First report of Alternaria black spot caused by Alternaria alternata on blue honeysuckle in Poland.
Symptoms of Alternaria leaf spot were observed on blue honeysuckle (Lonicera caerulea var. kamtschatica) plants growing in allotment gardens in Kanie (Mazovia Province) and Kopalino (Pomerania Province) in Poland in 2015 to 2016. The initial infections were noted on leaves at the end of June. Under favourable conditions, complete defoliation was observed at the beginning of August. Symptoms on leaves consisted of oval to irregularly shaped spots, 1 to 4 mm in diameter. They were initially black and later turned brown with a dark brown to black border. Over time, the centre of the spots developed a gray shade. The spots were surrounded by a yellowish halo. The lesions gradually enlarged and sometimes coalesced. In 2015 and 2016, infected leaves were collected. Based on morphological characteristics, molecular data (sequence analysis of the rDNA internal transcribed spacer region and translation elongation factor 1-α gene) and pathogenicity tests, the causal agent was identified as A. alternata. This is thought to be the first report of A. alternata on blue honeysuckle worldwide.