A new method for field evaluation of soybean red crown rot was developed based on the percentage of reddish to black discolored subepidermal area on a root peel (ca 6 cm long, 0.58–0.90 mm thick) from two sites on the primary root (near the soil surface) per plant that had turned. The size of the discolored area on the peel from 61 plants in 2022 and 74 plants in 2023 was positively correlated with the amount of DNA of the pathogen (Calonectria ilicicola) in the peel; thus, the proportion of discolored area was an indicator of the degree of colonization. More than 50% of the peel was discolored on severely colonized plants. We propose a new severity index: No discoloration means no disease, up to 50% discolored means mild disease, and more than 50% means severe disease.
In Saitama Prefecture, green papaya cultivation areas are rapidly increasing. Green papaya is harvested before the fruit is ripe and used as a vegetable. Wilt and root rot were found on 3-month-old papaya plants during the fruiting period in July and August in several fields in Saitama Prefecture in 2022 and 2023. A Pythium sp. was predominantly isolated from diseased tissues and identified as P. aphanidermatum based on morphological characteristics and nucleotide sequences of ITS region of rDNA and coxI genes. This is the first report of P. aphanidermatum causing disease on papaya trees in Japan.
Powdery mildew was found on watermelon (Citrullus lanatus) in Okinawa Prefecture, Japan in February and May 2024. The associated fungus was identified as Podosphaera xanthii based on morphological characteristics of the anamorph and molecular analysis of rDNA-ITS regions. No chasmothecium was observed. Podosphaera xanthii is proposed as another powdery mildew pathogen on watermelon in Japan.