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Chih-Cheng T. Chao

A pollination study was conducted using `Nules', `Fina Sodea', `Marisol', `Fina' Clementine, `Afourer', `Tahoe Gold', and `Gold Nugget' mandarin. The fruit sets from selfing of `Fina', `Marisol', `Fina Sodea', `Nules' Clementines and `Afourer' mandarin were very low or near 0. The open pollinated Clementines had very low fruit set and there were very few seeds per fruit. Fruit set was highest (20% to 40%) in cross-pollination between two Clementines, `Nules' and `Fina Sodea', and `Afourer' mandarin and their reciprocal crosses. There were averaged 23 to 32 seeds per fruit in Clementines × `Afourer' mandarin crosses and averaged 5 to 12 seeds per fruit in `Afourer' mandarin × Clementines crosses. Compatibility among Clementine mandarins and `Afourer' mandarin is very high and caution should be taken to properly isolate these two types of mandarins when planting to produce seedless fruit. The diploid `Nules' Clementine × triploid `Tahoe Gold' mandarin gave 14% and 17% fruit sets in 2002 and 2003, with an average 2 seeds and 9 seeds per fruit in 2002 and 2003, respectively. Caution should also be taken when planting triploid seedless `Tahoe Gold' mandarin near diploid `Nules' Clementine to avoid seeds. The compatibilities and seediness between diploid mandarin cultivars and new seedless triploid mandarin cultivars need to be tested to ensure the pollen of the new triploid cultivars will not cause seeds in the existing diploid cultivars.

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ChihCheng T. Chao

The citrus industry in California is changing, and growers are planting more easy-peeling, seedless, and nice-tasting mandarins. Our industry tries to develop new early- and late-season mandarin cultivars to be competitive in the global mandarin market. Seventeen satsuma mandarin (Citrus unshiu Marco.) cultivars were top-worked onto 4–6 Valencia orange [C. sinensis (L.) Osbeck] as interstocks and Carrizo citrange [C. sinensis (L.) Osbeck × Poncirus trifoliata (L.) Raf.] as rootstocks in 30 May 2001 near Santa Paula, Calif. All trees set the first crop in Fall 2003. Fruit maturity of all cultivars was measured based on °Brix level, percent acid, and S:A ratio on a weekly basis since the first week of Sept. 2004. Five cultivars, `Armstrong', `Kuno Wase', `Miyagawa', `S9' and `Xie-Shan' (`Wakiyama'), are very early- or early-season cultivars. A small-scale degreening experiment with 72 h treatment of 0.5 mg·L–1 ethylene with fruit harvested on 6 Oct. 2004 also showed the rind color of all five cultivars could be enhanced nicely. `Miyagawa' had very intense internal orange flesh color visible in the second week of Sept. 2004, comparing with other cultivars. All these five cultivars could potentially become early-season, completely seedless, and easy-peeling satsuma cultivars in California. `Miyagawa' and `Xis-Shan' could potentially be harvested as early as from late September to early October in the central coastal region and from late August to mid-September in the San Joaquin Valley. Both cultivars should command a high price when there is no seedless mandarin in the market.

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Jinggui Fang and ChihCheng T. Chao

DNA methylation plays an important role in the regulation of gene expression in eukaryotes. The extent and patterns of DNA methylation were assessed in the date palm (Phoenix dactylifera L.) mother plants and their offshoots using the methylation sensitive amplified polymorphism (MSAP) technique. Three types of bands were generated using 12 pairs of primers. Type I bands were present in both EcoR I + Hpa II and EcoR I + Msp I lanes; type II bands were present in EcoR I + Hpa II lanes, but not in EcoR I + Msp I lanes; and type III bands were present in EcoR I + Msp I lanes, but not in EcoR I + Hpa II lanes. The total numbers of these three types of bands were 782, 55, and 34. Among these three types of bands, the polymorphic bands were 34, 10, and 0, respectively. The distribution of polymorphic bands among mother-plants and offshoots could suggest the methylation variation occurred to the mother plants and offshoots. The methylation variation during offshoot growth of date palm was characterized as a process involving mainly of demethylation. Hypomethylation of DNA in offshoots compared with mother plants reflects the marked expression of this molecular feature, which may related to gene expression during development of offshoots. The methylation or demethylation status of specific loci in the mother plants and their offshoots might not relate their lineage but occurred randomly.

