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Pest/Pathogen of the Month: October

Scientific name: Cercospora zeina Crous & U.Braun

Common names: Gray leaf spot

In Africa, Cercospora zeina is the predominant causal pathogen of gray leaf spot disease of maize. This fungus is a threat to food security, since it can cause severe yield losses on both small-holder and large-scale farms. The foliar symptoms caused by this fungus are tan to gray rectangular lesions that are restricted within veins of maize leaves. After consuming its “maize meal” inside the leaf, the fungus bursts out of the leaf stomata with a fresh set of spores to infect the next leaf. Many things still puzzle scientists about this fungus, such as the questions “Where did it come from?” and “How has it moved around Africa?” Gray leaf spot disease was first reported in the 1980’s in KwaZulu-Natal, South Africa. Reports of the disease have since emerged from other maize producing countries in sub-Saharan Africa. Could this be due to international and local trade of maize material that may contain infected leaf sheaths and ear husks, or has it been hiding in a wild grass species? Molecular analysis has shown C. zeina to have high genetic diversity in Africa and that it undergoes cryptic sex. No one has yet observed its sexual stage, but we suspect that this contributes to its high diversity and aggressiveness. Clearly, there is need to design and employ integrated pathogen management strategies to limit its reproduction and dispersal to ensure optimal maize production and food security in Africa and globally. 

 

 

 

Pest/Pathogen of the Month: August

Scientific name:  Sclerotinia sclerotiorum (Lib) de Bary.

Common names: white mold, cottony root, watery soft rot, stem rot, drop, crown rot and blossom blight.

Sclerotinia sclerotiorum (Lib.) de Bary is an Ascomycete fungus in the order Helotiales. This species is a multi-host necrotroph that infects more than 400 plant species, with lettuce, sunflower, canola and sugar bean being of economic importance to the South African agriculture industry. Sclerotinia sclerotiorum is characterized by the production of long-term survival structures called sclerotia which form an important part of the infection cycle. These structures can lay dormant in the soil for up to 8 years until environmental conditions become conducive for germination. Carpogenic germination of sclerotia results in the formation of a sexual structure (the apothecia) at soil level, which releases millions of ascospores that start the infection cycle. Myceliogenic germination forms hyphae and mycelium that results in direct sub-terrain infection of host plants, although this is limited to a radius of about 2 cm around the sclerotia. Signs and symptoms of disease depend on the host plant infected and can include water-soaked lesions or dry lesions on stems, leaves, fruits, or petioles. The presence of white fluffy hyphae on the host surface during high humidity forms the basis of the name “white mold” that refers to the disease. 

Photograph:Sclerotia (black structures) mixed in with soybean (Photo by Lisa Rothmann, taken from The South African Sclerotinia Research Network (SASRN) website)

 

 

Pest/Pathogen of the Month: September

Scientific name:  Spongospora subterranea f. sp.subterranea (Sss)

Common names: Powdery scab of potato

Powdery scab, caused by the obligate plant pathogen Spongospora subterranea f. sp. subterranea (Sss), is an unsightly blemish disease on potatoes and is a major problem in the potato industry worldwide. Powdery scab is identified by purple-brown pimple-like lesions that rupture the tuber periderm, creating powdery filled lesions. The powdery mass consists of masses of sporosori (collections of resting spores). These resting spores are highly resistant to unfavourable environmental conditions, allowing the pathogen to survive in the soil for over 50 years. The presence of these lesions reduces quality and marketability of seed tubers or tubers intended for consumption, causing major yield losses in potato production. This plant pathogen is also responsible for causing two other diseases, namely root infection and root galling, which also lead to yield reductions. Powdery scab disease is most severe in fields when the soil temperature is cool (9-17 °C) and has a high water content. Although infection occurs under cool and wet conditions, diseases have been recorded in hot and dry climates too, especially where irrigation is applied. The host range of Sss is broad as it infects plant species belonging to at least 26 families. Many weeds and commercial crop species have been confirmed to be alternative hosts of Sss. Powdery scab is difficult to successfully control due to the pathogen’s ability to form resting spores and the scarcity of resistant cultivars. No single control method can completely control Sss, however, an integrated management approach is advised for management of Sss.

