Male sterility in alloplasmic Brassica rapa L. carrying Eruca sativa cytoplasm

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Abstract
For the development of a new cytoplasmic male sterility (CMS) system in Brassica rapa (2n= 20, AA), intergeneric hybridization was performed in Eruca sativa (2n= 22, EE)×B. rapa. The original amphihaploid F1 plant (2n= 21, EA) generated via embryo rescue produced a sesquidiploid F1 plant (2n= 31, EAA), from which the alloplasmic F3 plants were generated. In F3, some progenies with malformed anthers were maintained as male‐sterile lines up to the F5 generation. In the F6 and F7 generations, the alloplasmic male‐sterile plants were bred by backcrossing to several B. rapa genotypes and were then classified into the three distinctive types: petaloid, antherless and brown anther, in addition to three intermediate types between them. By southern blot analysis, each plant of the petaloid and antherless types was shown to carry the cytoplasm genome of E. sativa. These male‐sterile plants produced as many viable seeds as the corresponding male‐fertile plants, although their nectary gland development was minimal. Consequently, CMS lines of the petaloid and antherless types with enhanced seed fertility and nectary gland development could provide promising plant materials for F1 seed production in B. rapa.