Southeastern Fruit and Tree Nut Research Laboratory

Abstract The severity of plant diseases, traditionally the proportion of the plant tissue exhibiting symptoms, is a key quantitative variable to know for many diseases and is prone to error. Good quality disease severity data should be accurate (close to the true value). Earliest quantification of disease severity was by visual estimates. Sensor-based image analysis including visible spectrum and hyperspectral and multispectral sensors are established technologies that promise to substitute, or complement visual ratings. Indeed, these technologies have measured disease severity accurately under controlled conditions but are yet to demonstrate their full potential for accurate measurement under field conditions. Sensor technology is advancing rapidly, and artificial intelligence may help overcome issues for automating severity measurement under hyper-variable field conditions. The adoption of appropriate scales, training, instruction and aids (standard area diagrams) has contributed to improved accuracy of visual estimates. The apogee of accuracy for visual estimation is likely being approached, and any remaining increases in accuracy are likely to be small. Due to automation and rapidity, sensor-based measurement offers potential advantages compared with visual estimates, but the latter will remain important for years to come. Mobile, automated sensor-based systems will become increasingly common in controlled conditions and, eventually, in the field for measuring plant disease severity for the purpose of research and decision making.

Production and application technology is critical for the success of entomopathogenic nematodes (EPNs) in biological control. Production approaches include in vivo, and in vitro methods (solid or liquid fermentation). For laboratory use and small scale field experiments, in vivo production of EPNs appears to be the appropriate method. In vivo production is also appropriate for niche markets and small growers where a lack of capital, scientific expertise or infrastructure cannot justify large investments into in vitro culture technology. In vitro technology is used when large scale production is needed at reasonable quality and cost. Infective juveniles of entomopathogenic nematodes are usually applied using various spray equipment and standard irrigation systems. Enhanced efficacy in EPN applications can be facilitated through improved delivery mechanisms (e.g., cadaver application) or optimization of spray equipment. Substantial progress has been made in recent years in developing EPN formulations, particularly for above ground applications, e.g., mixing EPNs with surfactants or polymers or with sprayable gels. Bait formulations and insect host cadavers can enhance EPN persistence and reduce the quantity of nematodes required per unit area. This review provides a summary and analysis of factors that affect production and application of EPNs and offers insights for their future in biological insect suppression.

*Chilling requirement, together with heat requirement, determines the bloom date, which has an impact on the climatic distribution of the genotypes of tree species. The molecular basis of floral bud chilling requirement is poorly understood, despite its importance to the adaptation and production of fruit trees. In addition, the genetic nature of heat requirement and the genetic interrelationships among chilling requirement, heat requirement and bloom date remain unclear. *A peach (Prunus persica) F(2) population of 378 genotypes developed from two genotypes with contrasting chilling requirements was used for linkage map construction and quantitative trait loci (QTL) mapping. The floral bud chilling and heat requirements of each genotype were evaluated over 2 yr and the bloom date was scored over 4 yr. *Twenty QTLs with additive effects were identified for three traits, including one major QTL for chilling requirement and two major QTLs for bloom date. The majority of QTLs colocalized with QTLs for other trait(s). In particular, one genomic region of 2 cM, pleiotropic for the three traits, overlapped with the sequenced peach EVG region. *This first report on the QTL mapping of floral bud chilling requirement will facilitate marker-assisted breeding for low chilling requirement cultivars and the map-based cloning of genes controlling chilling requirement. The extensive colocalization of QTLs suggests that there may be one unified temperature sensing and action system regulating chilling requirement, heat requirement and bloom date together.

Because of their selectivity and safety, microbial control agents (MCAs) appear to be ready-made components of integrated pest management (IPM) systems that do not pose a threat to applicators or the environment and allow other natural enemies to function. Control of several orchard pest insects using MCAs, including viruses, Bacillus thuringiensis, fungi, and entomopathogenic nematodes (EPNs), have been demonstrated in apple, pear, stone fruits, citrus, and several nut crops. B. thuringiensis is the most used MCA for control of lepidopteran orchard pests. Significant use of EPNs in citrus for control of root weevils is also reported. The granulovirus of codling moth is used increasingly in apple and pear by organic growers, with interest also shown by conventional growers. Although some success has been achieved, in most orchard systems MCAs account for a relatively small proportion of the pest control tactics employed, and in some systems they are not used at all. Research toward improving MCA efficacy and economic competitiveness is required to enhance the role of MCAs in IPM.

