Effect of management practices on mycorrhizal infection, growth and dry matter partitioning in field-grown bean

The experiment was carried out on unsterilized field soil with low phosphorus availability with the objective of examining the effect of cultural practices on mycorrhizal colonization and growth of common bean. The treatments were: three pre-crops (maize, wheat and fallow) followed by three soil management practices ("ploughing", mulching and bare fallow without "ploughing" during the winter months). After the cultural practices, Phaseolus vulgaris cv. Canadian Wonder was grown in this soil. Fallowing and soil disturbance reduced natural soil infectivity. Mycorrhizal infection of the bean roots occurred more rapidly in the recently cropped soil than in the fallow soil. Prior cropping with a strongly mycorrhizal plant (maize) increased infectivity even further.

Physiological responses of maize and cowpea to intercropping

The effect of intercropping on plant water status, gas exchange and productivity of maize (Zea mays L.) cv. Centralmex, and cowpea (Vigna unguiculata L. (Walp)) cv. Pitiuba were evaluated under semi-arid conditions at the Embrapa-Centro de Pesquisa Agropecuária do Trópico Semi-Árido (CPATSA) at Petrolina, PE, Brazil. The treatments were: maize and cowpea as sole crops, at a population of 40,000 plants ha-1, and intercropped at a population of 20,000 plants ha-1. The results obtained in this paper appear to be related to the degree of competition experienced by the components, mainly for water and light. Maize intercropped had higher values of leaf water potential, stomatal conductance, transpiration and photosynthesis than as sole crop. Intercropped cowpea had higher values of leaf water potential but lower stomatal conductance, transpiration and photosynthesis than sole cowpea. Maize productivity increased 18% in relation to sole crop whereas a 5% decrease was observed with cowpea. Despite these facts the Land Equivalent Ratio obtained was 1.13 indicating intercropping advantage over the sole system. The higher partial Land Equivalent Ratio observed for maize suggests that this specie was the main component influencing the final productivity of the intercropping system studied.

New wheat genotypes tolerant to aluminum toxicity obtained by mutation induction

Seed from the sensitive wheat (Triticum aestivumL.) cultivar Anahuac was treated to gamma-ray irradiation and eleven Al3+ tolerant mutants selected. The objective was to compare these mutants to the original Anahuac and to the tolerant wheat cultivars IAC-24 and IAC-60 from 1994 to 1996 in acid (Capão Bonito) and limed (Monte Alegre do Sul) soil field trials, in the State of São Paulo, Brazil. Grain yield and agronomic characteristics were analyzed. All the mutant lines yielded higher than the sensitive Anahuac cultivar in the acid soils of Capão Bonito. Under limed soil conditions, 10 mutants had a similar yield to the original sensitive cultivar and one a lower yield. The majority of the mutants were similar in yield to the tolerant cultivars IAC-24 and IAC-60 under both conditions. Some of the mutants showed altered agronomic characteristics, but these alterations did not generally influence the grain yield. The results indicated that tolerant lines with good characteristics may be obtained from a susceptible cultivar by mutation induction, thus allowing cropping under conditions where Al3 + is a limiting factor.

Quinoa (Chenopodium quinoa) reaction to herbicide residue in a Brazilian Savannah soil

The quinoa (Chenopodium quinoa Willd.) cultivation, one of the most promising in double cropping with soybeans or maize, depends on weed control. The objective of this work was to evaluate quinoa reaction to herbicide residue in a savannah soil. Six herbicide treatments, trifluralin, pendimethalin, clomazone, imazaquin, trifluralin + imazaquin and control, were applied, prior to summer cultivation of soybean, in a Dark-Red Latosol (typic Haplustox). Soybean cultivar BR 9 Savana was grown and soil samples were collected at 15, 38, 100, 145 and 206 days after treatment and stored at -5ºC. Bioassays were conducted in greenhouse, using quinoa, cultivar Q18. Imazaquin was the most harmful to quinoa seedlings, up to 206 days after application, followed by clomazone 15-38 days after application; trifluralin and pendimethalin had no residual effect. These results suggest that a broad-base screening should be conducted.

