Reduction in sulfur deposition from power plant emissions has resulted in lower amounts of soil sulfur and, perhaps, in inadequate sulfur availability for corn. The objective of this study was to determine if corn (<i>Zea mays</i> L.) grain yield was responsive to S fertilization in Indiana and what soil and cropping system factors contributed to the likelihood of a response. Field scale experiments were conducted at 28 sites from 2017 to 2020, the majority in corn-soybean (<i>Glycine max</i> (L.) Merr) rotation. In-season measurements included soil sulfate-S concentration and soil texture from 0 to 60 cm in 20 cm increments, plant nutrient concentration in the whole plant at V3-V7, in the earleaf, and in the grain. Additional measurements were 1,000 kernel dry weight, total kernel rows per ear, and kernels per row. Sulfur treatment rates ranged from 0 to 34 kg S ha^‑1 as ammonium thiosulfate, and were applied as starter, sidedress, and both combined. Fertilizer S increased grain yield by 0.2 to 3.0 Mg ha^-1 at 10 of 28 Indiana site-years, approximately a 36% frequency of response. When a response to S fertilizer occurred, the lowest sidedress rate examined in that site-year, which ranged from 8 to 17 kg S ha^-1,was enough to maximize grain yield. On soils with 26 to 31 g kg^-1 OM, S fertilization increased yield 0.2 to 0.3 Mg ha^-1 at 2 of 10 site-years. Response to S fertilization at 8 of 10 site-years with soils with lower OM, 10 to 25 g kg^-1, had higher yield increases ranging from 0.7 to 3.0 Mg ha^-1. Grain yield responses occurred in both coarse- and fine-textured soils and were consistent and large at 2 sites. Sulfate-S concentration in the soil and S concentration in the whole plant (V4-V7) were not good indicators of response to S fertilization. For the majority of the site-years where grain yield increased with S fertilization, the grain S concentration, earleaf S concentration, and earleaf N:S were respectively <0.9 g kg^-1, <1.8 g kg^-1, and >15:1 without S treatment. These parameters improved with the addition of S but some site-years with these values did not have a yield response. These earleaf S and N:S ‘critical values’ may serve as reference for potentially S responsive sites, but more observations are necessary to validate these critical levels. Sites with higher basal values (without fertilizer treatment) for earleaf and grain S concentration and lower earleaf N:S still showed increased tissue S concentration upon S fertilizer application, albeit with no increase in grain yield. We encourage farmers to consider S fertilization at rates ranging from 8 to 17 kg S ha^-1 applied at sidedress. this recommendation for fields showing S deficiency symptoms or where R1 earleaf S concentration and N:S are below 1.8 g kg^-1 and above 15:1, respectively.

Thesis (M. A. (Agricultural Management)) -- University of Limpopo, 2020 / Field experiments were conducted at two locations; University of Limpopo (Syferkuil) and University of Venda (Thohoyandou) during 2015 and 2016 winter cropping seasons. The objectives of this study were to determine; the effect of genotype (ACC# 1, 3, 4 and 7) and planting density (33, 25 and 20 plants/m2) on four chickpea genotypes having contrasting growth patterns and also to determine the effect genotype and planting density on water use and water use efficiency of four chickpea genotypes having contrasting growth patterns. The experimental design was randomized complete block design in factorial arrangement with three replications. Plant height, number of primary and secondary branches, grain yield and yield components (number of pods per plant, number of seeds per pod, Harvest Index and 100 seed weight [100-SW] and above ground biomass, and were determined at different growth stages. Data obtained was subjected to analyses of variance using the general linear model of Genstat 17th edition. Significant differences between the treatments means were compared using the standard error of difference (LSD) of the means at 5% level. Correlation analyses were performed to assess the relationship between parameters. Plant height varied with genotype from 41 cm (84 DAE) to 44 cm (118 cm) at Syferkuil and 41 (56 DAE) to 44 cm (63 DAE) at Thohoyandou. Primary branches was not significantly affected by genotype and planting density at both locations and seasons. Planting density had significant effect on number of secondary branches, greater number was recorded at low (32, 6) density at Syferkuil in 2016. Above ground biomass was significantly affected by planting density at Syferkuil