Insect Feeding on Sorghum bicolor Pollen and Hymenoptera Attraction to Aphid-Produced Honeydew.

Pollinators are declining globally, potentially reducing both human food supply and plant diversity. To support pollinator populations, planting of nectar-rich plants with different flowering seasons is encouraged while promoting wind-pollinated plants, including grasses, is rarely recommended. However, many bees and other pollinators collect pollen from grasses which is used as a protein source. In addition to pollen, Hymenoptera may also collect honeydew from plants infested with aphids. In this study, insects consuming or collecting pollen from sweet sorghum, Sorghum bicolor, were recorded while pan traps and yellow sticky card surveys were placed in grain sorghum fields and in areas with Johnsongrass, Sorghum halepense to assess the Hymenoptera response to honeydew excreted by the sorghum aphid (SA), Melanaphis sorghi. Five genera of insects, including bees, hoverflies, and earwigs, were observed feeding on pollen in sweet sorghum, with differences observed by date, but not plant height or panicle length. Nearly 2000 Hymenoptera belonging to 29 families were collected from grain sorghum with 84% associated with aphid infestations. About 4 times as many Hymenoptera were collected in SA infested sorghum with significantly more ants, halictid bees, scelionid, sphecid, encyrtid, mymarid, diapriid and braconid wasps were found in infested sorghum plots. In Johnsongrass plots, 20 times more Hymenoptera were collected from infested plots. Together, the data suggest that sorghum is serving as a pollen food source for hoverflies, earwigs, and bees and sorghum susceptible to SA could provide energy from honeydew. Future research should examine whether planting strips of susceptible sorghum at crop field edges would benefit Hymenoptera and pollinators.

Genome-wide association mapping of resistance to the sorghum aphid in Sorghum bicolor.

Since 2013, the sorghum aphid (SA), Melanaphis sorghi (Theobald), has been a serious pest that hampers all types of sorghum production in the U.S. Known sorghum aphid resistance in sorghum is limited to a few genetic regions on SBI-06. In this study, a subset of the Sorghum Association Panel (SAP) was used along with some additional lines to identify genomic regions that confer sorghum aphid resistance. SAP lines were grown in the field and visually evaluated for SA resistance during the growing seasons of 2019 and 2020 in Tifton, GA. In 2020, the SAP accessions were also evaluated for SA resistance in the field using drone-based high throughput phenotyping (HTP). Flowering time was recorded in the field to confirm that our methods were sufficient for identifying known quantitative trait loci (QTL). This study combined phenotypic data from field-based visual ratings and reflectance data to identify genome-wide associated (GWAS) marker-trait associations (MTA) using genotyping-by-sequencing (GBS) data. Several MTAs were identified for SA-related traits across the genome, with a few common markers that were consistently identified on SBI-08 and SBI-10 for aphid count and plant damage, as well as loci for reflectance-based traits on SBI-02, SBI-03, and SBI-05. Candidate genes encoding leucine-rich repeats (LRR), Avr proteins, lipoxygenases (LOXs), calmodulins (CAM) dependent protein kinase, WRKY transcription factors, flavonoid biosynthesis genes, and 12-oxo-phytodienoic acid reductase were identified near SNPs that had significant associations with different SA traits. In this study, flowering time-related genes were also identified as a positive control for the methods. The total phenotypic variation explained by significant SNPs across SA-scored traits, reflectance data, and flowering time ranged from 6 to 61%, while the heritability value ranged from 4 to 69%. This study identified three new sources of resistant lines to sorghum aphid. These results supported the existing literature, and also revealed several new loci. Markers identified in this study will support marker-assisted breeding for sorghum aphid resistance.

Transfer of Meloidogyne incognita Resistance Using Marker-assisted Selection in Sorghum.

