1a.Objectives (from AD-416):
(1) Establish baseline metabolic profiles of commercial citrus products through the use of modern analytical methods, and
(2) Determine the influence of cultivar variety, environment and plant health on the metabolite composition by comparing the profiles obtained for these samples to those obtained for other citrus products, and
(3) Identify diagnostically significant metabolites.
1b.Approach (from AD-416):
Pepsico will provide the majority of the samples for this study. Additional samples may be obtained from commerical citrus growers or from citrus variety collections. Samples will be processed into juice and stored as such until analyzed by GC-MS, LC-MS, HPLC and NMR. Additional analyses will be performed as needed. Initial data analysis and the subsequent statistical analysis will be conducted at the Western Regional Research Center, Albany, California.
For the reporting period, orange juice samples from Florida were analyzed by GC-MS and NMR. Samples included juices prepared from fruit taken from disease free trees and the symptomatic and asymptomatic trees that are known to be infected with the bacterium Candidatus Liberibacter asiaticus. Samples were prepared from two different varieties of citrus and taken from three independent locations for each variety. Both NMR and GC-MS analyses were highly effective across multiple locations in distinguishing juices prepared from symptomatic fruit from juices prepared from fruit harvested from non-infected trees. These analytical techniques were not as effective in discerning between juices prepared from asymptomatic fruit and juices prepared from fruit from uninfected trees. In these cases, biological variability masked the metabolic changes induced by infection. Metabolic differences resulting from the intensity of infection and time passed since infection are probable causes for the high variability observed for asymptomatic fruit. Our results suggest that groves contain inherently high biological variability and that in order for metabolic monitoring of grove health to be effective, a baseline metabolic profile of each grove to be monitored must be established using multiple samples rather than relying on a general baseline profile derived from a sample prepared by pooling juices from multiple locations. All parent project objectives were addressed.