First Report of Potato Cyst Nematode, Globodera rostochiensis, Infecting Potato (Solanum tuberosum) in Tanzania

Publication Type

Journal Article

Journal Name

Plant Disease

Publication Date

1-1-2026

Abstract

The potato (Solanum tuberosum) is a key food and cash crop across East Africa. In Tanzania, average yields over the past five years have been 8 to 10 tons/ha, far below the potential 20 t/ha (FAOSTAT 2023). Potato cyst nematodes (PCNs; Globodera rostochiensis) are quarantine pests that have been reported from neighboring countries such as Kenya (Mwangi et al. 2015), Rwanda (Niragire et al. 2020), and Uganda (Cortada et al. 2020). In November 2019, 20 potato fields were sampled for PCNs in Arusha and Kilimanjaro in the north, neighboring Kenya, and 6 in Mbeya in the south neighboring Malawi. Each field was sampled from 10 to 20 locations from the upper 30 cm following a ‘W’ pattern to provide a composite soil sample (∼2 kg). Samples were thoroughly mixed, air-dried, and sieved (1-mm mesh), and cysts were extracted from 100-cm3 soil subsamples (Baunacke 1922). Cysts were recovered from 10 fields in the north and 3 in the south with mean counts ̅̅̅̅̅ �� = 3 cysts/100 cm3 of soil (min = 2; max = 11). DNA, extracted using the Qiagen DNeasy Blood and Tissue Kit (QIAGEN N.V., Venlo, The Netherlands), was amplified using ITSF/R primers (Bulman and Marshall 1997) for G. rostochiensis and G. pallida. Primers for G. pallida did not amplify a product in any case, while those for G. rostochiensis generated a product for cysts from five fields. In May 2024, another 20 potato fields were sampled in the north. Cysts were detected in eight fields, at up to 96 cysts/100 ml, recorded in West Kilimanjaro (2.87109°S, 37.18794°E), while the lowest density (48 cysts/100 ml) was recorded in Arusha (3.31354°S, 36.71322°E). Cysts (n = 10) and second-stage juveniles (J2s) (n = 30) were morphologically identified as G. rostochiensis. The cysts were brown, spherical, and smooth, with a protruding neck, circumfenestrate vulval area, and no anal fenestration. The number of ridges was 18.5 ± 0.9 (16 to 22), Granek’s ratio was 3.29 ± 0.16 (2.1 to 4.1) μm, and distance from anus to vulva basin was 65.6 ± 5.9 (47 to 70) μm. The J2 body length was 423 ± 21 (334 to 479) μm, tapering, mostly posterior and labial region sclerotized, and slightly offset; stylet length was 21.2 ± 2.99 (19 to 23) μm; and stylet knobs were rounded and sloping posteriorly. The tail was 45.3 ± 5 (40 to 52) μm long, with a prominent hyaline tail terminus measuring 22.3 ± 2.8 (25 to 21) μm. Identification was confirmed by analyses of 9 D2-D3 region of 28S, 10 ITS rDNA, and 9 COI of mtDNA sequences (Singh et al. 2020). Three sequences from each gene region, 28S (PV474227 to PV474229), ITS (PV474233 to PV474235), and COI (PV477210 to PV477212), all showing up to 100% similarity with reference sequences, were deposited in GenBank. All Tanzanian COI and ITS sequences clustered with other G. rostochiensis sequences in maximum and well-supported (PP: 0.97) clades. However, G. rostochiensis and G. pallida are in an unresolved position in the 28S-based phylogeny. Six 5-liter pots containing steam-sterilized soil were each inoculated with 1,000 eggs/J2 from crushed cysts onto potato cultivar ‘Obama’ at 14 days after germination and maintained in a screenhouse for 120 days. Subsequently, an average of 20 cysts per pot were recovered, each containing on average 96 eggs per cyst, resulting in a reproduction factor of 1.92 ± 4. This confirms that cultivar ‘Obama’, commonly grown by farmers in Tanzania, is a suitable host for the identified PCN. Field results also indicate rising PCN densities on potato in Tanzania. This first report of G. rostochiensis in Tanzania has significant phytosanitary and regulatory implications for potato growers, traders, and policymakers.

Keywords

economic impacts, field crops, nematodes, yield loss

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