Postinfection Development of Rotylenchulus reniformis on Resistant Gossypium barbadense Accessions

The reniform nematode (Rotylenchulus reniformis) causes significant cotton (Gossypium hirsutum) losses in the southeastern United States. The research objective was to describe the effects of two resistant G. barbadense lines (cultivar TX 110 and accession GB 713) on development and fecundity of reniform nematode. Nematode development and fecundity were evaluated on the resistant lines and susceptible G. hirsutum cultivar Deltapine 16 in three repeated growth chamber experiments. Nematode development on roots early and late in the infection cycle was measured at set intervals from 1 to 25 d after inoculation (DAI) and genotypes were compared based on the number of nematodes in four developmental stages (vermiform, swelling, reniform, and gravid). At 15, 20, and 25 DAI, egg production by individual females parasitizing each genotype was measured. Unique reniform nematode developmental patterns were noted on each of the cotton genotypes. During the early stages of infection, infection and development occurred 1 d faster on susceptible cotton than on the resistant genotypes. Later, progression to the reniform and gravid stages of development occurred first on the susceptible genotype, followed by G. barbadense cultivar TX 110, and finally G. barbadense accession GB 713. Egg production by individual nematodes infecting the three genotypes was similar. This study corroborates delayed development previously reported on G. barbadense cultivar TX 110 and is the first report of delayed infection and development associated with G. barbadense accession GB 713. The different developmental patterns in the resistant genotypes suggest that unique or additional loci may confer resistance in these two lines.     

Relationships Between Tolerance and Resistance to Meloidogyne incognita in Cotton

The southern root-knot nematode, Meloidogyne incognita, is the most damaging pathogen of cotton in the United States, and both resistance and tolerance to M. incognita could be valuable management approaches. Our objectives were to evaluate advanced cotton breeding lines for resistance and tolerance to M. incognita and to determine if a relationship between resistance and tolerance exists. Reproduction of M. incognita was evaluated on 17 breeding lines, a susceptible control (Delta and Pine Land DP5415), and a resistant control (M-120) in two greenhouse trials with six replications in a randomized complete block design. Two-week-old seedlings were inoculated with 8,000 M. incognita eggs and assessed for egg production 8 weeks later. Reproduction on the resistant control was only 10% of that on the susceptible control. Eight breeding lines supported 45% to 57% less (P <= 0.05) nematode reproduction than the susceptible control, and none of them were as resistant as M-120. Yield was determined in 2001 and 2002 in fumigated (1,3-dichloropropene at 56 liters/ha) and nonfumigated plots in a strip-plot design with three replications in a field naturally infested with M. incognita. Yield suppression caused by nematode infection differed among genotypes (P ≤ 0.05 for genotype × fumigation interaction). Six genotypes in 2001 and nine in 2002 were tolerant to M. incognita based on no difference in yield between the fumigated and nonfumigated plots (P ≥ 0.10). However, only three genotypes had no significant yield suppression in both years, of which two also were resistant to M. incognita. Regression analysis indicated that yield suppression decreased linearly as nematode resistance increased.     

Relative Efficacy of Selected Volatile and Nonvolatile Nematicides for Control of Meloidogyne incognita on Tobacco

Root-knot nematode control and tobacco yields in plots infested with Meloidogyne incognita and treated with the nonvolatile nematicides, aldicarb, Mocap ®, or Nemacur ® were greater than those on similar plots treated with volatile nematicides such as DD, DD + MENCS, SD14647 or tetrachlorothiophene. Root-knot control and tobacco yields in plots treated with carbofuran or Dasanit ® were eqtual to that obtained with DD + MENCS, but less than that obtained with the other volatile soil nematicides. The most efficient dosage was 3.4 kg/hectare active ingredient for aldicarb and Mocap ® and 10.0 kg/hectare for Dasanit ®. Carbofuran and Nemacur ® were equally as effective at 4.2 kg/hectare as they were at higher dosages. The most efficient dosage of DD and SD14647 was 84 liters/hectare. Aldicarb and Dasanit ® resulted in better nematode control and tobacco yields when incorporated into the top 15-20 cm of soil than when incorporated into the top 5-10 cm of soil. Nemacur ® and Mocap ® performed better when incorporated into the top 5-10 cm of soil, and carbofuran performed better when applied in the seed furrow (placed 15-20 cm deep in a 5-cm band and bedded).     