The existence of nickel (Ni) deficiency is becoming increasingly apparent in crops, especially for ureide-transporting woody perennials, but its physiological role is poorly understood. We evaluated the concentrations of ureides, amino acids, and organic acids in photosynthetic foliar tissue from Ni-sufficient (Ni-S) versus Ni-deficient (Ni-D) pecan (Carya illinoinensis [Wangenh.] K. Koch). Foliage of Ni-D pecan seedlings exhibited metabolic disruption of nitrogen metabolism via ureide catabolism, amino acid metabolism, and ornithine cycle intermediates. Disruption of ureide catabolism in Ni-D foliage resulted in accumulation of xanthine, allantoic acid, ureidoglycolate, and citrulline, but total ureides, urea concentration, and urease activity were reduced. Disruption of amino acid metabolism in Ni-D foliage resulted in accumulation of glycine, valine, isoleucine, tyrosine, tryptophan, arginine, and total free amino acids, and lower concentrations of histidine and glutamic acid. Ni deficiency also disrupted the citric acid cycle, the second stage of respiration, where Ni-D foliage contained very low levels of citrate compared to Ni-S foliage. Disruption of carbon metabolism was also via accumulation of lactic and oxalic acids. The results indicate that mouse-ear, a key morphological symptom, is likely linked to the toxic accumulation of oxalic and lactic acids in the rapidly growing tips and margins of leaflets. Our results support the role of Ni as an essential plant nutrient element. The magnitude of metabolic disruption exhibited in Ni-D pecan is evidence of the existence of unidentified physiological roles for Ni in pecan.

The emphasis of this review is on the use and potential of entomopathogenic nematodes (EPNs) as biological control agents in sustainable food production across a wide range of agricultural and other commodities. To aid with the understanding of the potential of EPNs in sustainable food production, this review also provides overviews on EPN biology and ecology, mass production and application technology, and interactions with other management tools. First discovered in the 1920s, their commercialization as biopesticides in the 1980s was accompanied and followed by an exponential growth in research on their application, biology, and ecology, followed by a further expansion in more basic research areas since the mid-2000s. This review summarizes significant progress made in the research and application of EPN in insect pest management in important food crops including orchards, small fruit, maize, vegetables, tuber crops, greenhouses, and mushrooms. Significant factors affecting the success of EPN commercialization are also discussed. A growing interest in alternatives to synthetic insecticides and in organic agriculture opens opportunities for EPNs, but EPNs will need to be further improved with respect to efficacy, reduced costs, and ease of use. Moreover, their potential to recycle in host population beckons to be further exploited for long term pest suppression.

Abstract Plant disease quantification, mainly the intensity of disease symptoms on individual units (severity), is the basis for a plethora of research and applied purposes in plant pathology and related disciplines. These include evaluating treatment effect, monitoring epidemics, understanding yield loss, and phenotyping for host resistance. Although sensor technology has been available to measure disease severity using the visible spectrum or other spectral range imaging, it is visual sensing and perception that still dominates, especially in field research. Awareness of the importance of accuracy of visual estimates of severity began in 1892, when Cobb developed a set of diagrams as an aid to guide estimates of rust severity in wheat. Since that time, various approaches, some of them based on principles of psychophysics, have provided a foundation to understand sources of error during the estimation process as well as to develop different disease scales and disease-specific illustrations indicating the diseased area on specimens, similar to that developed by Cobb, and known as standard area diagrams (SADs). Several rater-related (experience, inherent ability, training) and technology-related (instruction, scales, and SADs) characteristics have been shown to affect accuracy. This review provides a historical perspective of visual severity assessment, accounting for concepts, tools, changing paradigms, and methods to maximize accuracy of estimates. A list of best-operating practices in plant disease quantification and future research on the topic is presented based on the current knowledge.

