Hybrid crucifers have been produced via the S-allele controlled sporophytic incompatibility, a system which is generally limited by intensive labor input and occasional instability in the expression of certain S-alleles. Additionally, most F1 hybrids lack the broad spectrum of disease resistance essential for wide adaptability. A cytoplasmic male sterile (ems) system in brassica, induced by the substitution of Brassica nuclei into a ems Raphanus cytoplasm, R1 (3), has provided a potentially useful system for the production of brassica hybrids. Moreover, the pollen control provided by the R1 ems system facilitates the incorporation of disease resistance by backcrossing ems plants to resistant recurrent parents. Based on this approach, we have developed ems Brassica campestris L. germplasms with resistance to clubroot, (caused by Plasmodiophora brassicae Wor.), downy mildew [Peronospora parasitica (Pers.) Ex. Fr.], and turnip mosaic (turnip mosaic virus) (5). In this report, we describe the release of 5 lines of ems B. campestris ssp. pekinensis (Chinese cabbage): Badger 28A, 28B, 28C, 28D, and 28E; 2 lines of ems B. campestris ssp. chinensis (pak choy): Badger 29A, and 29B; one line of ems B. campestris ssp. narinosa: Badger 30; and one line of ems B. campestris ssp. rapifera (turnip): Badger 31. These breeding lines would be potentially useful for the production of multiple-disease-resistant (MDR) B. campestris F1 hybrids.
Forty-six Chinese cabbage [Brassica campestris spp. pekinensis (Lour) Olsson] lines consisting of open-pollinated cultivars, inbreds, and F1 hybrids from China were screened for seedling resistance to downy mildew (Peronospora parasitica) (Pers.) Ex. Fr. Thirty-seven lines of this collection were screened for turnip mosaic resistance. Five lines showed dual resistance to downy mildew and turnip mosaic. Resistance to downy mildew at the cotyledon stage, expressed as a reduction in the sporulation capacity of P. parasitica, was under dominant monogenic control. Turnip mosaic resistance was expressed as a hypersensitive reaction. Genetic analysis of a cross between turnip mosaic resistant and susceptible parents suggested that resistance was conditioned by 2 dominant genes.
Nectary development in cytoplasmic male sterile (cms) Brassica campestris L. was partially restored through 3 cycles of selection for nectary size and number. No major anatomical differences between nectaries of normal and cms plants were apparent under light and scanning electron microscopes (SEM). Half-sib family analysis of nectary development showed negligible additive genetic variance but a prominent maternal effect. Differential response to selection observed in 3 pedigrees suggests the possibility of capitalizing on nuclear-cytoplasmic diversity for the improvement of nectary function.