Rotylenchulus reniformis Management in Cotton with Crop Rotation

One-year crop rotations with corn or highly resistant soybean were evaluated at four locations for their effect on Rotylenchulus reniformis population levels and yield of a subsequent cotton crop. Four nematicide (aldicarb) regimes were included at two of the locations, and rotation with reniform-susceptible soybean was included at the other two locations. One-year rotations to corn or resistant soybean resulted in lower R. reniformis population levels (P ≤ 0.05) than those found in cotton at three test sites. However, the effect of rotation on nematode populations was undetectable by mid-season when cotton was grown the following year. Cotton yield following a one-year rotation to resistant soybean increased at all test locations compared to continuous cotton, and yield following corn increased at three locations. The optimum application rate for aldicarb in this study was 0.84 kg a.i./ha in furrow. Side-dress applications of aldicarb resulted in yield increases that were insufficient to cover the cost of application in 3 of the 4 years.     

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.     

Two Simple Methods for the Collection of Individual Life Stages of Reniform Nematode,Rotylenchulus reniformis

The sedentary semi-endoparasitic nematode Rotylenchulus reniformis, the reniform nematode, is a serious pest of cotton and soybean in the United States. In recent years, interest in the molecular biology of the interaction between R. reniformis and its plant hosts has increased; however, the unusual life cycle of R. reniformis presents a unique set of challenges to researchers who wish to study the developmental expression of a particular nematode gene or evaluate life stage–specific effects of a specific treatment such as RNA-interference or a potential nematicide. In this report, we describe a simple method to collect R. reniformis juvenile and vermiform adult life stages under in vitro conditions and a second method to collect viable parasitic sedentary females from host plant roots. Rotylenchulus reniformis eggs were hatched over a Baermann funnel and the resultant second-stage juveniles incubated in petri plates containing sterile water at 30°C. Nematode development was monitored through the appearance of fourth-stage juveniles and specific time-points at which each developmental stage predominated were determined. Viable parasitic sedentary females were collected from infected roots using a second method that combined blending, sieving, and sucrose flotation. Rotylenchulus reniformis life stages collected with these methods can be used for nucleic acid or protein extraction or other experimental purposes that rely on life stage–specific data.     

Tolerance to Rotylenchulus reniformis and Resistance to Meloidogyne incognita Race 3 in High-Yielding Breeding Lines of Upland Cotton

Field experiments in 1992 and 1994 were conducted to determine the effect of Rotylenchulus reniformis, reniform nematode, on lint yield and fiber quality of 10 experimental breeding lines of cotton (Gossypium hirsutum) in untreated plots or plots fumigated with 1,3-dichloropropene. Controls were La. RN 1032, a germplasm line possessing some resistance to R. reniformis, and Stoneville 453, a cultivar that is susceptible to reniform nematode. Several breeding lines produced greater lint yields than Stoneville 453 or La. RN 1032 in both fumigated and untreated plots. Average lint yield suppression due to R. reniformis for six of the 10 breeding lines was less than half of the 52% yield reduction sustained by Stoneville 453. In growth chamber experiments, R. reniformis multiplication factors for La. RN 1032 and breeding lines N222-1-91, N320-2-91, and N419-1-91 were significantly lower than on Deltapine 16 and Stoneville 453 at 6 weeks after inoculation. R. reniformis populations increased by more than 50-fold on all entries within 10 weeks. In growth chambers, the breeding lines N220-1-92, N222-1-91, and N320-2-91 were resistant to Meloidoglyne incognita race 3; multiplication factors were ≤1.0 at both 6 weeks and 10 weeks after inoculation compared with 25.8 and 26.5 for Deltapine 16 at 6 and 10 weeks after inoculation, respectively, and 9.1 and 2.6 for Stoneville 453. Thus, the results indicate that significant advances have been made in developing improved cotton germplasm lines with the potential to produce higher yields in soils infested with R. reniformis or M. incogaita. In addition to good yield potential, germplasm lines N222-1-91 and N320-2-91 appear to possess low levels of resistance to R. reniformis and a high level of resistance to M. incognita. This germplasm combines high yield potential with significant levels of resistance to both R. reniformis and M. incognita.     

