Plant pathogens, pests and weeds are responsible for significant crop losses that may reach up to 26-40% of the world annual agricultural production. Significant number of plant disease could be managed by routine control measures including pesticides. However, it is not easy to combat diseases caused by vascular pathogens using those routine practices. These agents caused by vascular few fungi and bacteria and particularly, by phytoplasmas and viruses to which no applied treatment measures have been known so far. Indeed, “Prevention from infection” or “Safeguarding” the plants plays the main role in controlling vascular agents. This is specifically important in local and international trading of planting materials and so, strict quarantine regulation have been implemented in international borders.

Development of sensitive and cost effective methods for diagnosis of vascular pathogens in planting materials, plays key role in safeguarding the plants. These methods, however, should be applicable for routine certification programs in which huge numbers of samples are tested in a given short time. It is worth noting that, the detection methods should be improved routinely for the newly emerged variants/isolates of pathogens that is common for plant viruses and virus-like agents. This is particularly important now days in the context of global warming that has been linked to the emergence of viral variants which may escape from detection by previously developed methods.

According to the Iranian national health standards for planting materials, viruses in seed potatoes are tested by ELISA. More than 120 thousands of potato subsamples are tested annually for either PVY/ PLRV, or simultaneously for other viruses including PVA, PVX, PVM and PVS as well, according to the class of seed potato tubers. However, serological detection methods are not reliable always due to several issues including uneven distribution of viruses within host tissues, low ability of commercial antibodies for detection of some native isolates and the need for simultaneous detection of several pathogens within a short certification period. Additionally, several graft-transmissible agents and particularly viruses and viroids are prone to mutation and/or recombination that affect the efficiency of detection methods. The emergence of new pathogenic variants has been enhanced due to the climate change that affect both host resistance and movement of biological vectors of viruses and phytoplasmas.

Taking all together, both protein- and nucleic acid-based detection methods should be improved routinely and in many cases, co-application of both methods needs for certification. The quality of plant nucleic acids and particularly RNA in molecular-based detection assays is affected tremendously by phytochemical contents of plants that in turn, influence the efficacy of detection methods. However, we normally use several nucleic acid extraction methods to circumvent these issues. Co-amplification of several targets in one reaction could make the certification process faster and plays a prominent role in certification successfulness. We developed several RT-PCR and IC-RT-PCR assays for simultaneous detection of viruses in planting materials. In addition, we developed qRT-PCR for faster and more reliable detection for certification of fruit trees nuclear stocks and mother blocks. Additionally, analysis of double stranded RNAs is routinely done for detection of unknown viruses in planting materials (nuclear stocks).

The Department of Planting Materials Improvement is one of the most active departments within SPCRI that manage both certification of vegetative planting materials and development/improvement of pathogen detection assays. We also survey the Iranian horticultural industries continuously to look for the possible emergence and reemergence of vascular plant pathogens to improve our detection procedures and to revise national health standards.