2018 ASHS Annual Conference

Several grapefruit cybrid plants were developed through the fusion of protoplast from cell suspension of citrus canker highly resistant ‘Meiwa’ kumquat and mesophyll protoplast of three selections of highly susceptible grapefruit. Plants recovered from all three combinations displayed the typical grapefruit phenotype and were all validated to be somatic cybrids. For disease resistance screening, most of the regenerated cybrid clones were evaluated by pressure infiltration inoculation of Xanthomonas citri subsp. citri (Xcc) suspension of attached leaves. Quantification of Xcc bacterial populations in planta was assessed. Cybrid clones showed a range of citrus canker resistance, but all grapefruit cybrids with a kumquat chloroplast had a significantly lower number of lesions and Xcc population compared to grapefruit controls. However, cybrid clones with grapefruit chloroplast had a significantly higher number of lesions compared to clones with kumquat chloroplast. These cybrids have the potential to provide a high level of citrus canker resistance in commercial grapefruit orchards, as well as, act as a valuable model for understanding the contribution of chloroplast to plant disease resistance. To understand the cytoplasmic/nuclear interaction in the regenerated grapefruit plants, the preliminary metabolic comparison between ‘Marsh; grapefruit cybrid and parents plants was initiated. ¹H NMR spectroscopy approaches are used to provide snapshots of the plant sample composition, and to evaluate the metabolic profile in cybrid and parents plants. Metabolite concentrations from leaves of ‘Marsh’ grapefruit plant were higher than ‘Meiwa’ kumquat and cybrid plant, including many amino acids such as isoleucine, tyrosine, alanine, proline, proline betaine, and leucine. The cybrid plant seems to contain an intermediate concentration of all the measured components compared to the parent plants. Proline, Proline betaine, carbohydrates, glutamine, and unidentified glucose product seems to present in a high amount in all the tested plants. Except for proline betaine, most of the top significant chemical shifts that give differences between the three plants are present in carbohydrate regions. These preliminary results about the metabolic profile of grapefruit cybrid plants and their respective parents provides a very useful information for designing a large-scale experiment to understand the natural mechanism of plant defense to create new varieties and/or genetically modified genotypes for tolerance/resistance against citrus canker and/or HLB (Huanglongbing or citrus greening).