Sensitivity of Meloidogyne incognita and Rotylenchulus reniformis to Fluopyram

Fluopyram is a succinate dehydrogenase inhibitor (SDHI) fungicide that is being evaluated as a seed treatment and in-furrow spray at planting on row crops for management of fungal diseases and its effect on plant-parasitic nematodes. Currently, there are no data on nematode toxicity, nematode recovery, or effects on nematode infection for Meloidogyne incognita or Rotylenchulus reniformis after exposure to low concentrations of fluopyram. Nematode toxicity and recovery experiments were conducted in aqueous solutions of fluopyram, while root infection assays were conducted on tomato. Nematode paralysis was observed after 2 hr of exposure at 1.0 µg/ml fluopyram for both nematode species. Using an assay of nematode motility, 2-hr EC₅₀ values of 5.18 and 12.99 µg/ml fluopyram were calculated for M. incognita and R. reniformis, respectively. Nematode recovery in motility was greater than 50% for M. incognita and R. reniformis 24 hr after nematodes were rinsed and removed from a 1-hr treatment of 5.18 and 12.99 µg/ml fluopyram, respectively. Nematode infection of tomato roots was reduced and inversely proportional to 1-hr treatments with water solutions of fluopyram at low concentrations, which ranged from 1.3 to 5.2 µg/ml for M. incognita and 3.3 to 13.0 µg/ml for R. reniformis. Though fluopyram is nematistatic, low concentrations of the fungicide were effective at reducing the ability of both nematode species to infect tomato roots.     

Efficacy of Aldicarb to Rotylenchulus reniformis and Biodegradation in Cotton Field Soils

The microbial degradation of aldicarb was examined in the greenhouse using soil from four cotton fields with a history of aldicarb use. The addition of aldicarb at 0.59 kg a.i./ha to natural soil increased Rotylenchulus reniformis numbers 6.6% in one soil and decreased R. reniformis numbers only 25.8% in another soil as compared to the corresponding natural soil without aldicarb. The use of increasing rates of aldicarb did not increase the efficacy of aldicarb in these soils. Rotylenchulus reniformis numbers were reduced 39.8, 22.6, and 6.8%, and increased 5.7% for aldicarb applied at 0.29, 0.59, 0.85, and 1.19 kg a.i./ha, respectively, in one natural soil. In another natural soil, R. reniformis numbers were reduced 42.5 and 21.9% for aldicarb applied at 0.29 and 1.19 kg a.i./ha, respectively, but increased 19.1 and 10.6% for aldicarb applied at 0.59 and 0.85 kg a.i./ha, respectively. Autoclaving the soils restored aldicarb toxicity in both soils, and R. reniformis numbers were reduced 96 and 99%, respectively, as compared to autoclaved soil without aldicarb. Bacterial populations were greater in the natural soils where aldicarb did not reduce R. reniformis numbers relative to the same soils that were autoclaved. However, no bacterial species was consistently associated with aldicarb degradation.     

