Mal secco  Mal secco is a disease caused by the conidia-producing fungal plant pathogen "Phoma tracheiphila". It mainly causes disease to citrus trees in the Mediterranean. In particular it causes damage to lemon trees in the Mediterranean basin. The plant pathogen, "Phoma tracheiphila", is rain- and wind-disseminated. Symptoms normally appear early in the spring as chlorosis of the shoot and leaf vein. There is also epinasty, or bent out and downwards, of the young leaves in the spring. This is followed by wilt and die back of leaves, twigs and branches. In most cases dieback is sectorial. Symptoms start out by resembling frost damage of the leaves and gradually progress to leaf and stem dieback. A salmon, pink, or red color develops in the wood due to the xylem producing a gum to prevent further damage. Flask shaped pycnidia are barely visible as black spots in the center of grey areas though hard to distinguish due to their placement in cortical tissues. Pycnidia are not arranged in a distinguishable pattern instead they are scattered sporadically. Severity of disease and symptoms depends on the age of a tree. The inoculum is spread more efficiently when the roots are infected versus a leaf infection. Often only a certain section of the canopy is infected until it gradually progresses basipetally. The main host of mal secco is the lemon; however other genera including Citrus, Severina, Fortunella, and Poncirus have all been reported to be susceptible. In addition to lemon, the disease has been observed to be highly destructive in Citron (C. "medica L".), lime (C. "latifolia Tan".), and bergamot (C. "bergamia Risso"). The most common lemons in the Mediterranean, the rough lemon (C. "jambiri Lush"), volkamer lemon (C. "volkameriana Ten. & Pasq".), and alemow (C. "macrophilla wester") are very susceptible. Infection is favored by frost, hail, and wind as well as other ways that create wounds to the plant. Infection occurs at a moderate temperature between 14 and 28 °C. Optimum temperature for growth of pathogen is higher at a range of 20-25 °C. A high relative humidity favors production of conidia and further infection.