Plant pathogenic mycoplasmalike organisms (MLOs) induce serious diseases in pome fruits, stone fruits, and grapevine in the European Communities. These organisms cannot be cultured yet in vitro and are, for that reason, poorly characterized and cannot specifically be detected. It is, therefore, unknown which organisms occur in the individual crops and in the different geographic areas. Another problem concerning MLO diseases is that they cannot be controlled satisfactory. Recommended measures such as insecticide application against the insect vectors and the use of healthy planting material are only partially successful.
Due to this situation the objective of the project is to develop tools for detection, differentiation and characterization of the organisms.
The objective of the project was to develop tools for detection, differentiation and characterization of mycoplasma like organisms (MLO) with emphasis given to serological methods and the techniques of molecular genetics. Investigation of the resistance to mycoplasma diseases of rootstocks for apple, pear, some stone fruit and grapevine cultivars, was inititated before this programme started. Several experimental rootstocks from this earlier work, as well as new selections were inoculated for resistance screening or for confirmation of previous results. A large number of mycoplasma sources were used to screen the genotypes of the individual crops. First results show that the various rootstock scion combinations respond differently to infection. Four different mycoplasma clusters have been discovered in fruit crops and grapevine by Southern blot hybridization. The stone fruit MLOs differ considerably in their virulence to the various stone fruit species which indicates host specificity despite very similar deoxyribonucleic acid (DNA) restriction patterns. Procedures for detecting fruit and grapevine MLOs by polymerase chain reaction (PCR) have been developed. These detection procedures are much more sensitive than serological methods and detection by nucleic acid hybridization. Monoclonal antibodies have been developed to detect the apricot chlorotic leaf roll mycoplasma by PCR.
Emphasis will be given to serological methods and the techniques of molecular genetics. These methods were recently introduced in MLO research after it became possible to obtain both MLO antigens and MLO DNA from infected plants. Improved control will b e achieved by detecting and developing resistant rootstocks and scion cultivars. In previous work it has been demonstrated that apple proliferation and pear decline, the MLO diseases of apple and pear, respectively, can successfully be controlled by the u se of resistant rootstocks. In stone fruit and grapevine, resistance of both rootstock and scion cultivar seems to be important for MLO control.
ME19 6BJ West Malling