Summary of Field Evaluations of Tomato Germplasm in Sanarate Guatemala, March 2003
Luis Mejía, Universidad de San Carlos, and Douglas Maxwell, University of Wisconsin-Madison
Goals: To evaluate the segregating (F2) populations from the diverse crosses of begomovirus-resistant lines by other germplasm with desirable characteristics of shape, size, firmness, disease resistance, etc.
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 had an extremely high whitefly population year around and inoculum for the tomato begomoviruses was always present. Germplasm was collected from various breeding programs, which were focused on resistance to Tomato yellow leaf curl virus in the Mediterranean region or Tomato leaf curl virus in Asia. 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 a particular begomovirus species.
From the initial field trials, the following points were established:
Conclusions from March 2003 field evaluation:
Populations were evaluated at 85 days after transplanting. The field test was extremely severe. The transplants showed 100% incidence in the commercial cultivars: Elios and Marina at 30 days after transplanting. By the 85 day after transplanting, Elios, a commonly planted hybrid, was severely infected with plants about 30 cm tall, greatly stunted, and very few fruit. Marina, another commercial hybrid, was dead!!! At 30 days, some breeding lines showed no symptoms; and also at this time, there was evidence of segregation for virus resistance in many populations.
All plants were scored for fruit size, fruit shape, fruit firmness, fruit color, and fruit taste (Luis and Rudi tasted about 200 fruits – they still were ready to eat tomatoes for dinner.), resistance, vigor, yield, and an overall plant rating. About 3,000 plants were evaluated.
About 100 individual plants were identified as having superior characteristics (all had moderate to high levels of resistance) and fruit were collected from these plants. This will result in a field trial of about 9,000 plants, which will be evaluated in September 2003.
Resistant plants of all kinds were selected, ie, large, round fruit; roma-type, firm fruits; round, small, sweet fruits; firm fruit; high yielding, vigorous plants, etc.
From population of the cross of Marina (Mi gene) x H5 [hybrid with L. hirsutum resistance (GF) and L. peruvianum resistance (GP10, TY198 source)], tissue was collected and the REX primers used along with the Taq restriction enzyme to determine the genotype (Williams et al., TAG 87:757). This worked very well and 60 plants were scored. At least two of the plants that were homozygous for the Mi gene were also moderately resistant to begomoviruses. The seedlings from both homozygous and heterozygous plants will be grown and tested for the Mi gene.
Two segregating populations were evaluated for tagging begomovirus-resistance gene(s). For each population of about 100 plants, fruit from the 8 most resistant and the 8 most susceptible plants were saved. Our general impression was that there were three interaction phenotypes: very susceptible, moderate resistance, and slight-moderate resistance. The four F2 populations were from the crosses of i) GF1 (from L. hirsutum, FAVI 9) x HC7880; ii) GF2 (from L. hirsutum, FAVI 12) x HC7880; iii) GF1 x M82; and iv) GF2 x M82. In general these fruits were less than 100 g and many were very firm. Some fruits were of the roma-type.
For F2 populations from crosses of the L. hirsutum resistance (eg, GF lines) x L. peruvianum resistance (TY198 lines), the begomovirus resistance was very high (slight symptoms), yield potential high, excellent fruit favor, and small fruits (< 100g). Resistance was outstanding!!!!
From the 74 plants of Marina x GS9, 18 plants had moderate to slight-moderate symptoms. Fruit were collected from four plants.
Observations from the Salama Valley:
The Salama Valley is about 4 hours by car from Guatemala City (NE of the City) and it is a major tomato growing area. They have had serious problems with begomoviruses and more recently with a problem called chocolate spot (unknown causal agent). AgroVida (a Bayer Co. and GTZ sponsored IPM program in Salama Valley) included Llanero 7 (a GF line x susceptible line) in their field evaluation. It was highly resistance to the begomoviruses and the chocolate spot. Currently, 100 g of this hybrid is being prepared in Israel for field testing in grower’s fields.
We observed a new planting of Elios that had 100% chocolate spot and a large field with 35-day-old transplants of Silverado, which had 100% incidence of begomoviruses. Unfortunately, for this latter case, other tomato fields are being planted adjacent to this field. These two fields provide excellent opportunities for studies on the economic impact of these diseases. Currently, Dr. Mejia is making arrangements for such a study.
Family garden/school garden project:
In the area around San Miguel Chicaj (west of Salama City), there are many small Mayan growers. They are plagued by begomoviruses in their peppers and tomatoes. In cooperation with World Vision and AgroVida, we will attempt to distribute a tomato hybrid for home gardens (huerto familiar / huerto escolar). This hybrid will have high resistance to begomoviruses and excellent yield for small, flavorful fruits. The idea is that this can be planted for home consumption; and thus, there is not the need for the a firm fruit with the roma-type shape. Dr. L. Mejia is going to ask Pilones de Antigua, if they will produce this hybrid seed.
Other tomato problems:
Chocolate spot — plants with typical chocolate spot symptoms were collected and tested for Tobacco streak virus, Tomato spotted wilt virus, and potyviruses. One sample gave a positive potyvirus reaction.
Fruit necrosis – this problem was evident is some cultivars at the Barcena University, where there is a large field trial. Several samples were tested for Tomato bushy stunt virus and all were negative.
Wilting syndrome – this is a problem in a valley near Agua Blanca and has reduced production for 560 ha to about 105 ha. It appears to be caused by a soil-borne pathogen. One option is bacterial wilt. Tomatoes produced here are shipped to Salvador and are mainly the hybrid Sheriff.
These three problems need serious attention as they are impacting tomato production and no controls are known, because the cause is not known.
Begomovirus bookmark:
During the January trip to Guatemala, Martha Maxwell suggested that some means of communicating with growers would be helpful. A draft of a bookmark with pictures of symptoms and control strategies was designed by the Maxwells. Luis Mejia used the bookmark on several occasions in March, and found it to be very effective. Currently, he is having another draft prepared and checking on costs for printing. The expectation is that it would be in Spanish, English and Arabic. We are currently looking for a sponsor to finance this project.
Seedling production and hybrid seed production:
Currently, 100 g of Llanero 7 (GF1 x commercial breeding line) are being produced by a commercial company in Israel at 1.5 cents/seed. Two of the three large tomato seedling producing companies, Pilones de Antigua and Agropecuana Popoyan, in Guatemala were contacted and managers of both companies indicated that they are interested in producing the seedlings and helping us locate growers for field testing.
Also, very initial discussions were made with Pilones de Antigua about producing hybrid seed. The general manager, Richard Rotter, was the general manager for Asgrow Seed Co. in Salama and has considerable experience in hybrid tomato seed production.
The plant breeder, Anna Peterson, and plant pathologists, John Kao, from Seminis Vegetable Seeds invited us to visit with them at their field station in Salama. These two scientists are located a Woodland, CA and were at Salama to evaluate their germplasm for geminivirus resistance. Doug Maxwell has known these two scientists for many years and Anna Peterson took several classes from him, as she graduated from UW-Madison in Plant Breeding and Genetics.
22 April 2003
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