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Oral: Promising Phenotyping Efforts for Understanding Genetic and Molecular Bases of Plant Disease Resistance


Molecular mechanisms behind the HLB symptom variations and rapid selection for variant citrus plants with greater HLB resistance/tolerance
Y. DUAN (1), M. Pitino (1) (1) USDA-ARS-USHRL, U.S.A.

Huanglongbing (HLB) is a devastating bacterial disease of citrus worldwide. Various HLB symptoms are observed in different species/varieties of citrus plants: from yellow shoots to blotchy mottles on the leaves, and from vein yellowing/vein corky to mosaic on the leaves, etc. These variations of symptoms not only present on individual plants from a variety but also exist on individual branches of an infected plant. Our results indicated that the adaptation of the bacterial populations, such as the population dynamics of ‘Candidatus Liberibacter asiaticus’ (Las), plays an important role in induction of symptoms, and the number of Las prophages/phages and the effectors may contribute to these difference. While the selection of the host plants for the bacterial populations is also critical for symptom expression during disease progression. Based on the severity of HLB symptoms, we divided them into four grades. Using a newly identified biomarker from host plants we were able to correlate HLB symptom severity with different concentrations of the biomarker. Gene expression profiling of different grades of infected leaves rationalized the differentiation based on the biomarker. Based on the variations of the HLB symptoms, the bacterial populations/titers, and the dynamics of the biomarker, we proposed new approaches to select variant citrus plants including bud sports with greater HLB resistance/tolerance along with protocols and criterial for evaluation.