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Summary of Field Evaluations of Tomato Germplasm in Sanarate Guatemala, March - April 2006

Evaluation team: Luis Mejía and Rudi Teni, Universidad de San Carlos; Martha D. Maxwell and Douglas Maxwell, University of Wisconsin-Madison

Goals:

To evaluate the segregating populations (F8 lines) from the diverse crosses of begomovirus-resistant lines by other germplasm with desirable characteristics of shape, size, firmness, disease resistance, etc. at Sanarate, where the virus pressure was extremely high.

To evaluate about 60 hybrids with resistance to begomoviruses produced by GenTropic Seeds S.A., which included XA's, XB's, and 4 XC's hybrids.

To share information on field evaluations with the Tomato MERC team from the Middle East.

MERC/CDR Team:

MERC scientists at Sanarate

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., 2005. Acta Hort. 695:277-288). Germplasm was collected from various breeding programs, which 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 S. 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 S. habrochaites (Formly, L. hirsutum) (Phytopathology 88:910-914) and line TY52 homozygous for the Ty1 gene from S. 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 S. habrohaites (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 (Ty-1 gene) and line H24 (Ty-2 gene) were susceptible with very high virus pressure and these sources were not used in the breeding program.
TY197 (peruvianum), TY198 (peruvianum), FAVI 9 (habrochaites), FAVI 12 (habrochaites) and lines from Scott (chilense source of resistance, Gc9, Gc16, Gc171) had high levels of begomovirus resistance. Other S. chilense-derived lines (Gc172 and Gc173) had lower levels of resistance than the previous lines. Lines were selected from each of these breeding lines under the Guatemala conditions. These lines were all used in crosses with other lines and hybrids to create new breeding lines.
The Pimpertylc J-13 population was moderately resistance and selections were made from this population, e.g., Gpim10.
Combining different sources of resistance increased the level of resistance, e.g., a line with habrochaites resistance x line with chilense resistance. This was first observed by Dr. Luis Mejia in a cross of habrochaites x peruvianum in about 2001. Vidavski et al., 2006 have found that the F1 from Ih902 x S. peruvianum gave the greatest resistance.
At least seven begomoviruses are present at the field site, as determined by sequencing PCR fragments.
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. Other soil-borne pathogens have killed some lines. The FAVI 9, FAVI 12 and Scott lines have been most resistant to these problems. Breeding lines from TY197 were very susceptible and those from TY198 were more resistant. By now, most breeding lines derived from TY197 or TY198 have been lost.
F1 populations from crosses of lines with S. habrochaites-resistant (Vidavski and Czosnek hybrids as source of resistance) by susceptible lines are moderately resistant.
F1 populations from crosses of lines with S. chilense-resistant (Scott lines as source of resistance) by susceptible lines are susceptible under high virus pressure. 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 (habrochaites resistance).
Ih902 breeding line (March 04) was segregating for green shoulder and resistance.

Information about trial in Sanarate for March-April 06:

The same field was used for this trial as for the one in fall 05. This is the second season in this field. This field had not been in tomatoes for several years and was usually planted to maize and beans (a milpa) during the rainy season. A susceptible tomato hybrid was transplanted in various locations througt the field about two weeks before the four-week-old transplants were planted. No insecticides were used in the field plots, except at the end of the growing season. Commerical cultivars, (Silverado and Sheriff), were planted throughout the plot area. In all cases these commerical hybrids had DSI of 4 (really, more like 6, but scale only goes to 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 (about 85 days after transplanting).

This area of Guatemala is normally very dry and has a few rains during the rainy season (May to October). Few tomatoes are planted in the Sanarate valley where our field trial is located because they usually have 100% incidence of begomovirus infection, and growers are switching to other crops, e.g., cucumbers. In January 06, a field near our plot was planted to peppers and these plants had 100% incidence of virus infection.

Naming lines: Breeding lines will start with letter "G" for Guatemala followed by a lower case letter indicating source of resistance, such as "h" for habrochaites, "c" for chilense, "p" for peruvianum, "pim" for pimpinellifolium and "u" for unknown (eiiter h, c or hc); and then a number (number for F1 cross). For example, Gh13 (habrochaites 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 (habrochaites resistance, F5 seeds, collected from this plant). Plants selected in block #1 have numbers and plants selected in block #2 have letters, Gh24-1-1-a-1.

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). Nipples and ogc were also scored, plus number of locules.

Conclusions from April 2006 field evaluation at Sanarate (high virus pressure):

Most lines were F7 or F8 populations (breeding lines, two blocks) and were evaluated for overall performance. Seeds from these plants will be saved and are licensed to GenTropic Seeds, S.A. and TomaTech for use in development of hybrids. Considerable time was devoted to selection of the best line among "sister" lines, i.e., which is the best Gc43 or Gc143 line? Bacterial wilt was a problem in some areas and some lines were dead. Overall, this evaluation was considered one of the most severe for begomovirus pressure.

All plants had mature fruit by April 8, 2006. 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 100 g is the most desirable fruit type for Guatemala. Silverado has returned as the most popular tomato cultivar for the major markets in Guatemala. Round tomatoes are available in the up-scale grocery stores and the Sheriff-type (plum shape) is sold to San Salvador.

Resistant lines: The best lines of "sister" lines were selected. Some examples are as follows:

Gc143

Gc43

Ghc175

GMh8632 (orginally selected in Morocco, and now selected three times in Guatemala)

Gh25

Gh187 (cherry type)

GMp6330 (orginally selected in Morocco, and this is the first time it was grown in Guatemala)

Environment by genotype interaction: It was also possible to observe some of these same lines planted in a trial on the Pacific Coast. There was very low virus pressure, but the climate was more "tropical", ie hotter and humid. In general, many of the lines that performed well at Sanarate also performed well at this Pacific Coast site. One difference noted was that the pear-shaped fruits were more evident at the Pacific Coast site than at the Sanarate site.
Conclusions from April 2005 field evaluation at Antigua (low virus pressure):

     Breeding lines at the F7 were evaluated at Sanarate and Antigua sites. The best plants were selected for F8 lines, and these will become the foundation of the breeding program for the current hybrids. It is interesting to note that there is still segregation for fruit shape among some of these F7 lines, particularly among those from the most diverse cross with germplasm from Pimpertylc J-13 (H. Laterrot). In collaboration with GenTropic Seeds hybrids at various stages are continuing to be developed. It is expected that there will be 100 of the best hybrids planted at Sanarate and Antigua for the MERC Team to view in April 2006. Also, XCxxx hybrids are being extensively evaluated as the final stage before commericalization by GenTropic Seeds. There were several F7 lines selected at Sanarate which will be evaluated in April 2006 as the last set of breeding lines generated with this grant.

Progress:

               LINES: Selection continued on selected lines from April 2005. 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. Resistant lines with determinate, semideterminate and indeterminate with resistance from either L. chilense or L. hirsutum and fruit shapes of saladette, blocky and rounds. Essentially, we have about 36 main types of germplasma lines, eg, semideterminate, saladette, 110 g. 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 and this company is now producing hybrids from the most advanced breeding lines. It is expected that one or more hybrids will be come available in 2007 for commercial use.

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

     Selections from the Moroccan lines (indeterminant types) where evaluated in April and October 05. The selections from Titrit were highly susceptible, but line Gh8xxxx was highly resistant. Also, a roma, indeterminant type that had been selected in Morocco was resistant in Guatemala.

November 2005, Douglas P. Maxwell

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