Different adaptability of Brassica rapa,Brassica juncea and Brassica napus in response to low nitrogen or low phosphorus stress

94 samples of Brassica rapa,Brassica juncea and Brassica napus were grown in fields under normal nutrition(CK),low nitrogen(LN) and low phosphorus(LP) conditions.Several agronomic traits such as seed yield,plant height,primary branch number,seed number per pod,thousand-seed weight,pod number and relative seed yield on LN or LP condition were studied in the mature period,to evaluate the difference of adaptability and yield potential of Brassica rapa,Brassica juncea and Brassica napus in the response to low nitrogen or low phosphorus stress.Results showed that Brassica napus had higher seed yield under three different nutrient treatments and larger potential for agriculture production than that of the other two types.Brassica rapa,which might have more genes involved in nitrogen or phosphorus utilization,showed the highest nitrogen and phosphorus efficiency.Whereas the nitrogen or phosphorus efficiency of Brassica juncea was in the middle between Brassica rapa and Brassica napus,and Brassica juncea had some other good traits such as yellow seed,large pod number and strong resistance to insects and diseases.These results suggested that both Brassica rapa and Brassica juncea could help to improve Brassica napus.Under different nutrition conditions,different correlations between seed yield and other traits were found in different types of rapeseeds.The great genetic variations among different cultivars or genotypes suggest that it is possible to select high nitrogen or phosphorus efficient rapeseed in intraspecific or interspecific if the number of samples collected is large enough.