Citrus

152 - Microbial Community Profiling in the Context of Citrus Phenologyof

Principal Investigator: Caroline Roper, Assistant Professor and Assistant Plant Pathologist, University of California, Riverside.

Next generation amplicon sequencing technologies have allowed us to characterize plant microbiomes at a much larger scale than ever before. Because of this, we now have a much better understanding of the composition of plant-associated microbiomes in the context of which organisms are there. The next frontier is to understand what role those native citrus microbes play in plant health and disease outcomes. The study proposed here will be a baseline study to determine the microbial communities associated with California citrus at the tissue niche level and how these communities fluctuate (or remain stable) over the different phenological stages of citrus. This information will have two outcomes. The first will be a framework from where we can begin to understand the role specific microbes or groups of microbes play in citrus health and development. The second will be a comprehensive characterization of the California citrus microbiome before (and if) citrus Huanglonbing (HLB) disease becomes established in the state.

148 - Neonicotinoid Uptake in Containerized Citrus

Principal Investigator: Dr. Frank J. Byrne, Assoc. Res. Entomologist, University of California, Riverside.

The project will examine the uptake of imidacloprid, dinotefuran and thiamethoxam into 4 varieties of citrus grown in containers. We require Lindcove to prepare the trees for this research study. The treatment and monitoring of uptake will occur at UCR. The data generated from this study will determine the minimum time interval after treatment when trees may be shipped from the production facility to a retail outlet. By establishing this time interval, we will ensure that trees are protected from potential infestation by Asian Citrus Psyllid

145 - Citrus Sensory Quality and Consumer Acceptance

Principal Investigator: Dr. Jean-Xavier Guinard, Professor and Sensory Scientist for Food Science and Technology, University of California Davis.

This research will build and expand on the sensory and consumer testing methodologies we developed, and the knowledge we generated regarding California consumers' preferences, knowledge, attitudes and beliefs about oranges and mandarins in Year 1 of our CRB project on citrus sensory quality and consumer acceptance. In Year 2, we will add flavor chemistry, flavoromics, genomics and metabolomics to the set of tools used to characterize the oranges and mandarins examined in the research, and we will start optimizing sensory quality and other fruit characteristics through the selection of varieties, the use of experimental designs and the manipulation of horticultural and post-harvest variables, both at the Lindcove Station and with select commercial partners. Finally, we will lay out the groundwork for the investigation of the effects of the microbiome on fruit quality in Year 3. This is an interdisciplinary and collaborative project that will enlist expertise and resources from several universities, UC's Lindcove Station and citrus growers and packers.

144 - Evaluating Cropfume for Bean Thrips Control

Principal Investigator: Dr. Sandipa Gautam, Department of Entomology, University of California Riverside

Bean thrips (Caliothrips fasciatus), native to USA, is a pest of export significance to the citrus industry because this species overwinters in the navel of navel oranges. For controlling bean thrips destined to Australian markets, the California industry practices a system’s approach and fumigation with cropfume after harvest is a final step in the process. However, regular interceptions of bean thrips by Australian authorities seems to suggest that current recommended parameters for cropfume fumigation based on Dr. Morse’s research trials from 2008-2011 are not fully effective and need to be re-evaluated. The research trials simulating a commercial packinghouse setting are particularly challenging because of the lack of facilities dedicated for conducting such trials. This project proposes to modify and use a cold storage room at Lindcove Research and Extension Center for cropfume fumigation and dedicate it for fumigation research. The first trials at this modified facility will be to compare the efficacy of one vs two applications of cropfume recommended for controlling bean thrips in navel oranges.

135 - Assessing Factors Influencing Post Harvest Mandarin Flavor

Mandarins are a small but growing component of the California citrus industry yet often lose flavor quality while in storage. Our prior work has demonstrated ways to minimize this flavor problem but we have not been able to completely prevent it under all circumstances. Previous research by our group also found that there is a lot of diversity between different mandarin varieties in the accumulation of ethanol and other off-flavor compounds during storage that are likely responsible for flavor quality decline. We propose to utilize this diversity and study why some varieties differ in the amounts of these compounds accumulated and attempt to find key differences that could be used in the development of new storage-tolerant mandarin varieties. This work will involve examining anatomical, biochemical and molecular mechanisms potentially involved in off-flavor development.

