The 2012 Lowell Summer Music Series will kick off at 7:30 p.m. Friday night, when reggae legend Ziggy Marley takes the stage at Boarding House Park on French Street. The following evening, a free concert featuring Canadian folk group Genticorum will celebrate the 100th anniversary of Lowell’s Jeanne D’Arc Credit Union. The series runs through Sept. 8 and features several notable acts from the worlds of rock, pop, blues, and more. Summer musical highlights include the 26th annual Lowell Folk Festival and the 33d annual Banjo and Fiddle Contests, all free events. For more information or to purchase tickets, visit lowellsummermusic.org. Season tickets also are available, offering more than 35 percent off the regular ticket price for all shows.