during in 2015 (5344 kg ha-1) and 2016 (3701 kg ha-1) growing seasons. Genotype and planting density did not affect number of pods plant-1, number of seeds plant-1, 100 SW (100 seed weight), and Harvest index were not significant at both locations and seasons. Grain yield was significantly affected by planting density at Syferkuil in 2015 and Thohoyandou in 2016. Grain yield increased with the increase in planting density at both locations. Two field experiments were conducted at University of Venda (Thohoyandou) during 2015 and 2016 winter cropping seasons. This study aimed at assessing the effect of genotype v and planting density on water use efficiency of four chickpea genotypes with contrasting growth patterns. Crop water use (WU) was determined by monitoring soil water content at 7-day intervals using a neutron probe and, water use efficiency (WUE) was determined as a ratio of crop biomass and grain yield to WU. Genotype and planting density had no significant effect on WU in 2015 and 2016. Genotype and planting density had no significant effect on biomass production (WUEb) and grain yield production (WUEg) in 2015. In contrast, WUEb and WUEg was significantly affected by planting density in 2016. WUEb was 43.2% greater at high density compared to low density. Similarly, WUEg was 39.3% greater at high density compared to low density. WUEb and WUEg increased with the increase with planting density. Therefore, manipulation of management practices such as planting density may increase chickpea production. Keywords: Planting density, genotype, grain yield and yield components, water use efficiency. / National Research Foundation (NRF) and University of Venda Capacity Development

Thesis (M. Sc. Agriculture (Agronomy)) -- University of Limpopo, 2019 / Cowpea (Vigna unguiculata) is a multi-purpose crop as it can be used for human consumption and livestock feeding. Cowpea serves as one of the cheapest sources of vegetable protein as the dry grain contains 25-30% protein. Its ability to tolerate drought and fix atmospheric nitrogen makes it suitable for marginal areas with low rainfall and poor soil fertility. However, low cowpea yields are common in Limpopo province due to shortage of improved varieties and lack of good seed for planting. The objectives of the present study were to determine growth, yield components and grain yield of elite cowpea genotypes across two locations and seasons, and to determine grain yield and yield components stability of the elite cowpea genotypes across the environments. The experiments were conducted at the University of Limpopo Experimental farm (Syferkuil) in Mankweng and Towoomba Research Station located in Bela-Bela, Limpopo Province during 2015/16 and 2016/17 growing seasons. The trials were carried out in a randomized complete block design (RCBD) consisting of three replications. Ten elite cowpea breeding lines (L1-L10) and a control check Bechuana White (BW) were planted at inter-row and intra-row spacings of 1 m and 0.3 m, respectively, in two rows of 6 m length. Round-up (isopropylamine salt of glyphosate) and Dual (S-metalachlor) at the rate of 3 L/ha and 0.5 L/ha, respectively, were used to control weeds at planting. Insecticide Karate (lambda-cyhalothrin) and Aphox (pirimicarb) at the rate of 1 L/ha and 500 g/ha were applied to control aphids, pod borers and other insects. Initial soil sampling was done at the depth of 0-20 cm to determine soil pH, organic matter, nitrate, ammonium, phosphorus and soil particle size. Agronomic data collected included number days to 50% flowering, number of days to 90% maturity, canopy width, plant height, peduncle length, number of pods per plant, pod length, hundred seed weight, fodder and grain yield. The collected data were subjected to analysis of variance using SAS software to determine the performance of the cowpea genotypes across the two locations and seasons. Means showing significant differences were separated using Duncan Multiple Range Test at the probability level of 5%. Data for number of days to 90% maturity, grain and fodder yields were further subjected to stability analysis through GGE biplot using Genstat software application. The results showed statistical differences for most of the studied traits as affected by genotype, location, seasonal effects and their interactions. Among the genotypes, average number of days to 50% flowering ranged from 53 to 60 days, while number of days to 90% maturity ranged from 89 to 96 days, with line L9 being the earliest to flower and mature. Tall plants were given by Line