Heredity And Its Difference Of Seed Color In Yellow-seeded Rapeseed (Brassica Napus L.) From Different Genetic Sources

Oilseed rape (Brassica napus L.), whose seed color usually includes yellow, brown and black, is one of the most important oilseed crops in the world. It has been shown that yellow seeds have thinner seed coat, less pigment, higher oil content and higher protein in the meal than black and/or brown seeds with the same genetic background. Developing yellow-seeded B. napus cultivars has been one of the approaches to enhance seed oil and improve quality. But the inheritance of seed color in Brassica napus is apparently different from those in Brassica campestris and in Brassica juncea. Many researches had been conducted to study the inheritance of seed color in Brassica napus, in which the seed color mainly be considered as a quality trait using segregating analysis of Mendel to postulate the genetic model according to the performances of segregating populations, or as a quantitative trait using traditional method to detect the effects at whole population level. With the deepening in understanding, quantitative trait was found to be controlled by genes with different effects, in which those with large effects were called major genes and those with few effects were called minor genes or polygenes. The segregating analysis of major gene plus polygene model of quantitative trait could separate the effect of major gene from the whole effects, which extended from segregating analysis of Mendel and unified biostatistical genetics and Mendel genetics. This method had been used to analysis the genetic system of seed color in Brassica napus in the paper, which aimed to explore the genetic mechanism of seed color and guide breeding for yellow-seeded Brassica napus lines.In this study, incomplete diallel cross was made between nine yellow-seeded Brassica napus lines and ten black-seeded lines, and every combination produced several generations. Digital image analysis was used to identify the seed color. The inheritance of seed color in Brassica napus was studied by applying major gene plus polygene model of quantitative trait through a joint segretation analysis of P₁, P₂, F₁, F₂ or F_2:3 families. The conclusions were mainly as follows:1. The results indicated that seed color in Brassica napus L. belonged to qualitative-quantitative trait, which controlled by two major genes plus polygenes. The major genes and polygenes had additive-dominant effects or additive-dominance-epistatic effects. One of the major genes contributed largerly to seed color trait than the other. All the additive, dominant and epistatic effects of the major genes were important to seed color. In some combinations, the polygenes also greatly influenced the seed color. The heritabilities of major genes (h_mg² ) in F₂ population were 82.55%～94.76%, with average 88.73%. So, the seed color in Brasscia napus was mainly controlled by major gene, and modified by polygene and influenced by environment.2. SH032, SH254 and SH315 possesed the highest yellow seed degree (YSD) and highest stability in heredity of seed color among the nine yellow-seeded lines. Two situations, yellow color being part dominant over or recessive to black color, were found in all the nine yellow-seeded lines corossed with different black-seeded lines. Except for SH219, which had poor performance in dominant effect on seed color and only slightly dominated over P05, the other eight yellow-seeded lines performed similarly when crossed to different black-seeded lines, almost all of which dominated over P17, P35 and P92 with different dominant degrees, but recessive to the other seven black-seeded lines.3. There were four segregation modes of seed color in F₂ generations:â‘ segregation ratio between yellow seed and black seed fitted to 1:63, this meant seed color was controlled by three pair genes;â‘¡segregation ratio agreed with 1:15, this meant by two pair genes;â‘¢segregation ratio fitted to 1:3, this meant by one pair genes;â‘£segregation ratio suited with 3:1, this meant by one pair genes with dominant effect over black seed. When crossed to different black-seeded lines, SH032, SH225, SH254 and SH279 exhibited the first, the third and the forth mode above; SH219 expressed the second, the third and the forth mode; the other four yellow-seeded lines exhibited the third and the forth mode.