Meloidogyne incognita is a wide-spread and damaging pathogen of many important crops in the southern United States, and most sorghum genotypes allow significant levels of reproduction by the nematode. A series of greenhouse evaluations were conducted to determine whether a quantitative trait locus (QTL) that imparts a high level of resistance to Meloidogyne incognita in sorghum can effectively be transferred into diverse sorghum genotypes using marker assisted selection. Using marker-assisted selection, the resistance QTL, QTL-Sb.RKN.3.1, from 'Honey Drip' sorghum was crossed into five different sorghum backgrounds that included forage, sweet, and grain sorghum until the BC1F6 generation. Repeated greenhouse experiments documented that the recurrent parent genotypes were all susceptible to M. incognita and statistically similar to each other. In contrast, the BC1F6 genotypes were all highly resistant and similar to each other and similar to the resistant standard, 'Honey Drip'. These results suggest that this resistance QTL could be introgressed using marker assisted selection into many sorghum genotypes and confer a high level of resistance to M. incognita. Thus, this QTL and its associated markers will be useful for sorghum breeding programs to incorporate M. incognita resistance into their sorghum lines.

Exogenous melatonin improves cotton (Gossypium hirsutum L.) pollen fertility under drought by regulating carbohydrate metabolism in male tissues.

Although exogenous melatonin can enhance the drought tolerance of plants, reports on the role of melatonin in drought tolerance in male reproductive organs are limited. To explore this, a pot experiment was conducted with cotton cultivar Yuzaomian 9110 to study the effects of exogenous melatonin (100, 200, and 1000 µM) on male fertility and related carbohydrate metabolism in anther under drought. Results showed that drought inhibited the translocation of carbon assimilates to anthers, however, melatonin application (100 and 200 µM) significantly improved the translocation of carbon assimilates to drought-stressed anthers. Drought reduced the deposition of starch, the hydrolysis of sucrose into hexoses, the generation of adenosine triphosphate (ATP) in anthers, restricting pollen viability and germination. Nevertheless, the appropriate melatonin concentrations (100 and 200 µM) increased the starch accumulation by enhancing ADP-glucose pyrophosphorylase and soluble starch synthases activities and accelerated the hydrolysis of sucrose by increasing sucrose synthase, acid and alkaline invertases activities in drought-stressed anthers. Appropriate melatonin concentrations (100 and 200 µM) also could help to generate more ATP for reproductive activities of drought-stressed anthers, finally increasing the pollen viability and germination of drought-stressed plants. These findings suggest that drought inhibited male fertility of cotton, but a precise melatonin application could regulate the carbohydrate balance of drought-stressed anthers to improve male fertility. This is the first report demonstrating the important role of exogenous melatonin in improving male fertility under drought conditions by regulating the carbohydrate metabolism in the male part of cotton.

A Novel QTL for Root-Knot Nematode Resistance is Identified from a South African Sweet Sorghum Line.

Southern root-knot nematodes, Meloidogyne incognita, feed on the underground portions of hundreds of plant species and affect nutrient partitioning and water uptake of the host plants. Sorghum (Sorghum bicolor) is often not significantly damaged by southern root-knot nematodes (RKN) but some sorghum genotypes support greater population densities of RKN than other genotypes. These higher nematode populations increase the risk of damage to subsequently planted susceptible crops. A previous study identified a major quantitative trait locus (QTL) for RKN resistance on sorghum chromosome (chr.) 3. To maintain long-term resistance, multiple resistance genes should be pyramided in a cultivar. In this study, we identified a new source of RKN resistance, created a mapping population, and identified single-nucleotide polymorphism markers using genotyping-by-sequencing of the segregating population. Use of single-marker analysis and composite interval mapping identified a single QTL on chr. 5 that was associated with egg number and egg number per gram of root from the resistant sweet sorghum line PI 144134. This region on chr. 5 and the prior QTL on chr. 3 can be potentially moved from PI 144134 and Honey Drip, respectively, into elite sorghum germplasm via marker-assisted selection for more durable resistance.

Mapping QTLs and Identification of Genes Associated with Drought Resistance in Sorghum.

