Tomato Corky Root Disease Caused by Pyrenochaeta lycopersici Grrlach et Shneider and its Control

Qusay AL- RHAYEH
General Commission for Scientific Agricultural Research-
Lattakia Research Center
Aleppo University, Faculty of Agriculture
2005

Abstract

A wide spread and high degrees of disease have been noticed accompanied by high density of its Microsclerotia accumulated in the soil by following the seasons arriving to maximum levels which don’t increase as a result for the plants’ roots not being able to develops or grow in the infected area, as a consequent not to have the capacity to increase the infection inoculums quantity represented in these Microsclerotia. And the disease causes big decrease in plants’ growth strength and productivity.
The disease is caused by various isolates of the Pyrenochaeta lycopersici fungus that have been isolated form the study area and they were identical in the classification description and close in the temperature requirements for the growth, but they differed in color and morphological shape of the fungus colony on (PDA) media, and in forming of Pycnidia on (TJA) media, or on infected root fragments, where only one isolate has been able of forming Pycnidia (isolate No5). All isolates shaped Microsclerotia, and the isolate No1 was the most spread in the study area and the most repeated in isolate operations, and they were the responsible for the disease damages whereas the other isolate were less to show out. All infecting fungus isolates have been distinguished by an ability of high infecting the young tomato’s plants.
Group of some soil fungi causing root rots, joins the Pyrenochaeta lycopersici infecting fungus, and most important kinds of their are Fuzarium oxysporum, Rhizoctonia solani and Colletotrichum coccodes, which are existed by low rates comparing with the rate of the infecting fungus, and they were responsible for the symptoms of the damping off disease at the beginning of season as well as its activity increased with the increase of the soil’s temperature in spring to colonize the root system and increase the tomato corky root disease infest.
The soil temperature has increase during its solarization to a lethal heat levels for the infected organism transferred in the soil on 10 and 20 cm depth, and significantly decrease the number of the Microsclerotia of the Pyrenochaeta lycopersici fungus, where these Microsclerotia are considered the main infected units responsible for renewal of the infection by the disease and its transfer and increase from a season to another. But the lethal heat levels have not been registered on the depth 30 cm in the soil, since the decrease of these Microsclerotia in this depth was not significant. Also, it was notice the decrease of the isolated Microsclerotia from the soil of control at this depth too.
The soil fertilization treatments decreased the infection degree of  tomato corky root disease and improved the plants productivity and vigorous growth significantly a lot, also it increased the average fruit weight by normal significance, and the best treatments was the solarization with addition to the cabbage remains and solarization by wetting the soil during the treatment, since the two were very close to each other and no relevant difference was obvious between them, but on the other hand the solarization without wetting was the weakest between all  studies solarization treatments.
The organic fertilizer’s effect has been only limited to on a simple significant increase in the productivity and vigorous growth of tomato plants infected by tomato corky root disease, but it has not decreased its infection degree by this disease and even sometimes it encouraged it. But it was distinguished by the collaborate effect with solarization and participated in increasing its effect by decreasing the infection degree and improving its production and vigorous growth, especially with solarization without wetting. Also the reaction of the organic fertilizer’s effect with the Bacillus subtilis Bacteria’s effect decreased the damage and increases the productivity and the plant vigorous growth, but its effect in the fruit weight average for the infected plant was low.
The Trichoderma harzianum and Trichoderma viride fungi were distinguished by their high antagonism capacity in lab conditions regarding the Pyrenochaeta lycopersici infest fungus at high temperatures degrees 20- 25° C and by low capacity at decreased temperature 15° C. But in field then the two types were distinguished by very weak effect in decreasing the infection or improving the plant production and its vigorous growth, and has never affected the average fruit weight. Also their effect were collaborated with solarization or with the organic fertilizer or with both of them was weak and without significant.
Bacillus subtilis Bacteria showed high antagonism ability for the Pyrenochaeta lycopersici infest fungus, and frustrated its growth in lab condition and it was the best biological factors used in the trials for controlling the disease. Since it contributed in decreasing the infestation degree and improved the growth and productivity of plants. As it showed collaborates effect with the solarization treatment, especially with solarization without wetting, or with organic fertilizer or with both of them, but by no significant difference.
The fungicide benomyl was distinguished by high effecting inhibition of the growth of Pyrenochaeta lycopersici fungus, and its low concentrations prevented the fungus growth in lab condition. But it was not affecting when tested in the field, since it has a weak effect in decreasing the infection degree of disease and in improving the vigorous growth and the plant productivity. The same has a weak effect when it has collaborated effect with solarization or organic fertilization or both together, and it has been noticed that it has a negative effect in some case by decreasing the solarization qualification instead of supporting it.