The pilot stated that he was conducting a cross-country flight and flying in instrument meteorological conditions at an altitude of 7,000 ft mean sea level (msl) when the airplane encountered turbulence. While climbing to a higher altitude, he encountered extreme turbulence at 8,500 ft msl. The pilot lost control of the airplane, which entered an uncontrolled dive, and descended to 5,600 ft msl before he was able to regain control. The pilot subsequently landed without further incident. A post-flight inspection of the airplane revealed substantial damage to the right wing spar. The pilot reported no preexisting mechanical malfunctions or failures with the airplane that would have precluded normal operation; however, he stated that he may have overstressed the airplane during the recovery from the uncontrolled descent. A review of weather data revealed that there were no SIGMETs or AIRMETs for turbulence issued for the area of the accident, around the time of the accident.