Lindcove Research and Extension Center
University of California
Lindcove Research and Extension Center


098 - Multi-location, Replicated Trials of Promising Citrus Scion Varieties for California

Principal Investigator: Dr. Tracy Kahn, Botany and Plant Sciences, University of California Riverside

A series of citrus variety trials have been initiated to systematically evaluate the most promising new scion cultivars in locations that represent the major California citrus production zones. Currently, new scion varieties that are imported into California are evaluated in trials of 1-3 trees at a few locations (UCR, Lindcove, and Thermal). Varieties developed in the UCR breeding program are evaluated in replicated trials at 7 locations, but these trials do not always compare new selections with many existing cultivars. This proposal will establish integrated trials that can include new varieties regardless of origin and standard cultivars that represent each major group. One of the locations chosen for these multi-location replicated trials is Lindcove. The trials will have sufficient replication (18 trees per location, 5 locations) to make it possible to estimate yields and measure fruit quality traits with a reasonable degree of accuracy. Promising imported Satsuma and Clementine scion selections were chosen for the first set.


112 - Rootstock Trials for Clementine and DaisySL Mandarins

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

The objectives of this project are to evaluate the performance of three mandarin scions on a range of commercial and experimental rootstocks. Mandarins are of increasing importance in California and frequently have compatibility problems with some commonly used rootstocks.  We selected 20+ rootstocks, collected seeds and propagated trees at Lindcove.  Tree were budded with 'Nules' Clementine, 'DaisySL' mandarin and 'Sidi  Aissa' Clementine.  There are currently relatively few rootstock trials for mandarins in California so it is important to initiate new trials. Tree size, health, crop and fruit quality data will be collected as the trees mature.

126 - Citrus Pre-Harvest Microbial Food 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.


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.

088 - Evaluation of Satsumas and Other Mandarins

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

China S-9 satsuma slices
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.

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.


083 - Compatibility of Fukumoto Navel on Trifoliate Hybrid Rootstocks

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.


056 - Citrus Variety Evaluation Orchard

Principal Investigator: Dr. Tracy Kahn, Department of Botany and Plant Sciences, University of California Riverside

During the past decade there have been significant changes in the number, types and varieties grown in California due in part to market changes within the global market for fresh citrus, and the increase in foreign imports and exports with intensified global competition. High quality citrus varieties which meet the market needs and are suited to California climates are crucial to the California citrus industry to maintain competitiveness in the global and domestic fresh citrus market. New varieties are released each year from the Citrus Clonal Protection Program (CCPP) which may have commercial potential for the California Citrus industry. The Lindcove Research & Extension Center (LREC) Variety Demonstration Orchard has two main objectives: 1. Provide a demonstration block of new and existing citrus cultivars for field days, fruit displays and for growers and industry representatives to evaluate fruiting trees of these varieties, and 2. Serve as a resource to other citrus research projects and for our CRB-funded projects which provides preliminary evaluation new citrus varieties entitled: Citrus Variety Evaluation for Trueness-to-Type and Commercial Potential.  The majority of the varieties in the collection are grown on each of two rootstocks; Carrizo citrange and C-35 citrange, or the most appropriate rootstock for the specific scion variety. Data collected on the fruit quality traits of new citrus varieties at the LREC Citrus Variety Demonstration Orchard contributes knowledge about the characteristics, adaptability and possible commercial potential relative to current commercial varieties in California.

075 - IR-4 Pesticide Residues

Principal Investigator: Dr. Jeff Dahlberg, Kearney Agricultural Center

The Inter-regional Research Project #4, or IR-4, was created by the U.S Department of Agriculture (USDA) in 1963 to aid growers of high-value specialty crops in obtaining pesticide registrations that would otherwise be unavailable. For a pesticide to be labeled for use, a tolerance, or the legal allowable limit of pesticide residues, must be established on that crop. The cost to register pesticides for specialty crops far exceeds the purchases made by the growers and packers. In response, the publicly funded national IR-4 Project was established to facilitate pest management solutions for specialty crop growers. Citrus, avocados and olives are specialty crops. By facilitating the registration of new pesticide uses in these crops, the IR-4 project helps the growers and packers use safer pesticides, use existing pesticides in more ways, have access to enough pesticides to help reduce the development of pesticide resistance in the pest populations, respond to invasive or new pests, and/or increase export market potential. This is done by having trials throughout the United States that mimic commercial practices, apply new pesticides to commodities, and send samples for analysis of residues. The field and lab data package is sent to EPA so that tolerances can be set and the new (often reduced-risk) pesticides or new uses of existing pesticides can be registered. The permanent plantings at Lindcove REC are used to conduct IR-4 trials on citrus, avocado and olive crops.

055 - Citrus Rootstock Evaluations

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

The objective of this project is to maintain seed source trees for experimental citrus rootstock selections. A single tree of most selections is planted, with two trees of some of the more promising ones. The selections include hybrids of sweet orange x sour orange; a few zygotic seedlings of various rootstocks identified using molecular markers, and various Phytophthora and salt-tolerant hybrids selected by the USDA breeding program at Indio. Seed is periodically collected from trees in order to establish field trials or to test for disease resistance or other traits. Some trees have also been used as parents in the breeding program. Seeds of several accessions have been distributed to citrus researchers in Florida, Texas, Brazil, and elsewhere for evaluation.

