First Report of Alternaria alternata Causing Leaf Spot Disease on Soybean (Glycine max) in Antalya Province of Turkey

Üstün R., Cat A., Uzun B., Catal M.

PLANT DISEASE, vol.103, pp.3284, 2019 (SCI-Expanded)

  • Publication Type: Article / Letter
  • Volume: 103
  • Publication Date: 2019
  • Doi Number: 10.1094/pdis-05-19-1026-pdn
  • Journal Name: PLANT DISEASE
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.3284
  • Akdeniz University Affiliated: Yes


Soybean (Glycine max L.) is one of the most valuable crops grown throughout the world and is an important source of vegetable protein and edible oil. This research was conducted after the observation of maturity group 3 and 4 soybean plants infected with a leaf spot disease in the experimental fields of Akdeniz University in Antalya Province of Turkey in 2017. Disease incidences of up to 30% were recorded, and infected plants displayed necrotic, circular to oval, and dark brown spots on the upper surfaces of the lower leaves. A fungus was isolated from both the infected tissues, and conidia were present in the leaf spots. The pieces of leaf tissues with the spots were cut with a sterile scalpel, surface sterilized in 10% sodium hypochlorite solution for 3 min, and rinsed twice in sterile water. Sterilized leaf tissues were placed in Petri plates containing potato dextrose agar, and those plates were then placed into an incubator set at 24°C for 7 days. The conidia were brown in color, and their morphology was consisted with Alternaria type characteristic, notably having one to two transverse and four to nine longitudinal septa. The dimensions of the conidia were measured at 29 to 59 × 13 to 26 μm (n = 100). Based on observed cultural and morphological features, this fungus was identified as Alternaria alternata (Simmons 2007). To further confirm the identity of the pathogen, genomic DNA was extracted using the CTAB method, and internal transcribed spacer region based sequencing was performed with the primers ITS1 and ITS4. The resulting sequences were compared with the sequences in the GenBank database using the BLAST function, which revealed that this pathogen shared 99.63% similarity with sequences of A. alternata (GenBank accession nos. KF881759 and JN618076). The sequence was deposited under the accession number MH124631. A pathogenicity assay was carried out on 2- to 3-month-old soybean plants of the same varieties under controlled greenhouse conditions. A spore suspension of 106 conidia/ml was applied to plants, which were then covered with polyethylene bags and incubated at 24°C for 7 to 10 days. A sterile water application was included as a nontreated control. The same symptoms of the disease were observed on the leaves 10 days after inoculation. The fungus was reisolated from the leaves of inoculated plants and identified again as A. alternata, fulfilling the Koch’s postulates. To our knowledge, this is the first report of a leaf spot disease caused by A. alternata on soybean in Turkey.