L5 (48.94 cm), followed by L7 (48.72 cm) and L10 (48.35 cm). Breeding line L7 recorded long peduncles with a mean of 36.37 cm. Number of pods per plant had a range of 16.00 to 25.52, while pod length varied from 14.46 to 17.63 cm, with line L7 having the highest number of pods per plant with long pods. Line L3 produced least number of pods per plant and shorter pods. Local check BW produced more number of seeds per pod as compared to all the breeding lines with a mean of 12.89 seeds/pod. One hundred seed weight varied from 15.67 g to 22.70 g among the genotypes. Grain yield among the genotypes ranged from 1441.20 to 2595.20 kg/ha with the best yielder being line L7, which was followed by line L2 (1928.00 kg/ha), L10 (1891.70 kg/ha) and Local variety BW (1858.70 kg/ha). The least grain yield was observed for line L8. Among the locations, Towoomba had significantly higher grain yield than Syferkuil with mean values of 1604.20 and 1982.20 kg/ha respectively. Significantly higher grain yield was recorded in 2016/17 season with a mean value of 1854.80 kg/ha than 2015/16 season (1732.30 kg/ha). Fodder yield ranged from 1934.20 to 3611.00 kg/ha, with line L3 being the highest yielder and it was followed by line L10 with an average of 3022.00 kg/ha. Local check BW produced the least fodder yields. The GGE biplot showed that lines L2, L9 and L4 matured earlier than all other lines including local variety BW and were stable across locations and seasons in terms of maturity. The biplot identified breeding lines L7, L2, L10 and Local check BW as the highest grain yielders but only line L7 and L2 were stable across the two locations and seasons. Lines L4, L10, L3, and L2 were the highest fodder yielders but only line L2 was stable across locations and seasons. Therefore, breeding lines L7 and L2 are recommended for both grain and fodder yield in both locations. Key words: cowpea, elite, breeding line, location, seasons, grain yield and stability.

Thesis (M. Sc. (Agronomy)) -- University of Limpopo, 2021 / Cowpea (Vigna unguiculata (L.) Walp) is an important annual leguminous crop grown in arid and semi-arid areas in Sub Saharan Africa. Most of the cowpea production in South Africa is mainly used for domestic consumption and, as seed for planting and little gets to be used in food processing, thus, there is a need to expand the utilization of cowpea through food processing. This study aimed to evaluate cowpea genotypes for phenotypic and canning quality traits. Field experiments were conducted at two locations in Limpopo Province, namely Syferkuil Agricultural Experimental Farm and Ga-Molepo village during the 2017/2018 growing season. The field experiment was comprised of 100 cowpea genotypes laid out in an Alpha Lattice Design replicated twice. Cowpea canning analysis was done using tomato puree following ARC-GC in-house method at the Agricultural Research Council-Grain Crops in Potchefstroom, North West Province of South Africa. Collected data on yield was analysed using Genstat 18th edition and XLSTAT 2021.1.1.1081 software for canning quality data. The results revealed significant differences among the cowpea genotypes based on the number of seeds per pod and 100 seed weight for Syferkuil. Significant differences were also observed among the studied genotypes for 100 seed weight at Ga-Molepo. The highest yield recorded across locations was for genotypes RV 555 (875.4 kg/ha), RV 207 (756,3 kg/ha), RV 439 (694.6 kg/ha) and RV 554 (682.3 kg/ha) respectively. The number of pods per plant recorded a high positive association with pod number per plant and number of seeds per pod. Grain yield of RV 558, RV 556, RV 207, RV 439 and RV 553 was high at Syferkuil and at Ga-Molepo RV 353, RV 194, IT99K-494-6, RV 341 and RV 202 recorded the highest yield. The Principal Component Analysis (PCA) revealed the three most important PCs contributing to a total variation of 76.71%. PC1, PC2, and PC3 contributed 51.01, 13.97 and 11.73%, respectively. For canning ability, out of 79 cowpea canned genotypes, only 11 genotypes were spoiled and had a bad odour. About 68 genotypes were suitable for canning including genotypes that had an excellent appearance without cracks or loose skins and even colour. Furthermore, there was vast variability among the genotypes based on yield and yield components as well as canning quality traits. Genotypes with high grain yield and had canning ability are recommended xi for canning. Data produced from this study will add useful information to the database of the characteristics of these cowpea genotypes.

