A significant association between Liriomyza huidobrensis leafminers and Alternaria solani fungus is reported here for the first time in a commercial potato (Solanum tuberosum) field in Brazil. We found that there was a high correlation (0.84) between the number of L. huidobrensis mines and A. solani lesions on infected plants.
Liriomyza leafminers can adversely affect agronomic crops by transmitting a number of disease pathogens, including fungi, bacteria, and viruses. Often this results from the physical damage to leaves following insertion of an ovipositor by females during the act of egg laying. For example, Durairaj et al. (2010) reported that L. trifolii (Burgess) (Diptera: Agromyzidae) females perforate leaves of Solanum lycopersicum L. (Solanaceae), predisposing the plant to infection by Alternaria (Pleosporales: Pleosporaceae) fungi. Similarly, Deadman et al. (2002) reported that leaf perforation during L. trifolii oviposition favored leaf necrosis caused by Alternaria alternata (Fr.) Keissl in S. tuberosum L. (Solanaceae). Alternaria spp. can reduce photosynthetic leaf area and subsequent tuber production in infected potato plants (Simmons 2000).
The economic impacts of Liriomyza are high. For example, Liriomyza spp. in Kenya have caused losses of US$54 and US$64.5 million in Pisum sativum L. and Phaseolus vulgaris L. (Fabaceae), respectively (Pratt et al. 2017). These species also are agronomic pests of other vegetable crops such as Beta vulgaris L. and Spinacia oleracea L. (Amaranthaceae) (Minkenberg 1988). Mujica and Kroschel (2013) reported that the leafminer L. huidobrensis (Blanchard) (Diptera: Agromyzidae) was responsible for leaf damage that subsequently reduced yields of S. tuberosum by up to 51% in the Cañete Valley (central coast of Peru). Here, we provide the first report on the association of L. huidobrensis as a facilitating agent of A. solani (Cooke) Wint infection to S. tuberosum in a commercial potato crop in Brazil.
Leafminer sampling was conducted twice between Sep 2013 to Apr 2014 in the municipality of Rio Paranaíba (Minas Gerais State, Brazil) on S. tuberosum leaves (cv. Ágata) from a field containing larval L. huidobrensis. The field (19.208744°S, 46.164902°W) consisted of 35 ha, with potato plants at the tuber formation stage (50 d after planting) (Meier 2001). The field was divided into 5 areas of 5 ha each. Each area was further divided into 10 parcels of 50 × 50 m (2,500 m2). We evaluated 50 plants per parcel.
Plants were spaced 80 to 87 cm apart with 12 to 15 stems per meter. Mines of L. huidobrensis larvae with A. solani lesions were visually counted following the method of Alves et al. (2014) (Fig. 1a). Spatial distribution of mines caused by L. huidobrensis and A. solani lesions was evaluated using the Moran Index (I) (P ≤⃒ 0.05) with the Z test (Seffrin et al. 2018). This index measures whether a distribution is irregular, even, or clustered. Indices closest to 1 indicate high spatial dependence (clustered values); those closest to zero are characterized as spatial independence, while indices closest to −1 indicate high level of dispersion.
We found a positive and significant correlation (r = 0.84; n = 500; P < 0.001) between the number of L. huidobrensis mines and A. solani lesions, with the dissemination of this pathogen in potato plants being influenced by the degree of spatial distribution of L. huidobrensis (I = +0.225; P = 0.001) and A. solani (I = +0.428; P = 0.001). Moreover, the presence of A. solani concentric halos in potato leaves associated with L. huidobrensis oviposition sites, coincided with growth of this fungus. Our results were similar to those of Durairaj et al. (2010) who reported that L. trifolii oviposition sites favored A. alternata infection in tomatoes. Indeed, Deadman et al. (2002) observed that as L. trifolii oviposition perforations in S. tuberosum leaf tissue increased, A. alternata lesions increased (Deadman et al. 2002).