Evaluation of the Genetic Diversity, Haplotype, and Virulence of Fusarium oxysporum f. sp. vasinfectum Field Isolates from Alabama.

The United States is the third largest producer of cotton and the largest exporter of cotton globally. Fusarium wilt, caused by the soilborne fungal pathogen Fusarium oxysporum f. sp. vasinfectum (Fov), was estimated to cause a $21 million cotton yield loss in 2022. Historically, Alabama was an important producer of cotton in the Southeastern United States and was the first state in which Fusarium wilt on cotton was described. To assess the genetic diversity of Fov field isolates in Alabama, 118 field isolates were collected from six counties across the state from 2014 to 2016. Phylogenetic analysis using TEF1 and RPB2 placed the Fov field isolates into 18 haplotypes. Upon profiling the Tfo1 transposon insertion in the NAT gene, it was determined that no race 4 isolates were recovered in Alabama. Representatives of all field isolate haplotypes caused disease on Upland cotton variety Rowden in a hydroponic test tube assay. Two haplotype A isolates were the most aggressive isolates recovered, and haplotype A isolate TF1 was more aggressive than the race 4 isolate 89-1A on Upland cotton and had similar symptom severity on Pima cotton. Karyotype profiling indicted an abundance of small chromosomes characteristic of karyotypes that include accessory chromosomes, with considerable variability between isolates. Collectively, our study indicates that Fov isolates from Alabama are genetically diverse, which may have been promoted by its persistence in cotton fields.

Characterizing the Diversity of Oomycetes Associated with Diseased Cotton Seedlings in Alabama.

Many oomycete species are associated with the seedlings of crops, including upland cotton (Gossypium hirsutum L.), which leads to annual threats. The diversity of oomycete species in Alabama needs to be better understood since the last survey of oomycetes associated with cotton in Alabama was 20 years ago-before significant updates to taxonomy and improvements in identification of oomycetes using molecular tools. Our current study aimed to identify oomycetes associated with Alabama cotton seedlings, correlate diversity with soil edaphic factors, and assess virulence toward cotton seed. Thirty symptomatic cotton seedlings were collected independently from 25 fields in 2021 and 2022 2 to 4 weeks after planting. Oomycetes were isolated by plating root sections onto a semiselective medium. The internal transcribed spacer (ITS) region was sequenced to identify the resulting isolates. A seed virulence assay was conducted in vitro to verify pathogenicity, and 347 oomycete isolates were obtained representing 36 species. Northern Alabama soils had the richest oomycete communities and a greater silt and clay concentration than sandier soils in the central and southern coastal plains. Globisporangium irregulare and Phytophthora nicotianae were consistently recovered from cotton roots in both years. Globisporangium irregulare was pathogenic and recovered from all Alabama regions, whereas P. nicotianae was pathogenic but recovered primarily in areas with lower sand content in northern Alabama. Many oomycete species have not been previously reported in Alabama or the southeastern United States. Altogether, this knowledge will help facilitate effective management strategies for cotton seedling diseases caused by oomycetes in Alabama and the United States.

Evaluation of Meloidogyne Incognita and Rotylenchulus Reniformis Nematode-resistant Cotton Cultivars with Supplemental Corteva Agriscience Nematicides.

Meloidogyne incognita- and Rotylenchulus reniformis-resistant new cotton cultivars have recently become available, giving growers a new option in nematode management. The objectives of this study were: (i) to determine the yield potential of the new cultivars PHY 360 W3FE (M. incognita-resistant) and PHY 332 W3FE (R. reniformis-resistant) in nematode-infested fields and (ii) to evaluate the effects of combining the nematicides Reklemel (fluazaindolizine), Vydate C-LV (oxamyl), and the seed treatment BIOST Nematicide 100 (heat killed Burkholderia rinojenses and its non-living spent fermentation media) with resistant cotton cultivars on nematode population levels and lint yield. Field experiments in 2020 and 2021 indicated M. incognita population levels were 73% lower on PHY 360 W3FE (R) and 80% lower for R. reniformis on the PHY 332 W3FE (R) at 40 days after planting. Nematode eggs per gram of root were further reduced an average of 86% after the addition of Reklemel and Vydate C-LV when averaging both cultivars over the two years. Tests with BIOST Nematicide 100 + Reklemel + Vydate C-LV (0.56 + 2.5 L/ha) in both M. incognita and R. reniformis fields produced higher lint yields. Overall, planting PHY 360 W3FE (R) and PHY 332 W3FE (R) improved yields an average of 364 kg/ha while limiting nematode population increases. The addition of the nematicides further increased yields 152 kg/ha of the nematode-resistant cultivars.

The heterologous expression of conserved Glycine max (soybean) mitogen activated protein kinase 3 (MAPK3) paralogs suppresses Meloidogyne incognita parasitism in Gossypium hirsutum (upland cotton).

Two conserved Glycine max (soybean) mitogen activated protein kinase 3 (MAPK3) paralogs function in defense to the parasitic soybean cyst nematode Heterodera glycines. Gene Ontology analyses of RNA seq data obtained from MAPK3-1-overexpressing (OE) and MAPK3-2-OE roots compared to their control, as well as MAPK3-1-RNA interference (RNAi) and MAPK3-2-RNAi compared to their control, hierarchically orders the induced and suppressed genes, strengthening the hypothesis that their heterologous expression in Gossypium hirsutum (upland cotton) would impair parasitism by the root knot nematode (RKN) Meloidogyne incognita. MAPK3-1 expression (E) in G. hirsutum suppresses the production of M. incognita root galls, egg masses, and second stage juveniles (J2s) by 80.32%, 82.37%, and 88.21%, respectfully. Unexpectedly, egg number increases by 28.99% but J2s are inviable. MAPK3-2-E effects are identical, statistically. MAPK3-1-E and MAPK3-2-E decreases root mass 1.49-fold and 1.55-fold, respectively, as compared to the pRAP15-ccdB-E control. The reproductive factor (RF) of M. incognita for G. hirsutum roots expressing MAPK3-1-E or MAPK3-2-E decreases 60.39% and 50.46%, respectively, compared to controls. The results are consistent with upstream pathogen activated molecular pattern (PAMP) triggered immunity (PTI) and effector triggered immunity (ETI) functioning in defense to H. glycines. The experiments showcase the feasibility of employing MAPK3, through heterologous expression, to combat M. incognita parasitism, possibly overcoming impediments otherwise making G. hirsutum's defense platform deficient. MAPK homologs are identified in other important crop species for future functional analyses.

Meta-Analysis of the Field Efficacy of Seed- and Soil-Applied Nematicides on Meloidogyne incognita and Rotylenchulus reniformis Across the U.S. Cotton Belt.

Meta-analysis was used to compare yield protection and nematode suppression provided by two seed-applied and two soil-applied nematicides against Meloidogyne incognita and Rotylenchulus reniformis on cotton across 3 years and several trial locations in the U.S. Cotton Belt. Nematicides consisted of thiodicarb- and fluopyram-treated seed, aldicarb and fluopyram applied in furrow, and combinations of the seed treatments and soil-applied fluopyram. The nematicides had no effect on nematode reproduction or root infection but had a significant impact on seed cotton yield response ([Formula: see text]), with an average increase of 176 and 197 kg/ha relative to the nontreated control in M. incognita and R. reniformis infested fields, respectively. However, because of significant variation in yield protection and nematode suppression by nematicides, five or six moderator variables (cultivar resistance [M. incognita only], nematode infestation level, nematicide treatment, application method, trial location, and growing season) were used depending on nematode species. In M. incognita-infested fields, greater yield protection was observed with nematicides applied in furrow and with seed-applied + in-furrow than with solo seed-applied nematicide applications. Most notable of these in-furrow nematicides were aldicarb and fluopyram (>131 g/ha) with or without a seed-applied nematicide compared with thiodicarb. In R. reniformis-infested fields, moderator variables provided no further explanation of the variation in yield response produced by nematicides. Furthermore, moderator variables provided little explanation of the variation in nematode suppression by nematicides in M. incognita- and R. reniformis-infested fields. The limited explanation by the moderator variables on the field efficacy of nematicides in M. incognita- and R. reniformis-infested fields demonstrates the difficulty of managing these pathogens with nonfumigant nematicides across the U.S. Cotton Belt.

Additional fertilizer and nematicide combinations on upland cotton to manage Rotylenchulus reniformis and Meloidogyne incognita in Alabama.

Plant parasitic nematodes are major pests on upland cotton worldwide and in the United States. The reniform nematode, Rotylenchulus reniformis and the southern root-knot nematode Meloidogyne incognita are some of the most damaging nematodes on cotton in the United States. Current management strategies focus on reducing nematode populations with nematicides. The objective of this research was to integrate additional fertilizer and nematicide combinations into current practices to establish economical nematode management strategies while promoting cotton yield and profit. Microplot and field trials were run to evaluate fertilizer and nematicide combinations applied at the pinhead square (PHS) and first bloom (FB) plant growth stages to reduce nematode population density and promote plant growth and yield. Cost efficiency was evaluated based on profit from lint yields and chemical input costs. Data combined from 2019 and 2020 suggested a nematicide seed treatment (ST) ST + (NH4)2SO4 + Vydate® C-LV + Max-In® Sulfur was the most effective in increasing seed cotton yields in the R. reniformis microplot trials. In R. reniformis field trials, a nematicide ST + (NH4)2SO4 + Vydate® C-LV at PHS supported the largest lint yield and profit per hectare at $1176. In M. incognita field trials, a nematicide ST + 28-0-0-5 + Vydate® C-LV + Max-In® Sulfur at PHS and FB supported the largest lint yields and profit per hectare at $784. These results suggest that combinations utilizing fertilizers and nematicides applied together across the season in addition to current fertility management show potential to promote yield and profit in R. reniformis and M. incognita infested cotton fields.

Evaluation of a new chemical nematicide, fluazaindolizine (ReklemelTM active), for plant-parasitic nematode management in bermudagrass.

Plant-parasitic nematodes are a major pest of turfgrass in the United States, yet there are few options for successful management. Most current management strategies rely on the use of a limited number of chemical nematicides, so finding a new management option for nematode suppression would be extremely valuable for turfgrass managers. The aim of this study is to evaluate a new nematicide, fluazaindolizine (Reklemel™ active), for its ability to reduce plant-parasitic nematode population density and improve turfgrass quality. Separate research trials were conducted on bermudagrass infested with Belonolaimus longicaudatus and Meloidogyne incognita in greenhouse, microplot, and field settings over 2018 and 2019. Both greenhouse evaluations demonstrated multiple rates of fluazaindolizine reduced B. longicaudatus population density, and one of the two M. incognita trials showed multiple rates of fluazaindolizine reduced nematode population density. Fluazaindolizine was also effective at reducing population density of both B. longicaudatus and M. incognita in microplot settings for both 2018 and 2019, and a significant improvement in turf quality was observed for both visual turfgrass ratings and NDVI. Field trials demonstrated a significant reduction for both B. longicaudatus and M. incognita population density by multiple rates of fluazaindolizine, but no significant differences in turf quality ratings were observed. Overall, fluazaindolizine shows promise as a chemical nematicide for plant-parasitic nematode management on turfgrass.

Enhanced biological control of root-knot nematode, Meloidogyne incognita, by combined inoculation of cotton or soybean seeds with a plant growth-promoting rhizobacterium and pectin-rich orange peel.

LC-MS analysis of plant growth-promoting rhizobacterium (PGPR) Bacillus velezensis AP203 supernatants indicated the presence of nematode-inhibiting compounds that increased in abundance when B. velezensis AP203 was grown on orange peel. Meloidogyne incognita J2 were incubated with B. velezensis AP203 spores and orange peel, spores alone, orange peel alone, or with a non-inoculated control, and the combination of B. velezensis AP203 with orange peel resulted in 94% mortality of M. incognita juveniles (p ≤ 0.05). The J2 mortality rate for B. velezensis alone was 53%, compared to 59% mortality with orange peel, and the non-inoculated control exhibited 7% mortality. When tested on soybeans raised in a greenhouse, it was observed that when grown in the presence of orange peel, B. velezensis AP203 culture broth, cell suspension or supernatant reduced the numbers of M. incognita eggs per g of root at 45 days after planting (DAP) compared to inoculated controls in soybean and cotton (p ≤ 0.05). Likewise, soybean root length and fresh root weight significantly increased after inoculation with B. velezensis AP203 amended with orange peel. In cotton, shoot and root length significantly increased after inoculation with cell pellets of B. velezensis AP203 amended with orange peel compared to the M. incognita inoculated control. These data indicate that B. velezensis AP203 responds to growth on pectin-rich orange peel by production of biologically active secondary metabolites that can promote plant growth and inhibit root-knot nematode viability.

First report of Meloidogyne incognita infecting Cannabis sativa in Alabama.

Hemp (Cannabis sativa L.) is a new crop in Alabama. In 2019, symptomatic plants with stunted growth, poor root development, and numerous galls were observed in hemp plants grown in Geneva County, AL. After harvest, soil samples were collected from areas with the symptomatic plants and root-knot nematode (Meloidogyne spp.) were found in the soil. Based on morphological features and the polymerase chain reactions using species-specific primers, it was identified as Meloidogyne incognita. Further, a host differential test in a greenhouse assay confirmed it to be M. incognita race 3. The pathogenicity of the nematode to the hemp was confirmed by a modified version of Koch's postulates. To our knowledge, this is the first report of M. incognita infecting Cannabis sativa in Alabama.

Plant health evaluations of Belonolaimus longicaudatus and Meloidogyne incognita colonized bermudagrass using remote sensing.

The objective of this study was to evaluate the ability of an unmanned aerial system (UAS) equipped with a multispectral sensor to track plant health in the presence of plant-parasitic nematodes in conjunction with nematicide applications. Four nematicides were evaluated for their ability to suppress Belonolaimus longicaudatus and Meloidogyne incognita in microplots, and three nematicides were evaluated on a golf course for their ability to suppress multiple plant-parasitic nematode genera. Visual ratings, Normalized Difference Vegetation Index (NDVI), and Normalized Difference RedEdge Index (NDRE) were reported throughout the trial to assess plant health. B. longicaudatus and M. incognita population density was significantly lowered by nematicide treatments in microplots and correlated with visual ratings, NDVI, and NDRE plant health ratings. On the golf course, all nematicides reduced total plant-parasitic nematode population density at 28, 56, and 84 days after treatment (DAT). Visual turf quality ratings, NDVI, and NDRE were positively correlated with lower nematode population density in the majority of evaluation dates. In the microplot and golf course settings, the parameters evaluated for plant health were correlated with plant-parasitic nematode population density: visual ratings, NDVI, and NDRE improved as nematode population density declined. These results show that remote sensing has the potential to be a beneficial tool for assessing plant-parasitic nematode infected bermudagrass.

Validation of the Chemotaxis of Plant Parasitic Nematodes Toward Host Root Exudates.

Plant parasitic nematodes (PPN) are microscopic soil herbivores that cause damage to many economic crops. For the last century, it has been proposed that chemotaxis is the primary means by which PPN locate host plant roots. The identities and modes of action of chemoattractants that deliver host-specific messages to PPN, however, are still elusive. In this study, a unique multidimensional agar-based motility assay was developed to assess the impacts of root exudates on the short-range motility and orientation of PPN. Three PPN (Rotylenchulus reniformis, Meloidogyne incognita and Heterodera glycines) and root exudates from their respective host and non-host plants (cotton, soybean, and peanut) were used to validate the assay. As predicted, R. reniformis and M. incognita were attracted to root exudates of cotton and soybean (hosts), but not to the exudates of peanut (non-host). Likewise, H. glycines was attracted to soybean (host) root exudates. These results underpinned the intrinsic roles of root exudates in conveying the host specificity of PPN. In particular, PPN selectively identified and targeted to hydrophilic, but not hydrophobic, fractions of root exudates, indicating that groundwater should be an effective matrix for chemotaxis associated with PPN and their host plant interactions.

Biological Control of Meloidogyne incognita by Spore-forming Plant Growth-promoting Rhizobacteria on Cotton.

In the past decade, increased attention has been placed on biological control of plant-parasitic nematodes using various fungi and bacteria. The objectives of this study were to evaluate the potential of 662 plant growth-promoting rhizobacteria (PGPR) strains for mortality to Meloidogyne incognita J2 in vitro and for nematode management in greenhouse, microplot, and field trials. Results indicated that the mortality of M. incognita J2 by the PGPR strains ranged from 0 to 100% with an average of 39%. Among the PGPR strains examined, 212 of 662 strains (or 33%) caused significantly greater mortality percent of M. incognita J2 than the untreated control. Bacillus was the major genus initiating a greater mortality percentage when compared with the other genera. In subsequent trials, B. velezensis strain Bve2 reduced M. incognita eggs per gram of cotton root in the greenhouse trials at 45 days after planting (DAP) similarly to the commercial standards Abamectin and Clothianidin plus B. firmus I-1582. Bacillus mojavensis strain Bmo3, B. velezensis strain Bve2, B. subtilis subsp. subtilis strain Bsssu3, and the Mixture 2 (Abamectin + Bve2 + B. altitudinis strain Bal13) suppressed M. incognita eggs per gram of root in the microplot at 45 DAP. Bacillus velezensis strains Bve2 and Bve12 also increased seed-cotton yield in the microplot and field trials. Overall, results indicate that B. velezensis strains Bve2 and Bve12, B. mojavensis strain Bmo3, and Mixture 2 have potential to reduce M. incognita population density and to enhance growth of cotton when applied as in-furrow sprays at planting.

Integrated signaling networks in plant responses to sedentary endoparasitic nematodes: a perspective.

Sedentary plant endoparasitic nematodes can cause detrimental yield losses in crop plants making the study of detailed cellular, molecular, and whole plant responses to them a subject of importance. In response to invading nematodes and nematode-secreted effectors, plant susceptibility/resistance is mainly determined by the coordination of different signaling pathways including specific plant resistance genes or proteins, plant hormone synthesis and signaling pathways, as well as reactive oxygen signals that are generated in response to nematode attack. Crosstalk between various nematode resistance-related elements can be seen as an integrated signaling network regulated by transcription factors and small RNAs at the transcriptional, posttranscriptional, and/or translational levels. Ultimately, the outcome of this highly controlled signaling network determines the host plant susceptibility/resistance to nematodes.

Nematicides enhance growth and yield of rotylenchulus reniformis resistant cotton genotypes.

Rotylenchulus reniformis resistant LONREN-1×FM966 breeding lines developed at Auburn University have demonstrated that the nematode resistance is accompanied by severe stunting, limited growth, and low yields. The objectives of this study were to evaluate the effects of applying nematicides to selected LONREN breeding lines on R. reniformis nematode populations, plant stunting, and yield. Four resistant breeding lines from the LONREN-1×FM966 cross, one susceptible line from the LONREN-1×FM966 cross, as well as LONREN-1, BARBREN-713, and the susceptible cultivar DP393 were evaluated with and without nematicides in the presence of R. reniformis. In the greenhouse, nematicides increased plant height across all genotypes compared with no nematicide. Rotylenchulus reniformis populations were 50% lower in the resistant lines compared with the susceptible lines at 45 days after planting (DAP). In microplot and field trials, the phenotypic stunting of all genotypes was reduced by aldicarb with increases in plant heights at 30 and 75 DAP. Increases in yields were evident across all genotypes treated with aldicarb. In all three trial environments, BARBREN-713 outperformed the LONREN-derived lines as well as 'DP393' in seed cotton yields, while having significantly lower R. reniformis egg densities than the susceptible genotypes.

Glycine max polygalacturonase inhibiting protein 11 (GmPGIP11) functions in the root to suppress Heterodera glycines parasitism.

Pathogen-secreted polygalacturonases (PGs) alter plant cell wall structure by cleaving the α-(1 â†’ 4) linkages between D-galacturonic acid residues in homogalacturonan (HG), macerating the cell wall, facilitating infection. Plant PG inhibiting proteins (PGIPs) disengage pathogen PGs, impairing infection. The soybean cyst nematode, Heterodera glycines, obligate root parasite produces secretions, generating a multinucleate nurse cell called a syncytium, a byproduct of the merged cytoplasm of 200-250 root cells, occurring through cell wall maceration. The common cytoplasmic pool, surrounded by an intact plasma membrane, provides a source from which H. glycines derives nourishment but without killing the parasitized cell during a susceptible reaction. The syncytium is also the site of a naturally-occurring defense response that happens in specific G. max genotypes. Transcriptomic analyses of RNA isolated from the syncytium undergoing the process of defense have identified that one of the 11 G. max PGIPs, GmPGIP11, is expressed during defense. Functional transgenic analyses show roots undergoing GmPGIP11 overexpression (OE) experience an increase in its relative transcript abundance (RTA) as compared to the ribosomal protein 21 (GmRPS21) control, leading to a decrease in H. glycines parasitism as compared to the overexpression control. The GmPGIP11 undergoing RNAi experiences a decrease in its RTA as compared to the GmRPS21 control with transgenic roots experiencing an increase in H. glycines parasitism as compared to the RNAi control. Pathogen associated molecular pattern (PAMP) triggered immunity (PTI) and effector triggered immunity (ETI) components are shown to influence GmPGIP11 expression while numerous agricultural crops are shown to have homologs.

Biocontrol of the Reniform Nematode by Bacillus firmus GB-126 and Paecilomyces lilacinus 251 on Cotton.

Due to increased restrictions on the use of chemical nematicides, alternative nematode management strategies, including biocontrol, are needed. The objectives of this study were to evaluate the potential of Bacillus firmus GB-126 and Paecilomyces lilacinus 251 in commercial formulations applied separately or concomitantly to manage Rotylenchulus reniformis in cotton grown under greenhouse, microplot, and field conditions. In the greenhouse, seed treated with B. firmus (1.4 × 107 CFU/seed), an application of P. lilacinus (0.3% vol/vol of water), or the combination of B. firmus and P. lilacinus reduced the number of females, eggs, and vermiforms of R. reniformis (P ≤ 0.02) and increased populations of free-living nematodes (P ≤ 0.01). In microplots and field conditions, populations of R. reniformis vermiforms decreased when exposed to B. firmus and P. lilacinus biocontrol agents at midseason (P ≤ 0.04). Furthermore, stem diameter and free-living nematode numbers increased (P ≤ 0.01) with the combination of B. firmus and P. lilacinus. In the field, numbers of females, eggs, and vermiform life stages at the end of the growing season decreased in the presence of the biocontrol agents applied individually or concomitantly (P ≤ 0.01). Cotton yields from the application of B. firmus GB-126 and P. lilacinus 251 were similar to those from aldicarb, the chemical nematicide standard.

The Effect of Soil Texture and Irrigation on Rotylenchulus reniformis and Cotton.

The reniform nematode, Rotylenchulus reniformis, is the most damaging nematode pathogen of cotton in Alabama. Soil texture is currently being explored as a basis for the development of economic thresholds and management zones within a field. Trials to determine the reproductive potential of R. reniformis as influenced by soil type were conducted in microplot and greenhouse settings during 2008 to 2010. Population density of R. reniformis was significantly influenced by soil texture and exhibited a general decrease with increasing median soil particle size (MSPS). As the MSPS of a soil increased from 0.04 mm in clay soil to > 0.30 mm in very fine sandy loam and sandy loam soils, R. reniformis numbers decreased. The R. reniformis population densities on all soil types were also greater with irrigation. Early season cotton development was significantly affected by increasing R. reniformis Pi, with plant shoot-weight-to-root-weight ratios increasing at low R. reniformis Pi and declining with increasing R. reniformis Pi. Plant height was increased by irrigation throughout the growing season. The results suggests that R. reniformis will reach higher population densities in soils with smaller MSPS; however, the reduction in yield or plant growth very well may be no greater than in a soil that is less preferential to the nematode.

Evaluation of the mechanism of action of Bacillus spp. to manage Meloidogyne incognita with split root assay, RT-qPCR and qPCR.

The goal of this research is to determine the mechanism of action of two Bacillus spp. that can manage Meloidogyne incognita population density in cotton. The overall objectives are 1) determine the efficacy and direct antagonistic capabilities of the Bacillus spp. and 2) determine the systemic capabilities of the Bacillus spp. The greenhouse in planta assay indicated B. amyloliquefaciens QST713 and B. firmus I-1582 could manage M. incognita similarly to the chemical standard fluopyram. An in vitro assay determined that B. firmus I-1582 and its extracted metabolites were able to directly manage M. incognita second stage juveniles by increasing mortality rate above 75%. A split root assay, used to determine systemic capabilities of the bacteria, indicated B. amyloliquefaciens QST713 and B. firmus I-1582 could indirectly decrease the nematode population density. Another species, B. mojavensis strain 2, also demonstrated systemic capabilities but was not a successful biological control agent because it supported a high population density in greenhouse in planta assay and in the split root assay. A RT-qPCR assay was used to confirm any systemic activity observed in the split root assay. At 24 hours both B. amyloliquefaciens QST713 and B. firmus I-1582 upregulated one gene involved in the initial stages of JA synthesis pathway but not another gene involved in the later stages of JA synthesis. These results point to a JA intermediate molecule, most likely OPDA, stimulated by the bacteria rather than JA in a short-term systemic response. After 1 week, the Bacillus spp. stimulated a SA-responsive defense related gene. The long-term systemic response to the Bacillus spp. indicates salicylic acid also plays a role in defense conferred by these bacteria. The final assay was a qPCR to determine the concentration of the bacteria on the cotton roots after 24 days. Bacillus amyloliquefaciens QST713 and B. firmus I-43 1582 were able to colonize the root successfully, with the concentration after 24 days not significantly differing from the concentration at inoculation. This study identifies two bacteria that work via systemic resistance and will help aid in implementing these species in an integrated management system.