Effects of plant population and nitrogen fertilizer on yield and efficiency of maize-bean intercropping

Nitrogen supply and plant population are basic parameters for cereal-legume intercropping. In order to study plant population and nitrogen fertilizer effects on yield and yield efficiency of maize-bean intercropping, a field experiment was established. Three bean plant populations and three nitrogen levels were used. Maize dry matter accumulation decreased with increases in bean plant population. Competitive effect of intercrop beans on maize yields was high at higher plant populations, being decreased by nitrogen fertilizer; application of 50 kg ha-1 N was very efficient in increasing maize cob yield. Intercropping significantly decreased harvest index of beans in all plant population and nitrogen fertilizer situations. The efficiency of intercropping, compared to sole cropping, was evidenced by the values obtained for Land Equivalent Ratio (LER) for biomass, cob and pod yields that increased with increases in bean plant populations and nitrogen fertilizer levels.

Leaf mineral composition of grafted eggplant grown in soil infested with Verticillium and root-knot nematodes

The objective of this work was to determine differences in leaf mineral composition between ungrafted and grafted onto (Solanum torvum) eggplant (Solanum melongena), cultivars 'Faselis' and 'Pala', grown in a soil infested with Verticillium dahliae and Meloidogyne incognita, or in a noninfested soil. Grafting increased leaf P and Mn concentrations, and decreased N concentrations, in both soils. Grafting also enhanced leaf Ca concentration of 'Pala', but it did not affect that of 'Faselis' depending on the cropping year. Leaf Mg concentration of grafted plants in infested soil was lower than that of ungrafted ones in noninfested soil. Results showed that, under the same fertilization program, the grafted 'Faselis' plants used the nutrients more efficiently than the 'Pala' ones. Use of S. torvum as a rootstock for 'Faselis' resulted in an effective protection against multiple pathogen infestation. Fertilization may be necessary when grafted 'Faselis' plants are grown in a soil infested with the pathogens, since grafting and infestation generally decrease leaf N, Mg, Ca and Fe concentrations, either by reducing the nutrient concentrations directly or by increasing leaf Mn concentration.

Induction of transgenic hairy roots in soybean genotypes by Agrobacterium rhizogenes‑mediated transformation

The objective of this work was to perform the screening of soybean genotypes as to their ability to respond to the induction of hairy roots by Agrobacterium rhizogenes‑mediated transformation. Four Brazilian soybean cultivars (BRSMG 68 Vencedora, BRS 137, Embrapa 48, and MG/BR 46 Conquista) and two North American ones adapted to Brazilian cropping conditions (Bragg and IAS‑5) were screened for their capacity to respond to A. rhizogenes in protocols for in vitro hairy root culture and ex vitro composite plant production. Four‑day‑old seedlings with uniform size were injected with A. rhizogenes harboring the plasmid p35S‑GFP. Seedlings expressing green fluorescent protein (GFP) in at least one hairy root were used to determine the transformation frequency. Using an axenic in vitro protocol, excised cotyledons from four‑day‑old seedlings were infected with A. rhizogenes harboring the pCAMBIA1301 plasmid, containing the gusA reporter gene. The transformation frequency and the number of days for hairy root emergence after bacterial infection (DAI) were evaluated. The transformation frequency and DAI varied according to the genotype. Cultivars MG/BR 46 Conquista and BRSMG 68 Vencedora are more susceptible to A. rhizogenes and can be recommended for transformation experiments.

