San Joaquin Valley Agricultural Sciences Center

Abstract Many countries operate trapping programs to detect incursions of tephritid fruit fly pests (Diptera: Tephritidae). Food-based attractants are an important component of trapping systems, as they are neither species- nor sex-specific. Liquid protein baits, including an aqueous solution of torula yeast plus borax (TYB), have traditionally been used. However, such baits are short-lasting and must be replaced frequently. Several dry, synthetic food baits, all containing ammonium acetate, putrescine, and trimethylamine hydrochloride, have been developed as potential replacements for TYB. A recent study reported that, in five different countries, a new vial-lure dispenser (containing these same three components) attracted similar or greater numbers of Mediterranean fruit flies, Ceratitis capitata (Wiedemann), than TYB-baited traps. In all locations the TYB was replaced weekly, while the vial-lures were not replaced over eight consecutive weeks of trapping. Here, we present additional data from three different regions on the performance of vial-lure dispensers relative to TYB and several other synthetic food-based lures. Results from Florida and Guatemala showed that traps baited with vial-lures captured an equivalent or greater number of C . capitata as traps baited with TYB, whereas in Hawaii TYB was significantly more attractive than the vial-lures. No consistent differences were evident between vial-lures and the other synthetic food baits tested. The present study does not identify the most effective replacement for TYB for monitoring C . capitata . Regardless of the specific bait used, however, the extended field longevity characteristic of synthetic food-based attractants will reduce the high servicing costs associated with TYB-baited traps.

Abstract Previous genetic mapping studies indicate that multiple haplotypes of the Pierce’s disease (PD) Resistance 1 (PdR1) locus occur in Vitis arizonica and its hybrids. To characterize sequence diversity at this locus, we assembled chromosome-scale diploid genomes for four PD-resistant (PD-R) accessions: b43-17 ( PdR1a⁺/PdR1b⁺ ), the backcross 07744-094 ( PdR1c⁺/PdR1⁻ ), b46-43 ( PdR1e⁺/PdR1f⁺ ), and b42-26 ( PdR1⁻/PdR1⁻ ), which displays quantitative PD resistance not associated with PdR1 . Haplotype resolution of PdR1a , PdR1b , PdR1c , and PdR1e revealed substantial variation in intergenic repeat content and gene composition between PdR1 and their alternative haplotype at the PdR1 locus not associated with PD resistance phenotype ( PdR1 - ), as well as among PdR1 haplotypes, demonstrating extensive sequence diversity at the PdR1 locus. Sequence graph analysis uncovered substantial structural divergence concentrated in approximately one quarter of the locus, together with smaller-scale variation across haplotypes. This analysis identified PdR1 -specific graph nodes, showing that PdR1a and PdR1b share most of their PdR1 -specific features, whereas PdR1c contains the highest number of private nodes, followed by PdR1e . Integration of sequence graph features with gene expression data further refined a set of defense-related candidate genes within PdR1c . Together, these results identify candidate genes for functional validation and indicate that multiple resistance determinants co-localized within the PdR1 locus may contribute to PD resistance, highlighting opportunities for targeted genetic improvement strategies.

