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Craig E. Kallsen and Dan E. Parfitt

‘Gumdrop’ is a new female pistachio (Pistacia vera L.) cultivar for California. It matures earlier than all commercial cultivars with equivalent yield and nut quality to ‘Kerman’. ‘Gumdrop’ can be harvested about 10–12 days before ‘Golden Hills’ pistachio (Parfitt et al., 2007) and 24 days before ‘Kerman’, the standard pistachio cultivar grown in California (Parfitt et al., 2012). ‘Gumdrop’ has very good yield, nut quality, and processed nut appearance similar to ‘Golden Hills’ and ‘Kerman’. ‘Gumdrop’ blooms about 5 days before ‘Golden Hills’ and 10–11 days before ‘Kerman’. ‘Gumdrop’, ‘Golden Hills’, and ‘Kerman’ comprise a harvest series, maturing over a 24–30 day period. The early nut maturity of ‘Gumdrop’ will permit pistachio growers to extend their harvest period. The earlier maturing date of ‘Gumdrop’ also makes it less susceptible to insect damage from navel orangeworm, a major pest of pistachio implicated in the occurrence of aflatoxin contamination. An application for a U.S. Plant Patent was submitted on 4 Apr. 2016.

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Craig E. Kallsen and Dan E. Parfitt

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Craig E. Kallsen and Dan E. Parfitt

Scion and rootstock circumferences of seven male and 26 female cultivars or potential cultivars of pistachio trees (Pistacia vera L.) were measured at 16 locations in the San Joaquin Valley of California. The trees were of variable age and on Pistacia integerrima-type or UCB1 (a P. atlantica Desf. × P. integerrima Stewart hybrid) rootstock. Differences were found in the ratio of scion to rootstock circumference (SRR) between the standard industry female cultivar Kerman and the other cultivars collectively. ‘Kerman’ produced a smoother trunk with a SRR closer to one than other cultivars. The SRR was also affected by rootstock with values closer to one for UCB1 as compared with higher values for P. integerrima rootstocks. The relationship between SRR and tree age demonstrated here can be a tool for comparing, evaluating, and selecting new rootstocks with growth rates to match those of newly developed or introduced scion cultivars.

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Dan E. Parfitt and Maria L. Badenes

PCR amplification and restriction analysis of a 3.2 kilobase hypervariable chloroplast DNA, as well as hybridization of the entire restricted chloroplast genome with tobacco chloroplast DNA probes permitted the development of a phylogeny for 10 Pistacia species. The genus divided into two major groups. P. Vera was most ancestral. P. weinmannifolia, an Asian species, is most closely related to P. texana and P. mexicana, new world species. The 3 sp. are more recently diverged, suggesting that a common ancestor of P. texana and P. mexicana originated in Asia. P. integerrima and P. chinensis are distinct species while species within two tertiary groups were monophyletic, P. vera:P. khinjuk and P. mexicana:P. texana. A general evolutionary trend from large to small nuts and leaves with few, large leaflets to many, small leaflets was documented. Pistacia had an unusually low chloroplast DNA mutation rate, more than 20x less than expected.

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Robert G. Fjellstrom and Dan E. Parfitt

RFLPs were studied in 41 populations of 13 Juglans species to study genetic diversity and phylogenetic relationships. 19 single locus nuclear RFLP loci were used to generate genetic distance/identity matrices based on allele frequencies. 21 probes were used to generate genetic distances and phylograms using shared-fragments with parsimony analysis. Parsimony analysis on fragment data produced a minimal length tree in general agreement with distance data trees, but with additional phylogenetic resolution resembling previous systematic studies. All analyses indicate an ancient origin of J. regia, which has been considered a recently derived species. A 10x difference in heterozygosity was seen among species. Genetic differentiation among conspecific east Asian populations was larger than among east Asian species. The opposite was true for American species. J. hindsii is classified as a distinct species and J. cinerea was included in section Cardiocaryon rather than Trachycaryon, from the diversity analysis.

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Maria L. Badenes and Dan E. Parfitt

Chloroplast DNA (cpDNA) mutations in 7 cultivated Prunus species were compared to establish the phylogenetic relationship among them. Mutations were detected in 3.2 kb and 1.5 kb regions of hypervariable cpDNA, amplified and cut with 21 and 10 restriction endonucleases, respectively, to reveal polymorphisms. Parsimony and cluster analyses were performed. Two groups of species, P. persica and P. dulcis and P. domestica and P. salicina were completely monophyletic. The subgenus Cerasus was the most recently derived, while the subgenus Amygdalus was the most ancestral and somewhat separate from the rest of Prunus. The results also suggest that the rate of mutation in the Cerasus chloroplast genome is significantly greater than for the other subgenera sampled.

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Robert G. Fjellstrom and Dan E. Parfitt

32 cloned probes from a walnut (Juglans sp.) PstI random genomic library were used to develop a linkage map for walnut. Low copy number walnut random genomic DNA probes were constructed and hybridized to restriction endonuclease digested DNA from parent walnut trees from a backcross of (J. hindsii × J. regia) with J. regia to identify parental polymorphism. 63 backcross progeny were analyzed to determine the inheritance and linkage of 48 RFLP loci. 66% of the probes detected duplicated, but unlinked loci. 42 of the RFLP loci could be placed on 12 linkage groups. The other 6 loci could not be placed on common linkage groups. (Theoretical maximum number of linkage groups is 16.) A Poisson probability method for estimating genome size was utilized to calculate the approximate walnut genome length as 1660 cm and to estimate that 138 markers would be needed to cover 95% the walnut genome within 20 cM of each marker.

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Dan E. Parfitt, Craig E. Kallsen, Brent Holtz and Joseph Maranto

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Dan E. Parfitt, Craig E. Kallsen and Joe Maranto

`Golden Hills' is a new female pistachio cultivar with improved performance characteristics compared to the standard female cultivar Kerman. `Golden Hills' produces a greater yield and higher percentage of split, edible nuts than `Kerman' while maintaining a similar low percentage of loose shells and kernels. Harvest date is 2–4 weeks earlier than `Kerman', which will permit growers to extend their harvest period and better utilize their harvesting equipment and personnel. Earlier harvest may reduce disease in the northern production areas of California by permitting an earlier harvest before fall rains, as well as reducing navel orangeworm infestations. The cultivar requires less chilling than `Kerman', which improves uniformity of foliation, bloom, nut set, nut fill, and uniformity of nut maturity at harvest in years with insufficient chilling for `Kerman'. Based on all of our evaluations, this cultivar appears to be an exceptional producer and has the potential to increase grower profits by more than 40%.