The reniform nematode is a major pest affecting common upland cotton in the United States. Management of this pest in cotton fields only gives partial control and is sometimes neither economical nor profitable. Past research has shown no resistance to the reniform nematode in currently available commercial cotton cultivars. Screenings of several currently available cotton cultivars for tolerance to the reniform nematode were conducted in the growing seasons of 2006 and 2007 at the Delta Branch Experiment Station in Stoneville MS. Several cultivars were identified as tolerant and productive including ‘Croplan Genetics 3520 B2RF,’ ‘DynaGrow 2520 B2RF,’ and ‘Stoneville 5242 BR.’ Other cultivars were tolerant but less productive, including ‘Deltapine 488 BG/RR,’ ‘Fibermax 960 B2R,’ and ‘Stoneville 5599 BR.’ ‘Deltapine 455 BG/RR,’ ‘Phytogen 370,’ and ‘Phytogen 485’ were shown to be productive, but not tolerant to the reniform nematode.

The objectives of this research were to evaluate management options for tobacco thrips, Frankliniella fusca (Hinds), and reniform nematode, Rotylenchulus reniformis (Linford & Oliverira), in cotton productions systems. When evaluating tillage practices for pest control, conservational tillage reduced thrips densities and damage, while the impact on nematode densities is less understood and in this study had no impact. Insecticide seed treatments remain a vital resource for controlling thrips in Mid-South cotton production systems. When incorporating an early season herbicide application for weed control, systems with an insecticide seed treatment generally tolerated herbicide injury better than those with early season stress from thrips and nematodes. When using foliar applications as an alternative option for thrips management, early season automatic applications at the cotyledon stage followed by one or two sequential applications provided similar efficacy to the insecticide seed treatment. For reniform nematode management, 1, 3-dichloropropene reduced densities lower than that of the untreated control or aldicarb; however, depending on environmental conditions this practice may not result in yield increases great enough to warrant the cost of application. These data highlight the importance of effective control of thrips whether it be via at-planting or foliar applications. 1, 3-dichloropropene reduced nematode densities and is an effective option in nematode management; however, nematodes are a stress pathogen and the ability to minimize other seasonal stresses ,such as water stress, will determine if a nematicide application may be needed. While environmental conditions may be optimal to allow for plant recoverability, effective early season pest management decreases the potential for delayed crop maturity which could lead to increased input cost or reduced yield later in the season.

Reniform nematode, Rotylenchulus reniformis is a semi-endoparasitic nematode infecting over 300 plant species including important fiber crops like cotton. Introgression of reniform nematode resistance from a distantly-related resistant species Gossypium longicalyx into cultivated upland species Gossypium hirsutum has been a challenge. An approach towards achieving nematode resistance in crop plants has been to identify candidate parasitism genes expressed in the nematode facilitating infection of host plant species, and silencing the same through reverse genetic approaches like RNAi. A cDNA library constructed from the sedentary female stage of reniform nematode revealed an EST coding for C-type lectins and occurring in high frequency. Identification and characterization of C-type lectins in reniform nematode is important in understanding the immune system of nematode and in planning strategies for the development of reniform nematode resistant cotton varieties. A total of 11 C-type lectin gene family members were identified across six life stages of reniform nematode, with each member expected to play a significant role in the development and parasitic establishment with the host plant. Conserved sites characteristic of C-type lectins found in other organisms have been identified in the C-type lectin genes in reniform nematode for binding of Ca+2 and mannose. The highest level of expression of C-type lectins was observed in the sedentary female stage indicating it to be possibly the most sensitive stage to microbial infection and so a likely stage to target for its management. The site of secretion of C-type lectins in the sedentary female stage could be identified by in situ hybridization as the hypodermal region of the exposed posterior body region which is not inserted into the host root tissue. Phylogenetic analyses of C-type lectin domains of various nematode groups placed the plant-parasitic nematodes in one group indicating the possibility of co-evolution and probably carrying out a similar function aiding in the establishment of parasitism with host plants. Our findings now extend the spectrum of known nematode C-type lectin genes and suggest that lectin activity might be a more general feature of parasitism which could be explored in better understanding the interactions occurring at the host-nematode and nematode-pathogen interfaces.