A Microviridae phage, CLasMV1, was recently identified in 'Candidatus Liberibacter asiaticus' (CLas), the bacterium associated with citrus Huanglongbing (HLB). The CLasMV1 strain GDHZ11D (CP045566) exhibited a circular genome of 8,869 bp containing eight open reading frames (ORFs). Phages of CLas play crucial roles in regulating bacterial population diversity that have potential use for HLB control. However, knowledge of CLasMV1 population diversity is currently limited. In this study, 1,520 CLas samples were collected from 10 citrus-growing provinces in China. PCR screening revealed that 1,042 samples (69%) harbored CLasMV1. Complete genome sequences of 43 CLasMV1 strains were obtained through Illumina HiSeq sequencing with genome sizes ranging from 8,696 to 8,881 bp. Variations were mostly related to single-nucleotide polymorphisms and sequence insertions/deletions. Notably, two hypervariable regions (HVRs) were identified. Two new ORFs were detected, ORF-A (144 bp) in HVR-1 and ORF-B (342 bp) in HVR-2. Whole-genome phylogenetic analysis using 43 strains from this study, 9 previously reported Chinese strains, and 2 Florida strains (CP040636 and MZ382797) delineated five genomic groups. Chinese strains dominated Groups 1 to 4, and Group 5 contained the Florida strains. Further analyses of HVR-1 across all 1,042 CLasMV1 samples detected a 173-bp sequence with suspected mobile activity. Analysis of a PacBio long-read assembly published previously detected a concatemer of the CLasMV1 sequence, suggesting that the phage used the rolling circle mechanism for its replication. These findings significantly enhance our understanding of CLasMV1 genomic diversity and will facilitate future research on CLasMV1 classification and HLB biology.

Blueberries are highly perishable and susceptible to storage spoilage, especially fruit rot diseases caused by fungal pathogens. Alternaria rot caused by Alternaria alternata and gray mold caused by Botrytis cinerea are the primary postharvest diseases of blueberries grown in California. We conducted a 3-year field experiment to evaluate the effects of preharvest application of acibenzolar- S-methyl (ASM) and potassium silicate (PSi) on Alternaria rot and gray mold in blueberry fruit inoculated with these pathogens after harvest as well as naturally occurring fruit rot, fruit-to-fruit spread of gray mold during cold storage, and fruit quality. After 4 weeks of cold storage, all inoculated fruit developed rots regardless of the treatments applied in the field. In noninoculated fruit, ASM significantly reduced the percentage of naturally occurring decayed fruit compared with the nontreated control in 2023 but not in 2021 and 2022. PSi significantly reduced the percentage of decayed fruit compared with the nontreated control in 2021 and 2023 but not in 2022. A significant increase in soluble solids and reduction in titratable acidity were observed in the fruit treated with ASM and PSi for the second and third years of the experiment, indicating that both treatments may have enhanced fruit maturity. Our results suggested that preharvest use of ASM and PSi had limited efficacy in postharvest disease control but may have potential as tools for adjusting fruit maturity of blueberries. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2025.

Three blueberry cultivars ('San Joaquin', 'Jewel', and 'Snowchaser') were harvested at commercial maturity and subjected to different degrees of fruit surface bloom removal (full natural bloom (FB), partial bloom (PB), and removed bloom (RB)) to assess the importance of the bloom to consumer preference. Sensory evaluation assessed flavor, appearance, and overall acceptance under different conditions (darkness and light). Panelists preferred berries with at least some degree of bloom, as influenced by appearance for all varieties, and in 'Snowchaser' and 'Jewel', flavor acceptance declined when the evaluation allowed the fruit to be visualized. Panelists were prompted to select the attribute most influencing their affective evaluations to better understand the basis for the differences due to the presence of bloom. FB and PB were rated as more appealing, except for 'Jewel', where PB was deemed unattractive. At the same time, bloom presence influenced firmness choices, and sweetness and tartness preferences were affected by both variety and evaluation conditions, suggesting complex interactions in multisensory perception. Principal component analysis reinforced the idea that treatments with bloom removal were less accepted overall, while 'Snowchaser' samples were consistently well-liked relative to the other two varieties. These findings highlight the importance of bloom presence in blueberry quality perception and consumer behavior.

