Create citrus varieties resistant or tolerant to Huanglongbing through transgenic and nontransgenic approaches

Create citrus varieties resistant or tolerant to Huanglongbing through transgenic and nontransgenic approaches

Report Date: 11/20/2018
Project: 15-020   Year: 2018
Category: Horticultural & Management
Author: Zhonglin Mou
Sponsor: Citrus Research and Development Foundation

The project has three objectives: (1) Obtain mature tissues of the best transgenic lines. (2) Determine whether transgenics prevent psyllids from being infected. (3) Continue testing generations of vegetative propagation from the best transgenic lines. The following work has been conducted in this quarter: (1) We have started to treat the three independent transgenic lines (�Duncan� 57-28, �Hamlin� 13-3, and �Hamlin� 13-29), which have gone through the long-term HLB test and exhibited robust tolerance to HLB disease. The first batch of plants, including two replicates of the transgenic line 57-28, three replicates of the line 13-3, and one replicate of the line 13-29, have been treated under the alternating temperature conditions (25�C for 4 hours and 42�C for 4 hours) for two months. These plants have generated some new shoots during the treatment. We have tested if heat treatment is able to remove CTV and the CLas bacteria. So far the new shoots are negative for both CTV and CLas, indicating that the treatment is effective. The new shoots will be used for generating citrus trees for field trials. (2) We have screened 28 new transgenic lines against HLB-infected psyllids. These lines were generated by the mature transformation laboratory. The following lines still look great and haven’t shown any HLB symptoms: #82-6 Hamlin, #70-4 Hamlin, #26 Hamlin, #65 Hamlin, #82 Hamlin, #73-5 Hamlin, #11 Pineapple, #33 Pineapple, #73-5 Pineapple, #78 Pineapple. Based on the nymph production phenotype, these plants should have been infected by HLB. We have tested bacterial titers in these plants by qPCR, and indeed, the majority of these plants are CLas positive. The bacterium-free plants (with low CLas titers) will be inoculated again. (3) The eight new transgenic lines (A99, A100, A102, A101, A72, A73, A97, and A98) were irrigated and fertilized regularly. After they reach appropriate size, they will be screened against HLB-infected psyllids. (4) The manuscript titled �Overexpression of the Arabidopsis NPR1 protein in citrus confers tolerance to Huanglongbing� has been revised and published in the Journal of Citrus Pathology in this quarter.


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