Morphological and genetic characteristics of F1 hybrids introgressed from Brassica napus to B. rapa in Taiwan.

Background: Unintentional introgression from genetically modified (GM) oilseed rape (Brassica napus) to a relative is inevitable in the open field. A feasible and practical strategy for restricting the spread of GM offspring is to set a reasonable isolated distance between GM B. napus and the relatives. To define the isolated distance, a pollen donor/recipient pair is a prerequisite to conducting the field trial of pollen flow. However, because the cultivation of GM B. napus is prohibited in Taiwan, it is difficult to obtain relevant information. Thus, this study explored the morphological and genetic characteristics of five varieties of B. napus (donor), three varieties of B. rapa (recipient), and the 15 corresponding F₁ hybrids, aiming to construct phenotypic data and genetic variation data and to select the most appropriate pollen donor/recipient for future field trials of pollen flow.

Results: The genome size of all F₁ hybrids estimated using flow cytometry showed intermediate DNA content between B. napus and B. rapa varieties. Most of the F₁ hybrids had intermediate plant height and blooming period, and the rosette leaves type and colors resembled those of B. napus varieties. The results of sequence-related amplified polymorphism (SRAP) showed an average of 9.52 bands per primer combination and 67.87 polymorphic bands among the F₁ hybrid population. Similarity and cluster analyses revealed higher similarity between F₁ hybrids and B. napus varieties than between F₁ hybrids and B. rapa varieties. Furthermore, we identified a specific 1100-bp band (LOC106302894) in F₁ hybrids and B. napus varieties but not in B. rapa varieties.

Conclusions: The rosette leaves and the DNA marker LOC106302894 observed in F₁ hybrids are consistent phenotypic and genetic characteristics that can be used to identify the presence of unintentional hybridization from B. napus to B. rapa in Taiwan. Due to the prohibition of GM crop cultivation, the hybridization system of non-GM Brassica species in this study can be utilized as a mimic scheme to conduct pollen flow trials, thus facilitating the determination of the proper isolated distance.