Internal browning of Brussels sprouts

Abstract

• 1. Investigations have been made of a condition of Brussels sprouts known as ‘internal browning’ (I.B.) which is characterised by necrosis of the internal leaves of a sprout button which is externally perfect. Whilst susceptibility to I.B. was probably heritable, the appearance of I.B. symptoms was influenced by environmental factors.

• 2. Sprouts from plants grown in the field but protected from frost by polythene covers had considerably less I.B. than sprouts from unprotected plants of the same variety.

• 3. Sprout buttons with a high internal density were rarely affected by I.B.; those of medium density had but little I.B.; whilst 75% of the I.B. occurred in sprouts of low internal density which were marketable, however, by commercial standards.

• 4. The percentage of sprouts with I.B. at any one pick was found to be correlated with both the percentage of low density sprouts present and the amount of frost which had occurred during a period of four weeks prior to the pick. The percentage of plants producing affected sprout buttons showed a similar correlation with frost and sprout density.

• 5. Progenies from plants selected for a high incidence of I.B., without reference to sprout density, had a higher proportion of I.B. and a higher proportion of low density sprouts than the variety from which the parent plants were selected. Differences in the percentage of sprouts with I.B. between these progenies, and between the progenies and the original variety, could be accounted for by differences in the percentage of low density sprouts present in each respective population.

• 6. No significant correlation was found between the amount of cover afforded to the sprout buttons by the large leaves of the main stem and the amount of I.B., though there was some evidence that the plant populations with the least natural leaf cover produced the greatest amount of I.B.

• 7. Marginal browning, a necrosis of the margins of the leaves of the terminal rosette of the plant, showed no correlation with susceptibility to I.B., of the sprouts on a plant so affected.

• 8. It is suggested that selection for absence of I.B. should be made when severe frost has occurred during the previous four weeks, and that the number of sprouts examined from each plant should be as large as possible. In addition, it is suggested that concurrent selection should be made for high sprout density, as an indirect means of limiting susceptibility to I.B.