American Univesity of Beirut

Plant-infectious disease by Dr. Yusuf Abou Jawdah

Dr. Yusuf Abou Jawdah, professor of plant pathology at the Department of Agriculture, has discovered a new species of a lethal plant disease that threatens stone-fruit production. His research gained national, regional, and international recognition. The disease, known as Almond Witches' Broom, has proved to be a critical plant-infectious disease that has spread over regions of Lebanon and Iran and the gravity of the disease could tremendously increase if it spreads to other countries. 

Dr. Abou Jawdah's research goals lie in preventing the spread of the disease at​ its initial stages of introduction into new locations by early diagnosis and eradication. Almond Witches' Broom is acute food security issue: it drastically affects farmers and farm owners, nearly eliminating the yield and threatening the economics of the nation's stone-fruit crops.

Dr. Abou Jawdah explains that the disease's causal agent is a phytoplasma, a   bacterium that has no cell wall and infects the phloem tissue, impacting meristematic tissues and causing the tree to form broom-like branches. The disease manifests only in almond, peach, and nectarine trees. The rapid spread of the disease has destroyed nearly 200,000 almond and nectarine trees, mainly in the north and south of Lebanon. Dr. Abou Jawdah was keen to discover the transmission methods of the disease, and after 15 years of research, proved that Asymmetrasca and Cixiida are the insect vectors of the disease that are likely to spread it throughout their life span, may also be transferred over long distances by asymptomatic seedlings.  In cooperation with Italian research teams from Milano & Torino universities, they revealed that the disease is also spread through native plants, such as Smilax aspera and Anthemis spp., which serve as reservoirs to the phytoplasma.  

“This disease may be very devastating once introduced into a new region, therefore the European Union considered it as a major quarantine pest in December 2017" confirmed Dr. Abou Jawdah. He explained that there is no known cure for the disease, once it manifests, and consequently, he steered his research toward halting the spread of the disease and eventually eradicating it. With the help of the Italian cooperation, the AVSI NGO, and the Lebanese Ministry of Agriculture, a national plan was developed to stop this phytoplasma from causing more harm to the economy and environment. The plan unfolds by:

  1. Removing (eradicating) all infected plants in regions where the disease has limited spread. Relying on reliable, fast, inexpensive diagnostic methods, for early detection of the phytoplasma.
  2. Containing the disease in the regions where it is epidemic.
  3. Conducting further studies on the ecology and epidemiology of the disease, including surveying for alternative hosts, potential vectors, and their respective management methods.
  4. Conducting awareness campaigns targeting all stakeholders (extension service, farmers, municipalities….)
  5. Performing field trials with grafting methods to get resistance to the disease, to allow reestablishment of almond production in already infested areas.
  6. Advising farmers on replacing infected crops with suitable non-susceptible crops.

​Dr. Abou Jawdah discovered that grafting infected trees with plum or apricot scions prevents the disease from killing the tree. Grafting almond on plum rootstock, may induce immunity in the almond scion, rendering it resistant to the disease. With the aid of the Lebanese Ministry of Agriculture and their trained contractors, the disease was completely eradicated from an experimental area in the district of Marjayoun (Southern Lebanon) and a few areas in the Bekaa. Chemical and mechanical methods were used to completely kill, remove and burn infected trees, ensuring complete eradication and preventing spread. In Marjayoun, the disease multiplied from a sample size of 9 to 70 in a single year (2009-2010). However, after following the eradication and management recommendations, it diminished to zero within 2 years.  Several farmer workshops were organized: most stone fruit farmers are aware of the disease and the importance of early eradication upon discovery in a new orchard or region. 

Dr. Abou Jawdah stressed the importance of cooperation between the international community, the national community, and the academic community. He did not limit his research to AUB, but sought guidance, aid and cooperation with several universities, research institutions and funders, including local and international funding agencies. He conducted a FAFS workshop on the detection of the disease using molecular techniques. Researchers from Lebanese Agricultural Research Institute (LARI), Lebanese University, and Holy Spirit University of Kaslik (USEK) attended the workshop. 

Dr. Abou Jawdah concludes with the message that there is much additional research and work to be done to ensure the eradication and management of Almond Witches' Broom Phytoplasma through the development of an effective integrated management strategy. He is currently working on methods to facilitate early and rapid detection of the disease. Such methods would prove more efficient in the long term. Dr. Abou Jawdah seeks cooperation with international research institutes and has applied jointly for a Partnership for Research and Innovation in the Mediterranean Area (PRIMA) research grant. “The severity and potentially huge economic losses inflicted by the disease necessitate the establishment of a national plan to follow up on this disease, including periodical monitoring of the disease where it was once eradicated, especially in regions where stone-fruit nurseries exist and containment of further spread. This of paramount importance to Lebanon and the Mediterranean region" stated Dr. Abou Jawdah.​​

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