The Gossypium genus includes 45 diploid and 5 tetraploid cotton species of which only 2 diploids and 2 tetraploids are cultivated in different parts of the tropics and sub-tropics, leaving the remaining diploid and tetraploid species as potential genetic sources for novel trait introgression. The reniform nematode (Rotylenchulus reniformis Linford and Oliveira) poses significant problems to US cultivated Upland cottons (Gossypium hirsutum L., 2n=52), all of which lack high resistance. This work was in collaboration with the USDA-ARS team that focussed on introgressing reniform nematode-resistance from a diploid cotton species, Gossypium longicalyx Hutch. & Lee into G. hirsutum by creating a tri-species hybrid, HLA and backcross breeding (Bell et al., 2007; Robinson et al., 2007). The main objectives of this work were [1] to cytogenetically evaluate and help select superior types at each introgressed generation; [2] to identify molecular markers tightly linked to the reniform nematode-resistance gene and to map the resistance loci; [3] (A) to introgress germplasm on a genome-wide basis, (B) to evaluate introgressed germplasm for traits of economic importance other than reniform nematode resistance, and (C) to evaluate breeding methodologies in terms of this specialized breeding material. Reniform nematode resistant plants were of diverse cytogenetic constitution but individuals that modally formed 26II chromosomal configuration were identified at BC2F1, BC3F1, BC4F1, and BC5F1 generations. Three SSR markers, BNL3279_114, BNL1066_156, and BNL836_215 and one phenotypic marker, green-colored fuzz (Fzglon), were identified to be tightly-linked to the resistance locus. Extension of the association analysis and linkage estimation to 16 susceptible self progeny (BC1S1, BC3S1 and BC6S1) and 374 susceptible backcross hybrids (BC2F1-BC8F1) mapped the resistance locus to chromosome 11 of cotton with BNL3279_114 on one side and Fzglon on the other at 0.8 cM and 2.8 cM, respectively. Besides reniform nematode-resistance introgression, genome-wide introgression efforts were also conducted. Low micronaire and high fiber strength were the two most promising traits identified in the HLA-derived introgressed generations. Most of the introgressed generations had high variability for the fiber-quality traits than the commercial checks, thus providing more opportunities for selection and improvement.

Cotton (Gossypium hirsutum) growth, development, and yield can be limited due to reniform nematode and bacterial blight infestation. Studies were conducted in 2016 and 2017 to evaluate the profitability of a soil fumigant application, seed treatments, and inurrow nematicides to protect cotton from nematode infestation as well as inoculation of bacterial blight at various growth stages in cotton to determine effects on yield. Research was conducted by applying various combinations of nematicides to cottonseed at planting and a fumigant prior to planting. Bacterial blight was conducted by inoculated on cotton at multiple growth stages throughout the year. Based on the results of these studies, a seed treatment plus inurrow application should be applied at planting in nematode infested fields to increase yield and economic returns in cotton. Bacterial blight infestation was greatest when inoculated at pinhead square in cotton.

