Dr Yolanda Petersen

For many years, the same person would deliver laboratory consumables, including PCR primers, to the ARC Infruitec-Nietvoorbij in Helshoogte Road. The PCR primers came in a flat, cardboard envelope.

“One day, the delivery man asked me what was inside these envelopes,” remembers plant pathologist Dr Yolanda Petersen. “He said he’s always wondered because whenever he delivers these packages to people, they get so excited.”

The primers hold the promise of discovery, explains Petersen. “You’ve designed those primers to answer questions, and getting them means you are this much closer to the answer,” she says.

As a senior researcher at the ARC Infruitec-Nietvoorbij, Petersen has worked on many bacterial diseases of crops, including stone fruit and grapevines. She is currently leading a Hortgro-funded project on crown gall in apples.

Petersen was born in Cape Town and completed her BSc in Botany and Microbiology at UCT. A third-year project sparked her interest in bacteriology. “It was on characterising Xanthomonas campestris,” she says. “I just loved doing that project.”

X. campestris subsequently featured in her MSc research. She admits to still loving Xanthomonas, except these days she works on X. arboricola pathovar pruni, which causes bacterial cankers in stone fruit.

In 1999, Petersen’s PhD took her to the University of Florida in Gainesville, where she was tasked with creating transgenic citrus trees resistant to citrus tristeza virus. She had an ARC bursary, so on her return she started work at the ARC Infruitec-Nietvoorbij, where she has been since 2004.

“I’ve always been drawn to bacteria,” she says. “In the past, I don’t think bacteria got the attention they deserved because plants have these dangerous fungi and devastating viruses. Then little Xylella came along, and people started getting interested in bacteria.”

Xylella fastidiosa has been wreaking havoc in crops such as olives, citrus, and grapevines in the Americas and Europe. “But we don’t have Xylella in South Africa, so it took people longer to realise that bacteriology is important,” says Petersen.

Asked whether she thinks bacteria are finally having their moment in the sun, Petersen agrees. “And I’m here for it,” she says.