Abstract
It is generally believed that domestication and breeding of plants has led to genetic erosion, including loss of nutritional value and resistances to diseases, especially in tomato. We studied the diversity dynamics of greenhouse tomato varieties in NW Europe, especially The Netherlands, over the last seven decades. According to the used SNP array, the genetic diversity was indeed very low during the 1960s, but is now eight times higher when compared to that dip. The pressure since the 1970s to apply less pesticides led to the introgression of many disease resistances from wild relatives, representing the first boost of genetic diversity. In Europe a second boost ensued, largely driven by German popular media who named poor tasting tomatoes Wasserbomben (water bombs). The subsequent collapse of Dutch tomato exports to Germany fueled breeding for fruit flavor, further increasing diversity since the 1990s. The increased diversity in composition of aroma volatiles observed starting from 1990s may reflect the efforts of breeders to improve fruit quality. Specific groups of aroma compounds showed different quantitative trend over the decades studied. Our study provides compelling evidence that breeding has increased the diversity of tomato varieties considerably since the 1970s.
Highlights
A recent paper in Nature Biotechnology on de novo domestication of tomato voiced the general belief that “breeding of crops over millennia for yield and productivity has led to reduced genetic diversity
The question remains whether the increase in diversity because of introgression has compensated the reduction of genetic diversity due to inbreeding and selection
We grouped the varieties per decade and calculated for each SNP the genetic diversity index (H) of Nei (Nei, 1973), referred to as expected heterozygosity
Summary
A recent paper in Nature Biotechnology on de novo domestication of tomato voiced the general belief that “breeding of crops over millennia for yield and productivity has led to reduced genetic diversity. Reduction of diversity among crop varieties poses risks for cultivation, especially when most varieties carry the same genetic basis for resistance to diseases and pests. Because the number of authorized pesticides has decreased and continues to decrease, Diversity of Modern Tomato Varieties crop protection has to rely more and more on resistances that should have not a narrow genetic basis. The question remains whether the increase in diversity because of introgression has compensated the reduction of genetic diversity due to inbreeding and selection. We have studied this for tomato, as in this crop there have been indications of serious genetic erosion (Lin et al, 2014). We looked at both genetic variation at the DNA level, and phenotypic variation, including disease resistances, fruit size, and flavor components
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