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  • Author or Editor: Esther van der Knaap x
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Reliable analysis of plant traits depends on the accuracy of scoring the phenotype. We report here on the efficacy of two methods in the detection of quantitative trait loci (QTL) controlling fruit morphology in three segregating tomato (Solanum spp.) F2 populations using the software program, Tomato Analyzer. The first method uses fruit morphology attributes such as fruit shape index, blockiness, pear shape, indentation area, and angles of the fruit along the boundary. The second method uses morphometric points to quantify shape. The morphometric data were subjected to principle components analysis (PCA). QTL that control the fruit morphology attributes and the morphometric PCA were identified that revealed that the methods were comparable in that they resulted in nearly identical loci. Novel attributes were added to Tomato Analyzer that improved versatility of the program in measuring additional morphological features of fruit. We demonstrated that these novel attributes permitted identification of QTL controlling the traits.

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Measuring plant characteristics via image analysis has the potential to increase the objectivity of phenotypic evaluations, provides data amenable to quantitative analysis, and is compatible with databases that aim to combine phenotypic and genotypic data. We describe a new tool, which is implemented in the Tomato Analyzer (TA) software application, called Color Test (TACT). This tool allows for accurate quantification of color and color uniformity, and allows scanning devices to be calibrated using color standards. To test the accuracy and precision of TACT, we measured internal fruit color of tomato (Solanum lycopersicum L.) with a colorimeter and from scanned images. We show high correlations (r > 0.96) and linearity of L*, a*, and b* values obtained with TACT and the colorimeter. We estimated genotypic variances associated with color parameters and show that the proportion of total phenotypic variance attributed to genotype for color and color uniformity measured with TACT was significantly higher than estimates obtained from the colorimeter. Genotypic variance nearly doubled for all color and color uniformity traits when collecting data with TACT. This digital phenotyping technique can also be applied to the characterization of color in other fruit and vegetable crops.

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There is a growing interest by consumers to purchase fresh tomatoes with improved quality traits including lycopene, total soluble solids (TSS), vitamin C, and total titratable acid (TTA) content. As a result, there are considerable efforts by tomato breeders to improve tomato for these traits. However, suitable varieties developed for one location may not perform the same in different locations. This causes a problem for plant breeders because it is too labor-intensive to develop varieties for each specific location. The objective of this study was to determine the extent of genotype × environment (G×E) interaction that influences tomato fruit quality. To achieve this objective, we grew a set of 42 diverse tomato genotypes with different fruit shapes in replicated trials in three locations: North Carolina, New York, and Ohio. Fruits were harvested at the red ripe stage and analyzed for lycopene, TSS, vitamin C, and TTA. Analysis of variance (ANOVA) revealed that there were significant differences (P < 0.05) among tomato genotypes, locations, and their interaction. Further analysis of quality traits from individual locations revealed that there was as much as 211% change in performance of some genotypes in a certain location compared with the average performance of a genotype. Lycopene was found to be most influenced by the environment, whereas TTA was the least influenced. This was in agreement with heritability estimates observed in the study for these quality traits, because heritability estimate for lycopene was 16%, whereas that for TTA was 87%. The extent of G×E interaction found for the fruit quality traits in the tomato varieties included in this study may be useful in identifying optimal locations for future field trials by tomato breeders aiming to improve tomato fruit quality.

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A melon (Cucumis melo L.) genomic library of near-isogenic lines derived from the cross between the Spanish cultivar Piel de Sapo and the exotic accession PI 161375 has been evaluated for fruit quality traits in four different locations. Traits evaluated were fruit weight, soluble solids content, maximum fruit diameter, fruit length, fruit shape index, ovary shape index, external color, and flesh color. Among these traits, soluble solids content showed the highest genotype × environment interaction, whereas genotype × environment interactions for fruit shape and fruit weight were low. Heritability was high for all traits except soluble solids content, with the highest value for fruit shape and ovary shape. Ten to 15 quantitative trait loci were detected for soluble solids content, fruit diameter, fruit length, and fruit shape; and four to five for ovary shape, external color, and flesh color. Depending on the trait, between 13% and 40% of the detected quantitative trait alleles from PI 161375 increased the trait, and between 60% and 87% of them decreased it, resulting in some PI 161375 alleles of interest for breeding. Most of the quantitative trait loci detected in previous experiments could be verified with the near-isogenic line population. Future studies with the melon near-isogenic line genomic library will provide a better understanding of the genetic control of melon fruit quality in a wider context related to agronomy, genetics, genomics and metabolomics studies.

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