeding lines with resistance both to begomoviruses and bacterial wilt.

               HYBRIDS: Hybrids are no longer being produced by San Carlos University. Breeding lines have been licensed to Gentropic Seeds, S.A., Antigua, Guatemala.

 Evaluation of tomato germplasm selected in Morocco for begomovirus resistance in Sanarate:

      Comparison of germplasm in Agadir, Morocco and Sanarate, Guatemala.

April 2005, Douglas P. Maxwell

[Breeding tomatoes for resistance-GT project]  [Projects for Breeding Tomatoes for Begomovirus Resistance]