Soon after being shoe-horned into the top ranks of Zimbabwe's ruling party, the wife of ageing leader Robert Mugabe has gained a PhD in orphanages, seen as the latest sign that she may be destined for high office.

In a country where the path to power is paved with academic letters, analysts said the timing of the first lady's surprise qualification was no coincidence.

Armed with a PhD, a seat in the Zanu-PF politburo and her 90-year-old husband's ear at home, Grace has become a political force as the battle hots up to succeed the only leader Zimbabwe has known since independence in 1980.

There is speculation that Africa's oldest leader is grooming his 49-year-old wife.

Although her Zanu-PF credentials are thin, a group of female members recently launched plans to install her at the helm of their women's league. Tongues wagged even more rapidly when she completed her doctorate last week, just three months after it was announced that she was doing one.

"This is a political conferment. A lot of politically connected individuals have been getting free degrees here and at other state universities," a source told The Zimbabwean, an opposition newspaper at the University of Zimbabwe.

Her husband is the chancellor of the university and has seven degrees.

Her qualification was celebrated in Zanu-PF, where it was also taken as a sign of her rising prominence.

One Zanu-PF politburo member said Mugabe could step down once he has secured a final five-year term in 2018 - by which time he will be 94 - to make way for his wife.