Summary of Field Evaluations of Tomato Germplasm in Sanarate Guatemala, October 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

 

 

 

Goals: 

To evaluate the segregating  populations (F3, F4) from the diverse crosses of begomovirus-resistant lines by other germplasm with desirable characteristics of shape, size, firmness, disease resistance, etc. as part of the GenTropic Seeds program to produce a new generation of breeding lines with begomovirus resistance.   Some advanced F6 lines were selected at Sanarate. Also, F7 breeding lines were grown at Sanarate and Antigua, which has very low virus pressure, and these lines were evaluated for horticultural characteristics.
   

To evaluate 76 hybrids with resistance to begomoviruses produced by GenTropic Seeds S.A.

 

Evaluation Team:

 

    Maxwell in the rain, Elevio - L. Mejia - Mynor, and growers

 

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:

 

 

Information about trial in Sanarate for Oct. 05:

After the last trail, which ended in April 05, a new field was selected to avoid problems with soil-borne pathogens. This field had not been in tomatoes for several years and was planted to maize and beans (a milpa). A susceptible tomato hybrid was transplanted in various locations througt the field about two weeks before the six-week-old transplants were planted. 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). This was an unusally wet season. Hurricane Stan influenced the rain fall and the week the plants were scored about 250 mm rain occurred in 5 days. As in October 04, a blight problem rapidly developed and this was thought to be caused by a bacterium.

Few tomatoes are planted in the Sanarate valley where are field trial is located because they usually have 100% incidence of begomovirus infection, 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 (g), jointless (j), determinate (T=1), semi-determinate (T=8), indeterminate (T=3).

 

 

 

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

 

            F2, F3, F4, F5, and F6 populations (breeding lines, two blocks), 20 new XA hybrids (two blocks), 43 old XA hybrids (two blocks) and 13 XB hybrids (two blocks) were evaluated at about 85 days after transplanting.  All 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 was 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.