A RECORD nine countries will participate in the second Reebok Challenge with Michael Chang, a series of junior tournaments being staged throughout the Asia-Pacific region this year. China, Indonesia, Thailand and the Philippines will join last year's hosts Hongkong, Japan, South Korea, Taiwan and Malaysia in staging the event. The Challenge, developed in association with Hongkong's favourite tennis star, Chang, was introduced last year to give aspiring youngsters aged 16 and under the opportunity to play competitively while developing the sport in the region. ''We believe such events have planted the seeds for future international Asian tennis pros,'' said Bill Sweeney, marketing director of Reebok International-Asia/Pacific. Nearly 5,000 spectators turned out for the qualifying rounds of the Hongkong leg last year. The Challenge gets underway in the Philippines on May 1 and runs until November. Hongkong's qualifying round takes place from September 24-26 followed by the main draw from October 1-3 at the Hongkong Sports Institute. A minimum of 32 boys and 32 girls will be selected to play in the main draw of each event. The top four boys and girls from each tournament will then advance to the Reebok Asia/Pacific Championships to compete for the overall regional titles, which will be held in the territory from December 27-31. Winners and runners-up of the two finals will be awarded a trip to compete in the Australian Open junior tournament. They will also be invited to attend an exclusive tennis clinic in Melbourne hosted by former French Open champion Chang.