Low-cost, high throughput genotyping methods are crucial to marker discovery and marker-assisted breeding efforts, but have not been available for many 'specialty crops' such as fruit and nut trees. Here we apply the Genotyping-By-Sequencing (GBS) method developed for cereals to the discovery of single nucleotide polymorphisms (SNPs) in a peach F2 mapping population. Peach is a genetic and genomic model within the Rosaceae and will provide a template for the use of this method with other members of this family. Our F2 mapping population of 57 genotypes segregates for bloom time (BD) and chilling requirement (CR) and we have extensively phenotyped this population. The population derives from a selfed F1 progeny of a cross between 'Hakuho' (high CR) and 'UFGold' (low CR). We were able to successfully employ GBS and the TASSEL GBS pipeline without modification of the original methodology using the ApeKI restriction enzyme and multiplexing at an equivalent of 96 samples per Illumina HiSeq 2000 lane. We obtained hundreds of SNP markers which were then used to construct a genetic linkage map and identify quantitative trait loci (QTL) for BD and CR.

Nineteen peach [ Prunus persica (L.) Batsch] genotypes and 45 plum ( Prunus salicina Erhr. and hybrids) genotypes with different flesh and skin color were analyzed for their antioxidant content and activity. Anthocyanin content, phenolic content, and antioxidant activity were higher in red-flesh than in light-colored flesh peaches. Carotenoid content was higher in yellow-flesh peaches than in light-colored ones. Red-flesh plums generally had higher anthocyanin and phenolic contents than the other plums but not necessarily greater antioxidant capacity. The total phenolic content had the most consistent and highest correlation with antioxidant activity, indicating that it is more important in determining the antioxidant activity of peaches and plums than are the anthocyanin or carotenoid contents. In general, the wide range of phytochemical content and antioxidant activity found indicates that the genetic variability present can be used to develop cultivars with enhanced health benefits.

The evergreen (EVG) peach, first described in Mexico, was used as a parent with deciduous (DE) peaches to develop F 1 and F 2 hybrid populations in Mexico, Florida, Georgia, and West Virginia. F 1 trees were DE and F 2 plants segregated 3 DE: 1 EVG. In West Virginia, the most temperate location, the heterozygous class could be distinguished in the first few years of growth by late leaf abscission in the fall. Segregation ratios suggest that the EVG trait is controlled by a single gene, evg , the EVG state being homozygous recessive. Evergreen trees were characterized by insensitivity of shoot tips to daylength and failure of terminal growth to cease growth until killed by low temperature. Lateral buds of EVG trees went dormant in the fall. Deep supercooling occurred in both EVG and DE trees, but it appeared later in EVG trees, was of shorter duration, and occurred to a lesser extent. Evergreen germplasm may be useful in developing peach cultivars for frost-free subtropic and tropical areas. It also presents a useful system for studying dormancy and cold hardiness.

ABSTRACT The anthocyanin and anthocyanidin pigment profiles of 46 authentic red raspberry juice samples were determined by HPLC. Total anthocyanin pigment content and percent polymeric color were also determined. This generated a database incorporating influences of cultivar, geographic origin, maturity, processing, and mold contamination. Cultivars exhibited characteristic patterns distinguished by quantitative rather than qualitative differences. Total pigment ranged from 4 to 1,102 mg/L. Commercial red raspberry juice concentrates (14) were also analyzed. Two were shown to be adulterated because of the presence of delphinidin glycosides. Three samples contained high amounts of polymerized pigments, indicating a history of processing or storage abuse.

(E,Z)-3,13-octadecadien-1-ol acetate, and (Z,Z)-3,13-octadecadien-1-ol acetate, isolated from the female lesser peachtree borer, Synanthedon pictipes (Grote and Robinson), and the female peachtree borer, Sanninoidea exitiosa (Say), respectively, strongly attract the respective males of these species in field bioassays. These compounds are the largest pheromones isolated thus far from a lepidopterous species. Sanninoidea exitiosa males did not respond to the synthesized (E,Z)-isomer, and low concentrations of it in the synthesized (Z,Z)-isomer did not interfere with their response to the (Z,Z)-isomer. In contrast, even very low concentrations of the (Z,Z)-isomer (1 percent) in the (E,Z)-isomer significantly inhibited the response of Synanthedon pictipes males.

