b'The Diversity Dynamics of Greenhouse Tomato VarietiesA CLOSER LOOK AT THE EFFECT OF PLANT BREEDING.BY: MARCEL BRUINSWHY IT MATTERS Apaper in Nature Biotechnology recent (Zsgn et al, 2018) on de novo domestica-A lot of people thinktion of tomato voiced the general belief that that domesticationbreeding of crops over millennia for yield and pro-and plant breedingductivity has led to reduced genetic diversity. As has led to genetica result, beneficial traits of wild species, such as erosion, includingdisease resistance and stress tolerance, have been loss of nutritionallost (). Despite the increases in yield conferred value, especiallyby domestication, the breeding focus on yield has in tomato. A recentbeen accompanied by a loss of genetic diversity and study (Schouten et al,reduced nutritional value and taste. To try and 2019) looked at thefind more data on this assumption, Wageningen diversity dynamicsresearcher Henk Schouten and his colleagues of greenhouselooked at the diversity dynamics of greenhouse tomato varieties intomato varieties in NW Europe over the last seven NW Europe over thedecades.last seven decades. Lo and behold,REDUCTION OF DIVERSITYthe study providedIt is safe to say that a reduction of diversity among compelling evidencecrop varieties poses risks for cultivation, especially that plant breedingwhen most varieties carry the same genetic basis has in fact increased!for resistance to diseases and pests. If a disease The diversity ofresistance has been overcome in one variety, other tomato varieties, avarieties become susceptible too. This leads to agri-whopping eight-foldcultural vulnerability which can affect the entire since the 1960s.chain, especially if there are no alternatives for Conclusion: thedisease control, such as appropriate and authorized concern that modernpesticides. History has provided several examples,Henk Schoutenplant breeding issuch as the Panama disease (Fusarium oxysporum decreasing diversityf. sp. cubense) epidemic in banana, or the southern among varieties, iscorn leaf blight (Helminthosporium maydis) out- size of fruits, no prickles or thorns etc.), leading not at all supportedbreak in maize. Because the number of authorizedto a loss of alleles and a decrease in genetic diver-by scientificpesticides has decreased and continues to decrease,sity of landraces compared to wild accessions. Two evidence, at least forcrop protection has to rely more and more on geneticprincipal occurrences affecting crop diversity have greenhouse grownresistances, introgressed into the varieties, thatbeen identified: 1) the replacement of landraces tomatoes in NWshould not have a narrow genetic basis. by commercial varieties; and 2) more recent addi-Europe. In contrast, ational changes in the diversity of commercial tremendous increaseTHE EFFECT OF PLANT BREEDING varieties caused by plant breeding. Breeding can in diversity wasThe loss of genetic variation in crops due to thereduce genetic diversity by continued selection in observed, both atmodernization of agriculture has been denoted asthe breeding germplasm or may broaden genetic the genotypic andgenetic erosion. During domestication preferreddiversity through the introgression of alleles from phenotypic level ofgenotypes were selected, most notably for thosewild relatives. The question remains whether the greenhouse growntraits which affect plant architecture and traitsincrease in diversity because of introgression has tomatoes. of the to be harvested product (i.e. no prematurecompensated the reduction of genetic diversity due sprouting, no spontaneous seed dispersal, largerto inbreeding and selection.38IEUROPEAN SEEDIEUROPEAN-SEED.COM'