 

Pest/Pathogen of the Month: July

Scientific name:  Teratosphaeria destructans

Common names: 

Teratosphaeria destructans is one of the most devastating pathogens to Eucalyptus forestry. It causes severe shoot and leaf blight on young Eucalyptus plantation trees and was, until recently, only known from South East Asia. In South Africa, T. destructans was first discovered in the KwaZulu-Natal Province by the FABI team in 2015. It has subsequently also spread to plantations of E. grandis and its hybrids in other sub-tropical parts of the country. Some good news is that the South African T. destructans population consists of a single genotype and mating type. This indicates that sexual reproduction is currently not possible and that the pathogen most likely entered South Africa as a single introduction. Care should be taken not to introduce the opposite mating type or additional genotypes.

Photo credit: https://www.fabinet.up.ac.za/index.php/news-item?id=274

 

New Publications

Botha I, Maduna SN, Hagen SB, Lall N, Berger DK. (2026) 3RAD-Guided SNP Discovery for Species Identification and Conservation of the Medicinal Southern African Tree Genus Greyia Hook. & Harv.. Ecology and Evolution 16(5):e73412, 1-29. 10.1002/ece3.73412
Dlamini CM, Matongera TN, Lawson SA, Healey M, Tanga A, Regasa K, Kassie W, Hurley BP, Germishuizen I. (2026) Modelling spatiotemporal dynamics of wattle plantations in northwestern Ethiopia using harmonised PlanetScope and RapidEye imagery. Trees, Forests and People 25:101293. 10.1016/j.tfp.2026.101293 PDF
Ndou M, Potts WM, Duong TA, Teske PR, Childs AR, Henriques R. (2026) Conspecific Scaffold-Level Genome Assembly Outperforms Heterospecific Chromosome-Level Assemblies for Assessing Genetic Indicators in a Threatened Marine Fish. Evolutionary Applications 19:e70247. 10.1111/eva.70247
Wingfield BD, Coetzee MPA, Wingfield BJ, Groenewald M, Pohl C, Wingfield MJ. (2026) The genetic blueprint of Cyclohexamide resistance: Analysis of 816 yeast species. Research Square 10.21203/rs.3.rs-9313202/v1
Paap T, White D, Bose T, Burgess TI. (2026) Diversity and phylogeny of Phytophthora Clade 9, including descriptions of three novel species. Mycological Progress 25:29. 10.1007/s11557-026-02140-4
Li GQ, Slippers B, Wingfield MJ, Chen SF. (2026) Diversity, distribution and host range of Botryosphaeriaceae in China. Forest Pathology 10.1111/efp.70077
Joubert M, van den Berg N, Theron J, Swart V. (2026) Leaf bleaching is associated with extensive transcriptional reprogramming in avocado trees with sunblotch disease. Virology 620:110903. 10.1016/j.virol.2026.110903 PDF
Nzuza P, Schroder ML, Slippers B, Maes WH. (2026) Spectral responses to larval and artificial defoliation in Eucalyptus dunnii: Implications for UAV-based detection of Gonipterus damage. Drones 10(4) 10.3390/drones10040250
Six DL, Marincowitz S, Duong TA. (2026) Ophiostoma ipsi-confusi sp. nov. Six, Marinc. & Duong, a consistent symbiotic fungus of the pinyon ips bark beetle, Ips confusus LeConte. Symbiosis 10.1007/s13199-026-01135-9
Yan Z, Zhao Y, Meng X, Gao M, Si H, Zhao G, Bose T, Chang R. (2026) New manganese-oxidizing Acremonium-like fungi from halophytic rhizospheres in the Yellow River Delta, China. Mycologia :1-13. 10.1080/00275514.2026.2627133
