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- Author or Editor: Dan E. Parfitt x
Excessive boron (B) in soil and water is a problem for pistachio (Pistacia vera L.) production in the San Joaquin Valley (SJV) of California. Although amenable, leaching of B requires more water than chlorine (Cl) or sodium (Na) and is increasingly difficult as B in irrigation water increases. The lack of subsurface drainage to the ocean increases soil salinity in many growing areas, especially on the west side of the SJV where B is often excessive natively in the soil and water. Pistachio rootstocks that can tolerate or exclude B may be a partial solution. For the past decade in California, the dominant rootstock has been seedlings and clonal selections of University of California Berkeley 1 (UCB-1), which is a hybrid of P. atlantica × P. integerrima. This reliance on a genetically similar pool of rootstocks has constrained Pistacia’s genetic potential for adapting to high-salt environments. This study compared scion and rootstock leaflet B concentration of novel hybrid experimental rootstocks with variable percentages of P. vera and P. integerrima heritage with UCB-1. Rootstocks with P. vera heritage limited B in both rootstock and scion leaflets compared with UCB-1. In six trials conducted over several years, leaflet B in ungrafted hybrid rootstocks having 62.5% to 75% P. vera and 25% to 37.5% P. integerrima heritage had 27.6% to 43.1% lower B leaflet concentration than did UCB-1. Depending on the experiment and year, grafted rootstocks having 37.5% P. vera and 62.5% P. integerrima heritage had 46.8% to 70.8% lower B scion leaflet concentration than did UCB-1. Genetic variation in B uptake in Pistacia species and interspecific hybrids, and among individual seedlings within populations, allows the breeding of pistachio rootstocks more tolerant of excess B.
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.
‘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 () and 24 days before ‘Kerman’, the standard pistachio cultivar grown in California (). ‘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.
Seven assays (hanging-drop slide and agar-plate germination, acetocarmine, three tetrazolium-based stains, and Alexander’s staining procedures) were used to estimate pollen viability in Prunus armeniaca L., P. avium L., P. dulcis Webb, P. persica (L.) Batsch, and P. salicina Lindl. The two in vitro germination tests (hanging-drop and agar-plate) were the most reliable and were highly correlated (r = 0.96). The pollen staining procedures were not reliable or consistent and were not positively correlated with the in vitro assays. Acetocarmine and Alexander’s stains stained dead pollen.
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.
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.
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.
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.