<p>Improved phenotyping technologies and data analytic strategies have the potential to reduce the phenotyping bottleneck in breeding programs, increase the number of genotypes that can be evaluated, and improve genetic gain of maize. Ear photometry and remote sensing were evaluated in this dissertation for their integration into breeding programs to understand the development of grain yield in diverse germplasm and to better predict yield performance. Ear photometry was used in Chapter 2 to characterize the testcross performance of temperate and tropical inbred lines. The effect of heterosis among the temperate heterotic groups was more noticeable in the ear-related characteristics rather than kernel-size characteristics. Yield components were generally more heritable than grain yield per ear, so they were explored for their use in multi-trait genomic prediction for grain yield on a plot or ear basis in Chapter 3. Multi-trait genomic prediction of grain yield was improved where ear characteristics were known in the testing set compared with single-trait genomic prediction.  Additionally, single-trait genomic prediction was more accurate in the temperate germplasm compared to the tropical germplasm. Thus, ear photometry is an efficient method to quickly assess yield components in maize and improve yield prediction in certain circumstances. In Chapter 4, the effect of row selection, plot size, and plot trimming on remote sensing trait repeatability and prediction accuracy of biomass yield in sorghum or grain yield in maize was evaluated. Decreased plot size and configuration has been suggested to increase the number of genotypes that can be evaluated per unit area. In this study, larger plot sizes were favorable for increasing repeatability and excluding outer rows improved predictive modelling. Plot trimming was never shown to be significantly different from non-trimmed plots in this study. Genomic prediction is another way to minimize experimental size and phenotypic data collection and was evaluated in Chapter 5. A reaction norm was used to model the trajectory of hybrid yield performance across a gradient of 86 environments. The heritability and prediction accuracy of grain yield were both improved in the higher-yielding environments compared to the lower-yielding environments. Single nucleotide polymorphisms with the highest magnitude of effects were selected in each environment. Twenty-one SNPs were selected indicating many SNPs were selected in multiple environments. Candidate genes in linkage disequilibrium with many of these SNPs were previously reported as stress adaptions. Genomic prediction and remote sensing were integrated for prediction of grain yield in Chapter 6. Heritability of remote sensing traits generally improved throughout the growing season. Prediction accuracy of BLUPs were improved through an integrated phenomic and genomic prediction model for all scenarios tested. In summary, ear photometry and remote sensing are technologies to evaluate large populations for unique plant trait characteristics that can be used in combination with genomic prediction to improve understanding of grain yield development and grain yield prediction.</p>

Doctor of Philosophy / Department of Entomology / Larry L. Buschman / C. Michael Smith / Several studies were conducted to develop soybean management options that could provide protection from the soybean stem borer, Dectes texanus LeConte. Selected soybean genotypes were screened for host plant resistance against D. texanus. Soybean plants were grown in a footprint that could be covered by a field cage. When beetles were flying in the fields they were collected and placed in the field cages to increase the insect feeding pressure on the test plants. A susceptible commercial soybean variety treated with the systemic insecticide fipronil was used as a positive antibiosis check. Both commercial soybean varieties and plant introductions (PIs) obtained from the USDA National Soybean Germplasm Collection in maturity groups (MG) VI to VIII were tested over a four-year period. Since the number of ovipositions per plant could not be controlled, the ratio of oviposition punctures (OP’s) per live larvae (OP/ Lv) was used as a novel index of potential plant antibiosis to D. texanus. Field evaluations identified PI165673 as a genotype with a very high OP/ Lv ratio - similar to that for the fipronil antibiosis control. PI165673 appears to be potential source of resistance to D. texanus. Factorial analysis indicated that soybean maturity group was not significant factor in the expression of resistance. The OP/ Lv ratio appears to be more sensitive means of identifying antibiosis than other more conventional damage indices. The use of field cages demonstrated consistent plant responses from year to year during the multi-year study. Greenhouse-grown soybean plants, including transgenic plants containing the Manduca sexta chitinase gene, were not morphologically appropriate for successful D. texanus oviposition because the greenhouse-grown plants were poorly developed and had not produced enough pith in petioles. Therefore the greenhouse results were inconclusive. Analysis of the vertical distribution of D. texanus oviposition on soybean plants revealed that D. texanus oviposition was most likely to occur on leaf petioles on the upper five nodes of the plant canopy. Histomorphological observations of plant petioles indicated that the proportion of the petiole perimeter occupied by vascular bundles might be related to D. texanus oviposition. Both foliar and seed applications of fipronil suppressed D. texanus larval damage on soybean plants. The efficacy of these treatments was sustained for long periods, even until adult beetles were present in early August. The effects of the fipronil seed-treatment and harvest date on grain yield were both significant while the interaction was not. A physiological yield loss of 8.2% and plant lodging losses of 2.9% were associated with D. texanus infestation.

