Genomic sequence data of bacterial isolates from pistachio trees and other woody plants in California are inconsistent with a role of Rhodococcus as the causative agent of Pistachio Bushy Top Syndrome

Pistachio Bushy Top Syndrome (PBTS) is a serious problem for pistachio growers in the western U.S. but the cause of this disorder remains controversial. Recently, it was proposed that the Rhodococcus species, R. fascians and R. corynebacterioides caused PBTS outbreaks in 2011 and 2015. To investigate the association of Rhodococcus spp with PBTS in California’s pistachio growing region, Rhodococcus-like isolates were collected from diverse hosts and environments, including pistachio nurseries and orchards. Whole genome sequence analysis of 231 isolates revealed their evolutionary relationships and identified six Rhodococcus species. Combined with data on geography and host of origin, the data reveal that Rhodococcus generally, and R. fascians specifically, is ubiquitous in nature, frequently occurring in both symptomatic and asymptomatic pistachio trees and on other woody and native species. Core gene and SNP-based phylogenies, and pan-genome analyses differentiate R. fascians into distinct genotypes. Although we found examples of common genotypes shared between nurseries and orchards, the observed patterns are most consistent with an environmental source of strains and do not support a scenario where individual nurseries are point sources of Rhodococcus. Moreover, none of the collected strains harbored known virulence genes, calling into question the role of these common, environmental bacteria in causing PBTS.

Identification and characterization of Phytophthora species associated with crown and root rot of pistachio trees in California.

Pistachio is one of the most widely cultivated nut crops in California with approximately 115,000 hectares of bearing pistachio trees. In recent years, several orchards were identified with declining trees leading to substantial tree losses. Symptoms included trees with poor vigor, yellowing and wilting of leaves, crown rot and profuse gumming on the lower portion of trunks. Thirty-seven Phytophthora-like isolates were obtained from crown rot tissues in the rootstock of grafted pistachio trees and characterized by means of multi-locus phylogeny comprising ITS rDNA, beta-tubulin and mt cox1 sequence data. The analysis provided strong support for the delineation and identification of three Phytophthora species associated with declining pistachio trees, including Phytophthora niederhauserii, P. mediterranea and P. taxon walnut. Pathogenicity studies in potted UCBI rootstocks (clonal and seeded) confirmed that all three Phytophthora species can cause crown and root rot of pistachio, thus fulfilling Koch’s postulates. The widespread occurrence of Phytophthora crown rot in recently planted pistachio orchards and the high susceptibility of UCBI rootstocks suggest this disease constitute an emerging new threat to the pistachio industry of California. To the best of our knowledge, this study is the first to report P. niederhauserii, P. mediterranea and P. taxon walnut as causal agents of crown and root rots of pistachio.

Effect of Spraying Zinc, Copper And Iron on Leaf Nutrient, Fruit Set And Some Fruit Quality of Pistachio Trees (pistacia Vera L.) Cv. Halebi

This study was conducted at a private orchard in the Ekmale village of Duhok Governorate, Kurdistan Region, Iraq during growing season (2020) to evaluate the effect of foliar sprays of three concentrations of zinc (0, 750, and 1500 mg.L−1 ), three concentrations of copper (0, 100, and 200 mg.L−1 ) and three concentrations of iron (0, 150, and 300 mg.L−1 ) on leaf nutrient, fruit set, as well as yield and quality of 18- years old " Halebi " pistachio trees. The nutrition solutions were sprayed on trees at two times (bud swell stage and green tip stage). Based on the obtained results, fruit set percentage, yield, and leaf nutrient were significantly affected by foliar application of a zinc, copper and iron each alone. In combination, the triple interactions among 1500mg.L−1 zinc plus 200mg.L−1 copper and 300mg.L−1 iron was the most affected one which exceed significantly on the control treatment, Moreover, nutrient treatment had a significant effect on the percentage of blankness. In general, these results show that Zn, Cu and Fe fertilizers is necessary for obtaining better yield and fruit quality in " Halebi " pistachio trees.

Effect of Natural Resin from Wild Pistachio Trees on Physical Properties and Durability of Beech Wood

This study was carried out to investigate the physical properties and decay resistance of beech wood treated with natural pistachio resin (PR) from Iranian wild pistachio trees (Pistacia atlantica), alone and in combination with boric acid (BA). Wood samples were impregnated with different concentration of PR dissolved in ethanol (3 to 20 %) with vacuum-pressure technology. The combination of PR (20 %) and BA (2 %) was also conducted to evaluate any interaction or synergistic effects. The water absorption, volumetric swelling, and decay resistance against Trametes versicolor fungi, before and after a leaching test (EN 84), were measured on treated and untreated samples. The chemical compositions of PR were also identified by gas chromatography–mass spectrometry (GC-MS) techniques. The chemicals analysis identified more than 20 different compounds in the PR, monoterpenoids being the predominant fraction and α-pinene the major component. The samples treated with a higher concentration of PR showed much higher weight gain percentage (WG%). The results showed that the increase in WG% reduced the average values of water absorption and volumetric swelling of treated samples even after long terms of soaking in water. The decay resistance of the treated samples increased against white rotting fungi as the values of WG% increased. Efficient protection was seen when a combined treatment of PR and BA was used. Even after the leaching process, the weight loss of the treated samples was less than 3 percent. The samples treated with BA alone largely lost their effectiveness against fungal attack after the leaching. The use of PR along with an environmental friendly co-biocide can also be recommended for wood preservation in places that require minimal toxicity.

Identification of the profile of endogenous cytokinin-like compounds during different plant growth stages and their effects on flower bud abscission in pistachio (Pistacia vera L.)

Alternate bearing is a significant economic problem that affects fruit producers, consumers and the economy of a country. Concentrations of cytokinin (CK)-like compounds in different tissues of pistachio trees (Pistacia vera ‘Uzun’) were measured to elucidate the relationship between endogenous CKs and flower bud abscission (alternate bearing). Identification and quantification of CK-like compounds of the Z, DHZ and iP types from different physiological stages and tissues were performed using high-performance liquid chromatography–electrospray ionisation–tandem mass spectrometry (HPLCESI-MS/MS) techniques. Five to seven different CK-like compounds were detected, respectively. Isopentenyl adenine riboside (iPR) and trans-zeatin-O-glucoside (t-ZOG) were the main isoprenoid CKs, as the dominant conjugates in all the analysed organs of pistachio trees. The leaves and shoots of ‘On’-year trees had significantly higher CK contents than those of ‘Off’-year trees on all the sampling dates. Interestingly, the relatively high CK activity was recorded before flower bud abscission in the fractions corresponding to iPR and t-ZOG, while this activity dropped considerably during the flower bud abscission period (55 DAFB). Consequently, the strong negative correlation between CK concentration and bud abscission could be the first indication of the role of CK-like compounds in this unique phenomenon in the ‘Uzun’ pistachio cultivar. It was concluded that CKs could have an important role in the alternate bearing in pistachio.