Abstract
Leek (Allium porrum) has become one of the major leafy vegetable crops in Egypt and all over the world. Iris yellow spot virus (IYSV) was observed on leek plants in eight different governorates in Egypt, in fields near to onion fields. The symptoms in infected leek plants included yellowish or tan diamond-shaped or irregularly shaped lesions on leaves and flower stalks. Necrotic areas developed on leaves, and some plants had elongated brown lesions or brown flecks resembling thrips injury. Moreover, thrips larvae and adults feed with a punch-and-suck behavior that removes leaf chlorophyll, causing white to silver patches and streaks, which were observed on all infected plants. The plant samples were collected and subjected to ELISA test using IYSV polyantiserum. The results revealed that about 90% of the collected samples with symptoms were positive. For further confirmation, the ELISA positive samples were subjected to PCR amplification using nuclear coat protein specific primers. The PCR results were in agreement with the results obtained by ELISA. Thrip tabaci adults were reared on the infected plant and biological transfer was performed onto new healthy plants. After 15 days to 4 weeks post inoculation, symptoms were observed on the plant. Biologically infected plant samples were collected at different times after thrips-inoculation and the extracted RNA was subjected to Real Time PCR using the coat protein gene primers. The results showed that the expression of the coat protein fluctuated but reached its peak on day five (264%). Differential display technique was performed on the newly infected plant tissues to identify changes in gene expression in leek elicited by IYSV that causes a symptomatic phenotype. Both up- and down- regulated genes were observed in infected plants conjugated with the healthy ones. Sequence analysis of the up-regulated genes was performed and the encoding sequence analysis showed that the obtained genes include: MFS family protein, Pathogenesis- related protein, Mitogen-activated protein kinase, N-acetylserotonin O-methyltransferase-like protein, Serine/threonine-protein kinase, and Putative Retrosat2 Ty3-Gypsy retroelement. On the other hand, only one down-regulated gene was identified, alpha- tubulin suppressor-like protein. Most of the identified genes are suppress defensin genes (innate/adaptive). It can be concluded that viral infection is capable of inducing a huge number of genes which are important in the plant immune system.