Variation of myrosinase activity in the cross progenies of two Brassica juncea lines with relatively low and high myrosinase activities

A crossing experiment was conducted to estimate the inheritance pattern for myrosinase activity in Brassica juncea. Myrosinase activities were measured in cotyledon tissue of the F, progeny and backcrosses from two doubled-haploid parental lines of B. juncea, one with relatively high myrosinase activity and one with relatively low myrosinase activity in cotyledon tissues. Myrosinase activity was measured in terms of the rate of hydrolysis of exogenous sinigrin by soluble protein extract of the cotyledons. Myrosinase activities of the parental lines were 0.63 nmol mg(-1) min(-1) ("High") and 0.22 nmol mg(-1) min(-1) ("Low") (P = 0.0001), and mean myrosinase activities for the F, progeny were 0.35 nmol mg(-1) min(-1) (with Low as the maternal parent) and 0.51 nmol mg(-1) min(-1) (with High as the maternal parent). This pattern suggests a maternal effect on myrosinase activity, which is expected because of the maternally dominated genome of cotyledon tissue. In a set of reciprocal backcrosses, significant effects of the original parental lines on myrosinase activity occurred when these lines were pollen receivers in the backcross, not when they were pollinators, also supporting a maternal inheritance pattern. A significant (P < 0.05) but weak simple additive genetic inheritance of myrosinase activity was also detected.