Symptoms of Myrothecium on Cucurbits

• Organs attacked :

• Symptoms :
  • Initially, small circular moist to greasy lesions (Figures 1 and 2).
  • Thereafter, the spots extend, turn brown, and progressively become necrotic (figures 3 to 5). A faint yellow halo surrounds them (figure 6). Their diameter can be much greater than one centimeter. They sometimes coalesce.
  • The center of the spots clears up more or less and presents well-marked concentric patterns.
  • Degraded fabrics dry out, split and eventually fall off; the blade is more or less perforated (figures 7 to 11).
  • Comparable lesions, more or less cankered, are sometimes visible on the petioles, the stem, or even the collar.
  • Alterations on the fruits in pre and post-harvest. On melon, they have a rather circular shape, a dark color and are more or less concave ( crater rot symptom), measuring several centimeters in diameter. The underlying flesh gradually rots. Surface tissues may rupture.

• >>> More pictures  

• Signs : presence of greyish to black sporiferous pads: sporodochia (figures 12 to 14). These structures are made up of numerous phialides which form at their end cylindrical conidia, hyaline to slightly olive-coloured.
• Possible confusion : bacteriosis at the start of the attack.

• Production areas affected :

•  Myrothecium spp. reported on Cucurbitaceae : M. roridum (melon, watermelon, cucumber)