Intergeneric hybridization was performed between Moricandia arvensis and four inbred lines of Brassica rapa following embryo rescue. Three F1 hybrid plants were developed from three cross combinations of M. arvensis × B. rapa, and amphidiploids were synthesized by colchicine treatment. Six BC1 plants were generated from a single cross combination of amphidipolid × B. rapa ‘Ko1-303’ through embryo rescue. One BC2 and three BC3 plants were obtained from successive backcrossing with B. rapa ‘Ko1-303’ employing embryo rescue. Alloplasmic and monosomic addition lines of B. rapa (Allo-MALs, 2n = 21) were obtained from backcrossed progeny of three BC3 plants (2n = 21, 22 and 23) without embryo rescue. An alloplasmic line of B. rapa (2n = 20) degenerated before floliation on 1/2 MS medium due to severe chlorosis. Allo-MALs of B. rapa (2n = 21) showed stable male sterility without any abnormal traits in vegetative growth and female fertility. Molecular analyses revealed that the same chromosome and cytoplasm of M. arvensis had been added to each Allo-MAL of B. rapa. This Allo-MAL of B. rapa may be useful material for producing cytoplasmic male sterile lines of B. rapa.
Intergeneric hybridization was performed between Brassica rapa and Diplotaxis tenuifolia following embryo rescue. Twenty-three F 1 hybrid plants were developed from the cross B. rapa · D. tenuifolia and confirmed to be amphihaploids with 21 chromosomes in mitosis. Chromosome doubling of F 1 hybrids by colchicine treatment resulted into five amphidiploid plants which exhibited (20-21) II + (0-2) I at metaphase I (MI) of pollen mother cells. Sib-crossing and/or openpollination among amphidiploid plants for more than four generations resulted in the development of an ADt-06 line with reproductive systems capable of maintaining an amphidiploid line. The ADt-06 line was intermediate in some morphological traits between two parental species, and was characterized by a slightly pungent taste as a physiological trait. Analyses for genomic DNA confirmed that this line was a hybrid between two species. This new amphidiploid ADt-06 line could be a useful genetic resource for the breeding of new leafy salad vegetables.Wide hybridization in the Brassicaceae family offers much potential for genetic research and crop improvement (Prakash et al. 1999). Diplotaxis tenuifolia (L.) DC. (tribe Brassiceae) has been documented to be a C 3 -C 4 intermediate in photosynthesis and provided a source for incorporating of agronomic traits into Brassica crops (Apel et al. 1996). In this communication, we report the production and characterization of novel intergeneric hybrids of Brassica rapa · D. tenuifolia with reference to the reproductive traits for subsequent plant breeding.Diplotaxis tenuifolia (2n = 22, DtDt) strain 1, an accession of Cruciferae Genetic Stocks in the Laboratory of Plant Breeding, Tohoku University and nine cultivars of B. rapa L. (2n = 20, AA) were used as pollen and pistillate parents, respectively. Embryo rescue techniques and cytogenetical analyses were performed according to Bang et al. (1996). Matured embryos developed in pods for about 6 weeks after pollination were examined to determine the female and seed fertility of each amphidiploid plant. Random amplified polymorphic DNA (RAPD)-specific markers were examined for the hybrids developed and compared with those of B. rapa and D. tenuifolia according to the method of Kaneko et al. (2001).Following embryo rescue, 23 intergeneric hybrids were recovered from only one cross B. rapa (cv. ÔChingensaiÕ) · D. tenuifolia, all of which were confirmed to be amphihaploid with 21 chromosomes in mitosis. Chromosome doubling with a 0.2% colchicine solution resulted in the development of five amphidiploid plants. Because of poor seed setting on selfpollination, alternative sib-crossings were carried out or the plants were allowed to open pollinate for four generations. Eventually, a new amphidiploid line exhibiting few variation in morphological traits was developed designated as ADt-06. These amphidiploid plants were intermediate in leaf, corolla and seed characters between the female and male parents, although they grew taller and developed larger pods compared with both par...
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