Basal stem rot of vegetables in controlled environment greenhouses in western Saudi Arabia : (B)‎ disease characterization

الملخص EN

Diseased cucumber (Cucumis sativus L.), cantaloupe (Cucumis melo var.

cantalopensis) and sweet pepper plants (capsicum annum L.) were received for diagnosis from various commercial controlled environment greenhouses at the Dept.

of Arid Land Agriculture at King Abdulaziz University.

They showed damping off of seedlings or severe wilting and necrosis at the lower parts of the stems of mature fruit-bearing plants.

The pathogen was identified earlier as Pythium aphanidermatum (Edson) Fitzp.

A pathogenicity test was performed by inoculating nine-day old seedlings of three plant genera grown in a conditioned growth room using agar plugs of the pathogen.

Inoculated seedlings showed early symptoms of damping off after 8 hr from inoculation for cucumber and 10 hr for sweet pepper and cantaloupe seedlings.

The highest percentage of infection of cucumber (90%) and cantaloupe seedlings (80%) was observed within 26 hr from inoculation.

However, the highest percentage of infection of sweet pepper seedlings (50%) of sweet pepper seedlings was observed within 18 hr from inoculation.

Symptoms started as a water soaking of the hypocotyl for a short period at the soil line, then immediately followed by girdling of the lesions that extended upward turning the hypocotyl into a thread-like organ.

In another pathogenicity test in controlled environment greenhouse, lower stem necrosis of cucumber, pepper and cantaloupe plants appeared after 3, 4 and 5 weeks from sowing, respectively.

Infected young cucumber and cantaloupe plants developed a severe wilting and a dark yellow lesions at the basal stem and crown area that extended up to 15 cm above the soil line.

Pepper plants developed dark purple to dark brown or black discoloration of the basal stems that extended up to the lower leaves.

For fruit-bearing cucumber and cantaloupe plants, on the other hand, the lesions were limited to the crown area and/or few centimeters above the soil line.

Pepper plants, however, expressed dark brown or black dry necrosis that extended up to 15 cm above the soil line.

Maximum pecentage of infected plants within ten weeks from sowing were 85% for cucumber and cantaloupe plants and 63% for sweet pepper plants.