Evaluation of Newly Developed and/or Released Citrus VarietiesSept 2021 Investigator: Nabil KillinyIn this project we are profiling the new scions and rootstocks for their tolerance to HLB by studying the metabolite content by GC-MS, and challenging new varieties with psyllids and HLB.Progress on Objectives: Objective 1To understand the mechanism behind the tolerance of different varieties toward HLB. The comparison between the varietal responses will allow us to determine the mechanism of tolerance to CLas. This quarter we continued our focus in four areas: 1) new mandarin hybrid Lucky (SugarBelle x Nava x Osceola); 2) new Valencia varieties, 3) CUPS new grapefruit varieties, 4) rootstock evaluations. In addition, we tried again to graft Marathon Mandarin onto Swingle and Carrizo unsuccessfully (0/10). We have not been able to get even a small number of Marathon from the citrus nurseries, so we assume they are also having problems with propagation.Findings: 1) For the mandarin hybrid we call Lucky and its parents, Sugar Belle and Nava × Osceola, we completed the volatile organic compound (VOC) analysis to determine if Lucky will have any of the chemical properties of Sugar Belle, which is considered tolerant to HLB. We found it has slightly more total VOCs than either of the parents, and about the same as `Valencia’ sweet orange, which we used for a comparison. We detected 50 VOCs and the dominant leaf volatiles were sabinine, linalool, trans-ß-ocimene, and ß-caryophyllene in the mandarin hybrid. Like other mandarins, they are low in d-limonene and almost completely lack neral and geranial, the aldehydes that dominate `Valencia’. In addition, we repeated the ACP choice experiment beginning in June using CLas-infected ACPs. The experiment just concluded with the final samples being collected on 9/3/21. We are looking for any chemical clues that indicate an induction of defense compounds after infestation with ACP. To achieve this, leaf samples from the 15 plants were collected 5 days, two weeks, and one month after adding psyllids to the cages. Thereafter, monthly leaf samples were taken in parallel with ACP population counts. The leaf samples need to be processed now for volatiles and HLB status. Currently there are no HLB symptoms, but the trees will be followed closely to determine how quickly they develop symptoms and when HLB can be detected by PCR. 2) For the evaluation of the new sweet oranges Valquarius and Vernia, the leaf samples for analysis of volatiles have been run on the GC-MS and integrated. The data analysis was completed. Qualitatively, the three sweet orange varieties are very similar, but the total VOC content was highest in Valencia, followed by Valquarius, then Vernia. We identified 47 VOCs in the hexane-extracted leaves of the three varieties. We did not detect any unique compounds among the three varieties. Those in the highest concentrations included sabinene, linalool, neral, geranial, ß-elemene, a-sinensal, and phytol. Many differences (37/47) were statistically significant because of the high content found in the traditional Valencia variety as compared to the two newer varieties. We have previously associated higher levels of VOCs to ACP attraction, so there may be a slight advantage to the newer varieties in having a lower VOC content. We plan to perform ACP choice tests on the new varieties by pairing them with Valencia in a new choice test apparatus we made for this purpose. 3) New grapefruit variety from CUPS – UF914 is being evaluated and compared to traditional Duncan, Ruby Red and Ray Ruby varieties for volatile and non-volatile metabolite content. UF-914 is a low furanocoumarin variety so special attention is being paid to these compounds. We have detected several coumarins and sterols in the grapefruit extracts and quantification is in progress. Objective 2 4) To understand the role of rootstocks in citrus tolerance to HLB. The comparison between rootstock metabolites will allow us to determine the best scion/rootstock combinations for tolerating CLas. a. The rootstock seeds from the USDA (US-802, 812, 897, 942, 1283, 1284, 1516) for metabolite profiling and HLB/nematode screening were moved outside to encourage growth, repotted into larger pots, and are now about 6 inches tall and 7 months old. We hope they will be ready for evaluations soon. We plan to challenge these rootstocks with ACP to determine their response to HLB.b. The grapefruit leaf samples collected from CUPS included Duncan on four rootstocks, and Ray Ruby on two rootstocks. We will make comparisons to see if there are any differences in the volatile and non-volatile metabolites due to the different rootstocks.