Soybean (Glycine max [L.] Merr.) is one of the most important crops in the world. The average annual yield losses due to soybean diseases and pests are estimated to be around 11% in the United States. Soybean yield losses due to sudden death syndrome (SDS), caused by the fungus Fusarium virguliforme O'Donnell & T. Aoki have been problematic in majority of the soybean producing states. In recent years, reniform nematode (RN, Rotylenchulus reniformis Linford and Oliveira) and frogeye leaf spot (FLS), caused by the fungus Cercospora sojina K. Hara have emerged as a major problem in the southern soybean producing states. Planting resistant cultivars is one of the most cost-efficient methods in managing SDS, RN, and FLS, therefore it would be critical to identify and map the quantitative trait loci (QTL) that underlie their resistances. Two soybean populations were evaluated in this study. The ‘Essex’ × ‘Forrest’ 77 near-isogenic lines were screened in the field to evaluate the disease index of SDS. The Essex × Forrest and ‘Flyer’ × ‘Hartwig’ recombinant inbred lines were screened in the greenhouse to assess the reproduction index of RN and the disease severity of FLS. The BARCSoySNP6k chip was used to genotype the two populations. Four QTL that underlie SDS resistances were mapped in the same region as Rfv06-01, Rfv06-02, Rfv13-01, and Rfv19-01. The Rfv06-02 interval in this study was smaller than the one previously reported. Rrr08-01, Rrr13-01, Rrr15-01, Rrr18-01, and Rrr18-02 were reported to confer resistances to RN. Rrr08-01, Rrr13-01 and Rrr15-01 were novel whereas Rrr18-01, and Rrr18-02 were mapped in previous studies. cqSCN-001 (soybean cyst nematode, Heterodera glycines Ichinohe) was identified in the same region as Rrr18-01, and Rrr18-02 whereas cqSCN-006 was identified in the same region as Rrr15-01. These findings provide further evidence that there are common sources of genetic resistances to RN and SCN. Rcs15-01 and Rcs15-02 were reported to confer resistances to FLS. Rcs15-01 was novel and Rcs15-02 was mapped at the same region as an Rcs mapped in a previous study. This indicated that Rcs15-02 has dual resistances to C. sojina races. Candidate genes were inferred in this study. The QTL mapped in this study could potentially be used in soybean breeding programs that aim to introgress genetic resources that confer resistances to SDS, RN, and FLS.

Reniform nematode (Rotylenchulus reniformis Linford and Oliveira) currently infests about 36% of the Mississippi G. hirsutum acres causing economic losses of $130 million annually. For more than 40 years nematodes, including R. reniformis, have been managed using an at-planting treatment of Temik 15G or with soil fumigants like Telone II. With the label loss of Temik 15G and expense of soil fumigants, there is a need to develop an integrated nematode management program centered around nematicide seed treatments (NST) with and without foliar applications of Vydate C-LV. In addition there is a need to better understand how new cotton cultivars provide improved growth, development and yield in nematode infested fields. Results from research at Auburn and Mississippi State Universities revealed tested varieties responded positively to NST and improved growth and yield without NST was variety specific especially early in G. hirsutum development (between nodes 1-9). Cutivars Phy 499, FM 1740 and Stv 5458 showed the greatest nematode tolerance while Phy 375 WRF had the least tolerance, benefitting greatly from NST. Trials involving NST with and without Vydate C-LV indicated yield of plants treated with Temik 15G was greater than plants treated with NST treatments. Aeris + Votivo with and without Vydate C-LV provided better plant growth and yield than Aeris alone or with Vydate C-LV. Relative to yield Vydate C-LV treatments increased pounds of lint cotton/acre across all treatments. There were no differences in fruit retention at fruiting site one during the square period with fruit loss primarily occurring between bloom and open boll. Vydate C-LV treatments increased overall fruit retention compared to all nematicide seed treatments making them comparable to Temik 15G.

