Research Library

This research project addresses the following research priorities as outlined in the 2009 CAC RFP:

1. Improving the quality of avocado fruit at retail and the identification of points in the handling and distribution chain where a loss of quality and profits may be occurring.
2. Define those fruit quality criteria or consumer perceptions of quality that may provide competitive advantage to California growers. Benchmark fruit quality against local harvest season timing, harvest conditions, imported fruit quality in the market in the same season, and/or environmental impacts of industry production practices on carbon and or pesticide footprints.

When ‘Hass’ avocado trees produce an on-bloom and set an on-crop, the apical (and axillary) buds on the spring shoots, which would normally produce vegetative shoots during the summer and fall, are inhibited by the young developing fruit. Inhibition of summer shoot growth reduces the number of nodes that can bear floral shoots the next spring. It is important to note that summer shoots contribute > 60% of the spring bloom. The objectives of the research were to adapt prior trunk-injected and foliar-applied PGR treatments that showed promise in overcoming correlative inhibition (auxin > cytokinin) of summer vegetative shoot growth and inhibition of spring bud break (endodormancy, ABA > cytokinin) during the on-crop year as foliar- and irrigation-applied PGR treatments for use on ‘Hass’ avocado.

Salinity has a broad range of effects on plants, therefore, there are also many different mechanisms for plants to tolerate this stress. Plants can reduce toxicity by reducing accumulation of toxic ions in the leaf blades (Na+ and Cl− exclusion), and/or by increasing their ability to tolerate the salts that they have failed to exclude from the shoot, such as by compartmentation into vacuoles (tissue tolerance; Munns and Tester 2008). The influence of chloride concentrations and other elements in the leaves was studied because California growers are faced with having to use irrigation water high in salts, especially high in sodium and chloride. 

California’s research information regarding cultural practices for avocados is growing. However, the majority of published research provides input for grove management decisions based on a calendar year and on growing conditions typical of the semi-arid subtropical conditions of Southern California. Anecdotally, the cooler, moister growing conditions of northern growing areas including San Luis Obispo County result in different phenological timing for major events like bloom, fruit set and shoot flush. This project will develop comparative phenological calendars, develop an interactive web-based mapping program to allow storage and retrieval of digital images that record growth stages, and expand digital methodology results.

In this research, we have modeled the relationships between leaf nutrient concentrations and the yields of avocado trees with the aim of developing decision support tools for improved fertilization and nutrient management to increase avocado fruit yields. Using a data base of ~3500 observations in which nutrient concentration profiles and yields of individual trees were examined over several harvest seasons, we now present in our final report a refined model that predicts nutrient-yield relationships based on all possible combinations for the 11 elements that are monitored by leaf analyses.

Avocado (Persea americana) is an important tropical and subtropical fruit tree crop. Traditional tree breeding programs face the challenges of long generation times and significant expense in land and personnel resources. Avocado selection and breeding can be more efficient and less expensive through the development and application of molecular markers. A total of 1524 individuals were genotyped with 384 SNPs creating the largest SNP genotype database for avocado. These individuals correspond to four extensive germplasm collections including two housed in Florida and two in California. In addition, hybrids and selections from two rootstock breeding programs have been genotyped. Genotype data were analyzed using an affinity propagation method to define 155 groups.

The overall goal of this program is to develop and provide elite rootstock material that is highly tolerant to Phytophthora root rot (PRR) and salinity. To address this goal we have divided the program into specific areas: 1) Screening for PRR tolerant rootstock varieties, 2) Screening for rootstock varieties with high tolerance to salinity and understanding PRR x salinity interactions to select for both PRR and salinity tolerant rootstocks, 3) Field testing, 4) Implementation of molecular-assisted breeding, and 5) outreach, education, and commercial release of elite rootstocks.

The overall research efforts for this proposed project is to maintain the plant material (scion and rootstock) that the UCR avocado breeding program currently has as well the personnel required to continue all the research and field activities related with the breeding program. This project will allow us to maintain the program and some of the activities related with the PRR and salinity rootstock screening until the full proposals are submitted to the California Avocado Commission on March 2015. 

Traditional avocado breeding programs have been successful in producing new varieties with favorable characteristics. However, in practice, these breeding programs are a time consuming and a costly endeavor. The high cost of the breeding program is attributed to the fact that majority of the trees that are selected are eventually discarded after being maintained for 5-10 years. Therefore, approaches to identify favorable varieties at an early stage of tree development would significantly reduce the breeding costs and increase the number of favorable varieties produced by the breeding program. Marker-assisted selection is aimed at reducing the costs the breeding programs by using molecular markers that predict favorable traits. The ability to predict favorable traits will allow breeders to select for trees at the seedling stage.

CAC-funded Research Examines Avocado Thrips Management Options