| Citrus psorosis disease is widespread and a limiting factor in citrus production worldwide. Besides grafting, it is suspected to be transmitted by a natural vector. Olpidium-like fungus was isolated from psorosis infected trees in an orchard in the south research farm of Texas A&M University Kingsville-Citrus Center (TAMUK-CC).;DNA was isolated from zoospores and molecular detection of zoospores was carried out by polymerase chain reaction (PCR). Four fragments of sizes approximately 300 bp, 750 bp and 1100 bp and 850 bp were amplified using the primers NS7-NS8, ITS4-ITS5, NS7-ITS4 and ITS1-ITS4, respectively. These fragments were sequenced and similarity search of sequences in Genbank database showed more than 90% identity to Fusarium solani. This may be due to contamination of inoculum with Fusarium. Multiple alignment of these sequences with the established Olpidium brassicae sequences showed some similarities which may evidence that resting spores found in psorosis infected roots are most likely O. brassicae.;Tomato, cabbage and lettuce seedlings were inoculated with Olpidium -like zoospores for infectivity studies and found that no symptoms were observed on the seedlings even after 5 weeks. Olpidium-like zoospores were inoculated into 6-month old seedlings of sour orange and C-22 rootstocks. Zoospores of Olpidium started establishing onto the seedlings within 2 h of inoculation. Hourly observations for 8 h showed that the number of zoospores and resting spores established on C-22 seedlings were more than in sour orange rootstock. Root samples were collected at 2 h and 8 h and stored at -80°C.;RNA was extracted from these samples and cDNA-AFLP was performed to study differential gene expression due to Olpidium-like zoospore inoculation. Differential amplicons obtained with different primer combinations were sequenced. Reverse Transcription-Polymerase Chain Reaction (RT-PCR) of leaves from 16 Pineapple sweet orange plants previously inoculated with Olpidium-like zoospores did not yielded in the expected 136 bp fragment. The 327 bp amplicon was observed in 9 samples which was previously shown to be aldehyde dehydrogenase of onion and sorghum. |
