Alterations in morphological and biochemical properties in ‘Namwa’ banana associated with freckles caused by Lasiodiplodia theobromae in Thailand

Fruit freckles of ‘Namwa’ banana (Musa x paradisiaca) are a disorder observed as small brown spots or freckles on the fruit surface that become scabby during the preharvest and postharvest stages. To investigate the cause of disorder, morphology and molecular properties of isolated fungi as well as the biochemical properties of infected bananas were examined. Scanning electron microscopy revealed the presence of fungal mycelia and cell death in response to the course of infection on banana peels. Bananas with freckles showed high total phenolic content in comparison to healthy bananas. Activities of polyphenol oxidase (PPO), peroxidase (POD) and chitinase (CHI) were detected at high levels in both green and ripened bananas with freckles. Fungal isolates were identified based on the morphology and molecular properties of the internal transcribed spacer (ITS) and translation elongation factor of 1-alpha (tef1-α) genes as Lasiodiplodia theobromae. Pathogenicity tests revealed L. theobromae causing freckles similar to those observed in natural infection to fulfill Koch's postulates. To our knowledge, this is the first report of L. theobromae causing freckles of ‘Namwa’ bananas in Thailand or elsewhere.