Rickettsia-like bacteria associated with plum leaf scald and phony peach diseases were isolated from diseased but not from healthy tissues and cultured on charcoal-yeast extract medium (BCYE) buffered with ACES (2-[(2-amino-2-oxoethyl) amino]-ethanesulfonic acid). Optimum conditions for isolation and growth on BCYE medium were pH 6.5 to 6.9 at 20 and 25 degrees C under normal atmosphere. Growth of primary colonies and first-passage subcultures was restricted, and colonies reached a maximum diameter of 0.6 mm in 60 days. After 12 passages, subcultures reached maximum growth in 21 days. The rickettsia-like bacteria from BCYE cultures were gram negative, serologically the same as those present in diseased peach and plum, and composed of rod-shaped cells measuring 0.35 by 5 mum (average diameter and maximum length) in a matrix of filamentous strands of similar width but of variable length.

Genome-enabled biotechnologies have the potential to accelerate breeding efforts in long-lived perennial crop species. Despite the transformative potential of molecular tools in pecan and other outcrossing tree species, highly heterozygous genomes, significant presence-absence gene content variation, and histories of interspecific hybridization have constrained breeding efforts. To overcome these challenges, here, we present diploid genome assemblies and annotations of four outbred pecan genotypes, including a PacBio HiFi chromosome-scale assembly of both haplotypes of the 'Pawnee' cultivar. Comparative analysis and pan-genome integration reveal substantial and likely adaptive interspecific genomic introgressions, including an over-retained haplotype introgressed from bitternut hickory into pecan breeding pedigrees. Further, by leveraging our pan-genome presence-absence and functional annotation database among genomes and within the two outbred haplotypes of the 'Lakota' genome, we identify candidate genes for pest and pathogen resistance. Combined, these analyses and resources highlight significant progress towards functional and quantitative genomics in highly diverse and outbred crops.

We studied the numerical importance of bees as pollinators of rabbiteye blueberry, Vaccinium ashei Reade, in the southeastern United States. Most of the 27 bee species were rare at V. ashei flowers. Three taxa of bees were often abundant at V. ashei: the honey bee, Apis mellifera L.; queens of four bumble bee species (Bombus spp.); and the southeastern blueberry bee, Habropoda laboriosa (F.). Most bee species that co-occur with cultivated V. ashei do not visit its flowers either because adults emerge late in the spring following bloom, or their tongues are too short to probe the flowers effectively. The more common bees varied in their regional, annual, and seasonal abundances at cultivated V. ashei, reflecting inherent differences in sociality, foraging predilections, voltinism, and adult phenologies. Our censuses showed that H. laboriosa is a Vaccinium specialist (2 yr, two states, four habitats). Compared with the other common bees, abundance of H. laboriosa at V. ashei was most variable regionally, least variable annually, and most predictable daily during a flowering season. For 6 yr, adult activity of Bombus queens and univoltine H. laboriosa generally spanned the season of V. ashei flowering. Spatial patchiness but local reliability of H. laboriosa may be an outcome of its oligolectic floral preferences. In contrast, polylectic honey and bumble bees were regionally ubiquitous. However, the temporal abundance of honey bees fluctuated markedly at V. ashei, perhaps reflecting their shifting preferences among competing members of a local flora.

Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) is among the most economically important insect pests of various vegetable crops in the Southern United States. This insect is considered a complex of at least 40 morphologically indistinguishable cryptic species. Bemisia tabaci Middle East-Asia Minor 1 (MEAM1) was initially introduced in the United States around 1985 and has since rapidly spread across the Southern United States to Texas, Arizona, and California, where extreme field outbreaks have occurred on vegetable and other crops. This pest creates extensive plant damage through direct feeding on vegetables, secreting honeydew, causing plant physiological disorders, and vectoring plant viruses. The direct and indirect plant damage in vegetable crops has resulted in enormous economic losses in the Southern United States, especially in Florida, Georgia, and Texas. Effective management of B. tabaci on vegetables relies mainly on the utilization of chemical insecticides, particularly neonicotinoids. However, B. tabaci has developed considerable resistance to most insecticides. Therefore, alternative integrated pest management (IPM) strategies are required, such as cultural control by manipulation of production practices, resistant vegetable varieties, and biological control using a suite of natural enemies for the management of the pest.