053 - Lane Late Navel Rootstocks

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

Lane late navel orange
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 Roostocks 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.  

043 - Propagation and Evaluation of Irradiated Citrus Budwood and New Hybrids

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

The objectives of this project are to identify seedless forms of cultivars that currently perform well in California, and to evaluate new seedless or low-seeded hybrids. The major emphasis is on mandarins, but some work on oranges, grapefruit and lemons is also conducted. Budwood is exposed to irradiation to induce mutations that block seed development, converting a seedy cultivar to a low-seeded one. Trees are propagated from the irradiated buds in the greenhouse at Lindcove REC, planted at Lindcove or at UCR, and evaluated for seediness and other traits. Only a few trees contain suitable mutations. Selected trees are then used as sources of budwood to propagate additional trees for testing at multiple locations. Since the irradiation breeding project was started in 1996, many thousands of trees from budwood irradiation of 36 different varieties or selections have been planted. Evaluation of these resulted in a total of 62 low-seeded selections from 19 varieties, but evaluation of the more recent plantings is still in progress. Selections made from irradiation experiments have now fruited in replicated trials. Most appear quite stable and productive, so the general approach seems to be successful. The University of California released 'Tango', a low-seeded mandarin selection of W. Murcott, in June 2006, and within the past several years 'KinnowLS', 'DaisySL', and 'FairchildLS' mandarins have been released.

033 - Citrus Scion Breeding and Evaluation

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

The objectives of the UCR citrus breeding program are to develop and release new citrus cultivars that are useful in California. The breeding project develops potential new cultivars by hybridization-selection (initially conducted in Riverside) and by mutation breeding to produce seedless forms of existing cultivars. The focus of this Lindcove REC project is on field evaluation of new selections in replicated trials at Lindcove and elsewhere. New selections from the breeding program are propagated in a greenhouse at Lindcove and replicated trials are planted at Lindcove and several other locations in the San Joaquin Valley and southern California. During the next three year period we plan to continue evaluation of existing trees for yield, seed content, other fruit quality traits, tree size and shape, tree health, and other important characters. Additional trees of hybrids and irradiated selections will be propagated for planting in trials at Lindcove and elsewhere. The number of trees to be propagated each year is difficult to predict because breeding is inherently uncertain, but we generally expect to make 3-8 new selections per year. Trees of discarded selections will be removed and replaced with new trees. As promising selections are identified in the replicated trials, registered budwood source trees will be established and new varieties will be released after consulting with University of California and citrus industry organizations.

037 - Citrus Clonal Protection Program

Principal Investigator: Dr. Georgios Vidalakis, Department of Plant Pathology, University of California, Riverside

The California Citrus Clonal Protection Program (CCPP) was established over 50 years ago and today stands as a cooperative program between the University of California, Riverside and the California citrus growers, represented by the California Citrus Research Board, and the California Department of Food and Agriculture (CDFA). The CCPP is responsible for the introduction, disease diagnosis, pathogen elimination, maintenance and distribution of true to type primary citrus propagative material for the needs of the California citrus industry and citrus researchers. The CCPP holds one of only two license permits issued by the USDA-Animal and Plant Health Inspection Services for the legal importation of citrus propagative material into the United States. As such the CCPP is a critical link in the introduction, movement and improvement of citrus not only for California, but has released worldwide over 40 varieties in the last three years alone. The main focus of CCPP remains the detection and elimination of bud-transmitted pathogens from citrus propagative material. This is accomplished with the careful testing of all newly imported varieties and the application of the appropriate therapy method. Citrus propagative material that successfully completes therapy and testing is maintained in CCPP’s Protection Foundation and Foundation-Evaluation Blocks, currently holding over 200 commercially important varieties as CDFA registered trees for budwood distribution. The CCPP distributed over 80,000 buds from its registered trees over the past three years. Registered trees receive periodic disease retesting as well as growth and fruit evaluation. The CCPP distributes evaluation and other citrus information on the web at

041 - Field Evaluation of Citrus and Induced Dwarfing

Principal Investigator: Dr. Georgios Vidalakis, Department of Plant Pathology, University of California, Riverside

The concept of dwarfing in citrus is a consideration for the improvement of production in terms of yield (i.e. high density plantings) and quality.  Trials with important commercial scions such as Parent navel and Oroblanco grapefruit hybrid, as well as the citrus rootstock varieties Trifoliate and Carrizo, have been established at Lindcove REC in order to evaluate the effects of Transmissible small nuclear RNAs (Tsn-RNAs) on citrus growth, yield, and fruit quality. A high density or close spacing planting pattern has also been evaluated. Dwarfing by Tsn-RNAs is a recent approach (CDFA approved their commercial use in 2001) for the control of vegetative growth. With the limitations imposed on long term plantings as a result of disease, the commercial importance of citrus, and the constant demand for new rootstock and scion varieties, the suggestion of dwarfing and the accompanying feasibility of closely spaced plantings of citrus merits further study.      

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