Randy G. Gardner

Genetic Improvement of Fresh Market Tomatoes for Yield and Fruit Quality Over 35 Years in North Carolina: A Review

Improving tomatoes (Solanum lycopersicum L.) for higher yield, disease resistance, and better quality is required to make the tomato industry more attractive for tomato growers. Advanced breeding lines and hybrids of fresh market tomatoes were developed and evaluated in replicated yield trials with the objective of identifying superior inbred lines and hybrids in North Carolina. Numerous breeding lines and hybrids have been released from the North Carolina State University tomato breeding program. The objective of this review was to estimate the genetic gain achieved through breeding fresh market tomatoes for fruit yield and quality traits over the period from 1975 through 2009. No review on genetic gain has been performed for a fresh market tomato breeding program. This review describes the current status of fresh market tomato breeding and provides a foundation for future studies. Analysis of the data from replicated yield trials revealed that, although there was no genetic gain for total yield, a significant genetic gain in early marketable yield at the rate of 227 kg·ha−1 per year has been made. Average genetic gain of 3.1 g fruit weight/year increased until 2009. Total yield data indicated that fruit yield improvement potential may have reached a plateau, but there is potential to improve quality traits and disease resistance.

Diversity Analysis of Tomato Cultivars Based on Coefficient of Parentage and RAPD Molecular Markers

Genetic diversity analysis provides information on the genetic base of the gene pool of released genotypes. The objectives of this study were to assess the diversity of tomato cultivars and breeding lines released from North Carolina State University based on their coefficient of parentage (COP) and RAPD markers, and to estimate the contribution of ancestors to these tomato cultivars and breeding lines. The COP analysis revealed that a single ancestor Walter constituted 25.17% of the North Carolina tomato gene pool followed by Blazer (11.57%) and Fla. 2153 (6.29%). Walter was used in developing 30 lines, whereas Blazer and Fla. 2153 were used in developing 29 lines each. The highest COP value (0.828) was between Summit and Monte Verde, indicating that they were the most similar lines. Similarity coefficients based on the RAPD molecular markers ranged from 0.461 to 0.935, with an average of 0.77. The similarity coefficient of NC3Grape with NCEBR8 was the lowest (0.461), whereas it was the highest (0.935) between NC1CS and NC946. On the basis of molecular data, first and second principal components accounted for 78% and 3.3% of the total variation, respectively. A significant positive correlation (r = 0.19, p = 0.04) existed between two similarity matrices based on the RAPD and the pedigree. This information may be useful for selecting the parents in breeding programs, particularly to widen the genetic base for designing future breeding strategies.

GGE Biplot Analysis of Tomato F1 Hybrids Evaluated Across Years for Marketable Fruit Yield

Genotypes are generally evaluated in multi-environments to determine their consistent performance across locations and years. Several techniques are available to conduct such valuations. We used GGE biplot technique to understand the genotypic and genotype × year interaction in tomato (Solanum lycopersicum L.). Five F1 hybrids of tomato were evaluated from 2003 to 2008 in North Carolina for total marketable fruit yield. Significant (P < 0.05) genotype × year interaction indicated the necessity of further analysis to select the genotype that had high yield and stability across years. ‘Mountain Fresh’ was the best hybrid as far as yield and stability across years were concerned, followed by ‘Crista’; ‘Mountain Glory’ was highly unstable for marketable fruit yield. We concluded that ‘Mountain Fresh’ could be considered an ideal hybrid that can also be used as control for evaluation of other F1 hybrids. Close association between field performance and GGE biplot findings indicated that GGE biplot is a useful tool to graphically visualize the high-yielding and stable genotypes across years.