Interrelationships of Rotylenchulus reniformis with Rhizoctonia solani on Cotton

The interrelationships between reniform nematode (Rotylenchulus reniformis) and the cotton (Gossypium hirsutum) seedling blight fungus (Rhizoctonia solani) were studied using three isolates of R. solani, two populations of R. reniformis at multiple inoculum levels, and the cotton cultivars Dehapine 90 (DP 90) and Dehapine 41 (DP 41). Colonization of cotton hypocotyl tissue by R. solani resulted in increases (P ≤ 0.05) in nematode population densities in soil and in eggs recovered from the root systems in both 40- and 90-day-duration experiments. Increases in soil population densities resulted mainly from increases in juveniles. Enhanced reproduction of R. reniformis in the presence of R. solani was consistent across isolates (1, 2, and 3) of R. solani and populations (1 and 2) and inoculum levels (0.5, 2, 4, and 8 individuals/g of soil) of R. reniformis, regardless of cotton cultivar (DP 90 or DP 41). Severity of seedling blight was not influenced by the nematode. Rhizoctonia solani caused reductions (P ≤ 0.05) in cotton growth in 40- and 90-day periods. Rotylenchulus reniformis reduced cotton growth at 90 days. The relationship between nematode inoculum levels and plant growth reductions was linear. At 90 days, the combined effects of these pathogens were antagonistic to plant growth.     

Effect of Controlled Cold Storage on Recovery of Rotylenchulus reniformis from Naturally Infested Soil

Rotylenchulus reniformis is rapidly becoming the most economically important pest associated with cotton in the southeastern United States. Incentive programs have been implemented to support sampling of production fields to determine the presence and abundance of R. reniformis. These sampling programs have dramatically increased the number of soils samples submitted to nematology laboratories during autumn. The large numbers of samples overwhelm most labs and require placement in cold storage until extraction. Therefore, the objective of this study was to examine the length of time soils infested with R. reniformis can be stored before nematode extraction without compromising the accuracy of estimates of population densities. A sandy loam and a silty loam were the two cotton production soils used in this study. Rotylenchulus reniformis numbers decreased 61%during the first 180 days of storage in both soils. Rotylenchulus reniformis numbers from the initial sampling through 180 days decreased as a linear function. The decline of R. reniformis numbers during storage was estimated as 0.28% of the population lost daily from the maximum population through 180 days. The diminution of nematode numbers from 180 through 1,080 days in storage continued, but at a slower rate. Numbers of R. reniformis declined to less than 89%, 93%, and 99% of the initial population within 360, 720, and 1,080 days, respectively, of storage. The reduction of R. reniformis numbers over 180 days can be adjusted, allowing a more accurate estimation of R. reniformis levels in soil samples stored at 4 °C.     

Host Suitability of Soybean Cultivars and Breeding Lines to Reniform Nematode in Tests Conducted in 2001

Reproduction of reniform nematode Rotylenchulus reniformis on 139 soybean lines was evaluated in a greenhouse in the summer of 2001. Cultivars and lines (119 total) were new in the Arkansas and Mississippi Soybean Testing Programs, and an additional 20 were submitted by C. Overstreet, Louisiana State Extension Nematologist. A second test of 32 breeding lines and 2 cultivars from the Clemson University soybean breeding program was performed at the same time under the same conditions. Controls were the resistant cultivars Forrest and Hartwig, susceptible Braxton, and fallow infested soil. Five treatment replications were planted in sandy loam soil infested with 1,744 eggs and vermiform reniform nematodes, grown for 10 weeks in 10 cm-diam.- pots. Total reniform nematodes extracted from soil and roots was determined, and a reproductive factor (final population (Pf)/ initial inoculum level (Pi)) was calculated for each genotype. Reproduction on each genotype was compared to the reproduction on the resistant cultivar Forrest (RF), and the log ratio [log₁₀(RF + 1) is reported. Cultivars with reproduction not significantly different from Forrest (log ratio) were not suitable hosts, whereas those with greater reproductive indices were considered suitable hosts. These data will be useful in the selection of soybean cultivars to use in rotation with cotton or other susceptible crops to help control the reniform nematode and to select useful breeding lines as parent material for future development of reniform nematode resistant cultivars and lines.     