126 - Citrus Pre-harvest Microbial Safety

Principal Investigator: Dr. Trevor Suslow, Department of Plant Sciences, University of California Davis

The purpose of this field study is to develop the first baseline information of predicted pre-harvest survival of nonpathogenic bacteria (generic E. coli and Pseudomonas fluorescens) and an attenuated isolate of Salmonella as surrogates of human bacterial pathogens on navel and Valencia oranges under California conditions. Regardless of the perceived low risk position for many tree fruit, such as citrus, it is clear that pressure to adopt standards and ‘metrics’ of Commodity-Specific Guidance and Audit Criteria by other sectors of the produce industry is increasing. At the request of the California Citrus Quality Council and California Citrus Research Board, we have become engaged in a proactive effort to characterize the microbial food safety Risk Profile for California citrus within an initial specific priority food safety objective as follows;

Determine the persistence of pathogen surrogates on citrus fruit, predominantly navel oranges, during the California harvest season at the UC Lindcove Research and Extension Center (LREC) experimental orchards.

The primary immediate goal is to develop risk assessment information for survival post-contamination in pre-harvest phases under open environment conditions to assist in current dialogue with the USFDA during produce safety rule-making.

093 - Cold Hardy Mandarins and Clementines in Northern California

Principal Investigator: Deborah Giraud, University of California Cooperative Extension Farm Advisor, Del Norte County

Trees of cold hardy mandarin varieties will be planted at several small mixed farms in Humboldt County in the inland valleys where peaches, grapes and kiwi are currently successful. Olives are also being planted as a new crop. Growers are interested in exploring diversification and have started to plant mandarin varieties. The Farm Advisor is interested in cold hardy citrus varieties to be able to make science-based recommendations and in maintaining citrus germplasm in isolated areas far from disease sources.

092 - Assessement of Systemic Neonicotinoid Insecticides for Management of Asian Citrus Psyllid

Principal Investigator: Dr. Frank Byrne, Department of Entomology, University of California, Riverside

Dr. Byrne mixing up an imidacloprid soil drench

The Asian Citrus Psyllid (ACP) threatens the citrus industry in California. Although foliar insecticide treatments can provide immediate knockdown of resident populations, their persistence can vary. In particular, new flush shoots, preferred by the ACP for feeding and reproduction, would require constant retreatment to provide consistent protection to the trees. Systemic neonicotinoids may provide more effective control of ACP on citrus. Following application to the soil for uptake through the roots, these insecticides are distributed throughout the trees via the xylem vascular system. The insecticide then moves to different plant tissues, including the phloem where the ACP feeds. The target threshold for imidacloprid required for ACP control has been estimated at between 200-250 ppb. In this study, we will evaluate the impact of irrigation on the uptake of imidacloprid applied at 2 rates. Our objective is to determine the irrigation conditions that will promote optimal uptake of the insecticide from the soil to ensure that effective concentrations are reached that will protect the trees from ACP feeding.

090 - Mandarin Pest Management

Principal Investigator: Beth Grafton-Cardwell, Department of Entomology, University of California, Riverside and Director of Lindcove Research and Extension Center

The California citrus industry is increasingly planting mandarin varieties due to the consumer demand for these ‘easy peelers’, especially the seedless varieties. Some of the insect pests appear to be attracted to and to develop better on mandarins, possibly due to their flushing patterns and dense growth. Problematic insects include citrus thrips, cottony cushion scales and aphids. Thresholds for economic damage by pests are not available for mandarins. An additional constraint for the mandarin industry is that theses fruit can not be high pressure washed to ameliorate problems of sooty mold caused by soft scales and California red scale infestations, thus tolerance for some pests will be lower than for navels and Valencias. A single variety block of mandarins being used at LREC for pesticide trials and economic threshold studies of citrus leafminer.

