''Supermarkets is still the core of our business and our most important business,'' Mr O'Brien said. ''While home improvement is a good medium-term opportunity, the supermarket business, in my view, offers us the largest opportunity for growth going forward, therefore it should and will receive that sort of attention.'' Woolworths shares closed down 19¢, or 0.7 per cent, after the news, to close at $26.95. The succession plan was an unwanted distraction as Woolworths faces a renewed onslaught from Coles, which has trumped the earnings growth of its competitor during the past year and sparked a price war in January. Coles also claimed to have won market share. Mr O'Brien said that despite a rejuvenated Coles and a downturn in retail - Woolworths recently issued its first profit downgrade in years - retailing was always a challenge.