Identification of Rotylenchulus reniformis Resistant Glycine Lines

Identification of resistance to reniform nematode (Rotylenchulus reniformis) is the first step in developing resistant soybean (Glycine max) cultivars that will benefit growers in the mid-South region of the United States. This study was conducted to identify soybean (G. max and G. soja) lines with resistance to this pathogen. Sixty-one wild and domestic soybean lines were evaluated in replicated growth chamber tests. Six previously untested soybean lines with useful levels of resistance to reniform nematode were identified in both initial screening and subsequent confirmation tests: released germplasm lines DS4-SCN05 (PI 656647) and DS-880 (PI 659348); accession PI 567516 C; and breeding lines DS97-84-1, 02011-126-1-1-2-1 and 02011-126-1-1-5-1. Eleven previously untested moderately susceptible or susceptible lines were also identified: released germplasm lines D68-0099 (PI 573285) and LG01-5087-5; accessions PI 200538, PI 416937, PI 423941, PI 437697, PI 467312, PI 468916, PI 594692, and PI 603751 A; and cultivar Stafford (PI 508269). Results of previously tested lines evaluated in the current study agreed with published reports 69.6% of the time for resistant lines and 87.5% of the time for susceptible lines. Soybean breeders may benefit from incorporating the newly identified resistant lines into their breeding programs.     

Effect of Soil Temperature on Infectivity and Development of Rotylenchulus reniformis on Resistant and Susceptible Soybeans,Glycine max

The effect o f soil temperature on parasitism and development of Rotylenchulus reniformis on resistant (''Peking'' and ''Custer'') and susceptible (''Hood'' and ''Lee'') soybean (Glycine max) cultivars was studied. Soil temperatures of 15, 21.5, 25, 29.5 and 36 C ± 1 C were maintained in temperature tanks in a greenhouse. R. reniformis developed best at 25 and 29.5 C. The female life cycle can be completed within 19 days after inoculation under favorable conditions at 29.5 C. Plant root growth was best at 21.5 C. During a 27-day period, no egg masses were present on nematodes feeding on roots grown at 15 and 36 C. Egg masses developed on Hood but not on Lee when nematodes were introduced into soil and maintained at 29.5 C for 2 days before raising the temperature to 36 C.     

Using Geostatistical Analysis to Evaluate the Presence of Rotylenchulus reniformis in Cotton Crops in Brazil: Economic Implications

In recent years, the productivity of cotton in Brazil has been progressively decreasing, often the result of the reniform nematode Rotylenchulus reniformis. This species can reduce crop productivity by up to 40%. Nematodes can be controlled by nematicides but, because of expense and toxicity, application of nematicides to large crop areas may be undesirable. In this work, a methodology using geostatistics for quantifying the risk of nematicide application to small crop areas is proposed. This risk, in economic terms, can be compared to nematicide cost to develop an optimal strategy for Precision Farming. Soil (300 cm³) was sampled in a regular network from a R. reniformis-infested area that was a cotton monoculture for 20 years. The number of nematodes in each sample was counted. The nematode number per volume of soil was characterized using geostatistics, and 100 conditional simulations were conducted. Based on the simulations, risk maps were plotted showing the areas where nematicide should be applied in a Precision Farming context. The methodology developed can be applied to farming in countries that are highly dependent on agriculture, with useful economic implications.     

Effects of Temperature on Resistance in Phaseolus vulgaris Genotypes and on Development of Meloidogyne Species

Phaseolus vulgaris lines with heat-stable resistance to Meloidogyne spp. may be needed to manage root-knot nematodes in tropical regions. Resistance expression before and during the process of nematode penetration and development in resistant genotypes were studied at pre- and postinoculation temperatures of 24 °C and 24 °C, 24 °C and 28 °C, 28 °C and 24 °C, and 28 °C and 28 °C. Resistance was effective at all temperature regimes examined, with fewer nematodes in roots of a resistant line compared with a susceptible line. Preinoculation temperature did not modify resistance expression to later infections by root-knot nematodes. However, postinoculation temperatures affected development of Meloidogyne spp. in both the resistant and susceptible bean lines tested. The more rapid development of nematodes to adults at the higher postinoculation temperature of 28 °C in both bean lines suggests direct temperature effects on nematode development instead of on resistance expression of either of two gene systems. Also, resistance was stable at 30 °C and 32 °C.     

