Phenotypic Characterization of a Diversity Panel of TomatoPhenotypic Characterization of a Diversity Panel of TomatoLarry D. Robertson, Teri Balch, Susan M. Sheffer, and Joanne A. Labate

UDSA-ARS, Plant Genetic Resources Unit, Geneva, NY 14456

Plant MaterialsThe 50 diverse accessions of tomato grown in this study are listed in Table 1. These included a landrace panel of 30 PGRU tomato accessions assembled based on results of RAPD analyses including 14 accessions from the primary center of diversity and 12 accessions from countries contiguous with the primary center previously reported (Labate et al., 2009). This set was expanded by selection of additional accessions based on geography and time of collection or date of cultivar release.

MethodsTomato Analyzer:Tomato Analyzer is a software application which demonstrates objective quantitative measurements of fruit shape, size and color (Gonzalo et al., 2009). Mid-height, longitudinal dissections were made on each of 10 to 15 fruit per accession. The halves were placed on a Microtek Scanmaker 9800XL 11” x 17” scanner bed and scanned with a black background at 300 dpi (pixels per inch). The images were saved as .jpg files and analyzed using Tomato Analyzer 2.2.0.0, manual adjustments were made for boundary and proximal and distal end shape. Mean perimeter and mean area were extrapolated from the data.

Fruit shape, uniformity and color:Fruit shape, uniformity and color were determined based on descriptors presented by the Tomato Crop Germplasm Committee (CGC) (http://www.ars-grin.gov/npgs/descriptors/tomato). Fruit shape was determined via visual selection between the following shapes: flat, slightly flattened, round, plum, blocky, pear, oblong, high round and heart. Uniformity was based on a sliding scale of 1 through 9 with 1 indicating no uniformity and 9 indicating very high uniformity. Color was determined using visual selection of colors as presented by the Tomato CGC report (red, orange, yellow, gold, white and green).

°Brix:Brix degree data, refractive index at 20°C (Carli et al., 2009), were collected using a Model DR103L digital refractometer (QA Supplies). Juice from randomly selected cut fruit pieces was squeezed onto the refractometer. For each sample the °brix was calculated as a mean of 3 readings of separate fruit within each accession. °Brix is a measure of the soluble sugar content including glucose and fructose in ratios of approximately 1:1 to 1:1.5. Brix degree is considered a measurement of fruit sweetness; high °brix equates to higher sweetness.

Lycopene:Fruit pieces were homogenized in a commercial grade Waring blender (one to ten fruits per accession). An aliquot of homogenate was transferred to a 5 cm petri dish, and readings were taken using a Minolta Chroma Meter CR-300 by pointing the sensor close to the homogenate surface. Values were recorded for L*a*b* (also referred to as CIELAB) color space. L* indicates lightness, a* (red-green) and b* (blue-yellow) are chromaticity coordinates (http://en.wikipedia.org/wiki/Lab_color_space). Each L*a*b* value represented the average of three measurements. Lycopene was estimated using a regression model based on the transformed a*4 value (Hyman et al. 2004).

Vitamin C:Fruit pieces were homogenized in a commercial grade Waring blender (one to ten fruits per accession). A 100 ul aliquot of homogenate was pipetted into a 1.5 ml eppendorf tube, 500 ul of 6% metaphosphoric acid was added and the tube was vortexed. Samples were centrifuged at 15K rpm for 10’ at 4°C, 100 ul of clear supernatant was transferred to a 1.5 ml tube containing 100 ul of 5% metaphosphoric acid. Samples were then assayed using a Cosmo Bio Co. Ltd. (Japan) Vitamin C assay kit (Prod. No. SML-ROIKO2-EX) according to the kit protocol. Vitamin C was estimated based on absorbance at 530 nm using a standard curve of known concentrations.

Table 1. Tomato accessions used in this studyID Country Year NameG 29393 Spain 1905 Rosa o MonserratG 29883 China 1905 Zhongza No. 4G 29886 Bolivia 1989 Tomate del LugarG 30627 Italy 1992 Pomodoro Superselezione di MarmandeG 32403 Taiwan 2001 AVRDC #6G 32414 United States 2002 Flora-dadePI 97538 Argentina 1905 "Cherry"PI 98097 Cuba 1932 RinonPI 99782 Peru 1932 TomatePI 109834 France 1935 Merville des MarchesPI 117563 Brazil 1936 Sao PauloPI 118783 Venezuela 1936 RinonPI 121662 Canada 1937 AbelPI 124035 Peru 1937 naPI 124037 Chile 1937 naPI 125831 Afghanistan 1937 Rumi BanjanPI 127820 Bolivia 1938 naPI 127825 Peru 1938 Ccoilo-ChumaPI 128586 Chile 1938 naPI 128592 Chile 1938 naPI 129026 Ecuador 1938 naPI 129033 Ecuador 1938 naPI 129084 Colombia 1938 naPI 129128 Panama 1938 naPI 129142 Ecuador 1938 naPI 155372 Peru 1946 naPI 157993 Italy 1947 ProsperoPI 158760 China 1947 Chih-Mu-Tao-SePI 159009 Peru 1947 naPI 159198 United States 1947 Vetomold (121 Mass.)PI 196297 Nicarragua 1951 naPI 212062 Costa Rica 1954 TurrialbaPI 258474 Ecuador 1959 naPI 258478 Peru 1959 naPI 262995 Netherlands 1960 Ailsa CraigPI 268107 Mexico 1960 Cotaxtla IPI 270206 United States 1960 PonderosaPI 270408 Mexico 1960 naPI 270430 Mexico 1960 naPI 272703 Guatemala 1961 naPI 281555 Japan 1962 Kiyosu No. 2PI 291337 China 1963 Hong KongPI 294638 United Kingdom 1964 Devon SurprisePI 341134 United States 1969 Heinz 1370PI 390510 Ecuador 1974 naPI 406952 Nicarragua 1976 ChilcarojoPI 452026 Mexico 1980 A-1770PI 452027 Mexico 1980 A-1771PI 505317 Colombia 1986 1091-Chonto 21 (Mataverde) (3-21-2)PI 600920 United States 2003 Peto 460

