* About 55 pct of Topix companies go ex-dividend * Nikkei falls to two-week low * Semi-related firms suffer as Infineon sees weaker Q4 By Dominic Lau TOKYO, Sept 26 (Reuters) - Japan's Nikkei average shed 1.6 percent to below the key 9,000-mark on Wednesday as a raft of companies went ex-dividend, while concerns over whether debt-laden Spain will seek a bailout also dampened sentiment. About 55 percent of Topix companies have passed the deadline for buyers of the stocks to get rights to first-half dividends. The Nikkei dropped 142.37 points to 8,949.17, hitting a two-week low and breaking below its 25-day moving average at 8,985.54. Toyota Motor Corp, Nissan Motor Co and Honda Motor Co were among the companies trading ex-dividend, down between 1.5 and 4.1 percent. The Asahi newspaper said Toyota has indicated to its main parts makers that it plans to halt car production in China during October as anti-Japanese sentiment in the country hurts demand. Nissan said it would suspend car production at its Chinese joint venture from Sept. 27, three days earlier than a scheduled holiday from Sept. 30 to Oct. 7. A senior dealer at a foreign brokerage said the production halt was positive for the carmakers as they could run down their excess inventories. "The fact that these guys have a nice excuse to cut down production in China where they are running what could be argued as being slightly excessive inventory levels is good news to the companies," he said. China-related companies have been taken a battering on concerns over faltering Chinese growth, while anti-Japanese sentiment in the country arising from a territorial dispute, could add to their difficulties. The Nikkei China 50, made up of Japanese firms with heavy exposure to the world's second largest economy, shed 2.3 percent. Construction machinery maker Komatsu Ltd and Hitachi Construction Machinery Co Ltd, whose fortunes are closely tied to China and global growth, eased 2 and 2.9 percent, respectively. Their U.S. rival Caterpillar Inc, the world's largest earth-moving equipment maker, cut its 2015 earnings outlook on Monday. Sluggish global growth, even though the U.S. Federal Reserve launched another round of stimulus, are biting into company earnings. The Nikkei is down 0.6 percent this quarter, which ends this week. On Tuesday, German chipmaker Infineon Technologies said sales and profits would fall more than previously expected in forthcoming quarters. The news weighed on Japanese semiconductor-related firms, with Advantest Corp, Tokyo Electron Ltd, Shinko Electric Industries Co Ltd and Dainippon Screen Manufacturing Co Ltd off between 3 and 3.9 percent. The broader Topix index lost 1.6 percent to 745.38. "European troubles are of course in focus, but relatively stable exchange rates are underpinning stocks. Some investors could also be buyers for window-dressing purposes as this is the last trading week of the quarter, but more of that buying might emerge later in the week," said Kenichi Hirano, operating officer at Tachibana Securities. Protesters clashed with police in Spain's capital on Tuesday as the government prepared a new round of unpopular austerity measures for the 2013 budget to be announced on Thursday. Spain is at the centre of the euro zone debt crisis on concerns the government cannot control its finances and those of highly-indebted regions, bitten by a second recession since 2009 that has put one in four workers out of work.