EVALUATION OF HUANGLONGBING TOLERANCE IN CITRUS BREEDING POPULATIONS | ||||
| Journal of Productivity and Development | ||||
| Article 10, Volume 24, Issue 2, April 2019, Page 371-390 PDF (802.08 K) | ||||
| Document Type: Original Article | ||||
| DOI: 10.21608/jpd.2019.41443 | ||||
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| Authors | ||||
| Amany Mira1; Shieen Yu1; Mass Matia1; elsayed mohamed2; Ahmed El aiedy2; Usama Elabasy2; fried Gmitter1 | ||||
| 1Department of Horticultural Sciences, IFAS, Citrus Research and Education Center, University of Florida, Lake Alfred, Florida 33850, USA. | ||||
| 2Department of Horticulture, Faculty of Agriculture, Tanta University, Tanta, Egypt. | ||||
| Abstract | ||||
| Huanglongbing (HLB) or greening disease is one of the most destructive disease of citrus industry all over the world. This disease had become widespread in Florida, USA since 2005. It is caused by a phloem limited bacterium called Candidatus Liberibacter asiaticus (CLas). Hybrids and populations produced by citrus breeding programs have likewise been ravaged by the disease. Thousands of unique genotypes have been exposed to natural CLas infection in the field for more than 10 years now, citrus researchers have had an opportunity to observe very substantial differences in the speed with which different types become affected by HLB, as well as the severity of symptoms. In the winter of 2015-16, we examined HLB responses in over 5000 citrus trees from hundreds of crosses made by the UF-CREC breeding program since 1986. The parentage of the crosses included pomelo, mandarin, sweet orange, grapefruit, trifoliate orange, and other miscellaneous citrus species. Ploidy levels in the populations included diploid, triploid and tetraploid. Depending on our field evaluation and symptoms of HLB disease on the trees, we divided all the trees to 5 categories according to the following ranking system (1=tolerant, 2=good looking, 3=medium, 4=bad, 5=dead). In total, only 5.3% trees among all other categories showed a very healthy appearance and no symptoms for HLB that we characterized them as HLB tolerant trees. Crosses {(Clementine x Temple) x C. ichangensis} followed by {(Clementine x Temple) x Swingle} had most tolerant trees among all of them trees. By using qPCR to determine CLas titer in visual tolerant trees, we conducted that 48.7% were CLas-positive, which have CT value less than 32, while 47.3% were CLas-negative with CT value equals or more than 32, it means that some trees have the bacteria but still don’t show any symptoms for the disease. The crosses [DPI 4-6 (Red Java) x H.B, (Clementine X Minneola) X Chinotto, VB Temple X (Nova + Ortanique), VB Temple X (Nova + Succari), (Clementine X Temple) X c. ichangensis] present the best crosses because they have CT value =40, that means no CLas in those trees. On the other hand, some characters of this category of tolerant trees had been studied such as, production of fruits, seediness and taste of fruits. A positive correlation between CT values and production of mature fruits among the tolerant trees. Concerning to seediness of fruits, most of seedless trees have been infected by Clas, while seedy trees tend to produce more non-infected trees with HLB. Taste of fruits from non-infected trees was better than those from infected trees. Conclusively, from these results, it could be concluded that, within individual species and among some citrus hybrid, number of progenies can be found that display substantial tolerance, and an ability to overcome and sometimes outgrow symptoms, this disease tolerance is not well correlated with estimated CLas populations. Future research utilizing these results for genomic selection in citrus populations will be performed. | ||||
| Keywords | ||||
| Huanglongbing; citrus; Evaluation; crosses; tolerance | ||||
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