. 1990. Effect of row spacing and seeding rates on summer rape in Southern Manitoba. Can. J. To determine the effects of varying plant densities on summer rape (Brassica napus L.), the cultivar Westar was seeded in 15-and 30-cm row spacings at seeding rates of 1.5, 3.0, 6.0, and 12.0 kg ha-r. Plants seeded in 15-cm rows yielded more per area, produced more pods per plant and lodged less than those in 30-cm rows. Higher yields were associated with a more even plant distribution and a lower degree of intrarow competition. There were no significant protein, oil and chlorophyll conce!tration differences between the row spacing treatments. The highest yields (kg ha ') were achieved with the 1.5 and 3.0 kg ha 'seeding rates. Summer rape compensated for lower plant densities with the production of more branch racemes. As seeding rate increased, competitive mortality increased, resulting in greater etiolation at bolting, and greater lodging at harvest. Seed

SUMMARYThe major photoperiod gene Ppd2 was identified on chromosome 2B of wheat using homozygous recombinant lines developed from a cross between Chinese Spring (CS) and the substitution line CS (Marquis 2B). Genetic analysis of these lines, using disease marker genes on the long arm of chromosome 2B, the yellow rust (Puccinia striiformis) gene Yr7 and the stem rust (P. gra minis) genes Sr9g and Sr16, showed these genes segregated independently from Ppd2. It was concluded that Ppd2 is located on the short arm of chromosome 2B. The classification of the disease resistance genes was used to identify a second gene (s) influencing the ear emergence time of the lines within each of the Ppd2 and ppd2 gene classes. The second gene(s) was associated with the disease genes on the long arm of chromosome 2B. The early allele of this gene(s) was found on Marquis chromosome 2B and the late on Chinese Spring 2B, so that early alleles of the two gene(s) influencing ear emergence time in this study were dispersed between the parental chromosomes.Following a winter sowing in the field, differences in ear emergence time were associated with the Ppd2 locus and the gene(s) on the long arm. Following a spring sowing, differences were confined to the gene(s) on the long-arm only. This confirms the photoperiodic sensitivity of Ppd2 and suggests that the second genetical effect was acting independently of the environment.

RAPDs (Randomly Amplified Polymorphic DNAs) were used to discriminate among 23 cultivars of oilseed rape (Brassica napus) selected from several breeding programs. A set of 100 random sequence 10-mer primers were tested, of which 70 produced bands and 22 showed evidence of polymorphism. A selection of six primers produced 23 polymorphic bands of between 300 to 2200 base pairs in size, sufficient to distinguish between the cultivars. An analysis of seed of five cultivars obtained from four different sites showed stability of banding pattern over source of seed. The analysis was repeated using four different thermocyclers, each of which produced the same band pattern. UPGMA cluster analysis indicates that the relationships among some of the cultivars is closer for those from the same breeding program than for those from different programs. The results of this study show that RAPDs can be used as a method of identification for oilseed rape cultivars.

Modifying the fatty acid composition of Brassica seed oil to increase its value as a nutritional or as an industrial oil has been a major objective in Brassica breeding programs worldwide. The conventional approach to fatty acid modification has explored natural or induced mutations occurring in the same plant species or close relatives within the Brassica genus. These mutations have been shown to be associated with a few enzymes in the biosynthetic pathway of the fatty acids. Several types of Brassica oil with significantly altered levels of the long chain fatty acid erucic acid (C22:1) and medium chain fatty acids such as oleic acid (C18:1) and linolenic acid (C18:3) have been developed for different end uses through conventional breeding. When the necessary genetic variation is not available within Brassica species, gene transfer by genetic transformation has been applied, as this approach is not restricted by the sexual incompatibility barrier across species. The fatty acids targeted by the transgenic approach included fatty acids with various carbon chain lengths ranging from C8 to C22, with different numbers of double bonds, and with various functional groups such as epoxy and hydroxy fatty acids. A commercial specialty oil with high level of a novel fatty acid, lauric acid (C12:0), was produced as a result of the transfer of a FatB thioesterase gene from a distantly related plant species that produces seed oil with high level of this unusual fatty acid. Considerable progress has been achieved in altering the relative levels of the fatty acids found in Brassica oils for increased health and economic benefits and in developing Brassica oils which contain other unusual fatty acids, mainly through genetic transformation. Although the use of natural or induced mutations in the fatty acid biosynthesis within Brassica remains a valid option for oil modification, the transgenic approach will play an increasingly important role in the development of Brassica oils with altered novel fatty acid composition.

The influence of temperature during seed development on the fatty acid composition of oilseed rape (Brassica napus L.) was studied in one low-linolenic and one conventional canola cultivar. The cultivar Regent produces seed oil with ~20% linoleic acid (C18:2) and ~8% linolenic acid (C18:3), whereas Stellar is relatively high in C18:2 (~25%) and low in C18:3 (~2.5%). Both cultivars were grown in the field, and the fatty acid compositions of the seed oils were monitored throughout the period of seed development. In the field, the content of saturated (C16:0 + C18:0) and monounsaturated (C18:1) fatty acids in the seed oil increased when seed developed under high temperatures. C18:3 levels were higher in seed harvested at sites with lower average daily temperatures. The low C18:3 trait of the cultivar Stellar was relatively stable over environments. Both temperature and duration of exposure to the temperature during seed development affected the fatty acid composition of the seed in a controlled environment study. Plants subjected to a high-temperature treatment (30/25°C day/night) for 40 d produced seed with the lowest C18:3 content and the highest levels of C16:0 + C18:0 and C18:1. This was observed in both cultivars. JAOCS 75, 759-766 (1998).