Differential response of oilseed rape (Brassica napus L.) cultivars to lowboron supply

Three experiments were carried out on an alluvial sandy loam (Udifluvent) a t Tonglu, Zhejiang Province, P.R. China from 1992 to 1995, to determine the genotypic range in boron (B) efficiency of 16 oilseed rape (Brassica napus L.) cultivars, to identify the B-efficient cultivars and to identify speci fic responses which can be utilised for selection in a breeding program. Th e 16 cultivars which included high-quality and conventional types differed significantly in survival, plant height, leaf area, shoot dry weight and se ed yield; however, the ranking of the cultivars for their seed yield or oth er plant traits differed with B treatment. With severe B deficiency (CaCl2 extractable B < 0.26 mg/kg) and no boron applied, none of the cultivars exh ibited significant B efficiency, with seed yield <300 kg/ha. With moderate B deficiency (CaCl2 extractable B 0.34 mg/kg or 0.17 kg B/ha applied), seed yield varied significantly among the cultivars from 397 to 1889 kg/ha in y ear 1 and from 616 to 1260 kg/ha in year 3. Zhongyou 821 and 92-13 were the most B-efficient and Wanyou 324, Huashuang 2 and Su 2051 were the most B-i nefficient cultivars under moderate B deficiency. Significant differences w ere found among the cultivars in leaf B concentration; however, there was n o close relationship between leaf B concentration and seed yield responses to B of oilseed cultivars. Of all the growth parameters measured, leaf area was the early indicator best correlated with subsequent seed yield and may be useful for evaluating the response of cultivars to low B supply. Contra ry to current opinion, it was also found that high-quality oilseed rape cul tivars were not all sensitive to low B supply nor were all conventional cul tivars B-efficient.