Lauko bandymas tiriant biologinių preparatų Fosfix ir NPK Magic įtaką žieminių kviečių produktyvumui skirtinguose azoto trąšų fonuose atliktas 2013 m. ASU Bandymų stotyje. Dirvožemis IDg8-k (LVg-p-w-cc) – karbonatingas sekliai glėjiškas išplautžemis (Calc(ar)i-Epihypogleyic Luvisols). Tyrimo objektas: Žieminių kviečių (Triticum aestivum L.) veislė ʽAdaʼ. Darbo metodai: Derliaus nuėmimo metu kiekviename bandymo laukelyje buvo išpjauti 4 – iose vietose 0,25 m2 apskaitiniai ploteliai. Kiekvieno laukelio kviečių pėdai atnešti į laboratoriją. Nustatyti derliaus struktūros elementai. Po to apskaičiuoti vidutiniai rodikliai. Tyrimų duomenys statistiškai įvertinti vieno veiksnio kiekybinių požymių dispersinės analizės metodu, taikant kompiuterinę programą ANOVA (Tarakanovas, Raudonius, 2003). Darbo rezultatai: NPK magic esmingai didino žieminų kviečių derlingumą, grudų skaičių varpose bei varpos produktyvumą visuose tręšimo fonuose. Atitinkamai derlingumo skirtumas lyginant su kontrole panaudojus NPK Magic 1,5t/ha. Pasėlio tankumui ir 1000 grudų masei NPK Magic esminiai pokyčiai nepastebėti. Išpurškus tuo pačiu metu preparatą Fosfix jo veiksmingumas pastebėtas mažesnis, tačiau visuose rodikliuose neesmingas lyginant su NPK Magic. Panaudojus Fosfix ir patręšus N140 ir N180 gautas esminis žieminų kviečių derlingumas (7,32 t/ha) lyginant su kontrole. / Field testing for biological agents Fosfix and NPC Magic on winter wheat productivity of different nitrogen fertilizer backgrounds were made in 2013 ASU test station. Soil IDg8 -k (LVg - pw - cc ) - shallow calcareous luvisol ( Calc ( ar) i - Epihypogleyic Luvisols) . Object of the work: winter wheat ( Triticum aestivum L. ) variety ʽAdaʼ. Method of the work: on harvest time for each test field was cut in 4 different places of 0.25 m2 plots accounting. Each box of wheat sheaves were bringed to the laboratory. Set vintage structure elements. Research data to statistically assess the quantitative characteristics of a factor analysis of variance method using a computer program ANOVA ( Tarakanovas, Red, 2003) . The results of the work: NPK magic substantially increased winter wheat yield, grain number per ear and ears productivity in all fertilization backgrounds. Accordingly yields compared to the control using NPK Magic 1.5 t / ha. Stand density and weight of 1000 grains NPK Magic fundamental changes were not noticed. Droplets at the same time with the product Fosfix efficacy had lower, but not essential in all indicators compared with NPK Magic. Using Fosfix and N140 and N180 fertilized received substantial winter wheat yield ( 7.32 t / ha) compared to the control.

