Interspecific hybridization between Coffea arabica L. and tetraploid C. canephora P. ex Fr. I. Fertility in F1 hybrids and backcrosses to C. Arabica

Summary The interspecific (C. arabica × tetraploid C. canephora) F₁ hybrid showed a low but highly variable fertility. An almost complete restoration to normal fertility was observed in individual trees of BC₁ and BC₂ generations with C. arabica as recurrent parent. From a comparison of various tests of fertility, it was found that pollen viability is a satisfactory measure of fertility.     

Transfer of resistance to race 2 of Plasmodiophora brassicae from Brassica napus to cabbage (B. Oleracea spp. Capitata). IV. A resistant 18-chromosome B1 plant and its B2 progenies

Summary The somatic karyotype and meiotic chromosome behavior were studied in an 18-chromosome B₁ plant derived from backcrossing a triploid (Brassica napus x B. oleracea ssp. capitata) F₁ hybrid to cabbage. It is considered that cabbage chromosomes no. 1 and no. 7 were substituted by two shorter B. napus chromosomes. Meiotic disturbances were more apparent during the late stages of second division. Seed fertility of this plant was largely restored in the second backcrosses with both cabbage and broccoli. 18-chromosome B₂ plants resistant to race 2 of Plasmodiophora brassicae were recovered among the progenies.Contribution no. J. 725 from the Research Station, Research Branch, Agriculture Canada, St-Jean, Québec J3B 6Z8.     

甘蓝型油菜与萝卜属间杂种的获得及其酶学分析

甘蓝型油菜（ＡＡＣＣ）与萝卜（ＲＲ）杂交以导入抗性基因，应用“胚胎挽救”技术在本研究中产生了１３３株Ｆ１代杂种株与油菜栽培品种回交的第１代杂种株，１４５株回交第２代杂种株．细胞学和同工酶（ＧＰＩ，ＰＯＸ）酶谱分析表明，回交后代中萝卜的抗性Ｒ基因通过染色体工程可望导入到甘蓝型油菜栽培品种中．     

Inheritance,heritability and breeding behaviour of three sources of resistance to Septoria tritici in wheat

Summary We examined the inheritance, heritability, and breeding behaviour of resistance to Septoria tritict in the spring wheat cultivars Seabreeze, Veranopolis, and IAS-20 in crosses to the susceptible Australian spring cultivar Gamenya. Resistance in Seabreeze was higher than that in Veranopolis and IAS-20. Inheritance of resistance in Seabreeze seems to be determined by at least three recessive genes. Resistance in Veranopolis and IAS-20 might be due to a single gene. Similarity of inheritance patterns and breeding behaviour of the resistance from Veranopolis and IAS-20 and the common ancestry of these two cultivars suggest that they may carry the same gene. Standard unit heritabilities of Septoria scores, as measured by correlation of F₂ plant with F₃ family mean data, were high (57–68%). Parent offspring genetic correlations confirmed previously reported associations between resistance and lateness and resistance and tall plant height, but correlations were not sufficiently high to be a major obstacle to selection. Resistance in Veranopolis and IAS-20 were easily recovered in first backcrosses while that in Sea breeze was more difficult to recover.Contribution from the Department of Agriculture Western Australia.     

Cytoplasmic substitution inSolanum. II. Tuber characteristics of reciprocal backcross progeny

Summary Recurrent backcrosses (BC) were used to introduce nuclear factors ofS. tuberosum L. ssp.tuberosum into the cytoplasm of Andean potatoesS. tuberosum ssp.andigena (Juz. and Buk.) Hawkes andS. phureja Juz. and Buk. Each generation BC was produced in reciprocal directions to test the effect of cytoplasmic substitution on yield. This report analyses tuber number, tuber weight, and tuber length of BC₂ and BC₃ substitution into ssp.andigena cytoplasm and BC₂ and BC₂ substitutions intoS. phureja cytoplasm. Direction of cross had no consistent significant effect on yield components of ssp.andigena substitution lines. InS. phureja reciprocal progenies direction of cross was responsible for significant differences of some reciprocal sets. When there were significant differences the higher yield usually occurred when ssp.tuberosum was the pistillate parent, but in some progenies when ssp.tuberosum was the pistillate parent the yield was significantly lower than in the reciprocals. It is suggested that differences between reciprocals resulted from chromosomally encoded gene action, resulting from maternal and/or paternal effects, rather than cytoplasmic factors. Authorized for publication as paper No. 7494 in the Journal Series of The Pennsylvania Agriculture Experiment Station.     

Pre- and post-fertilization barriers to backcrossing the interspecific hybrid between Allium fistulosum L. and A. cepa L. with A. cepa

Summary To facilitate the introgression of desirable traits of Allium fistulosum into the genome of A. cepa, several accessions of the hybrid between these species were pollinated with A. cepa as the recurrent parent, and in vitro ovary and ovule culture were performed to obtain an increase in the recovery of backcross progeny. Compared to the results obtained from seed development in planta, the increase in the number of backcross progeny was generally very limited, and in some cases even a decrease was found. Raising the sucrose concentration in the ovary culture medium resulted in a higher frequency of ovules developing back seed coats but this was not followed by an increase in the number of backcross progeny obtained. Pollen tube growth of A. cepa was disturbed in the styles of the interspecific hybrids. Per ovule, frequencies of micropylar penetration exceeded frequencies of backcross progeny only to a limited extent. Hence, it was concluded that in the tested interspecific hybrid accessions the attainable gain in viable backcross progeny by the application of in vitro culture techniques is limited by strong pre-fertilization barriers acting at the level of stylar incongruity.     

Trifolium ambiguum as a source of variation in the breeding of white clover

Summary Hybrids between T. ambiguum and T. repens were successfully established after ovule culture. The hybrids were male sterile but one of the hybrids produced a single seed when backcrossed to T. repens, while the other produced a significantly greater number of seeds. The majority of the backcross hybrids from the latter had 48 chromosomes, being produced from the fertilisation of unreduced gametes of the F1 hybrid by T. repens pollen. Regular meiosis in the BC1 hybrid resulted in the production of balanced gametes containing the full complement of T. repens chromosomes and the polyhaploid set of T. ambiguum chromosomes. There was no difficulty in establishing a substantial population of BC2 hybrids. The meiotic behaviour of the BC1 hybrid indicated that it should be possible to transfer genes from T. ambiguum into white clover T. repens. The significance of the results in terms of the use of alien variation in the improvement of white clover is discussed.