Gene exchange between wild and crop in Beta vulgaris : how easy is hybridization and what will happen in later generations?

Abstract

AbstractFour conditions are needed for the introgression of crop genes into wild relatives: (i) pollination is possible; (ii) zygotes are formed (compatibility of pollen and ovules); (iii) F1 hybrids and later hybrid generations are viable and fertile; and (iv) there is no selection against the introduced gene in backcross generations. In our study area, France, wild (Beta vulgaris ssp. maritima) and cultivated (ssp. vulgaris) beets have several zones of contact where pollination is possible: in the seed production areas with the surrounding wild populations, and in the sugarbeet fields with weedy forms or with wild coastal populations. Limiting factors, apart from distance, are male sterility and, in the sugarbeet fields, the low percentage of flowering crop plants. The difference in ploidy level may diminish the success of hybridization. The resulting F1 hybrids, unless they have a triploid cultivated parent, are vigorous plants, very well adapted to the agroecosystem. The cultivated characteristics, however, may be a handicap in natural ecosystems. Further generations are also known to be very successful in the agroecosystem, albeit only in the sugarbeet crop: these are the weed beets, which behave like annual weeds with a long-lived soil seed bank. We did not find substantial evidence for introgression of cultivated traits into wild populations outside the agroecosystem, either in the wild populations near the seed production areas in southwest France, or in coastal populations. The fate of transgenes, however, is not necessarily exposed to the same selection pressures as genes for classical cultivated traits. Herbicide tolerance and virus or nematode resistance may be selected for in situations where the corresponding herbicide is used or where plants live in contact with the enemy in question.