The Supreme Court has heard an Adelaide woman accused of burning her husband to death only meant to burn his genitals so he would not leave her for another woman.

Rajini Narayan is on trial for murder.

The prosecution told the jury she set her husband, Satish Narayan, on fire at their Unley house in December 2008 because she believed he was having an affair.

The prosecution said Narayan told her neighbours immediately after the fire that she intended to burn only her husband's genitals.

The court heard he died in hospital from his burns three weeks later.

The defence told the jury Narayan had been physically and emotionally abused by her husband for 20 years but that she loved and idolised him.

The defence said she formed an irrational view that if she burnt part of her husband's genitals he would stay with her, but that she ended up throwing a container of petrol and a candle on his back when he dismissed her threat.