Orientador: Marcelo Carvalho Minhoto Teixeira Filho / Resumo: A utilização de bactérias promotoras de crescimento de plantas (BPCPs) pode promover aumento na eficiência da fixação biológica de nitrogênio (FBN), com benefícios no desenvolvimento e produtividade de grãos de soja. Diante o exposto, objetivou-se avaliar os efeitos da coinoculação entre rizóbios e seis BPCPs (Azospirillum brasilense, Bacillus amyloliquefacens, B. licheniformis, B. pumilus, B. subtilis e Pseudomonas fluorescens), inoculadas via semente ou em jato dirigido na base da planta no estádio V3, sobre a nodulação, nutrição, acúmulo de nutrientes e produtividade de grãos de soja no Cerrado. Os experimentos foram conduzidos em sistema plantio direto na Fazenda Experimenal da Faculdade Unesp, Campus de Ilha Solteira, localizada no município de Selvíria – MS, Brasil. num Latossolo Vermelho Distrófico de textura argilosa, em cultivo irrigado. O delineamento experimental foi em blocos ao acaso com quatro repetições, dispostos em esquema fatorial 6x2+3, sendo coinoculação de rizóbios com seis BPCPs (Azospirillum brasilense, Bacillus amyloliquefacens, B. licheniformis, B. pumilus, B. subtilis e Pseudomonas fluorescens), inoculadas na semente ou em jato dirigido na base da planta no estádio V3 da soja; além da testemunha sem inoculação e N, inoculação de sementes apenas com rizóbios (Bradyrhizobium japonicum), e tratamento com adubação nitrogenada (ureia). A coinoculação da soja com as bactérias promotoras de crescimentos via semente ou em estádio V3 proporciona maior número ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The use of plant growth promoting communities may increase the biological nitrogen efficiency, with benefits in the development and productivity of soybean grains. Given the above, the objective of this study was to evaluate the effects of co-inoculation between rhizobia and six species of growth promoting bacteria (Azospirillum brasilense, Bacillus amyloliquefacens, B. licheniformis, B. pumilus, B. subtilis e Pseudomonas fluorescens), inoculated via seeds or directed jet at the base of the plant in V3 stage, on nodulation, nutrition, nutrient accumulation and yield of soybean grains at Cerrado. The experiments were conducted under no-tillage system at the Experimenal Farm belonging to Unesp-Ilha Solteira, located in Selvíria-MS, Brazil, in irrigated cultivation. The experimental design adopted was randomized blocks, with four replicates, arranged in 6x2+4 factorial outline, being co-inoculation of rhizobia with six species of growth promoting bacteria (Azospirillum brasilense, Bacillus amyloliquefacens, B. licheniformis, B. pumilus, B. subtilis e Pseudomonas fluorescens) inoculated in the seed or directed jet at the base of the plant in V3 stage in soybean, beyond the control without inoculation and nitrogen, seed inoculation only with rihzobia (Bradyrhizobium japonicum), and treatment with nitrogen fertilization (urea). The co-inoculation of soybean with growth promoting bacteria via seed or in the V3 stage provides greater numbers of nodules per plant relative to conventio... (Complete abstract click electronic access below) / Mestre

Orientador: José Roberto Môro / Banca: Cícero Beserra de Menezes / Banca: Robert Eugene Schaffert / Banca: Dilermando Perecin / Banca: Rinaldo César de Paula / Resumo: O trabalho objetivou identificar e classificar linhagens de sorgo, eficientes e ineficientes ao P avaliadas em ambientes com estresse e sem estresse de P, identificar a importância relativa da eficiência de aquisição e a eficiência de utilização em relação à eficiência de uso de P, obter as estimativas dos coeficientes de correlação genética e fenotípica, realizar análise de trilha e identificar os componentes principais. Avaliou-se 243 linhagens de sorgo e duas testemunhas adicionais divididas em três látices 9x9 com três repetições. Avaliaram-se as seguintes características nos ambientes com e sem estresse de P: florescimento, altura de plantas e produtividade de grãos. As características teor de fósforo nos grãos, eficiência de aquisição, eficiência de utilização interna de P, eficiência de uso de P, índice de colheita de P e quociente de utilização, foram avaliadas somente no ambiente com estresse de P. Foram identificadas e classificadas 107 