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ChihCheng T. Chao and Robert R. Krueger

Date palm (Phoenix dactylifera L.) is one of the oldest fruit crops grown in the arid regions of the Arabian Peninsula, North Africa, and the Middle East. The most probable area of origin of the date palm was in or near what is now the country of Iraq, but date cultivation spread to many countries starting in ancient times. Dates are a major food source and income source for local populations in the Middle East and North Africa, and play significant roles in the economy, society, and environment in these areas. In addition to serving directly as a food source, dates are packed and processed in a number of ways, and other parts of the tree are used for various purposes. The date palm is a diploid, perennial, dioecious, and monocotyledonous plant adapted to arid environments. It has unique biological and developmental characteristics that necessitate special propagation, culture, and management techniques. Thousands of date palm cultivars and selections exist in different date-growing countries. Different genetic marker systems have been used to study genetic relationships among date palm cultivars. The long life cycle, long period of juvenility, and dioecism of date palms make breeding challenging. Worldwide date production has grown from 1,809,091 t in 1962 to 6,924,975 t in 2005. Worldwide date production will continue to grow, especially in the Middle East, despite current and future challenges.

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Boyang R. Cao and Chih-Cheng T. Chao

Polymorphisms of 21 date cultivars (Phoenix dactylifera L.) in California were determined by amplified fragment length polymorphism (AFLP) analysis with near infrared fluorescence labeled primers. Four primer sets were used to detect polymorphisms. Based on the UPGMA-cluster analysis of 328 polymorphic bands, the majority of the cultivars was separated into two major groups. Cultivars Abada, Amir Hajj, Ashrasi, Bentamoda, Boyer No. 11, Deglet Beida, Horra, Javis No. 1, Khadrawy, and Thoory belonged to group I. Cultivars Badrayah, Dayri, Halawy, Haziz, Khir, Medjool, Sayer, and Zahidi belonged to group II. Cultivars Barhee and Deglet Noor were further separated from groups I and II. `Hayany' was distinct from all other date cultivars tested. These results demonstrated that AFLP markers could efficiently identify individual date cultivars. The information will be useful for future date germplasm collection and facilitated selection of diverse parents for cross hybridization in a breeding program.

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Chih-Cheng T. Chao, Jinggui Fang and Pachanoor S. Devanand

Production of seedless mandarins such as `Nules' clementine mandarin (Citrus clementina Hort. Ex Tan.) and `Afourer' mandarin [C. sinensis (L.) Osbeck × C. reticulata Blanco] is increasing in California as consumers' interest in seedless, easy peeling, and good tasting mandarins increases. The fruit would produce seeds if cross-pollination with compatible pollen source occurred. It is almost impossible to prevent cross-pollination between compatible mandarin cultivars by honeybees (Apis mellifera L.) within the multi-faceted agricultural environment in California. To produce seedless mandarin, growers either plant a single cultivar in a large solid block or try to use pollen-sterile navel oranges (C. sinensis) or satsuma mandarins (C. unshiu Marco.) as buffers to prevent cross-pollination. The question of how many rows of buffer trees or spacing can effectively prevent cross-pollination by honeybees between compatible mandarins is unclear. We initiated a study using fluorescent-labeled AFLP markers to determine the pollen parentages of `Nules' clementine seedlings and `Afourer' mandarin seedlings from two orchards in California. The longest distance of pollen flow at an orchard near Madera was 521 m. The pollen of `Minneola' tangelo (C. reticulata × C. paradisi Macf.) was able to disperse across a minimum of 92 rows of `Lane Late' navel oranges plus two rows of `Afourer' mandarins to pollinate `Afourer' mandarins. We also found that all the seedlings of `Nules' clementine mandarin at an orchard near Bakersfield had been pollinated by `Afourer' mandarin pollen. The pollen of `Afourer' mandarin was able to disperse up to distances between 837 and 960 m to pollinate `Nules' clementine. The pollen dispersal distance found in this study was at least 16 times longer than previously reported in a citrus orchard. Growers need to consider a much larger space or buffer rows to prevent cross-pollination and produce seedless mandarins in California.