Water limits global agricultural production. Increases in global aridity, a growing human population, and the depletion of aquifers will only increase the scarcity of water for agriculture. Water is essential for plant growth and in areas that are prone to drought, the use of drought-resistant crops is a long-term solution for growing more food for more people with less water. Sorghum is well adapted to hot and dry environments and has been used as a dietary staple for millions of people. Increasing the drought resistance in sorghum hybrids with no impact on yield is a continual objective for sorghum breeders. In this review, we describe the loci, quantitative trait loci (QTLs), or genes that have been identified for traits involved in drought avoidance (water-use efficiency, cuticular wax synthesis, trichome development and morphology, root system architecture) and drought tolerance (compatible solutes, pre- and post-flowering drought tolerance). Many of these identified genes and QTL regions have not been tested in hybrids and the effect of these genes, or their interactions, on yield must be understood in normal and drought-stressed conditions to understand the strength and weaknesses of their utility.

Method for DNA Isolation From Sweetpotato Weevil (Coleoptera: Curculionidae) Collected in Pheromone-Baited Traps.

This study provides a protocol for the isolation of high-quality DNA from sweetpotato weevils (Cylas formicarius elegantulus (Summers)) collected from pheromone-baited aerial funnel traps. This study was based on our discovery that a 2-wk collection interval of sweetpotato weevils from pheromone traps did not permit isolation of intact high-quality genomic DNA. To test the effect of collection methods, i.e., sample collection interval and preservation method, on quality of isolated DNA, we placed freshly killed male sweetpotato weevils into aerial funnel traps in the field and removed subsamples at several times thereafter. DNA yield from freshly isolated (day = 0) samples was significantly greater than samples preserved in 70% ethanol or at -20°C, whereas there was no difference between 70% ethanol and -20°C storage. Likewise, DNA yield from freshly isolated (day = 0) samples was significantly greater than for later sampling times. Quality assessment of genomic DNA through gel electrophoresis and polymerase chain reaction (PCR) indicated isolation of high molecular weight DNA for all samples collected at t ≤ 7 d, but that DNA quality was degraded by 14 d. Our goal was to develop a reliable method for isolation of genomic DNA from field-collected sweetpotato weevil suitable for direct use in PCR. We discovered that it is critical to collect specimens from traps at an interval of 1 wk or less. Our findings allow for scheduling of sampling at reasonable intervals without the need for special materials. This has the added benefit of allowing individuals without special training to collect and prepare sweetpotato weevil specimens for genetic studies.

Pearl millet genome sequence provides a resource to improve agronomic traits in arid environments.

Pearl millet [Cenchrus americanus (L.) Morrone] is a staple food for more than 90 million farmers in arid and semi-arid regions of sub-Saharan Africa, India and South Asia. We report the ∼1.79 Gb draft whole genome sequence of reference genotype Tift 23D2B1-P1-P5, which contains an estimated 38,579 genes. We highlight the substantial enrichment for wax biosynthesis genes, which may contribute to heat and drought tolerance in this crop. We resequenced and analyzed 994 pearl millet lines, enabling insights into population structure, genetic diversity and domestication. We use these resequencing data to establish marker trait associations for genomic selection, to define heterotic pools, and to predict hybrid performance. We believe that these resources should empower researchers and breeders to improve this important staple crop.

Chemical Analysis of Fermentable Sugars and Secondary Products in 23 Sweet Sorghum Cultivars.