Submitted by ADRIANA APARECIDA GABIA null (adrianagabia@hotmail.com) on 2017-03-24T21:52:58Z No. of bitstreams: 1 Tese - Adriana Aparecida Gabia.pdf: 962569 bytes, checksum: 97661626b3aac943cf38c28fda2300d6 (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-03-29T18:23:09Z (GMT) No. of bitstreams: 1 gabia_aa_dr_bot.pdf: 962569 bytes, checksum: 97661626b3aac943cf38c28fda2300d6 (MD5) / Made available in DSpace on 2017-03-29T18:23:09Z (GMT). No. of bitstreams: 1 gabia_aa_dr_bot.pdf: 962569 bytes, checksum: 97661626b3aac943cf38c28fda2300d6 (MD5) Previous issue date: 2017-02-02 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O nematoide reniforme, Rotylenchulus reniformis, considerado de interesse secundário, passou a ser um dos mais importantes problemas fitossanitários na cultura da soja. Os objetivos desse trabalho foram avaliar a interferência de diferentes cultivos na população de R. reniformis e a distribuição horizontal, vertical e temporal da população desse nematoide em área de cultivo de soja, determinando o número de subamostras necessárias para a formação de uma amostra composta representativa. O experimento foi realizado na Fazenda Experimental Lageado, município de Botucatu, SP, em área naturalmente infestada por R. reniformis. Para avaliar a interferência de diferentes sistemas de cultivo sobre a população do nematoide reniforme, o experimento foi conduzido por quatro anos consecutivos, amostrando solo e raiz de 100 pontos distribuídos em 1 ha. As amostragens foram realizadas aos 80 e 140 dias após a instalação de cada cultura (soja, milho e aveia) e na segunda quinzena de outubro, para os anos de entressafra sem cultura. Para estudar a distribuição horizontal, vertical e temporal da população desse nematoide em área de cultivo de soja, uma malha regular de 100 pontos equidistantes (10m x 10m), distribuídos em 1 ha, foi amostrada. As amostras de solo foram retiradas nas profundidades 0,0–0,2 e 0,2–0,4 m. Para verificar a existência e estimar o grau de dependência espacial entre as populações, utilizou-se a análise geoestatística. Após o ajuste do variograma foi realizada a krigagem e sequencialmente o mapa de distribuição espacial de nematoides na área. No estudo realizado para avaliar a interferência de diferentes cultivos sobre a população de R. reniformis, pode-se verificar que o manejo da entressafra com cultivo da aveia e/ou sem cultura, mas com livre crescimento de plantas invasoras, não interferiu na população do nematoide. No estudo da distribuição de R. reniformis em área cultivada com soja, verificou-se na distribuição horizontal, as populações se apresentaram mais elevadas na região central da área amostrada, com populações intermediárias nas extremidades. Nesse caso, o espaçamento de subamostras de solo para compor uma amostra representativa da população de R. reniformis na área amostradas foi de 20,4 metros, necessitando de 21 subamostras para compor uma amostra representativa, e o período mais adequado para a amostragem, nesse caso, é aos 80 ou 140 dias após o plantio, amostrando o perfil de 0-40 cm. Verificou-se ainda, que a população do nematoide reniforme é menor no período que antecede a instalação da cultura e que sua distribuição vertical pode variar de acordo com o ciclo da cultura de soja. / The reniform nematode, Rotylenchulus reniformis, considered of secondary interest to soybean, has become one of the most important phytosanitary problems in the crop. The objectives of this work were to evaluate the interference of different crops system in the R. reniformis population and horizontal and vertical distribution of the nematode population in a soybean growing area, determining the number of subsamples necessary for the formation of representative composite sample. The experiment was carried out at Experimental Farm Lageado, municipality of Botucatu, SP, in an area naturally infested by R. reniformis. To evaluate the interference of different cropping systems on the reniform nematode population, the experiment was conducted for four consecutive years, sampling soil and root of 100 points distributed in 1 ha. Samples were taken at 80 and 140 days after the installation of each crop (soybean, corn and oats) and in the second fortnight of October, for the off-crop years. In order to study the horizontal and vertical distribution of the nematode population in a soybean growing area, a regular mesh of 100 equidistant points (10m x 10m) distributed in 1 ha was sampled. Soil samples were taken at depths of 0.0-0.2 and 0.2-0.4 m. To verify the existence and to estimate the degree of spatial dependence among the populations, the geostatistical analysis was used. After adjustment of the variogram, kriging and sequentially the map of spatial distribution of nematodes in the areas were performed. In the study to evaluate the interference of different crops on the population of R. reniformis, it can be verified that the management of the oyster crop and / or without crop, but with free growth of invasive plants, did not interfere in the nematode population and The survival of this can be influenced by the presence of invasive plants of the cultivated area. In the study of the distribution of R. reniformis in cultivated area with soybean, verified in the horizontal distribution that the populations were higher in the central region of the sampled area with intermediary populations in the extremities. In this case, the spacing of soil subsamples to compose a representative sample of the population of R. reniformis in the sampled area was 20.4 meters and the best period for sampling, in this case, is at 80 and 140 days after planting, sampling the profile of 0-40 cm. It also verified that the population of the reniform nematode is smaller in the period that precedes the installation of the culture. And their vertical distribution may vary according to the development of the soybean crop.