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Ed Stover, William Castle and Chih-Cheng T. Chao

The world market for citrus (Citrus spp.) products has undergone dramatic shifts over the last decade. These shifts are influencing development and planting of new citrus cultivars. Seedlessness and very easy peeling have become paramount in mandarin types (C. reticulata and hybrids), and new cultivars are being developed through plant breeding and selection of new sports. In both sweet orange (C. sinensis) and grapefruit (C. paradisi), essentially all important cultivars are derived from a single original hybrid of each fruit type, and plant improvement has focused on selection of sports with redder color and extended maturity. The existence of many active citrus breeding programs makes it likely that we will continue to see evolution of new citrus cultivars over the foreseeable future.

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Jinggui Fang, Pachanoor S. Devanand and ChihCheng T. Chao

Single-nucleotide-polymorphism (SNP) is the most abundant genetic variation among individuals within a species. SNPs can be used as markers for gene discovery and for assessment of biodiversity. We established a practical strategy for discovering candidate SNPs in fruiting-mei (Prunusmume Sieb. et Zucc.), a non-model tree fruit, from amplified-fragment-length-polymorphism (AFLP) fragments. Eighty-one of the 150 chosen bands from 10 cultivars of fruiting-mei were successfully re-amplified and 67 of these re-amplified PCR products yielded 13 groups of reliable sequences. The sequencing results from both directions of 23 randomly selected PCR products using the corresponding selective primers showed that all the purified fragments from the gels were EcoR I-EcoR I fragments. The sequence alignment of 13 groups of sequence yielded 95 SNPs from a total of 5252 bp, averaging one SNP every 55 bp. Among these SNPs, 73 were heterozygous in the loci of some individual cultivars. The SNPs distribution were: 58% transition, 40% transversion, and 2% InDels. There were also one di-nucleotide polymorphism and one tetra-nucleotide deletion. The procedure of SNP isolation from AFLP fragments can be useful for transferring AFLP markers into sequence-tagged-site markers.

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Chih-Cheng T. Chao, Themis J. Michailides and Dan E. Parfitt

Alternaria late blight of pistachio caused by Alternaria alternata, has become a serious problem in pistachio orchards in California. As part of the California pistachio improvement program, we evaluated the resistance/susceptibility of the breeding progenies to Alternaria late blight at two locations. The heritability of resistance ranged from 0.35 to 0.38 based on half-sib progenies analysis. Open-pollinated (OP) progenies from three cultivars showed moderate to high resistance. Greenhouse inoculation confirmed that OP progenies of cultivars Bronte and Trabonella had the greatest resistance. OP progenies of cultivar Red Aleppo were highly susceptible in greenhouse inoculations compared to moderate resistance found in field evaluations. OP progenies of the only commercial cultivar Kerman in California were susceptible in both field and greenhouse evaluation. The results show the potential for development of resistant cultivars is available in the breeding population of the California pistachio improvement program.

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Chih-Cheng T. Chao, Dan E. Parfitt and Themis J. Michailides

Pistachio (Pistacia vera L.) progeny from the California cultivar improvement program were evaluated at two locations for their resistance to alternaria late blight [Alternaria alternata (Fries) Keissler] from 1995 to 1997. Large differences between seedlings were observed for disease resistance. Narrow sense heritabilities were calculated from half-sib analysis of 20 open pollinated families. Heritabilities of 0.48 and 0.11 at Kearney Agricultural Center were observed in 1995 and 1997, respectively. Narrow-sense heritability estimates were 0.56 and 0.54 at the Wolfskill Experimental Orchard near Davis for 1995 and 1997, respectively. Differences among progeny families to alternaria late blight infection were highly significant and were associated with the female parents. Greenhouse inoculation experiments were not strongly correlated with field results. Fifty-eight highly resistant seedlings were identified for use in future cultivar improvement efforts.