2008 Annual Report Variety Development Citrus Research Board

Citrus Variety Evaluation for Trueness-to-Type and Commercial Potential

Tracy L. Kahn Botany and Plant Sciences, UC / Riverside

California leads the nation in the production of fresh citrus for the domestic

and export market. The increasing demand for seedless easy-to-peel mandarins and attractive citrus varieties once only available from countries where traditionally consumed is fueling changes in the global fresh citrus market. Importation of new citrus varieties from other parts of the world by the Citrus Clonal Protection Program and the development of new varieties by the UCR Citrus Breeding Program provides California citrus growers with a diversity of citrus available for production.

Our project provides the industry with preliminary data on the characteristics of new citrus varieties in California and evaluates trueness-to-type of varieties distributed by the Citrus Clonal Protection Program. Our project also maintains the citrus demonstration blocks in Lindcove, Thermal and the Citrus Variety Collection (CVC) in Riverisde as resources for the evaluations of new varieties and to allow growers to view trees and fruit of existing commercial and new citrus varieties.

During the 2007-2008 season our evaluations focused on selected new

mandarin, blood orange navel orange, valencia oranges and specialty varieties including ‘Yuzu’, ‘Sudachi’ and a UCR developed pummelo hybrid called ‘Valentine’. Based on availability, fruit for these evaluations was collected from the demonstration blocks and the CVC to permit us to screen these varieties for adaptability to California growing conditions and climates. Each of the 48 varieties was sampled from two or three trees at each location three to six times during the season. Highlights of our results are described below. Results of this and other groups of varieties were discussed at the growers meetings, fruit displays and field days this past season and will be summarized for future publications and posted on our website (http://citrusvariety.ucr.edu).

2008 Annual Report Variety Development Citrus Research Board

Figure 2. Photographs of fruit from a 7-year-old tree of

‘Miho Wase’ on Carrizo from Riverside California.

2008 Annual Report Variety Development Citrus Research Board

Figure 1. Fruit quality traits for fruit of Satsuma mandarin selections sampled from Lindcove October 10, 2007.

Figure 3. Photographs of fruit from a 6-year-old tree of ‘China S-9’ on Carrizo from Riverside California.

2008 Annual Report Variety Development Citrus Research Boar

Figure 4. Table of the average percentage acidity and solids-to-acid ratio for fruit of Valencia selections sampled from three locations during the week of June 16, 2008.

Last season we evaluated fruit quality traits of 13 Satsuma mandarin

selections three times from Lindcove and Riverside in comparison to ‘Frost Owari’, the mid-season standard and two early season selections, ‘Okitsu Wase’ and ‘Kuno Wase’. Fruit quality data for selections sampled from Lindcove at the October sample date are shown in Figure 1. Note that both tree samples of fruit of ‘Miyagawa’, ‘Okitsu Wase’, ‘Miho Wase’, ‘Frost Owari’, ‘Armstrong’ and ‘China S-9’ had rind at or past color break (5.0) by early October 2007, an indicator of early maturity. In September 2008 at the first session of a series of informal Satsuma Tasting events at Lindcove Research and Extension Center, ‘Okitsu Wase’, ‘Miho Wase’, ‘Miyagawa’, and ‘China S-9’ received the highest ratings for fruit appearance, and ‘Miho Wase’ and ‘China S-9’ had the highest ratings for taste.

2008 Annual Report Variety Development Citrus Research Boar

This past season, a second year of evaluations were conducted for new navel orange selections from Lindcove and Riverside four times during the season. Fruit of Cogan, Johnson and Parent Washington had earlier external rind coloration than the other selections in both 2006 and 2007 at both locations. All of the selections had solids-to-acid ratios above legal maturity (8:1) by middle of November, but only Cogan, Johnson and Parent Washington had ratios at or above 10:1 by this sample date at both locations. Cogan appears to be earlier maturing than Washington navel and earlier than the others tested. Higher percentage acid levels of Ceridwen and Robyn and Johnson at multiple locations and sample dates indicate they might be later maturing than Ricalate, Cogan and Washington.

Two seasons ago, we initiated evaluations of ‘Valencia Late’ and

‘Harward Late’, two reportedly late Valencia selections in comparison with ‘Olinda’ Valencia. Fruit of all varieties sampled at the mid June 2008 sample date from Thermal and Riverside had average percentage acidity below 0.7 (Figure 4). Yet when sampled at this same date from Lindcove, ‘Haward Late’ fruit had average percentage acidity below 0.6, but the percentage acidity of fruit of Valencia Late and Olinda was above 0.7. At this point, fruit of these new Valencia introductions do not appear to mature later than ‘Olinda’ fruit.

NOTICE: The research results included in this publication are summary reports for the benefit of the Citrus Research Board and the growers it serves. They are not to be taken as recommendations from either the individual reporting or the agency doing the research. Some of the materials and methods mentioned are neither cleared nor registered for commercial use. The summaries were written by the project leaders identified. Both technical names and registered trademarks of materials are used at the discretion of the authors and do not constitute any endorsement or approval of the materials discussed. Questions on possible applications should be directed to the local University of California Extension Specialist, a licensed PCA, or the appropriate regulatory agency.