Circular minichromosomes could be useful tools for plant biotechnology, yet their long-term structural stability, heritability, and effects on phenotype remain poorly understood. In this study, we report a multi-generational analysis of the Arabidopsis mini1a ring minichromosome, which originated from the chromosome 1 centromere in a haploid induction cross. Is mini1a unstable, as suggested by classical studies on other ring chromosomes? Using whole-genome sequencing of individuals carrying mini1a representing multiple successive generations, we uncovered a major catastrophe driven by DNA breaks and novel junction formation, resulting in a new version of mini1a, that carries a 1.3 Mb deletion in the centromeric region (mini1aΔ). We identified 20 new breakpoints, of which 7 disrupted gene bodies—a frequency unlikely to occur by chance. Interestingly, both mini1a and mini1aΔ could exist in one or two copies and could co-exist in a single plant. Although they were inherited efficiently, their presence was sometimes associated with plant sectors with 100% sterility. These findings highlight the structural plasticity of mini1a. At the same time, they raise questions regarding the mechanisms underlying the observed reduced plant fertility. In summary, circular minichromosomes can be deleterious and biotechnology applications based on the manipulation of minichromosomes will require careful planning and testing.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10577-025-09776-0.

CLas is a destructive pathogen responsible for causing the severe citrus disease known as huanglongbing. Our study presents the first fully sequenced Brazilian strain of CLas, designated as 9PA, and includes an analysis of two prophages occurring in this strain. The main objective of our research was to compare the genome features of this Brazilian strain with other fully sequenced genomes and to identify its hypervariable genetic regions. These regions were subsequently used to assess genomic variability within both the chromosomal and prophage regions in Brazilian isolates of CLas. Our findings offer valuable insights into the diversified adaptation of CLas.

Xylella fastidiosa (Xf) bacteria form biofilm on the cuticular surfaces of the functional foregut (precibarium and cibarium) of its vectors, xylem fluid-ingesting sharpshooter leafhoppers and spittlebugs. While much is known about Xf biofilm development and maturation in vitro, little is known about these processes in vectors. Real-time (RT)-PCR was used to quantify Xf genomes daily in the functional foreguts of blue-green sharpshooters, Graphocephala atropunctata, over 7 days of exposure to infected grapevines. Scanning electron microscopy (SEM) was used to examine Xf biofilm formation at 4 and 7 days of that time course. PCR showed populations building and reducing over a 4-day cycle. SEM revealed that foreguts at 4 days showed variability in quantity and location of bacterial attachment. Only early-stage biofilm formation occurred in low-turbulence areas of the cibarium, while high-turbulence areas of the cibarium and precibarium had rare but older, more developed macro-colonies. Biofilm was almost absent at 7 days but left behind adhesive material and remnants of prior colonization. Evidence supports the hypothesis that bacterial colonization was repeatedly interrupted and constrained by the vector. Behaviors such as egestion and enzymatic salivation likely can loosen and eject Xf biofilm, perhaps when profuse biofilm interferes with ingestion. Thus, vector acquisition of Xf is a dynamic and stochastic process of interactions between bacteria and insects. We further hypothesize for future testing that the insect can regulate this interaction. A deep understanding of Xf acquisition will aid the ongoing development of grapevine resistance to vector transmission of xylellae diseases.IMPORTANCEXylella fastidiosa (Xf) is one of the most destructive invasive plant pathogens in the world, able to hijack new vectors when it invades a region; yet the temporal interplay of bacterial colonization and insect behavior is unknown. This paper describes important findings about the process of Xf biofilm formation and maturation in a vector, contrasting similarities and differences with such formation in vitro. Results support the hypothesis that the behavior of the vector constrains and may regulate Xf biofilm formation, in dynamic competition with the bacterium. The data from this paper partly explain why Xf is so successful at invasion. Because the bacterium can be acquired and inoculated very quickly, it can move readily from old to new vectors and host plants in all-new environments. Our findings are relevant to biosecurity decisions because they demonstrate the importance of identifying potential vector species in the Xylella invasion front.

This study compared the weed suppression ability of a native cover crop species phacelia (Phacelia tanacetifolia), an introduced cover crop species rye (Secale cereale L.), and a no cover crop (herbicide‑managed) system in a vineyard. Cover crops were sown in the interrow spaces of the grapevine rows. Percent weed cover after the cover crop termination was lower in the interrow of the phacelia than the no cover crop plots. During the cover crop growing season, phacelia suppressed weeds more than rye. However, the weed seedbank of the cover crop plots was greater than that of the no cover crop plots.