Abamectin is a blend of B1a and B1b avermectins that is being used as a seed treatment to control plant-parasitic nematodes on cotton. Data on the toxicity of abamectin and its effectiveness as a seed treatment to control Meloidogyne incognita or Rotylenchulus reniformis on cotton are lacking. The toxicity of abamectin was based on an assay of nematode mobility, LD50 values of 1.56 µg/ml and 32.9 µg/ml were calculated based on 2 hr exposure for M. incognita and R. reniformis, respectively. There was no recovery of either nematode after exposure for 1 hr to its LD50 concentration. Sublethal concentrations greater than 0.39 µg/ml for M. incognita and 8.2 µg/ml for R. reniformis reduced (P = 0.05) infectivity on tomato. In field trials, suppression (P = 0.05) of M. incognita was observed 32 DAP by abamectin seed treatment whereas no suppression of R. reniformis was observed. No suppression of M. incognita was perceived by abamectin seed treatment in microplots. Suppression of M. incognita was observed in microplots by harpinEA and harpingαβ as a seed treatment and foliar spray, respectively. Seed cotton yields were variable for abamectin-treated seed, but numerically positive for harpin-treated cotton. Initial gall formation on developing taproots was suppressed (P = 0.001), and penetration of 5-cm long taproots by M. incognita and R. reniformis was numerically suppressed by abamectin-treated compared to non-treated seed, but infection increased with root development. Using an assay of nematode mobility, the proportion of dead second-stage juveniles (J2) was higher (P = 0.05) following exposure to an excised radicle from abamectin-treated seed than non-treated seed, but lower (P = 0.05) than J2 exposed to the abamectin-treated seed coat. Thus a higher concentration of abamectin remained on the seed coat than emerging radicle. The concentration of abamectin transferred from the seed coat to the developing roots was limited, which contributed to the variability in suppression of plant-parasitic nematodes on cotton.

Abamectin is a blend of B1a and B1b avermectins that is being used as a seed treatment to control plant-parasitic nematodes on cotton. Data on the toxicity of abamectin and its effectiveness as a seed treatment to control Meloidogyne incognita or Rotylenchulus reniformis on cotton are lacking. The toxicity of abamectin was based on an assay of nematode mobility, LD50 values of 1.56 µg/ml and 32.9 µg/ml were calculated based on 2 hr exposure for M. incognita and R. reniformis, respectively. There was no recovery of either nematode after exposure for 1 hr to its LD50 concentration. Sublethal concentrations greater than 0.39 µg/ml for M. incognita and 8.2 µg/ml for R. reniformis reduced (P = 0.05) infectivity on tomato. In field trials, suppression (P = 0.05) of M. incognita was observed 32 DAP by abamectin seed treatment whereas no suppression of R. reniformis was observed. No suppression of M. incognita was perceived by abamectin seed treatment in microplots. Suppression of M. incognita was observed in microplots by harpinEA and harpingαβ as a seed treatment and foliar spray, respectively. Seed cotton yields were variable for abamectin-treated seed, but numerically positive for harpin-treated cotton. Initial gall formation on developing taproots was suppressed (P = 0.001), and penetration of 5-cm long taproots by M. incognita and R. reniformis was numerically suppressed by abamectin-treated compared to non-treated seed, but infection increased with root development. Using an assay of nematode mobility, the proportion of dead second-stage juveniles (J2) was higher (P = 0.05) following exposure to an excised radicle from abamectin-treated seed than non-treated seed, but lower (P = 0.05) than J2 exposed to the abamectin-treated seed coat. Thus a higher concentration of abamectin remained on the seed coat than emerging radicle. The concentration of abamectin transferred from the seed coat to the developing roots was limited, which contributed to the variability in suppression of plant-parasitic nematodes on cotton.