linhagens eficientes ao P e 138 linhagens ineficientes avaliadas em ambientes com e sem estresse de P. Na importância relativa das eficiências o índice eficiência de aquisição foi o que melhor se relacionou com a eficiência uso de fósforo. De acordo com os resultados das correlações fenotípicas e genotípicas o índice de eficiência de uso de fósforo pode ser avaliado indiretamente, pela avaliação da produtividade de grãos em ambiente com estresse de P. Dentre as variáveis explicativas na análise de trilha, o teor de P total na planta foi a que melhor explicou os efeitos diretos nas variáveis básicas de eficiência de aquisição e uso de P. Foram identificados três componentes principais (PCA 1, 2 e 3), que juntos explicaram 81% da variação original dos dados / Abstract: This study aimed to identify and classify sorghum lines for P efficiency in environments with high and low P, to identify the relative importance of acquisition efficiency and utilization efficiency in relation to P use efficiency, to obtain the estimates of correlation coefficients and evaluate genetic and phenotypic path analyzes through the development of the direct and indirect effects of independent variables on the dependent variables, and identify the major components. Two hundred forty-three sorghum lines and two additional controls divided into three 9x9 lattices with three replications. Flowering, plant height and grain yield were evaluated in low and high P environments. Phosphorus content in the grain, P acquisition efficiency, P utilization efficiency of internal P, P use efficiency, harvest index and P utilization quotient were evaluated in the low P environment. One hundred and seven lines were identified and classified as P efficient and 138 lines as P inefficient. The relative efficiency of the P acquisition index was the most highly correlated with the efficiency of phosphorus use. These results suggest that the phenotypic correlation index of phosphorus use efficiency can be evaluated indirectly by the assessment of grain yield in P environments total P content in plant was the variable that best explained the direct effects, in the path analysis, of variables in the basic efficiency of acquisition and use. Three main components; 1, 2 and 3, together explained 81% of the variation of the original data / Doutor

Este é o primeiro relato da presença de bactérias diazotróficas dos gêneros Achromobacter e Zoogloea como endófitas de plantas de trigo, que foram identificadas pela análise das seqüências do DNA ribossomal 16S. Com o objetivo de estudar a localização dos isolados: IAC-AT-8- Azospirillum brasiliense, IAC-HT-11- Achromobacter insolitus, IAC-HT-12- Zoogloea ramigera nas plantas de trigo, foi realizado um experimento em condições axênicas. Após 15 dias da inoculação, as plantas foram observadas em microscópio eletrônico e visualizou-se a presença das bactérias externamente nas raízes e internamente no córtex, na região de alongamento. Para estudar possíveis benefícios propiciados por estes isolados à cultura do trigo em condições de campo, foram instalados dois experimentos no ano de 2002, com dois genótipos de trigo (ITD-19 e IAC-370) e três doses de N. As análises foram realizadas no estádio de quatro folhas e de perfilhamento. A inoculação promoveu maior massa de matéria seca e N acumulado e aumentou a produtividade de grãos, principalmente na presença de adubo nitrogenado adicional, porém, revertendo em lucro para o agricultor. As respostas variaram em relação ao local de cultivo. Em 2003, foi realizado outro experimento muito semelhante aos anteriores, entretanto, as análises foram realizadas no estádio perfilhamento e de maturidade fisiológica. A inoculação promoveu benefícios à cultura do trigo independentemente do genótipo utilizado, ou seja, aumento do N acumulado no grão, com a inoculação do isolado IAC-AT-8, e da produtividade de grãos na maior dose de N, com o isolado IACHT- 11. Os benefícios propiciados às plantas pela inoculação de bactérias diazotróficas podem estar relacionados à capacidade de síntese de fitormônios. Por isso instalou-se um experimento no ano de 2005 com o objetivo de relacionar a capacidade de síntese de indóis com os possíveis benefícios à cultura do trigo em condições de campo. Os isolados diferiram quanto a