Robigalia Roundup LXXXIX: The pathogen that started a famine and still costs USD 10 billion a year

Hello {{first_name | Robigalia readers}},

Fancy putting your name on a document that labs in 180-plus countries will use to identify a pest?

The IPPC is looking for authors for three new diagnostic guides: one on the khapra beetle (Trogoderma granarium), and two on plant viruses, tomato mottle mosaic virus and Begomovirus solanumdelhiense.

These guides, called Diagnostic Protocols, are what laboratories worldwide use to confirm whether a pest or pathogen is present. Once adopted, they become an agreed international standard. Writing one means joining a small team led by an experienced coordinator, working mostly over email with the odd video call. No travel involved.

It's a slow process by design, usually four to five years from first draft to final sign-off, with your input needed at a few key points rather than constantly.

You can't nominate yourself directly to the IPPC. Nominations have to go through your country's official IPPC contact, usually housed within your national plant protection agency, or through a regional plant health body. If one of these three topics is your area, the first move is a conversation with that contact. You'll need a short summary of your expertise, a signed commitment form, and your CV.

Applications close 31 August 2026.

Now, onto this week’s edition:

Let’s dive in!

Mediterranean potato growers are watching their storage losses climb alongside summer temperatures, and the usual suspects behind tuber rot are being joined by some less familiar names.

A paper by Catalani et al., published in the Journal of Plant Pathology, examines how sustainable tillage and fertilisation practices reshape the fungal communities responsible for potato tuber rot under a warming Mediterranean climate.

Rising temperatures are already shifting which pathogens dominate field crops, and potato tuber rot offers a clear test case. Several key rot-causing fungi thrive above 28°C, conditions increasingly common during Italian summers.

This study, part of a five-year field trial at the University of Tuscia's farm in Viterbo, compared conventional ploughing against two conservation tillage methods (subsoiling and spading), each combined with either compost or mineral fertilisation.

Diseased tubers harvested in 2023 were surface-sterilised, and fungi isolated from lesion tissue were identified morphologically and confirmed using ITS and translation elongation factor-alpha sequencing. A representative Macrophomina phaseolina isolate was then tested against Koch's postulates on wounded tubers incubated at 20, 25, 30 and 35°C to assess temperature-dependent virulence.

Compost-treated plots showed 33.4% less rot than mineral-fertilised plots, with the lowest disease incidence in the compost-spading combination. Macrophomina phaseolina emerged as the single most frequent pathogen (16.2% of isolates), a finding the authors describe as the first documented report of this species causing potato tuber rot in Italy. Pathogenicity testing confirmed the isolate caused wet and charcoal rot, with lesion size increasing sharply with temperature, from roughly 0.7 cm at 20°C to 5.7 cm at 35°C.

Fusarium equiseti and F. brachygibbosum were also prevalent, together with Fusarium species accounting for 37.9% of isolates. Beneficial fungi, principally Linnemannia elongata, Trichoderma gamsii and Mortierella alpina, made up 34.8% of the pathobiota and were most abundant under compost and spading treatments.

The results point to a practical lever for managing tuber rot as Mediterranean summers grow hotter. Organic inputs and reduced-disturbance tillage appear to favour antagonistic fungi over warm-adapted pathogens, though the authors note the shifts may also reflect compost's buffering effects on soil moisture and temperature rather than biological antagonism alone.

Late blight arrived in the United States around the port of Philadelphia in 1843, crossed the Atlantic to Belgium by 1845, and within two years had triggered a famine that killed roughly a million people in Ireland and forced a million more to emigrate. Few plant diseases have altered the course of human history so directly.

Phytophthora infestans (Mont.) de Bary is an oomycete in the family Peronosporaceae, part of the Stramenopiles rather than the true fungi, though it behaves like one in the field. It is heterothallic, requiring both A1 and A2 mating types to reproduce sexually and form durable oospores, and hemibiotrophic, feeding on living tissue before switching to a necrotrophic phase that kills the host outright.

Under cool, humid conditions its sporangia release biflagellate zoospores that swim through free water on the leaf surface before encysting and penetrating the epidermis, a mode of dispersal that lets an epidemic move across a field within days.

The pathogen attacks potato and tomato along with other Solanaceous hosts, producing water-soaked lesions on leaves and stems that expand rapidly and develop a pale sporulating margin on the underside in humid weather. Infected tubers show a reddish-brown dry rot beneath the skin that renders them unmarketable and, in storage, a route for further spread.

Phytophthora infestans is thought to have originated in the Toluca Valley of central Mexico, where it still coexists with wild potato relatives, and it now occurs wherever potatoes are grown. Annual losses from crop damage and control costs are estimated at up to USD 10 billion worldwide, making it the most economically damaging disease of the world's third most important food crop.

Management leans on an integrated approach, forecasting models that trigger fungicide timing around infection-favourable weather, destruction of volunteer plants and cull piles that carry the pathogen between seasons, and resistance genes bred in from wild potato relatives such as Solanum americanum, though individual Rpi genes are routinely overcome by new pathogen races. That breeding challenge, durable resistance drawn from wild potato germplasm, is exactly where this week's featured pathologist has staked his research.

This week, we meet Babatunde Kareem, a doctoral candidate in the Plant Pathology and Plant-Microbe Biology Section at Cornell University, where he studies late blight resistance in potato.

Babatunde's interest in plant pathology began in Nigeria, after a documentary showed him how plant diseases could devastate agriculture. The idea stayed with him through his undergraduate thesis on bacterial wilt of tomato, where he saw first hand that plant disease was not confined to a classroom. It shaped yield, farmers' income and the stability of food production, and that realisation set the course he has followed since.

His path since then has moved through several research environments. The International Institute of Tropical Agriculture in Nigeria gave him his early grounding in applied plant pathology. A period of research in Hungary deepened his interest in potato disease resistance specifically, and time at the Sainsbury Laboratory in Norwich sharpened his focus on molecular plant-microbe interactions. Cornell has given him the space to bring those threads together in a search for durable resistance in wild potato germplasm.

At Cornell, Babatunde has screened around 200 clones of Solanum boliviense for resistance to Phytophthora infestans, identifying clones that combine reduced disease with localised cell death responses characteristic of a hypersensitive reaction. Some of these clones were independently retested through a potato research programme at the United States Department of Agriculture, with broadly consistent results.

Using transcriptomics, he has gone on to identify candidate nucleotide-binding leucine-rich repeat immune receptor genes that may help explain that resistance, work that has taken him to the 2025 Potato Association of America Annual Meeting and to APS Plant Health 2026, where he was recognised with an APS Foundation Student Travel Award.

You can follow Babatunde's research on LinkedIn and Twitter/X, or read more about his work on breeding for durable, multi-disease resistance in potato on his blog.

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P.S. Why Robigalia? The name originates from the Ancient Roman festival dedicated to crop protection. You can read all about the history here: