土壤镰孢菌Real-Time QPCR定量方法的建立及应用

基于镰孢菌ITS序列,设计一对应用于实时荧光定量PCR(Real-Time QPCR)反应的镰孢菌属特异性引物TS和TR,并建立了相应的Real-Time QPCR体系。应用该反应体系,绝对定量了无肥(NF)、化肥(NP)以及化肥配施有机肥(NPM)等3种施肥措施下大豆田土壤镰孢菌DNA含量。结果表明:引物TS和TR对镰孢菌属真菌有较好的特异性;Real-Time QPCR反应的扩增曲线中各梯度浓度标准品的循环阈值(Ct值)间隔均匀,熔点曲线无杂峰,标准曲线的相关系数R2=0.993,斜率为-0.2927;在大豆生育时期的苗期,NF、NP及NPM措施下土壤镰孢菌总DNA每克干土中含量分别为18.33、44.61和140.83 pg,且NPM措施含量极显著高于NF及NP措施(P<0.01)。

Rapid Detection of Wheat Blast Pathogen Magnaporthe oryzae Triticum Pathotype Using Genome-Specific Primers and Cas12a-mediated Technology

Wheat blast,caused by the fungus Magnaporthe oryzae Triticum(MoT)pathotype,is a devastating disease persistent in South America and Bangladesh.Since MoT generally fails to cause visual symptoms in wheat until the heading stage when the infection would have advanced,disease control by fungicide application solely based on the detection of visual symptoms is ineffective.To develop an accurate and sensitive method to detect MoT at the seedling and vegetative stages for disease control,we sequenced the genomes of two MoT isolates from Brazil and identified two DNA fragments,MoT-6098 and MoT-6099,that are present in the MoT genome but not in the genome of the rice-infecting Magnaporthe oryzae Oryzae(MoO)pathotype.Using polymerase chain reaction(PCR),we confirmed the specificity of the two markers in 53 MoT and MoO isolates from South America and Bangladesh.To test the efficiency of the two markers,we first established a loop-mediated isothermal amplification(LAMP)method to detect MoT at isothermal conditions,without the use of a PCR machine.Following this,we used the Cas12a protein and guide RNAs(gRNAs)to target the MoT-6098 and MoT-6099 sequences.The activated Cas12a showed indiscriminate single-stranded deoxyribonuclease(ssDNase)activity.We then combined targetdependent Cas12a ssDNase activation with recombinase polymerase amplification(RPA)and nucleic acid lateral flow immunoassay(NALFIA)to develop a method that accurately,sensitively,and cost-effectively detects MoT-specific DNA sequences in infected wheat plants.This novel technique can be easily adapted for the rapid detection of wheat blast and other important plant diseases in the field.

Evaluation of maize inbred lines for resistance to pre-harvest aflatoxin and fumonisin contamination in the field

Two important mycotoxins, aflatoxin and fumonisin, are among the most potent naturally occurring carcinogens, contaminating maize(Zea mays) and affecting crop yield and quality.Resistance of maize to pre-harvest mycotoxin contamination, specifically aflatoxin produced by Aspergillus flavus and fumonisin produced by Fusarium verticillioides, is a goal in breeding programs that screen for these important traits with the aim of developing resistant commercial hybrids. We conducted two years of field evaluations on 87 inbred lines originating primarily in China and Mexico and not previously screened for resistance.The objectives of our study were to identify resistant germplasm for breeding purposes and to examine possible relationships between resistances to the two mycotoxins. Aflatoxin and fumonisin were present in samples harvested from all lines in both years.Concentrations of total aflatoxin ranged from 52.00 ± 20.00 to 1524.00 ± 396.00 μg kg^(-1),while those of fumonisin ranged from 0.60 ± 0.06 to 124.00 ± 19.50 mg kg^(-1). The inbred lines TUN15, TUN61, TUN37, CY2, and TUN49 showed the lowest aflatoxin accumulation and CN1, GT601, TUN09, TUN61, and MP717 the lowest fumonisin accumulation. TUN61 showed the lowest accumulation of both mycotoxins. This study confirmed previous observations that high levels of aflatoxin can coexist with fumonisin, with 55 maize lines showing a positive correlation coefficient between the concentrations of aflatoxin and fumonisin and 32 lines showing a negative correlation coefficient. These selected lines,particularly TUN61, may provide sources of resistance to mycotoxin contamination in breeding programs. However, the mechanism of resistance in this germplasm remains to be identified. Future research should also address factors that influence the fungus–plant interaction, such as herbivory and environmental stress.

接种茄病镰刀菌(Fusarium solani f. sp. glycines)对不同基因型大豆植株和须根的影响(英文)

摘要：茄病镰刀菌（Fusarium solani f．sp．glydne）是一种土生细菌，通过侵染大豆根系引发猝死综合症。利用温室盆栽试验和须根培养试验研究了接种茄孢镰刀菌对13个不同基因型大豆的影响。结果表明：接种后所有盆栽大豆主根都有明显深褐色的侵染病斑；移植后21d测定了盆栽植株叶部发病程度，Peking表现最为严重，然后依次为Spencer，Ripley，P3981，Williams82，Essex，Forrest，Iroquois，PI520733，Hartwig，PI567650B，Jack，和PI567374。叶部发病程度与冠高（r=-0．422，P=0．0018）、冠重（r=-0．857，P〈0．0001）和根重（r=-0．732，P〈0．0001）呈显著负相关。主根病斑长度与叶部发病程度没有相关性，表明大豆对病原菌的抗性不能仅通过根系得到充分控制。对培养的大豆须根接种茄病镰刀菌菌丝体10d后，不同基因型大豆的菌落直径的变化范围为17—40mm，差异显著（P=0．05），其中Spencer和Peking须根上的菌落直径显著（P=0．05）大于PI567374和PI520733。对Spencer和PI567374的须根接种10灿茄病镰刀菌常量成分悬浮液，10d后菌落直径分别为50和38mm，差异显著（P=0．05）。通常，不同基因型大豆间茄病镰刀菌在培养须根上的生长与整株的症状间有一定的相关性，但不总是这样，这是因为即使根系对毒素产生抗性来减少叶部病害症状，但并不是所有的大豆都表现出明显的根系抗性。

Bioherbicidal Efficacy of a Myrothecium verrucaria-Sector on Several Plant Species

Comparative studies were conducted on mycelial preparations of the bioherbicide, Myrothecium verrucaria (MV) strain IMI 361690 and a recently discovered sector (MV-Sector BSH) of this fungus. The whitish sector was discovered, isolated, grown in pure culture on PDA and found to be a stable, non-spore producing mutant when cultured over several months under conditions that cause circadian sporulation during growth of its MV parent. Application of MV and MV-Sector BSH mycelial preparations to intact plants (hemp sesbania and sicklepod) and leaf discs (kudzu and glyphosate-resistant Palmer amaranth) showed that the sector efficacy was generally equal to, or slightly lower than MV. Bioassays of MV and this sector on seed germination and early growth of sicklepod and hemp sesbania seeds demonstrated that hemp sesbania seeds were slightly more sensitive to the fungus than sicklepod seeds and that the sector bioherbicidal activity was slightly less than that of MV. SDS-PAGE protein profiles of cellular extracts of MV and the sector and their respective culture supernatants showed several differences with respect to quantity and number of certain protein bands. Overall results showed that the isolate was a non-spore producing mutant with phytotoxicity to several weeds (including weeds tolerant or resistant to glyphosate), and that the phytotoxic effects were generally equivalent to those caused by MV treatment. Results of this first report of a non-sporulating MV mutant that suggest additional studies on protein analysis, and an extended weed host range under greenhouse and field conditions are needed in order to further evaluate its possible bioherbicidal potential.

A comparison of methods used to determine the oleic/linoleic acid ratio in cultivated peanut (Arachis hypogaea L.)

There is an increasing demand in the peanut industry for high oleic peanuts and also for the incorporation of the high oleate trait into newly released varieties. Early generation screening of breeding lines for high oleic acid content greatly increases the efficiency of developing new peanut varieties. The objective of this study was to compare the accuracy of methods used to classify individual peanut seed as high oleic or not high oleic. Results from capillary electrophoresis (CE), two variations of near-infrared reflectance spectroscopy (NIRS), and real-time polymerase chain reaction (RT-PCR) genotyping, were compared with the traditionally accepted reference standard results from gas chromatography (GC). Three hundred and seventy-four (374) seeds, spanning twenty-three (23) genotypes and all four peanut market-types (runner, Spanish, Valencia and Virginia), were individually tested by each method. Percent accuracy levels for rating individual seed as high oleic (H) ranged from 97.4% (NIRS) to 99.5% (CE). All of the methods examined in this study carry only a minor risk for miss-classification (loss of material) and are suitable for use by peanut breeding programs in early generation breeding line screening.

Evaluation of phosphorus and nitrogen balances as an indicator for the impact of agriculture on environment: A comparison of a case study from Poland and Mississippi US

The objective of this research was to quantify the changes of nitrogen (N) and phosphorus (P) balances in Poland and Mississippi (MS), USA. Nutrient balances were calculated as difference between input and output in the agricultural system according to Organisation for Economic Cooperation and Development (OECD) methodology. A positive nutrient balance means that a potential environmental problem may result from that nutrient;a negative nutrient balance means there is a potential yield loss. The N and P soil surface balances for Poland and MS were calculated for the year 1998 through 2008. The results showed that both MS and Poland had positive N and P balances, indicating that there was a surplus of N and P. The average balance for N was 48 kg·ha-1 in Poland and 102 kg·ha-1 in MS. For P, it was 3 kg·ha-1 in Poland and 19 kg P kg·ha-1 in MS per cultivated area. This research demonstrated that the nutrient balance of N or P depended on the efficient use of each nutrient and type and source of fertilizer used. This research is significant for N and P fertilizer management and their impact on agriculture production and environment health.

Biological Control of the Weed Sesbania exaltata Using a Microsclerotia Formulation of the Bioherbicide <i>Colletotrichum truncatum</i>

Colletotrichum truncatum, grown on rice grain (3 to 4 weeks, 22°C to 24°C) produced a fungus-infested rice mixture of microsclerotia and conidia (spores) in a ratio of ~9:1, respectively. Greenhouse tests of this formulation (0.4 to 50 mg finely-ground fungus-rice product) which applied pre-emergence to 5 cm2 of soil surface, caused 22% to 96% hemp sesbania plant mortality, after 14 days. Post-emergence treatment (fungus-rice aqueous formulation;2.4 × 105 microsclerotia ml-1, 30% unrefined corn oil and 0.2% Silwet L-77 surfactant) of weeds surviving the pre-emergence application, resulted in 93% mortality, after 14 days. Based on greenhouse results, field tests were undertaken: 1) pre-emergence treatment (fungus-rice formulation at 2.4 × 105 microsclerotia cm-2), 2) post-emergence (fungus-rice product in 30% unrefined corn oil, 0.2% Silwet) only treatment, applied 15 days after planting and 3) pre-emergence treatment followed by post-emergence treatment (fungus-rice product in 30% unrefined corn oil, 0.2% Silwet) applied 15 days after planting to surviving weeds. Control treatments were: 1) autoclaved rice product sans fungus, 2) unrefined corn oil (30% unrefined corn oil, 0.2% Silwet in water) and 3) untreated plants. Planting dates were: early season (April-May), early-mid season (June-July), late-mid season (July-August), and late season (September-October). Weed mortality was recorded at 15 days for the pre-plus post-treatment, and at 30 days after planting for the pre-emergence only and the post-treatment only. The early season, pre-emergence treatment caused 67% hemp sesbania mortality (3-yr average) within 15 days and the post-emergence treatment caused 91% mortality of the surviving weeds. In the late-mid-season, pre-emergence treatment caused minimal (<5%) mortality at 15 days, but mortality in the post-emergence treatment was >80%. Results suggest that seasonal environmental conditions are important in the efficacy of this C. truncatum-rice product formulation when applied pre- or post-emergence to this onerous weed.

Extending the Shelf-Life of <i>Myrothecium verrucaria</i>, a Bioherbicide

The shelf-life of a bioherbicide product is an important factor with regard to its commercial potential. The bioherbicidal efficacy of freshly fermented Myrothecium verrucaria (strain IMI 368023) (MV) mycelia formulations and MV mycelia preparations that had been freeze-dried and then stored at -20&deg;C for 8 years was compared. Two concentrations of each formulation (1.0x and 0.5x) were tested, utilizing bioassays on seedlings of the weed, hemp sesbania (Sesbania exaltata) under greenhouse conditions or in darkness utilizing hydroponically grown seedlings. Freeze drying of freshly prepared MV mycelium produced a light, brownish-colored powder. Efficacy tests of this reconstituted 8-year-old dried material showed that some bioherbicidal activity was lost during long-term storage, i.e., ~20% and ~60% seedling dry weight reduction at the 1.0x and 0.5x rate, respectively. Although plant mortality was greater in the fresh mycelial preparations treatments versus the freeze-dried and stored samples at all time points in the time-course, the stored material still caused >80% mortality, 15 days after treatment. Comparative disease progression ratings also showed a similar trend. Overall results show that freeze-drying MV is a useful method to reduce the bulk and cumbersomeness of storing heavy liquid fermentation product, while retaining bioherbicidal activity. These findings increase the utility of this bioherbicide and offer the potential to use the dried material in soil treatments or in a more concentrated form than attainable via the fermented product.

Interactions of Auxinic Compounds on Ca2+ Signaling and Root Growth in <i>Arabidopsis thaliana</i>

Auxinic-like compounds have been widely used as weed control agents. Over the years, the modes of action of auxinic herbicides have been elucidated, but most studies thus far have focused on their effects on later stages of plant growth. Here, we show that some select auxins and auxiniclike herbicides trigger a rapid elevation in root cytosolic calcium levels within seconds of application. Arabidopsis thaliana plants expressing the Yellow-Cameleon (YC) 3.60 calcium reporter were treated with indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), 1-naphthalene acetic acid (NAA), and two synthetic herbicides, 2,4-dichlorophenoxyacetic acid (2,4-D) and mecoprop [2-(4-chloro- 2-methylphenoxy) propanoic acid], followed by monitoring cytosolic calcium changes over a 10 minute time course. Seconds after application of compounds to roots, the Ca2+ signaling-mediated pathway was triggered, initiating the plant response to these compounds as monitored and recorded using Fluorescence Resonance Energy Transfer (FRET)-sensitized emission imaging. Each compound elicited a specific and unique cytosolic calcium signature. Also primary root development and elongation was greatly reduced or altered when exposed at two concentrations (0.10 and 1.0 μM) of each compound. Within 20 to 25 min after triggering of the Ca2+ signal, root growth inhibition could be detected. We speculate that differences in calcium signature among the tested auxins and auxinic herbicides might correlate with their variation and potency with regard to root growth inhibition.

Characterization and in Plant Detection of Bacteria That Cause Bacterial Panicle Blight of Rice

Burkholderia glumae presumably induces a grain rot symptom of rice that is threatening to rice production in most rice producing states of the USA. The present study was to identify the causal agent of bacteria panicle blight (BPB), virulence based on hypersensitive reactions and distribution of the pathogen within a plant. 178 rice panicles samples were analyzed with semi-selective media (CCNT), polymerase chain reaction (PCR) with bacterial DNA gyrase (gyrB) specific markers, and hypersensitive reactions on tobacco leaves. A total of 73 samples out of 178 produced a yellow bacterial colony with similar morphology on CCNT medium suggesting they were bacterial panicle diseases. However, with PCR reactions we only determined that 45 of 73 were due to B. glumae, and the causal agent for the remaining samples was undetermined. Within the 45 samples, 31 highly, 6 moderately, and 5 weakly virulent isolates were grouped based on lesion sizes of the hypersensitive reactions. Pathogenicity variability among the 45 B. glumae detected suggests that different degrees of pathogenicity exist. To determine the existence of bacteria in different plant tissues, naturally infected plant parts were examined with CCNT media and PCR analysis. B. glumae was again isolated from seeds followed by stems and sheaths from light yellow pigmented CCNT media. In contrast, roots and leaves show no visible yellow pigment on CCNT. Consistent PCR products were produced from the stem, sheath, and seed, but not from the root and leaves. These findings suggest that B. glumae is distributed in the stem, sheath, and seed, and not in the leaf and root. Together this study demonstrated the usefulness of artificial culture media, tobacco reactions, and DNA test with PCR for characterization of BPB, and distribution of bacteria in plants. These findings will help to understand the mechanism of bacteria translocation in plants.

Effects of <i>Myrothecium verrucaria</i>on Ultrastructural Integrity of Kudzu (<i>Pueraria montana var. lobata</i>) and Phytotoxin Implications

The fungus Myrothecium verrucaria (Alb. & Schwein.) (MV), originally isolated from diseased sicklepod (Senna obtusifolia L.), has bioherbicial activity against kudzu and several other weeds when applied with low concentrations of the surfactant Silwet L-77. To more fully understand the initial events of MV infection or disease progression, and to improve knowledge related to its mechanism of action, the effects of MV and its product (roridin A) on kudzu seedlings were examined at the ultrastructural level. Ultrastructural analysis of MV effects on kudzu seedlings revealed a rapid (~1 h after treatment) detachment of the protoplast from the cell wall and plasmodesmata appeared to be broken off and retained in the wall. These symptoms occurred well in advance of the appearance of any fungal growth structures. Some fungal growth was observed after severe tissue degeneration (24 to 48 h after treatment), but this occurred primarily at the extra-cellular location with respect to the kudzu tissues. Kudzu seedlings treated with roridin A, a trichothecene produced by the fungus, exhibited some symptoms similar to those induced by the fungus applied in spore formulations with surfactant. The overall results are the first to report the ultrastructural effects of this bioherbicide on plants and suggest that penetration of a phytotoxic substance(s) in the fungal formulation was facilitated by the surfactant, and that roridin A exerts phytotoxicity toward kudzu.

Biological Control Potential of <i>Colletotrichum gloeosporioides</i>for Coffee Senna (<i>Cassia occidentalis</i>)

A fungal pathogen, Colletotrichum gloeosporioides was isolated from a greenhouse-grown seedling of coffee senna (Cassia occidentalis) and evaluated as a mycoherbicide for that weed. Host range tests revealed that coffee senna, wild senna (C. marilandica), and sicklepod (C. obtusifolia) were also affected by this pathogen, but 35 other crop and weed species, representing 8 botanical families were not affected. The fungus sporulated prolifically on solid and liquid media with maximum spore germination and growth occurring at 20°C - 30°C. Optimal environmental conditions included at least 12 h of free moisture (dew) at 20°C - 30°C. Spray mixtures containing approximately 1.0 × 105 or more conidia·ml–1 gave maximum control when coffee senna seedlings were sprayed until runoff occurred. Coffee senna seedlings that were in the cotyledon to first-leaf growth stage were most susceptible to this pathogen. Weed control efficacy studies under field conditions demonstrated that control of coffee senna was directly proportional to the inoculum concentration applied. Results of these tests suggest that this fungus has potential as a mycoherbicide to control coffee senna, a serious weed in the southeastern U.S.

Interaction of the Bioherbicide Myrothecium verrucaria and Glyphosate for Kudzu Control

Kudzu is an exotic invasive weed in the southeastern U.S. that is difficult to control with current commercial herbicides. Some success for its control has been achieved using a bioherbicidal agent, Myrothecium verrucaria (MV). Spore and mycelial formulations of MV were tested alone and in combination with glyphosate for control of kudzu (Pueraria lobata) under greenhouse and field conditions in naturally-infested areas. In greenhouse and field experiments, kudzu control increased as the concentration of spores or mycelia increased. Glyphosate alone provided 10%, 35%, 50% and 60% control in field experiments at 0.25, 0.50, 0.75 and 1.0X rates, respectively and MV alone spores provided 15%, 50%, 65% and 85% control at 0.25, 0.50, 0.75 and 1.0X rates, respectively. However, when MV spores were combined with glyphosate, significantly higher control occurred than that caused by either component alone. Similar levels of control were observed for MV mycelial formulations applied alone or with glyphosate at equivalent concentrations of the fungus. The rate of disease progression was more rapid and severe at all fungal spore or mycelial formulations and herbicide rates when these propagules were applied in combination with glyphosate. In field tests, 24 h after application, only 20% of kudzu plants were severely damaged by MV alone (0.25X), whereas 80% were severely diseased when MV spores and glyphosate were mixed and applied at 0.25X rates each. A similar trend occurred with the MV mycelial formulation applied at these rates. Synergist interactions on kudzu control were observed, especially when lower levels of MV (spores or mycelia) and glyphosate were combined and applied to kudzu in the greenhouse or in the field. These results suggest that it may be possible to incorporate glyphosate to improve the bioherbicidal control potential and reduce herbicide and inoculum requirements of M. verrucaria spores or mycelium for controlling kudzu.

Maternal Environment Effects on Phenolic Defenses in <i>Abutilon theophrasti</i>Seeds

A class of phenolic compounds, ortho-dihydroxyphenols (hereafter “o-DHP”), has been implicated with seed survival. Based on expectations of the growth-differentiation balance hypothesis, we predicted that seed o-DHP concentration exhibits a curvilinear response to increasing resource availability in the maternal environment, with maximum o-DHP occurring at moderate resource levels. To test this hypothesis, Abutilon theophrasti seeds were produced under field conditions at two locations. Each location included twelve maternal environments established through factorial combinations of soil compost (+/-), species assemblage (A. theophrasti with and without maize), and soil nitrogen fertilizer (0, 0.5× or 1× local recommendations for maize). Resource availability with respect to A. theophrasti growth was summarized by above-ground biomass at seed harvest (maternal biomass). Results indicated that seed o-DHP concentrations increased then decreased in response to increasing maternal biomass. This relationship was modeled with a unimodal function specific to location (Location 1, y = 1.18 + 0.03xe-0.02x, pseudo-R2 = 0.59, p = 0.003;Location 2, y = 1.40 + 0.006xe-0.005x;pseudo-R2 = 0.34, p = 0.05). Seed protein concentrations remained constant across maternal biomass levels. Because inherent vulnerability to predation and decay is considered a consequence of chemical protection relative to nutritional offering, our results suggest that A. theophrasti seed susceptibility to lethal attack is influenced by resource levels in the maternal environment. More broadly, our results suggest that the growth-differentiation balance hypothesis can be extended to maternal effects on seed phenolics.

Pepper plants growth, yield, photosynthetic pigments, and total phenols as affected by foliar application of potassium under different salinity irrigation water

Irrigation with high salinity water influences plant growth, production of photosynthetic pigments and total phenols, leading to reduction in crop yield and quality. The objective of this study was to investigate the effects of potassium (K) foliar application in mitigating the negative effects of salt stress on pepper plants. A greenhouse experiment was conducted to investigate the effects of foliar application of potassium (K) on pepper plants grown with different salinity water irrigation (3000 and 6000 ppm as compared to tap water with salinity level of 300 ppm). Irrigation using high salinity water decreased plant height, biomass production, and fruit yield as compared to those of the plants irrigated by tap water. Photosynthetic pigments and total phenols increased in the former as compared to those of the latter plants. The most serious affect was for the plants under highest salinity irrigation (6000 ppm) as compared to that of the plants under moderate salinity irrigation (3000 ppm). Foliar application of potassium mono phosphate (KMP) at 200ppm concentration increased the plant growth, biomass production, and fruit yield. Chlorophyll_a content and total phenols increased significantly with foliar application of 100 ppm KMP. Further increase in foliar KMP concentration to 200 ppm had no significant benefits on photosynthetic pigments and total phenols content. This study demonstrated that foliar application of KMP, to some extent, mitigated the negative effects of high salinity water irrigation on pepper plant growth and fruit yield.

A Serratia marcesens Strains Involved in Cotton (<i>Gossypium hirsutum</i>) Boll Infection by a Prokaryote

A boll infection caused by non-traditional cotton pathogens was first reported to occur in the southeastern U.S. Cotton Belt (year 2000) and has since spread to Texas causing significant yield losses. This study was aimed towards investigating the verde plant bug (Creontiades signatus) link between interior boll disease in Texas, USA. Using glasshouse grown bolls, bacteria recovered from locules with disease symptoms from field-grown cotton bolls caged with the piercing-sucking C. signatus were analyzed for the capacity to inflict the disease. For pathogenicity testing, spontaneously generated rifampicin resistant (Rifr) variants were utilized to track the antibiotic resistant bacterium and deter growth of endophytic and contaminating bacteria. To simulate C. signatus feeding, a needle (31 gauge) was employed to inoculate bolls at 13 - 15 days after flower bloom. Bacterial suspensions ranged from 101 - 106 colony forming units/ml. Field infection symptoms were duplicated after two weeks of bacterial exposure. Infectious strains were best categorized as Serratia marcescens based on traditional carbon utilization and enzyme production testing, and a 99% nucleotide sequence identity of 16S ribosomal DNA. Putative S. marcescens representatives isolated from rotted bolls exposed to C. signatus were shown to reproduce field infection symptoms upon inoculation into greenhouse grown fruit. Serratia spp. can inflict disease in alfalfa, cucurbits, and sunflower. The presented data are the first to definitively show that a Serratia sp. has the capacity to infect cotton.

Scanning Mode Application of Neutron-Gamma Analysis for Soil Carbon Mapping

Soil carbon mapping is extremely useful in assessing the effect of land management practices on soil carbon storage. Applications of neutron-gamma analysis in scanning mode for mapping of soil carbon are discussed. A Global Positioning System(GPS) device and softwares required to simultaneously acquire gamma signals and geographical positions during scanning operations were added to an existing measurement system. The reliability of soil carbon measurements in scanning mode was demonstrated to be in agreement with results acquired from static mode. The error analysis indicated that scanning measurements can be conducted with the same accuracy as static measurements in approximately one fourth the time. To obtain results suitable for mapping analogous to traditional chemical analyses(i.e.,± 0.5 in weight percent or ± 0.5 w%), scanning time over a given site should be ca. 15 min using the current measurement system configuration. Based on this measurement time, a reasonable towing speed of 3–5 km h^-1, the necessity for complete site coverage during scanning, the number of sites(within the surveyed field), and the required total measurement time can be estimated. Soil carbon measurements for 28 field sites(total area ca. 2.5 ha) were conducted in ca. 8 h. Based on acquired data,a soil carbon distribution map was constructed utilizing various softwares. The surveyed field area included an asphalt road that had carbon readings higher than the surrounding land. The clarity with which these carbon-rich zones were delineated on the constructed map represents evidence supporting the veracity of this method. Neutron-gamma analysis technology can greatly facilitate timely construction of soil carbon maps.

Long-Term Cropping System, Tillage, and Poultry Litter Application Affect the Chemical Properties of an Alabama Ultisol

Sustainable agricultural practices have been steadily increasing in the last couple of decades. These management practices frequently involve cover crops, less or no-tillage, and organic fertilization. In this study, we evaluated the effects of cropping systems,tillage and no-tillage, and the application of poultry litter(PL) on selected soil physicochemical properties and soil test nutrients. Soil samples were collected from the topmost surface(0–5 cm) and subsurface(5–10 cm) layers. The general effect trend was PL application > no-tillage > cover crop > cropping type. There were more statistically significant(P ≤ 0.05) correlations between the 18 soil attributes at the topmost surface than at the subsurface. This could be due to the accumulation of external C inputs and nutrients by crop residues and PL application as well as the retaining effects of no-tillage on less mobile nutrient components. Because of their high mobility and volatile nature, total nitrogen(N), ammonia-N(NH_4^+-N), and nitrate-N(NO_3^--N) levels varied greatly(high standard deviations), showing no consistent patterns among the treatments. Compared to the soybean cropping system, corn, especially with the wheat cover crop, contributed more to the total carbon(C) and sulfur(S) in the topmost surface soils(0–5 cm). Poultry litter application greatly increased pH, cation exchange capacity(CEC), base saturation, magnesium(Mg), phosphorus(P), calcium(Ca),sodium(Na), potassium(K), manganese(Mn), copper(Cu), and zinc(Zn) in both soil layers. Contrast comparisons revealed that PL application had more of an effect on these soil chemical properties than no-tillage and cropping systems. These results will shed light on developing better nutrient management practices while reducing their runoff potentials.

Compost Input Effect on Dryland Wheat and Forage Yields and Soil Quality

Organic agricultural systems rely on organic amendments to achieve crop fertility requirements, and weed control must be achieved without synthetic herbicides. Our objective was to determine the crop yield and soil quality as affected by a transition from grass to dryland organic agriculture in the Central Great Plains of North America. This study evaluated three beef feedlot compost(BFC)treatments in 2010–2015 following biennial application rates: 0(control), 22.9, and 108.7 t ha^(-1) on two dryland organic cropping systems: a wheat(Triticum aestivum)-fallow(WF) rotation harvested for grain and a triticale(Triticosecale)/pea(Pisum sativum)-fallow(T/P-F) rotation harvested for forage. The triticale + pea biomass responded positively to the 108.7-t ha^(-1) BFC treatment,but not the 22.9-t ha^(-1) BFC treatment. The wheat biomass was not affected by BFC addition, but biomass N content increased.Beef feedlot compost input did not increase wheat grain yields, but had a positive effect on wheat grain Zn content. Soil total C and N contents increased with the rate of 108.7 t ha^(-1) BFC after three applications, but not with 22.9 t ha^(-1) BFC. Soil enzyme activities associated with N and C cycling responded positively to the 108.7-t ha^(-1) BFC treatment. Saturated salts were high in the soil receiving 108.7 t ha^(-1) of BFC, but did not affect crop yields. These results showed that BFC was effective in enhancing forage yields, wheat grain quality, and soil C and N, as well as specific microbial enzymes important for nutrient cycling. However, the large rates of BFC necessary to elicit these positive responses did not increase grain yields, and resulted in an excessive buildup of soil P.