Crown rot in strawberry caused by Pestalotiopsis

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Pestalotiopsis longisetula is a well-known pathogen of strawberry fruit and leaves in subtropical areas. In 2015, Pestalotiopsis spp. were repeatedly isolated from crown tissues of wilting strawberry plants from the cultivars 'Sonata', 'Jive', 'Elsanta', 'Malling Centenary' and 'Portola' in Belgium. Young transplants developed necrotic tissues in leaf axis and parts of the upper crown. The orange brown marbled necrosis developed further into a basal crown rot causing infested plants to collapse during flowering. In most cases, other fungi (such as Phytophthora cactorum or Phytophthora fragariae) were also found which all contributed to the collapse of the plants. Initial trials involved the artificial inoculation of healthy disease free plants with isolates of Pestalotiopsis. Cold stored runnerplants of 'Elsanta' were inoculated using three techniques. In the first group of plants, a conidial suspension (1×105 spores mL-1) was poured over the young unexpanded leaves. The second group was treated with the same suspension however this time poured directly onto the peat substrate surrounding the base of the plants. The third group was inoculated by putting small blocks of agar containing cultured Pestalotiopsis next to the crowns. For the second and third group, roots of healthy plants were damaged artificially with a needle before planting in pots filled with a peat substrate. All the plants were kept in a growth chamber at 20°C and 14 h day length. After 8 weeks plant mortality was assessed. In the inoculated plants, plant losses ranged from 80 to 100%. Pestalotiopsis was subsequently re-isolated from necrotic crowns of wilting plants, hence confirming the pathogenicity of Pestalotiopsis on strawberry crowns. In a second trial five strawberry cultivars were screened for their susceptibility to Pestalotiopsis in a climate chamber experiment. Out of this trial it could be concluded that different cultivars show different levels of susceptibility towards Pestalotiopsis.