quantidade de indóis que sintetizaram, entretanto, houve benefícios para a cultura, principalmente com a adição de adubo nitrogenado, demonstrando que outros mecanismos podem ser responsáveis pelas respostas positivas. Assim, foi realizado um experimento em casa de vegetação para estudar a influência da inoculação no metabolismo do nitrogênio das plantas e avaliar a colonização em substrato não esterilizado. Os isolados foram marcados com resistência a antibióticos. Após 40 dias da inoculação todos os isolados estavam presentes no interior das raízes, entretanto, não foram detectados no solo. O isolado IAC-HT-11, influenciou o metabolismo do nitrogênio das plantas, propiciando maior atividade das enzimas redutase do nitrato e sintetase da glutamina, e maior teor de clorofila, resultando no aumento da eficiência de utilização do N. Apesar das respostas terem sido variáveis, em todos os experimentos realizados foram obtidas respostas positivas à inoculação do isolado IAC-HT-11 de Achromobacter insolitus, na presença de adubo nitrogenado adicionado. A inoculação é uma prática não onerosa, portanto, viável economicamente, aumentando a produtividade de grãos e gerando lucro para o agricultor. / This study reports for the first time the endophytic nature of Achromobacter and Zoogloea in wheat plants, that were identified by 16S rDNA gene sequence analyses. To find out the localization of the bacterial cells (IAC-AT-8- Azospirillum brasiliense, IACHT- 11- Achromobacter insolitus, IAC-HT-12- Zoogloea ramigera) in/on wheat plants, an experiment was set up under axenic conditions. Fifteen days after inoculation, the plants were observed under electron microscope. All the strains could be visualized on the external part of the root and in the inner part at the elongation zone, in the cortex cells. Two field experiments were carried out in year of 2002, with the aim of evaluating the benefits from inoculation of these strains in wheat plants, with two wheat genotypes (ITD-19 and IAC-370) and three levels of nitrogen fertilizer. The plants were evaluated at four leaves and at tillering stage. Inoculated plants presented increases in dry matter, N accumulation and grain yield, especially in combination with N fertilizer, generating financial profits for the farmer. The responses to inoculation varied according to the location. A field experiment was carried out, in year of 2003, with the same experimental set up used at the previous year. However, the plants were evaluated at tillering stage and at maturity stage. Grain yield and the main yield components were evaluated at harvest. Independent of the cultivar or the nitrogen dose, plants inoculated with the strain IAC-AT-8 presented increases in grain N accumulation and, at the highest nitrogen dose, the strain IAC-HT-11 increased grain yield. The plants? benefits due to the inoculation of endophytic diazotrophic bacteria may also result from their indole synthesis, a field experiment was carried out to find out which had been the main mechanisms for improvement of plant growth and yield, in 2005. The employed strains produced variable amounts of indoles, however, the inoculation brought benefits to wheat plants, mainly in the presence of added N, demonstrated that others mecanisms could be acting for the positive responses to inoculation. In this way, a greenhouse experiment was carried out with the aim of evaluating the influence of inoculation on nitrogen metabolism in wheat plants, and the colonization in unsterilized substratum. The strains were selectively market with antibiotic resistence to. Forty days after inoculation, all three strains had been established in the interior of the roots, however, they could not be detected in the soil. The strain IAC-HT-11 influenced the N metabolism of the plants, increased the nitrate reductase and glutamine synthetase activities, and the chlorophyll content, causing higher efficiency in N utilization. In spite of the great variability of the inoculation response, IAC-HT-11, Achromobacter insolitus, generated the greatest yield increase when combined with nitrogen fertilizer. Inoculation of diazotrophic bacteria is an inexpensive technique, that is economically sound, promoting the increase in grain yield and generating financial profits for the farmer.