Eshetu FB, Barnes I, Nahrung HF, Fitza KNE, Slippers B. (2026) A Century of invasion: How biosecurity influenced populations of Sirex noctilio and Its fungal symbiont in Australasia. Molecular Ecology 35(6):0962 - 1083. 10.1111/mec.70311
Viljoen A, Duong TA, Kanzi AM, Wingfield BD. (2026) Comparative analysis of mitochondrial genomes in the Ceratocystidaceae reveals highly conserved gene organization despite substantial genome size variation. BMC Genomics 10.1186/s12864-026-12755-2
Ribeiro MF, Cavallini G, Solce GN, Favoreto AL, De Souza Passos J-R, Barbosa LR, Hurley BP, Wilcken CF. (2026) Cold storage of Gonipterus platensis (Coleoptera: Curculionidae) eggs for Anaphes nitens (Hymenoptera: Mymaridae) rearing. PeerJ :1-14. 10.7717/peerj.20903 PDF
Pham NQ, Marincowitz S, Marpaung YMAN, Tarigan M, Wingfield BD, Wingfield MJ. (2026) Two Cryphonectriaceae species from Eucalyptus leaves in North Sumatra and their stem inoculation outcomes. Fungal Systematics and Evolution 17:69–79. 10.15761/fuse.2026.17.05 PDF
Nickles GR, Stokes CK, Narh DL, Lynn KMT, Fuqua SR, Bryan C, Allen BM, Bivins CP, Bok JW, Brewer JS, Buthelezi ST, Clark JPRM, Coon KL, Corby LR, Coetzee MPA, Dewing C, Duong TA, Harris MA, Keller NP, Kopotsa K, Lane FA, Nichols HL, Nieuwoudt A, Nuñez MA, Medina Munoz ME, Park SC, Pham NQ, Ryan KT, Solís M, Vilgalys R, Wallace JM, Wang YW, Wingfield BD, Wingfield MJ, Worley TK, Zallek TA, Zamanian M, Hoeksma JD, Drott M, Pringle A. (2026) Equipped for success: Genomes and metabolites of the European Amanita muscaria are conserved in its novel South African range. New Phytologist 10.1111/nph.71064
Pham NQ, Wingfield MJ, Duong TA, Wingfield BD. (2026) Draft genome sequence of Elsinoe masingae: the causal agent of Eucalyptus scab in South Africa. Australasian Plant Pathology 55:37. 10.1007/s13313-026-01082-5
Pham NQ, Marincowitz S, Wingfield BD, Crous PW, Santos SA, Durán A, Tarigan M, Wingfield MJ . (2026) Pseudoteratosphaeria supramediana sp. nov. (Teratosphaeriaceae, Mycosphaerellales), a new foliar pathogen on Eucalyptus in Indonesia. Australasian Plant Pathology 55:28. 10.1007/s13313-026-01092-3
Nel WJ, Jali S, Barnes I, Wondafrash M, Hurley BP. (2026) Outbreaks of a native jewel beetle, Agrilus grandis (Coleoptera: Buprestidae), on commercial black wattle, Acacia mearnsii, plantations in South Africa. African Entomology 34(1):1-5. 10.17159/2254-8854/2026/a24625
Postma A, Klynsmith L, Duong TA, Allison JD, Smidt W, Waterhouse RM, Lesny P, Oeyen JP, Petersen M, Martin S, Liu S, Zhou X, Ziesmann T, Donath A, Mayer C, Misof B, Niehuis O, Peters RS, Podsiadlowski L, Coetzee MPA, Joubert F, Slippers B. (2026) Genome and transcriptome-based identification and expression profiling of chemosensory gene families across developmental stages and tissues in Sirex noctilio (Hymenoptera: Siricidae). Insect Molecular Biology :1-14. 10.1111/imb.70029
Aylward J, Visagie CM, Roets F, Wingfield BD, Wingfield MJ. (2026) Genome analyses reveal two novel species of Seiridium from Acacia mearnsii. Mycological Progress 25:8. 10.1007/s11557-026-02121-7