Fitness of Hybrids between Weedy and Cultivated Radish: Implications for Weed Evolution

Abstract

Abstract. Weed species are known to evolve rapidly with their associated crops. A better understanding of the mechanisms and rates of weed evolution could aid in limiting or at least anticipating this process. Spontaneous hybridization between crops and related weed species can transfer crop genes coding for fitness-enhancing traits to wild populations, but little is known about how easily this takes place in various weed-crop complexes. We studied interspecific hybrids between wild and cultivated radishes (Raphanus raphanistrum ϫ R. sativus), which often co-occur and share pollinators. To determine whether the F 1 generation represents a strong barrier to subsequent introgression, we compared the fitness of wild plants and wild-crop hybrids. Two experiments were carried out in Michigan, USA, one with potted plants and the other involving four artificially established populations. In the artificial populations, we used white flower color, a dominant, crop-specific allele, to document the persistence of crop genes over time. Wild plants had yellow flowers, which is a recessive trait. F 1 hybrids had lower fitness than wild plants due to lower pollen fertility, fewer seeds per plant, and delayed flowering. Despite these disadvantages, hybrids contributed substantially to each population's gene pool. After 3 yr, frequencies of whiteflowered plants in the artificial populations ranged from 8% to 22%, demonstrating that crop genes persisted. Other studies of flower color variation in wild populations of R. raphanistrum provide circumstantial evidence for frequent crop-to-wild gene flow. We predict that, if cultivated radish is engineered to possess transgenes coding for traits such as resistance to insect herbivores, disease, herbicides, or environmental stress, these fitnessrelated crop genes will easily spread to R. raphanistrum.

The risk of pollen-mediated gene flow from exotic Corymbia plantations into native Corymbia populations in Australia

“…Such gene movement has received considerable attention following concerns over the escape of genetically modified crops (Hoffman, 1990;Raybould and Gray, 1994;Chapman and Burke, 2006), as well as in regard to the evolution and invasion of weeds from short-rotation crop species (Small, 1984;Van Raamsdonk and Van Der Maesen, 1996;Snow et al, 2001). Increasingly, however, the potential impacts of pollen flow from exotic species into native populations are receiving attention (Shapcott, 1998;Figueroa et al, 2003;Brock, 2004;Vanden Broeck et al, 2005).…”

Weed evolution after crop gene introgression: greater survival and fecundity of hybrids in a new environment

“…The Michigan common garden also included plants representing G 1 founders of the eight populations. of crop-wild radish hybrids, known as wild or feral R. sativus, appear to have displaced the original populations of R. raphanistrum in CA during the past few decades (Snow et al 2001;Hedge et al 2006).…”

“…Raphanus has emerged as a model system in plant evolutionary ecology and has been particularly useful for evaluating the ecological consequences of crop-to-wild gene flow (e.g. Klinger & Ellstrand 1994;Snow et al 2001;Hedge et al 2006), although there are no immediate plans to create transgenic radish varieties (Biosafety Clearing-House, http://bch/bch.biodiv.org/). Flower petal colour frequencies differ between species and can be used as a cropspecific marker (Snow et al 2001).…”

Relative Fitness of Transgenic vs. Non-Transgenic Maize × Teosinte Hybrids: A Field Evaluation

“…If hybrid fitness is lower, introgression of crop alleles into the wild will be slowed; if that fitness is higher, introgression will be accelerated (Ellstrand 2003). Motivated by concerns regarding unintended transgene flow, studies have compared one or more fitness-related traits of conventional (non-transgenic) crop 3 wild hybrids to one or both parental species in sorghum (Arriola and Ellstrand 1997), rice (Song et al 2004), carrot (Hauser 2002), sunflower (Snow et al 1998), radish (Snow et al 2001), and canola (Hauser et al 1998a, b). The results vary with the system; in some cases, estimated hybrid fitness was lower; in others it was higher.…”