Influence of Tomato spotted wilt virus uneven distribution on its serological detection in tomato, pepper and ornamentals

Reliable detection of plant pathogens does not only mean the development of sufficiently sensitive laboratory techniques for their routine testing. Regardless of the sensitivity of applied methods, the proper selection of samples to be tested has crucial influence on method reliability. Due to uneven distribution of Tomato spotted wilt virus (TSWV) in naturally infected systemic host plants, the collection and sampling of material for assaying is a critical moment upon which the reliability of laboratory procedure depends. The effect of irregular virus distribution on its serological detection was examined in tomato, pepper and four ornamental species, as its most important host plants in our country. The reliability of virus detection, depending on its uneven distribution, was assessed by serological testing of tomato and pepper symptomatic leaves and fruits, and symptomatic and asymptomatic young and old leaves, as well as flower petals of ornamentals. Although TSWV was detected using ELISA in the majority of plants included in the experiment, the tests indicated an uneven distribution and unequal concentrations of TSWV in different parts of the plants. The virus could not be detected in a certain number of subsamples, prepared from infected tomato and pepper fruits and older ornamental leaves. The virus also could not be detected in some ornamentals and tomato plants with intensive symptoms. Conversely, the virus was detected in three ornamental plants without any symptoms. Examining the virus distribution in different plant parts indicated that the reliability of ELISA could be reached not only by sampling younger ornamental leaves, but also by preparing compound samples with as much leaves as possible, or by testing a greater number of subsamples of the tested plant. Considering a small possibility of TSWV detection in tomato and pepper fruits, the infection of these should be established by testing their leaves. Besides, the data show that negative test results for the known host plants with characteristic symptoms require tests to be repeated using more sensitive methods than ELISA. These results are important as guidelines for growers and professionals who submit samples, as well as for laboratories performing routine testing.