088 - Assessment of Mandarin Varieties

Principal Investigator: Dr. Mikeal Roose, Botany and Plant Sciences, University of California, Riverside

China S-9 satsuma slices

A variety trial of eight mandarins, six satsumas and two other types was established by Dr. Chao at Lindcove in 2003. The purpose of this trial is to evaluate these new releases for tree and fruit characteristics in order to formulate recommendations on their use by the California citrus industry. Each cultivar is budded on four commonly used rootstocks, Carrizo, C35, Rich 16-6 trifoliate and Rubidoux trifoliate, so the trial also tests compatibility issues. We collect data on tree size, tree health, yield, and fruit quality.

083 - Compatibility of Fukomoto Navel on Trifoliate

Principal Investigator: Dr. Mikeal Roose, Botany and Plant Sciences, University of California, Riverside

The objective of this experiment is to investigate the causes of decline of Fukumoto navel orange on certain trifoliate hybrid rootstocks. In some, but not all, locations trees of Fukumoto on Carrizo and C35 citranges (and possibly other rootstocks) show severe declines within a few years after planting. The decline appears similar to a bud union incompatibility with excessive suckers growing from the bud union, slow tree growth, and eventual tree death in some places. No pathogen associated with this disorder has been identified. The purpose of this experiment is to determine if the decline is bud transmissible. Budwood was collected from 24 declining trees at 4 locations, and from 24 healthy trees at 4 other locations. Trees were propagated at Lindcove REC on C35, Carrizo, and Volkameriana (a rootstock apparently not affected by the decline). The trees were planted in the field in 2005. Buds from both healthy and declining trees grew normally in the greenhouse. During the first year after planting, many trees had foaming gum on some branches, but this was not associated with the bud source. This problem has not been observed since 2006. Although there are significant differences in tree size among rootstocks, no substantial differences in tree health were observed among rootstock or bud sources through December 2008. In commercial groves, decline often does not appear until trees are at least 5 years old.

076 - Insecticide Trials for Citrus Pests

Principal Investigator: Dr. Beth Grafton-Cardwell, Department of Entomology, University of California Riverside and Director of the Lindcove Research and Extension Center

This research program provides critical information to the citrus industry about the efficacy and selectivity of registered and unregistered pesticides against key pests of citrus. Knowledge of the best uses of pesticides (rate, timing addition of surfactants, and level of selectivity favoring natural enemies) helps pest control advisors and citrus growers make more informed decisions about the most appropriate pesticide to use and so minimizes pesticide use. Citrus pest tested have included California red scale, citricola scale, cottony cushion scale, ants, katydids, citrus peelminer, citrus leafminer, Fuller rose beetle, and citrus red mite. When new insects enter the region, such as citrus leafminer in 2006, screening work is done at Lindcove REC to find the most efficacious and selective insecticides to incorporate into the citrus IPM program. We also determine the impact of pesticides on natural enemies such as parasitic wasps, ladybeetles and predatory mites.

053 - Lane Late Navel Rootstock Trial

Principal Investigator: Dr. Mikeal Roose, Department of Botany and Plant Sciences, University of California Riverside

This trial of 29 rootstocks includes standards, eight Florida selections, and some selections from the USDA breeding program previously based in Indio, CA. It was designed to evaluate the performance of Lane Late navel orange on various rootstocks because a very late maturing variety may respond quite differently to rootstocks than the early or mid-season varieties tested previously in California. The trial was planted in 1990 with eight single-tree replications of each rootstock. Some rootstocks in the trial, particularly Yuma Ponderosa and rough lemon types were badly affected by a freeze in December 1990. Yield records have been collected since 1994, as well as tree measurements and health and bud union ratings. This trial has identified several promising new rootstocks.

046 - Greenhouse and Rootstocks for Citrus IPM Research

Principal Investigator: Dr. Beth Grafton-Cardwell, Department of Entomology, University of California Riverside, and Director of the Lindcove Research and Extension Center

The Lindcove Research and Extension entomology greenhouse is used to grow seedlings, and Madam Vinous, Mexican lime and pummelo field trees provide seed for various experiments. Currently, the seedlings are used to rear citrus leafminer, cottony cushion scale and Fuller rose beetle, and test their responses to pesticides. Field trees are used to provide lemons for rearing California red scale colonies at Kearney Agricultural Research and Extension Center (KARE) and for testing these colonies for their response to insecticides and fumigants designed to replace methyl bromide.

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