Phenotypic characteristics of interspecific hybrids between wild and cultivated soybean with and without insect-protected biotechnology traits

Wild soybean (Glycine soja Sieb. and Zucc.) and cultivated soybean (Glycine max (L) Merr.) can cross-pollinate, albeit at a very low frequency, potentially resulting in an interspecific hybrid with a biotechnology trait inherited from the cultivated soybean parent. As part of environmental risk assessment, it is informative to understand the competitiveness potential of these hybrids in natural habitats. The objective of this research was to evaluate the phenotypic characteristics of the interspecific hybrids and compare them with cultivated and wild soybean. Secondly, the comparisons were conducted between the interspecific hybrids with and without an insect-protected (IP) biotechnology trait. Two wild soybean populations were crossed with cultivated soybean containing either MON 87701 or MON 87751, the IP traits developed to control specific lepidopteran pests. Hybrid plants with and without the IP trait and parental entries were evaluated in growth chamber trials for the plant, pollen and seed characteristics. Compared to the parents, the hybrids had intermediate values for most of the measured characteristics. Compared to the wild soybean parent, hybrids had less twining, shorter plants, fewer seeds and pods, thicker stems, bigger seeds and pollen grains, as well as reduced seed dormancy-all due to domestication genes inherited from cultivated soybean. However, when compared to parents, hybrids had significantly reduced pollen viability (51.8-73.3% vs. > 95%) and number of seeds per pod (1.6-1.7 vs. 2.3) indicating partial reproductive sterility due to chromosome interchange between nonhomologous chromosomes. Seed coat color of the F₃ hybrids segregated in a manner that seems to involve two major genes (I and T) with some level of inter-locus interaction and/or partial dominance resulting in an observed ratio of 9 green (iⁱ-T-): 3 black (iiT-): 3 brown (-itt): 1 yellow (iⁱiⁱtt) seeds. A combination of recessive genes (ii from wild and tt from cultivated soybean) resulted in hybrid seeds with defective, cracked seed coat contributing to reduction in seed dormancy. Generally, hybrids with and without the IP traits had comparable performance indicating that the biotechnology IP trait did not have unintended effects on phenotypic characteristics. However, there were some characteristics that differed. The F₃ hybrids with MON 87751 had significantly lower seed dormancy (8.1%) compared to hybrids without the transgene (15.1%) likely due to the proximity of the transgene to soybean native domestication-related gene and their co-segregation in hybrid generations. In summary, the results obtained in this research suggest that the fitness, overwintering and general ability of hybrids to compete and persist in nature is reduced when compared to wild soybean. The main contributors to lower survival of hybrids are: (i) domestication genes inherited from the soybean parent, (ii) partial sterility of hybrids due to chromosome interchange, (iii) inferior performance of hybrids compared to either parent, and/or (iv) the transgene proximity to soybean domestication-related genes and their co-segregation in interspecific hybrid generations. These factors should be considered when assessing potential impact of soybean biotechnology traits if transgenic cultivars inadvertently cross with wild soybean.