A diarrheagenic toxin from culture extracts of Aspergillus wentii Wehmer isolated from weevil-damaged Chinese chestnuts was identified as emodin (2-methyl-4,5,7-trihydroxyanthraquinone). The orange-red, crystalline toxin (mp 255 to 257 C) showed ultraviolet absorption maxima in ethyl alcohol at 223, 250, 267, 290, and 442 nm, and infrared absorption maxima at 3,400 cm-1 (OH), 1,635, and 1,625 CM-1. Chemical shifts and coupling constants of the proton magnetic resonance spectra of the A. wentii toxin and of authentic emodin agreed. Mean lethal dose of emodin orally administered to 1-day-old DeKalb cockerels was 3.7 mg/kg.

The loss of methyl bromide as a soil fumigant and minimal advances in the development and registration of new chemical fumigants has resulted in a resurgence of interest in the application of organic amendments (OAs) for soilborne plant pathogen and plant-parasitic nematode management. Significant progress has been made in the characterization of OAs, application of strategies for their use, and elucidation of mechanisms by which they suppress soilborne pests. Nonetheless, their utility is limited by the variability of disease control, expense, and the logistics of introducing them into crop production systems. Recent advances in molecular techniques have led to significant progress in the elucidation of the role of bacteria and fungi and their metabolic products on disease suppression with the addition of OAs. Biosolarization and anaerobic soil disinfestation, developed to manipulate systems and favor beneficial microorganisms to maximize their impact on plant pathogens, are built on a strong historical research foundation in OAs and the physical, chemical, and biological characteristics of disease-suppressive soils. This review focuses on recent applications of OAs and their potential for the management of soilborne plant pathogens and plant-parasitic nematodes, with emphasis primarily on annual fruit and vegetable production systems.

Response to chilling temperatures is a critical factor in the suitability of peach [ Prunus persica (L.) Batsch] cultivars to moderate climates such as in the southeastern United States. Time of bloom depends on the innate chilling requirement of the cultivar as well as the timing and duration of cold and warm temperatures experienced by the buds. Most current chilling models have considered dormancy break a sequential process: after appropriate chilling is received, a fixed amount of heat accumulation will produce bloom. This research shows that as chilling exposure increases, the time and heat accumulation required for peach floral budbreak decreases in an exponential relationship. When chilling is ample, a sequential, two-part dormancy model is adequate to describe budbreak, and increased chilling has little effect on heat requirement. In lower-chilling situations relative to a particular cultivar, the curvilinear relationship between chilling and heat requirement results in more heat being required for budbreak. This relationship, in conjunction with the range of chilling requirement found among the buds on a tree, results in an extended, asymmetrical budbreak.

The anthophorid bee, Habropoda (=Emphoropsis [R. W. Brooks, personal communication]) laboriosa (F.), is a locally abundant, vernal, univoltine species. It flies from February through April in Georgia and Alabama. In these states, females are oligolectic on Vaccinium spp., particularly V. ashei Reade and V. corymbosum L., with Gelsemium sempervirens (L.), Quercus alba L., and Cercis canadensis L. as minor, alternate pollen hosts. Pollen-harvesting female H. laboriosasonicate V. ashei flowers to release pollen, averaging 5.7 buzzes during their average 2.6-s floral visit, which is a handling rate 3 times faster than coforaging Bombus spp. Furthermore, mean floral handling rates of H. laboriosa females at V. ashei are individually more uniform than those of coforaging, polylectic Bombus spp., a hitherto undemonstrated but expected evolutionary outcome of oligolecty. Sonicated pollen accumulates on a ventral cephalic "safe site" of both sexes, which is the common site of V. ashei stigmatic contact. Floral probes are strictly legitimate (no robbing). Based upon its relative abundance at Vaccinium spp., phenology, floral handling behaviors and rates, and pollen preferences in the southeastern United States, we conclude that H. laboriosa is an oligolege adapted to species of Vaccinium for its pollen and nectar resources.