Relationship between Meloidogyne incognita and Rotylenchulus reniformis as Influenced by Soybean Genotype

The effect of soybean genotype on competition between Meloidogyne incognita race 2 (Mi) and Rotylenchulus reniformis (Rr) was evaluated in greenhouse and microplot replacement series experiments. Soil in pots containing seedlings of ''Davis'' (susceptible to Mi) or ''Buckshot 66'' (resistant to Mi) was infested with 1,000 vermiform individuals in the following Mi:Rr ratios: 0:0, 100:0, 75:25, 50:50, 25:75, or 0:100. After 91 days, the relative nematode yields (number of nematodes in mixed culture divided by the number in nonmixed culture) of each species were calculated based on soil and root nematode populations expressed as nematodes per gram of dry root tissue. To define the relationship between the two species, calculated relative nematode yields were compared with a theoretical noncompetition model using lack-of-fit regression. In the greenhouse, Mi populations on ''Davis'' were stimulated in the presence of Rr. In microplots, low Mi and Rr population densities likely resulted from severe galling and destruction of feeder roots that probably occurred early in the season. Enhanced susceptibility to Mi was not observed on ''Buckshot 66'', which remained resistant to Mi even when colonized by Rr. Host resistance is a key factor in determining the nature of the relationship between Mi and Rr.     

Screening Soybeans for Resistance to Reniform Nematode Disease in the Philippines

Sixty-five soybean varieties were tested in the field for resistance to Rotylenchulus reniformis. Criteria for resistance or susceptibility were root necrosis, nematode recovery from roots and soil, and egg production. Nine varieties were resistant, 13 moderately resistant, 26 moderately susceptible, and 17 susceptible. Linear correlations between resistance rating and each assessment parameter were highly significantly positive, suggesting that any of the parameters could be used to identify resistance. There were also highly significant positive linear correlations between any two combinations of parameters, indicating that they were reciprocally related.     

Comparisons of Female and Egg Assays to Identify Rotylenchulus reniformis Resistance in Cotton

More plants can be screened for reniform nematode resistance each year if the time involved can be shortened. In this study, the hypothesis that female counts are as efficient as egg counts in identifying resistant genotypes was tested. In two greenhouse experiments Gossypium genotypes which varied from resistant to susceptible to reniform nematode (Rotylenchulus reniformis) were compared to a susceptible control cultivar. Infested field soil served as the inoculum source for the first experiment, and vermiform stages extracted from greenhouse cultures were used to infest soil in the second experiment. Six replicates of each genotype were harvested 25 d after planting and swollen females were counted. The remaining plants were harvested 35 d after planting and eggs extracted from the roots were counted. Processing and counting times recorded in the first experiment were similar for both assessment methods, but 10 additional days were required for egg-based assessment. Contrast analyses showed that assessments based on females per gram of root were equivalent to assessments based on eggs per gram of root for the five genotypes tested in the first experiment and for an expanded set of 13 genotypes tested in the second experiment. The results indicated that either life stage can be used to screen for resistance.     

Suppression of Rotylenchulus reniformis 122-cm Deep Endorses Resistance Introgression in Gossypium

Nine sources of resistance to Rotylenchulus reniformis in Gossypium (cotton) were tested by measuring population density (Pf) and root-length density 0 to 122 cm deep. A Pf in the plow layer less than the autumn sample treatment threshold used by consultants was considered the minimum criterion for acceptable resistance, regardless of population density at planting (Pi). Other criteria were ample roots and a Pf lower than on the susceptible control, as in pot studies. In a Texas field in 2001 and 2002, no resistant accessions had Pf less than the control but all did in microplots into which nematodes from Louisiana were introduced. An environmental chamber experiment ruled out nematode genetic variance and implicated unknown soil factors. Pf in field experiments in Louisiana, Mississippi, and Alabama were below threshold for zero, six and four of the accessions and above threshold in the control. Gossypium arboreum A2–87 and G. barbadense GB-713 were the most resistant accessions. Results indicate that cultivars developed from these sources will suppress R. reniformis populations but less than in pots in a single season.