General ObservationsThese accessions exhibited many traits not seen in modern cultivars of tomato. Variation in foliage color was observed (Fig. 2). Modern tomato has non-exserted stigmas (Fig. 3). However, many of these accessions expressed exserted stigmas (Fig. 4). Several accessions

Figure 4. Exserted stigma

Figure 2. Variation of foliage color in tomato landraces

Figure 5. Flowers of PI 258474 Figure 6. Fruits of PI 258474

Figure 3. Non-Exserted stigma

expressed floral abnormalities, with multiple ovules (Fig. 5), which resulted in multiple fused fruit with a spherical, fasciated shape (Fig. 6).

Literature CitedCarli, P, Arima S, Fogliano V, Tardella L, Frusciante L, Ercolano MR (2009). Use of network analysis to capture key traits affecting tomato organoleptic quality. Journal of Experimental Botany 60: 3379–3386. Gonzalo T., M.J. Brewer, M.T., Anderson, C., Sullivan, D., Gray, S., van der Knaap, E (2009). Tomato fruit shape analysis using morphometric and morphology attributes implemented in tomato analyzer software program. J. Am. Soc. of Hort. Sci. 134: 77-87. Hyman J.R., J. Gaus, and M.R. Foolad (2004). A rapid and accurate method for estimating tomato lycopene content by measuring chromaticity values of fruit puree. J Amer Soc Hort Sci 129:717-723. Labate JA, Robertson LD, Baldo AM (2009). Multilocus sequence data reveal extensive departures from equilibrium in domesticated tomato (Solanum lycopersicum L.). Heredity 103: 257-267. Robertson LD, Labate JA (2007). Genetic resources of tomato (Lycopersicon esculentum Mill.) and wild relatives. In: Razdan MK,Mattoo AK (eds). Genetic Improvement of Solanaceous Crops. Science Publishers: Enfield, NH. Vol. 2: Tomato, pp 25–75.

AcknowledgementsWe thank William Garman III, John Oughterson, Paul Kisly, and Jonathan Spencer for excellent technical support. This study was funded by CRIS Project 1910-21000-019-00D and the Tomato CGC.

BackgroundThousands of open-pollinated populations and inbred lines of domesticated tomato (Solanum lycopersicum L.) are conserved in germplasm centers such as the USDA, ARS Plant Genetic Resources Unit (PGRU) (Robertson and Labate, 2007). These collections provide a publicly available resource for experimentation and breeding to a broad community of users around the world. Landrace germplasm from the center of origin is expected to have a higher diversity than modern cultivars. Such germplasm can provide a source of novel alleles.

Figure 1. Fruit of 50 tomato accessions evaluated for this study

This study reports on an evaluation of a set of 50 geographically diverse PGRU accessions (Fig. 1) for fruit morphological traits, size and nutritional traits.

SummaryThis diversity panel of 50 PGRU tomato accessions represents only a small fraction of the available diversity preserved in the National Plant Germplasm System. There was a large variation expressed for all traits. Fruit size, color, shape and uniformity were as expected in landraces and vintage cultivars. Variation in the nutritional traits is potentially useful for crop improvement. PI 212062

Figure 12. PI 212062

was an outlier for both lycopene and Vitamin C (Figs. 11 and 12). This accession deserves further investigation.

Figure 10. Fruit weight (g) and perimeter (cm) for 50 tomato accessions, sorted by fruit weight

Fruit SizeSize of the fruit of this tomato diversity panel was measured using average perimeter (cm) and average fruit weight (g). Fruit weight ranged from 1.2 to 37.2 g and perimeter ranged from 9.8 to 32.4 cm (Fig. 10). Fruit weight and perimeter of fruit were highly correlated (r=0.93**, df=48).

Fruit Morphological TraitsFruit color, fruit shape and fruit uniformity are shown in Figs. 7-9. Most accessions were red fruited and most were slightly flat to flat. Fruit uniformity was low, as expected from less-improved populations.

Figure 8. Fruit shape for 50 tomato accessions

Figure 7. Fruit color for 50 tomato accessions

Figure 9. Fruit uniformity for 50 tomato accessions; 1=no uniformity, 9=completely uniformity.

Nutritional TraitsLycopene, Vitamin C, and obrix were recorded for the 50 tomato accessions in this diversity panel. Relationships among these traits are shown in Fig. 11. The accession with the highest Vitamin C (14.5 ug/ml) and highest lycopene (13.0 ug/g) was PI 212062 (Fig. 12). There was a very high correlation between lycopene and vitamin C (r=0.94**, df=48). The correlation of oBrix and Vitamin C was also significant (r=0.38*, df=48).

Figure 11. Brix content, Lycopene, and Vitamin C for 50 tomato accessions, sorted by Vitamin C