Sorghum (Sorghum bicolor (L.) Moench) is a heat- and drought-tolerant crop that has promise to supplement corn (Zea mays L.) for biofuel production from fermentable sugars (for sweet cultivars) and lignocellulosic biomass. Quantitative relationships are lacking to predict the accumulation of primary (stem sugars) and secondary (organic acids, phenolics, and inorganic species) products that could either expand (as the value-added product) or limit (as the fermentation inhibitor) the market value of a cultivar. Five male (Atlas, Chinese, Dale, Isidomba, N98) and three female (N109B, N110B, and N111B) inbred lines and their hybrids (23 cultivars total) were planted on a Tifton loamy sand in April, May, and June of 2015 in a triplicate split-plot design and were harvested at the hard-dough maturity stage. Stalk juices were analyzed for sugar (glucose, fructose, and sucrose) and organic acid (citrate, oxalate, and cis- and trans-aconitic acid) concentrations, Brix, pH, electric conductivity (EC), total organic carbon (TOC), and total nitrogen (TN), and by fluorescence excitation emission spectrophotometry with parallel factor analysis (EEM/PARAFAC). Later plantings consistently (p < 0.05) (1) increased sucrose, total sugar, and trans-aconitic acid concentrations, Brix, and TOC and (2) decreased EC. Sucrose, total sugar, pH, EC, and Brix showed significant cultivar × planting date interactions. Observed linear relationships (Pearson's) could be used to deploy simple and inexpensive electrode (EC) and fluorescence-based field methods to predict the primary products from secondary products, and vise versa.

Carbon Monoxide Interacts with Auxin and Nitric Oxide to Cope with Iron Deficiency in Arabidopsis.

To clarify the roles of carbon monoxide (CO), nitric oxide (NO), and auxin in the plant response to iron deficiency (-Fe), and to establish how the signaling molecules interact to enhance Fe acquisition, we conducted physiological, genetic, and molecular analyses that compared the responses of various Arabidopsis mutants, including hy1 (CO deficient), noa1 (NO deficient), nia1/nia2 (NO deficient), yuc1 (auxin over-accumulation), and cue1 (NO over-accumulation) to -Fe stress. We also generated a HY1 over-expression line (named HY1-OX) in which CO is over-produced compared to wild-type. We found that the suppression of CO and NO generation using various inhibitors enhanced the sensitivity of wild-type plants to Fe depletion. Similarly, the hy1, noa1, and nia1/nia2 mutants were more sensitive to Fe deficiency. By contrast, the yuc1, cue1, and HY1-OX lines were less sensitive to Fe depletion. The hy1 mutant with low CO content exhibited no induced expression of the Fe uptake-related genes FIT1 and FRO2 as compared to wild-type plants. On the other hand, the treatments of exogenous CO and NO enhanced Fe uptake. Likewise, cue1 and HY1-OX lines with increased endogenous content of NO and CO, respectively, also exhibited enhanced Fe uptake and increased expression of bHLH transcriptional factor FIT1as compared to wild-type plants. Furthermore, we found that CO affected auxin accumulation and transport in the root tip by altering the PIN1 and PIN2 proteins distribution that control lateral root structure under -Fe stress. Our results demonstrated the integration of CO, NO, and auxin signaling to cope with Fe deficiency in Arabidopsis.

The Dynamic Changes of the Plasma Membrane Proteins and the Protective Roles of Nitric Oxide in Rice Subjected to Heavy Metal Cadmium Stress.

The heavy metal cadmium is a common environmental contaminant in soils and has adverse effects on crop growth and development. The signaling processes in plants that initiate cellular responses to environmental stress have been shown to be located in the plasma membrane (PM). A better understanding of the PM proteome in response to environmental stress might provide new insights for improving stress-tolerant crops. Nitric oxide (NO) is reported to be involved in the plant response to cadmium (Cd) stress. To further investigate how NO modulates protein changes in the plasma membrane during Cd stress, a quantitative proteomics approach based on isobaric tags for relative and absolute quantification (iTRAQ) was used to identify differentially regulated proteins from the rice plasma membrane after Cd or Cd and NO treatment. Sixty-six differentially expressed proteins were identified, of which, many function as transporters, ATPases, kinases, metabolic enzymes, phosphatases, and phospholipases. Among these, the abundance of phospholipase D (PLD) was altered substantially after the treatment of Cd or Cd and NO. Transient expression of the PLD fused with green fluorescent peptide (GFP) in rice protoplasts showed that the Cd and NO treatment promoted the accumulation of PLD in the plasma membrane. Addition of NO also enhanced Cd-induced PLD activity and the accumulation of phosphatidic acid (PA) produced through PLD activity. Meanwhile, NO elevated the activities of antioxidant enzymes and caused the accumulation of glutathione, both which function to reduce Cd-induced H2O2 accumulation. Taken together, we suggest that NO signaling is associated with the accumulation of antioxidant enzymes, glutathione and PA which increases cadmium tolerance in rice via the antioxidant defense system.

