The effect of colchicine on embryogenesis induction and chromosome doubling during microspore culture was evaluated in two F1 hybrids of winter oilseed rape (Brassica napus L.). Colchicine treatment (50 and 500 mg/L) of isolated microspores during the firt 15 h in culture stimulated embryogenesis and produced large amounts of healthy-looking embryos. These normal embryos germinated well at 24℃ after being transferred to solid regeneration medium and an initial period of low temperature (2℃) for 10 days, and could directly and rapidly regenerate vigorous plants. A high doubling efficiency of 84-88% was obtained fronl 500 mg/L colchicine treatment for 15h with low frequency of polyploid and chimeric plants. A colchicine treatment duration of 6h was less effective on embryogenesis and doubling efficiency. The present experiment also showed that changing of induction medium 15h after microspore isolation produced higher spontaneous doubling efficiency, as compared with medium change 6h after isolation.

The effect of colchicine on induction of embryogenesis and chromosome doubling during microspore culture was evaluated in two F1 hybrids of spring oilseed rape (Brassica napus L.). Immediate colchicine treatment of isolated microspores with the concentrations 50 and 500 mg/L for 15 h stimulated embryogenesis and produced large amounts of healthy-looking embryos. These normal embryos germinated well at 24 ◦C after being transferred to solid regeneration medium and an initial period of low temperature (2 ◦C) for 10 days, and could directly and rapidly regenerate vigorous plants. A high doubling efficiency of 83-91% was obtained from 500 mg/L colchicines treatment for 15 h with low frequency of polyploid and chimeric plants. The present experiment showed that a treatment duration of 30 h revealed less positive effects on embryogenesis and doubling efficiency, especially at higher colchicine concentration (1000 mg/L). Poor embryogenesis and embryo germination were observed from ordinary microspore culture without change of induction medium and colchicine treatment, and several subcultures were required for induction of secondary embryogenesis and plant regeneration.

Using three varieties of Brassica rapa, cv. Hauarad (accession 708), cv. Maoshan-3 (714) and cv. Youbai (715), as the maternal plants and one variety of B. oleracea cv. Jingfeng-1 (6012) as the paternal plant, crosses were made to produce interspecific hybrids through ovary culture techniques. A better response of seed formation was observed when ovaries were cultured in vitro at 9-12 days after pollination on the basal MS and B5 media supplemented with 6-benzylaminopurine (BA) and naphthylacetic acid (NAA). The best response was observed for cross 714×6012 with the rate of seeds per ovary reaching 43.0%. Seeds for cross 715×6012 showed the best germination response (66.7%) on the regeneration medium (MS + 1.0 mg l−1 BA + 0.05 mg l−1 NAA). In all three cross combinations, good response in terms of root number and length of plants was observed on the root induction medium (MS+1.0 mg l−1 BA + 0.1 mg l−1 NAA). A better response was observed for the regenerated plants cultured for 14 days than for 7 days. The ovary-derived plants with well-developed root system were hardened for 8 days and their survival rate reached over 80%. Cytological studies showed that the chromosome number of all plants tested was 19 (the sum of both parents), indicating that these regenerated plants were all true hybrids of B. rapa (n=10)×B. oleracea (n=9). The regenerated plants were doubled with colchicine treatment, and the best response in the crosses 708×6012, 714×6012 and 715×6012 was observed when treated with 170 mg l−1 colchicine for up to 30 h and their doubling frequency reached 52, 56 and 62%, respectively.

A substantial amount of seed is left in the fields before and during harvest of oilseed rape. Although this crop exhibitslittle or no primary dormancy, the absence of certain environmental cuesthat promote germination of imbibed seeds induces secondary dormancy. The work reported investigated the extent to which environmental stress conditions, including osmotic stress, low oxygen stress and anaerobiosis, induce secondary dormancy in oilseed rape, and examined the ariation in development of secondary dormancy between and within genotypes. Osmotic stress was most effective in inducing dormancy. Anaerobic treatment produced very few dormant seeds, asdid an atmosphere low in oxygen and high in nitrogen. The development of secondary dormancy under osmotic stress varied considerably between and within genotypes. Dormancy ranged from almost zero to about 60% for winter genotypesand about 85% for spring types. Within genotypes, variations occurred between seed lots and years of harvest. Temperature variations affected the percentage of dormant seeds. More dormant seeds were likely to be produced with incubation under water stress at 20℃ than at 12℃. In winter genotypes, fewer dormant seeds were produced when incubation temperature and germination test temperaturesdiffered. Thus, incubating at 20℃ and 12℃, followed by germination tests at 20℃and 12℃, respectively, produced most dormant seeds. Also, in the winter genotypes, the potential development of secondary dormancy waspos itively correlated with the pattern and speed of germination of untreated seeds.

Root parasites of the genus Orobanche are serious weeds in agriculture. An aseptic infection system of host roots using calli of three Orobanche species was developed for the study of host