Evaluation Of Phosphorus Efficiency Of Natural Population Of Oilseed Rape(Brassica Napus L.)

Oilseed rape(Brassica napus L.) is one of the most important oil crops in C hina. Low soil phosphphate availability is the main limited factors of seed production in the middle and downstream of Yangzi river. Phosphorus(P) is an essential mineral nutrient for higher plants’ growth and development. Oilseed rape needs much more P and shows more sensitive to P deficiency than other crops. There existed significant differences in response to P deficiency among different B. napus varieties. Screening of P-efficient germplasm and breeding P-efficient cultivars is an important approach to deal with this problem. In this study, hydroponic culture was used to evaluate the P efficiency of 400 varieties of Brassica napus(here after referred to as ‘natural population’) from all over the country under normal phosphorus(250 μmol/L) and low phosphorus(5 μmol/L) conditions at seedling stage. The main results were as follows.1. The distribution of RDW, SDW, RS, PRL, PEC and correlations among them of natural population under low P and normal P conditionsUnder normal P conditions, RDW, SDW, RS, PRL and PEC of the natural population all showed normal distribution, indicating there existed abundant genetic variation in the natural population. The average values of shoot dry weight(SDW) were 0.3680 g plant-1(coefficient of variation, CV, 39.3%) and 0.3796 g plant-1(CV 39.9%), respectively; of root dry weight(RDW) were 0.0326 g plant-1(CV 38.5%) and 0.0325 g plant-1(CV 37.5%), respectively; of root:shoot ratio(RS) were 0.0920(CV 26.9 %) and 0.0916(CV 37.0%), respectively; of primary root length(PRL) 25.9 cm(CV 14.3 %) and 24.6 cm(CV 9.9 %) in the screening experiment Ⅰ(EXP. Ⅰ) and Ⅱ(EXP. Ⅱ), respectively under normal P conditions. Under low P conditions, RDW, SDW, RS, PRL and PEC of the natural population all also showed normal distribution, indicating there existed abundant genetic variation in the natural population. The average values of shoot dry weight(SDW) were 0.1293 g plant-1(coefficient of variation, CV, 20.9 %) and 0.1030 g plant-1(CV 26.3 %), respectively; of root dry weight(RDW) were 0.0411 g plant-1(CV 20.0 %) and 0.0322 g plant-1(CV 23.5 %), respectively; of root:shoot ratio(RS) were 0.3219(CV 14.1 %) and 0.3205(CV 19.0 %), respectively; of primary root length(PRL) 31.2 cm(CV 8.3 %) and 32.4 cm(CV 11.1 %) in the screening experiment Ⅰ(EXP. Ⅰ) and Ⅱ(EXP. Ⅱ). Phosphorus efficiency coefficient(PEC) investigated in screening EXP. Ⅰ(0.4047) were higher than EXP. Ⅱ(0.3115), but CV of EXP.Ⅰ(43.5 %) wereless than EXP. Ⅱ(49.1 %).At NP in both EXP. Ⅰand EXP. Ⅱ, SDW significantly positively correlated with RDW, but negatively correlated with PEC and RS; RDW were significantly positively correlated with RS, negatively correlated with PEC; RS significantly positively correlated with PEC. At LP, SDW significantly positively correlated with RDW, PEC and PRL, but negatively correlated with RS; RDW significantly positively correlated with RS, PRL and PEC; RS negatively correlated with PEC, but positively correlated with PRL; PEC significantly positively correlated with PRL.2. The validation of P-efficient and inefficient candidate cultivars of oilseed rape(Brassica napus L.)P efficiency of the natural population of Brassica napus at the seedling stage were determined by first parameter of SDWLP and second parameter of PEC(SDWLP/SDWNP). 17 P-efficient and 13 P- inefficient candidate varieties were choosed in EXP. Ⅰ; 17 P-efficient and 18 P- inefficient candidate varieties were choosed in EXP. Ⅱ. Cultivars no. 49 and 102 were identified as P-efficient candidates in EXP. Ⅰand EXP. Ⅱ, while no P-inefficient candidate varieties was identified in both experiments.17 P-efficient and 13 P-inefficient candidate varieties screened in EXP.Ⅰwere confirmed with field trials. Results showed that, under no P application treatments, seed yield of P-efficient candidates were positively correlated with agronomic P use efficiency at the seedling stage, negatively correlated with P EC, not correlated with SDW; PEC of P-efficient candidates at the mature stage were greatly negatively correlated with P EC of them at the seedling stage, positively correlated with agronomic P use efficiency at the seedling stage. Seed yield of P-efficient candidates(nos. 25, 56, 70, 92, 130, 333 and 360) and P-inefficient candidates(nos. 349 and 397) were more than the average values of 31.35 g plant-1 under no P application treatments and the average values of 38.03 g plant-1 under P application treatments, which could be as P-efficient candidates for further study. Seed yield of the P- inefficient candidates(nos. 81, 151 and 396) and P-efficient candidates(nos. 35, 42, 45 and 49) were less than the average values of 20 g plant-1 under no P application treatments and the average values of 31.35 g plant-1 under P application treatments, which could be as P-inefficient candidates for further study.