[Genetic analysis of a specially long pod character in artificially resythesized Brassica napus L].

Two hybrid combinations were made with a resynthesized specially-long pod line in H218 Brassica napus L., namely H218 x Zhongyou 821, H218 x MSP334 and their six generations F(1), F(2), backcrosses B(1) and B(2) and their parents P(1) and P(2) were used to study the inheritance of 3 pod related traits, namely the full pod length, the pod body length and the pod beak length. The results were the followings: the three traits in the F(2) population of the two combinations had a continuous normal distribution, indicating that these traits were quantitative in nature and controlled by polygenes. The broad-sense heritabilities of the full pod length, pod body length and pod beak length of the two combinations were 65.89%-70.77%, 60.14%-63.38% and 26.36%-46.44%, respectively. The narrow-sense heritabilities were 44.01%-46.78%, 46.89%-47.38% and 18.08%-37.87%, respectively. The results from the two combinations consistently showed that full pod length, pod body length and pod beak length were controlled by 5, 6 and 2 genes respectively. The preliminary study on the gene effect demonstrated that the three traits in the two combinations all fit the additive-dominant model and the epistatic effect was significant. The additive effects and the dominant effects of the three traits in the two combinations were both significant. Of the full pod length and the pod body length, the dominant effect was more significant than the additive effect; and it is the same case for the pod beak length.

[Cytological observation on intergeneric hybrid between Brassica. Chinensis and Crambe abyssinica].

The intergeneric hybrid from a cross between Brassica. Chinensis and Crambe abyssinica was observed with 2n=55 chromosomes in the original progenies. After several generations of in-vitro propagation by tissue culture, the chromosomes of the intergeneric hybrid were remarkably reduced, varying from 25 to 28, averaged at 26.In meiosis of the PMC of the hybrid, the average configuration of chromosome pairing was 0.06 III + 11.26 II + 3.80 I. The number of bivalents varied from 8 to 13. The majority of PMC cells showed 10 II, 11 II and 12 II bivalents with frequencies of 24.58%, 23.91% and 30.98% respectively. The number of univalents varied from 0 to 8. The reduction of chromosomes in the hybrid and the high numbers of bivalents were possibly due to the chromosome of Crambe abyssinica eliminating and the genome of Brassica. Chinensis doubling in the hybrid cells. Triade cells, chromosome lagging, and chromosome bridges were observed in anaphase II.

[Study on induction of polyploidy in Salvia bowleyana by colchicine treatment].

OBJECTIVE: To explore the technique of induction of polyploidy in Salvia bowleyana by colchicine treatment. METHOD: The three kinds of explant of bud, leaf and calli were induced by colchicine treatment. RESULT: The induction effects were better when the calli was treated by colchicines (15 mg x L(-1)) and the leaf was pre-cultured for one week. The doubling rate was 33.33%, while the majority were wholy doubled plants, and the leaves were thicker and broader, the color was darker, the root was thicker and the stoma size was obviously bigger than the diploid plants. The number of chromosome were 8 to 64. Isoenzyme analysis showed that the enzyme activities between the polyploid and the diploid plants were quite different. CONCLUSION: Induction of polyploidy by colchicine treatment is efficacious. The part of the doubled plants were identified as homologmous tetraploids.

Multiple Evolutionary Events Involved in Maintaining Homologs of Resistance to Powdery Mildew 8 in Brassica napus.

The Resistance to Powdery Mildew 8 (RPW8) locus confers broad-spectrum resistance to powdery mildew in Arabidopsis thaliana. There are four Homologous to RPW8s (BrHRs) in Brassica rapa and three in Brassica oleracea (BoHRs). Brassica napus (Bn) is derived from diploidization of a hybrid between B. rapa and B. oleracea, thus should have seven homologs of RPW8 (BnHRs). It is unclear whether these genes are still maintained or lost in B. napus after diploidization and how they might have been evolved. Here, we reported the identification and sequence polymorphisms of BnHRs from a set of B. napus accessions. Our data indicated that while the BoHR copy from B. oleracea is highly conserved, the BrHR copy from B. rapa is relatively variable in the B. napus genome owing to multiple evolutionary events, such as gene loss, point mutation, insertion, deletion, and intragenic recombination. Given the overall high sequence homology of BnHR genes, it is not surprising that both intragenic recombination between two orthologs and two paralogs were detected in B. napus, which may explain the loss of BoHR genes in some B. napus accessions. When ectopically expressed in Arabidopsis, a C-terminally truncated version of BnHRa and BnHRb, as well as the full length BnHRd fused with YFP at their C-termini could trigger cell death in the absence of pathogens and enhanced resistance to powdery mildew disease. Moreover, subcellular localization analysis showed that both BnHRa-YFP and BnHRb-YFP were mainly localized to the extra-haustorial membrane encasing the haustorium of powdery mildew. Taken together, our data suggest that the duplicated BnHR genes might have been subjected to differential selection and at least some may play a role in defense and could serve as resistance resource in engineering disease-resistant plants.