Expression of male sterility in alloplasmic <i>Brassica juncea</i> with <i>Erucastrum canariense</i> cytoplasm and the development of a fertility restoration system

<jats:title>Abstract</jats:title><jats:p>An alloplasmic mustard, <jats:italic>Brassica juncea</jats:italic>, has been synthesized by placing its nucleus into the cytoplasm of the related wild species <jats:italic>Erucastrum canariense</jats:italic> to express cytoplasmic male sterility. To achieve this, the sexual hybrid <jats:italic>E. canariense</jats:italic> (2<jats:italic>n</jats:italic>=18, E<jats:sup>c</jats:sup>E<jats:sup>c</jats:sup>) ×<jats:italic>Brassica campestris</jats:italic> (2<jats:italic>n</jats:italic>= 20, AA) was repeatedly backcrossed to <jats:italic>B. juncea (2n</jats:italic>= 36, AABB). Cytoplasmic male‐sterile (CMS) plants were recovered in the BC<jats:sub>4</jats:sub> generation. These plants are a normal green and the flowers have slender, non‐dehiscing anthers that contain sterile pollen. Nectaries are well developed and female fertility is > 90%. The fertility restoration gene was introgressed to CMS <jats:italic>B. juncea</jats:italic> from the cytoplasmic donor <jats:italic>E. canariense</jats:italic> through pairing between chromosomes belonging to <jats:italic>B. juncea</jats:italic> with those of the <jats:italic>E. canariense</jats:italic> genome. The restorer plants have normal flowers, with well‐developed anthers containing fertile pollen. Meiosis proceeds normally. Pollen and seed fertility averaged 90% and 82%, respectively. F<jats:sub>1</jats:sub> hybrids between CMS and the restorer are fully pollen fertile and show normal seed set. Preliminary results indicate that restoration is achieved by a single dominant gene. The constitution of the organelle genomes of the CMS, restorer and fertility restored plants is identical, as revealed by Southern analysis using mitochondrial and chloroplast probes <jats:italic>atp</jats:italic> A and <jats:italic>psb</jats:italic> D, respectively.</jats:p>