Diversity and temporal distribution of Fusarium oxysporum f. sp. vasinfectum races and genotypes as influenced by Gossypium cultivar.

This study assess the population diversity and temporal variability of caused by Fusarium oxysporum f. sp. vasinfectum (FOV) races/genotypes infecting cotton cultivars with either FOV or Meloidogyne incognita resistance. All plants sampled demonstrated typical symptoms of FOV including wilting, chlorosis and necrosis of the leaves, and discoloration of the vascular tissue in the stem. A diverse population of FOV was characterized. Eight races/genotypes of FOV were collected throughout the three site years. FOV race 1 was the most predominant in all tests (AUDPC=101.1); statistically higher numbers of isolates from LA-108 (AUDPC=59.9), race 8 (AUDPC=47.5), and race 2 (AUDPC=38.6) were also found compared to other races and genotypes collected. FOV race 1, race 2, race 8, and 108 were the most virulent races identified. The genotypes MDS-12, LA-110, and LA-127/140 were found in all tests but at a low incidence, and LA-112 was only found in trace amounts. MDS-12, LA-110, LA-112, and LA-127/140 produced less disease pressure. FOV race 4 which is highly virulent and present in California and Texas was not found in Alabama. A positive correlation was observed between the accumulation of growing degree days and FOV race 1, race 2, race 8, LA-108, and LA-110. Later symptom expression influenced by seasonal heat partially mitigates damage allowing cotton to produce bolls though they may be reduced in number and lint quality. Plant resistance to the FOV as expressed in these cultivars appears to provide better protection than M. incognita resistance. PhytoGen 72, which is resistant to FOV races/genotypes had low levels of FOV infection even though it sustained a high level of M. incognita root population density. The M. incognita resistant cultivars Deltapine 1558NR B2RF and PhytoGen 480 W3FE supported a lower nematode population density, however, FOV disease incidence was not reduced. FOV races/genotypes did not vary significantly between the nematode resistant and nematode susceptible cultivars.

Glycine max Homologs of DOESN'T MAKE INFECTIONS 1, 2, and 3 Function to Impair Heterodera glycines Parasitism While Also Regulating Mitogen Activated Protein Kinase Expression.

Glycine max root cells developing into syncytia through the parasitic activities of the pathogenic nematode Heterodera glycines underwent isolation by laser microdissection (LM). Microarray analyses have identified the expression of a G. max DOESN'T MAKE INFECTIONS3 (DMI3) homolog in syncytia undergoing parasitism but during a defense response. DMI3 encodes part of the common symbiosis pathway (CSP) involving DMI1, DMI2, and other CSP genes. The identified DMI gene expression, and symbiosis role, suggests the possible existence of commonalities between symbiosis and defense. G. max has 3 DMI1, 12 DMI2, and 2 DMI3 paralogs. LM-assisted gene expression experiments of isolated syncytia under further examination here show G. max DMI1-3, DMI2-7, and DMI3-2 expression occurring during the defense response in the H. glycines-resistant genotypes G.max [Peking/PI548402] and G.max [PI88788] indicating a broad and consistent level of expression of the genes. Transgenic overexpression (OE) of G. max DMI1-3, DMI2-7, and DMI3-2 impairs H. glycines parasitism. RNA interference (RNAi) of G. max DMI1-3, DMI2-7, and DMI3-2 increases H. glycines parasitism. The combined opposite outcomes reveal a defense function for these genes. Prior functional transgenic analyses of the 32-member G. max mitogen activated protein kinase (MAPK) gene family has determined that 9 of them act in the defense response to H. glycines parasitism, referred to as defense MAPKs. RNA-seq analyses of root RNA isolated from the 9 G. max defense MAPKs undergoing OE or RNAi reveal they alter the relative transcript abundances (RTAs) of specific DMI1, DMI2, and DMI3 paralogs. In contrast, transgenically-manipulated DMI1-3, DMI2-7, and DMI3-2 expression influences MAPK3-1 and MAPK3-2 RTAs under certain circumstances. The results show G. max homologs of the CSP, and defense pathway are linked, apparently involving co-regulated gene expression.