Physiological Mechanisms Of The High Boron Efficiency And Mapping Of The High Boron Efficiency Genes In Brassica Napus

Boron (B) is an essential microelement in higher plants, and B deficiency always causes the decrease of the crop yield and quality. Oil seed rape (B. napus L.), one of the main oil crops in the world, is sensitive to B deficiency. Genetic variation in B utilization efficiency exists among different Brassica napus germplasms. 8 high B-efficiency cultivars and 2 low B-efficiency cultivars were screened from 211 cultivars of oilseed rape (B. napus) by two-step-method. Some work on the boron efficiency mechanisms had been done and the high boron efficiency gene in Brassica napus (BE1) was located on the ninth linkage group. The paper reviewed the main results obtained during the recently years in the following aspects: boron efficiency in crops and boron pool, advances on the genes allelism in crops, QTL mapping of the important agriculture traits in Brassica, comparative mapping between Brassicas, Brassicas and A. thaliana..9 cultivars of oilseed rape (B. napus) in different research fields were used to conduct the experiment so as to exploit the B. napus germplasms sufficiently and study the physiological mechanisms of the high boron efficiency in B. napus. The high B-efficiency cultivars, 'Qingyou 10', and the low B-efficiency cultivars, 'Bakow' of rapeseed were described previously. 'Bakow' was used as the female parent in this cross. One F₁ plant derived from the cross was self-pollinated to produce an F₂ population. The F₂ individuals were selected at random and self-pollinated to generate the F_2:3 lines. The lines were used to do genetic analysis and map the high boron efficiency gene. The main results as follows:1. '8Z05' and 'Ningyou 7' were proved to be the high B-efficiency tendency cultivars; 'Huashuang 3', '6-203', '97009' and '97081' be the middle B-efficiency cultivars; 'Tapidor' be a low B-efficiency cultivars according to the responses of 'Qingyou 10' and ' Bakow' to boron deficiency by pot culture experiments. Under boron deficiency, the high B-efficiency cultivars could try their best to distribute boron absorbed to the growth centers, or preferential translocation of boron to young organs, and they need less boron to satisfy the growth than the low B-efficiency cultivars. Maybe it was one of the high boron efficiency mechanisms.2. The high B-efficiency cultivars, 'Qingyou 10' and the high B-efficiency tendency cultivars, 'Ningyou 7' and the low B-efficiency cultivars, 'Bakow' and 'Tapidor' were used to study the effect of boron and phosphorous deficiency on the growth in the seedlings by water culture experiment. 'Qingyou 10' and 'Ningyou 7' grew better than 'Bakow' and 'Tapidor', and phosphorous content and accumulation of the former were more than the latter. B-efficiency coefficients of 'Qingyou 10' and 'Ningyou 7' were respectively 0.480 and 0.497, whereas 'Bakow' and 'Tapidor' respectively 0.243 and 0.287. Results showed that the high B-efficiency cultivars and the high B-efficiency tendency cultivars behave P efficiency and the low B-efficiency cultivars behave P inefficiency, which indicated that phosphorous efficiency was positive correlation with boron efficiency. Effects ofboron deficiency were more than of phosphorous deficiency on the shoot of the low B-efficiency cultivars.3. 'Qingyou 10' and '8Z05' had been proved to be the high B-efficiency cultivars, 'Bakow' be a low B-efficiency cultivars by pot culture experiment. The F2 population of '8Z05'x 'Qingyou 10' was planted in boron deficient soil from 2000 to 2001. At the flowering stage, the ratio of the high B-efficiency plants to the low B-efficiency plants was 574:14. The ratio at seeding stage was similar to the result of the flowering stage, which showed that major genes controlling the boron efficiency traits in the two high B-efficiency cultivars were allelic. Another minor genes probably had some contributions to the traits of high boron efficiency, but the location of them may be different. The results obtained from 2001 to 2002 showed the same rule.4. Field experiments were conducted to study the genetic control of boron efficiency in oilseed rape by boron efficient coefficient (BEC, ratio of the seed yield at the critical boron level to that at the boron sufficient level) with 657 F2:3 lines, which was derived from a cross between a high B-efficiency cultivars, 'Qingyou 10' and a low B-efficiency cultivars, 'Bakow'. Results showed that the parents showed significant differences in both seed yield under boron deficiency treatment and BEC. The distribution of the seed yield of the 657 F2:3 lines showed normal distribution (mean=81.88g; SD=20.56) under supplied sufficient boron. Boron deficiency decreased the seed yield of Brassica napus significantly and the distribution of BECs of the F2:3 lines showed a bimodal distribution. The 657 F2:3 lines were grouped into high B-efficiency lines and low B-efficiency lines depended on the bimodal distribution of BECs. The ratio of high B-efficiency to low B-efficiency lines fitted the expected ratio of 3:1, indicating that one major gene controlled the B-efficiency trait, which further confirmed the results we obtained from a F2 population with 183 individuals (Xu F S, 2002).5. The 118 F2;3 lines selected randomly in the population, whose distributions of the BEC and seed yield under 2 treatments were similar to the population, were used to narrow down the target regions involved in B-efficiency. Using a combined RFLP, SSR and SSLP linkage map of the population, 8 RFLP markers from N2, 2 RFLP markers and 4 SSR markers from Brassica DB and 20 RFLP markers from LG9 were constructed 3 linkage groups, which were collinear with the LG9. Integration of the three linkage groups, 2 QTLs related to seed yield, 3 QTLs related to boron efficiency were mapped on it. QTLs of BE1-Y and BEl-Cl were identified at the same region flanking pa28c-pbl34b, accounted for 34.9% and 63.2% of the phenotypic variation respectively. The genetic distance of the boron efficiency gene BEl-Cl (BE1) was 5.1 cM with the new flanking markers O110A05a and wglalOa. QTL of BE1-C2 were closely linked with BEl-Cl, maybe they were the same gene according to the segregation of BEC of the population. Combination of the TRAP, AFLP techniques and BSA was an important way to get the tightly linked markers to be used to screen the recombinant individuals for further mapping the boron efficiency gene.