Inheritance and Identification of a Major Quantitative Trait Locus (QTL) that Confers Resistance to Meloidogyne incognita and a Novel QTL for Plant Height in Sweet Sorghum.

Southern root-knot nematodes (Meloidogyne incognita) are a pest on many economically important row crop and vegetable species and management relies on chemicals, plant resistance, and cultural practices such as crop rotation. Little is known about the inheritance of resistance to M. incognita or the genomic regions associated with resistance in sorghum (Sorghum bicolor). In this study, an F2 population (n = 130) was developed between the resistant sweet sorghum cultivar 'Honey Drip' and the susceptible sweet cultivar 'Collier'. Each F2 plant was phenotyped for stalk weight, height, juice Brix, root weight, total eggs, and eggs per gram of root. Strong correlations were observed between eggs per gram of root and total eggs, height and stalk weight, and between two measurements of Brix. Genotyping-by-sequencing was used to generate single nucleotide polymorphism markers. The G-Model, single marker analysis, interval mapping, and composite interval mapping were used to identify a major quantitative trait locus (QTL) on chromosome 3 for total eggs and eggs per gram of root. Furthermore, a new QTL for plant height was also discovered on chromosome 3. Simple sequence repeat markers were developed in the total eggs and eggs per gram of root QTL region and the markers flanking the resistance gene are 4.7 and 2.4 cM away. These markers can be utilized to move the southern root-knot nematode resistance gene from Honey Drip to any sorghum line.

A major QTL associated with Fusarium oxysporum race 1 resistance identified in genetic populations derived from closely related watermelon lines using selective genotyping and genotyping-by-sequencing for SNP discovery.

KEY MESSAGE: A major quantitative trait locus (QTL) for Fusarium oxysporum Fr. f. sp. niveum race 1 resistance was identified by employing a "selective genotyping" approach together with genotyping-by-sequencing technology to identify QTLs and single nucleotide polymorphisms associated with the resistance among closely related watermelon genotypes. Fusarium wilt is a major disease of watermelon caused by the soil-borne fungus Fusarium oxysporum Schlechtend.:Fr. f. sp. niveum (E.F. Sm.) W.C. Snyder & H.N. Hans (Fon). In this study, a genetic population of 168 F3 families (24 plants in each family) exhibited continuous distribution for Fon race 1 response. Using a "selective genotyping" approach, DNA was isolated from 91 F2 plants whose F3 progeny exhibited the highest resistance (30 F2 plants) versus highest susceptibility (32 F2 plants), or moderate resistance to Fon race 1 (29 F2 plants). Genotyping-by-sequencing (GBS) technology was used on these 91 selected F2 samples to produce 266 single nucleotide polymorphism (SNP) markers, representing the 11 chromosomes of watermelon. A major quantitative trait locus (QTL) associated with resistance to Fon race 1 was identified with a peak logarithm of odds (LOD) of 33.31 and 1-LOD confidence interval from 2.3 to 8.4 cM on chromosome 1 of the watermelon genetic map. This QTL was designated "Fo-1.1" and is positioned in a genomic region where several putative pathogenesis-related or putative disease-resistant gene sequences were identified. Additional independent, but minor QTLs were identified on chromosome 1 (LOD 4.16), chromosome 3 (LOD 4.36), chromosome 4 (LOD 4.52), chromosome 9 (LOD 6.8), and chromosome 10 (LOD 5.03 and 4.26). Following the identification of a major QTL for resistance using the "selective genotyping" approach, all 168 plants of the F 2 population were genotyped using the SNP nearest the peak LOD, confirming the association of this SNP marker with Fon race 1 resistance. The results in this study should be useful for further elucidating the mechanism of resistance to Fusarium wilt and in the development of molecular markers for use in breeding programs of watermelon.