0431 GMT May 19, 2019
Accepting a lengthy standing ovation from delegates, many tearful and holding "Thanks, boss" placards aloft, a visibly moved Merkel said the party had won four national elections under her by holding fast to its principles, AFP reported.
"In difficult times we shouldn't forget our Christian and democratic stance," she said.
Pointing to the rise of populism worldwide and what she called a breakdown of shared Western values, Merkel said the order she had championed was at risk.
"Whether it's the rejection of multilateralism, the return to nationalism, the reduction of international cooperation to deal-making or threatened trade wars... hybrid warfare, destabilization of societies with fake news or the future of our EU – we Christian Democrats must show in the face of all these challenges what we've got," she said.
The two main candidates, CDU general secretary Annegret Kramp-Karrenbauer, known as AKK, and corporate lawyer Friedrich Merz are locked in a battle over whether to embrace or break with the veteran chancellor's legacy.
A third contender, Health Minister Jens Spahn, 38, an outspoken critic of Merkel's 2015 decision to welcome more than one million asylum seekers to Germany, is running a distant third.
Merkel surprised the country and her party in late October when she announced she would not seek reelection as CDU leader at the party conference in Hamburg after a series of poll setbacks rooted in controversy over her liberal refugee policy.
The contest's outcome is expected to be crucial in deciding whether the influential leader can realize her stated goal of completing her fourth term in 2021 and then leaving politics.
"I hope we emerge from this party conference well-equipped, motivated and united," Merkel said. "I am confident we will succeed."
Merkel has led Germany since 2005, and moved her party steadily toward the political centre. More generous family leave, an exit from nuclear power and an end to military conscription are among her signature policies.