Fusarium wilt incidence and common bean yield according to the preceding crop and the soil tillage system

The objective of this work was to evaluate the effects of preceding crops and tillage systems on the incidence of Fusarium wilt (Fusarium oxysporum f. sp. phaseoli) and common bean (Phaseolus vulgaris) yield. The cultivar BRS Valente was cultivated under center‑pivot irrigation in the winter seasons of 2003, 2004 and 2005, after several preceding crops established in the summer seasons. Preceding crops included the legumes Cajanus cajan (pigeon pea), Stylosanthes guianensis, and Crotalaria spectabilis; the grasses Pennisetum glaucum (millet), Sorghum bicolor (forage sorghum), Panicum maximum, and Urochloa brizantha; and a consortium of maize (Zea mays) and U. brizantha (Santa Fé system). Experiments followed a strip‑plot design, with four replicates. Fusarium wilt incidence was higher in the no‑tillage system. Higher disease incidences corresponded to lower bean yields in 2003 and 2004. Previous summer cropping with U. brizantha, U. brizantha + maize consortium, and millet showed the lowest disease incidence. Therefore, the choice of preceding crops must be taken into account for managing Fusarium wilt on irrigated common bean crops in the Brazilian Cerrado.

Ruzigrass affecting soil-phosphorus availability

The objective of this work was to evaluate the effectiveness of ruzigrass (Urochloaruziziensis) in enhancing soil-P availability in areas fertilized with soluble or reactive rock phosphates. The area had been cropped for five years under no-till, in a system involving soybean, triticale/black-oat, and pearl millet. Previously to the five-year cultivation period, corrective phosphorus fertilization was applied once on soil surface, at 0.0 and 80 kg ha-1 P2O5, as triple superphosphate or Arad rock phosphate. After this five-year period, plots received the same corrective P fertilization as before and ruzigrass was introduced to the cropping system in the stead of the other cover crops. Soil samples were taken (0-10 cm) after ruzigrass cultivation and subjected to soil-P fractionation. Soybean was grown thereafter without P application to seed furrow. Phosphorus availability in plots with ruzigrass was compared to the ones with spontaneous vegetation for two years. Ruzigrass cultivation increased inorganic (resin-extracted) and organic (NaHCO3) soil P, as well as P concentration in soybean leaves, regardless of the P source. However, soybean yield did not increase significantly due to ruzigrass introduction to the cropping system. Soil-P availability did not differ between soluble and reactive P sources. Ruzigrass increases soil-P availability, especially where corrective P fertilization is performed.

Estimates of genetic parameters for fruit yield and quality in custard apple progenies

Apparently, there are no custard apple cultivars defined for the northeastern region of Brazil. The establishment of breeding programs aimed at the selection of types from productive locations for later cloning is desirable. This work's objective was to evaluate the yield (during the first three crops) and quality (first crop) of fruits from 20 half-sibling custard apple tree progenies, selected from home orchards. An additional objective was to estimate genetic parameters for the traits evaluated. A micro sprinkling-irrigated experiment was conducted in Mossoró-RN, Brazil, as random blocks with five replications. In characteristics evaluated for periods longer than a year (diameter, height and mean weight of fruits, number of fruits ha-1 and fruit yield (kg ha-1), and a split-plot design was adopted, with progenies considered as plots and annual cropping seasons as subplots. The best progenies in terms of fruit yield (A3 and A4) are not necessarily the best for fruit dimensions and fruit mean weight (A2, FE4, JG1, JG2, SM1, SM7, and SM8). These progenies show great potential to be used in future studies on crosses or on vegetative propagation. In this regard, progeny JG2 should be highlighted as promising in terms of yield and fruit size. The progenies are not different with regard to percentages (in relation to mean fruit mass) of pericarp, endocarp, seeds, and receptacle, in the fruit, and fruit volume, number of seeds/fruit, and total soluble solids content in the fruit pulp, but progeny FE4 presents higher total titratable acidity in the fruit pulp. Narrow-sense heritability estimates were relatively high for all characteristics in which there was variability between progenies, with higher values for number of fruits ha-1 (80 %) and fruit yield (78 %). Relatively high coefficients of genotypic variation (around 20%) were observed for number of fruits ha-1 and fruit yield, with lower values for the other characteristics. There were positive genotypic and phenotypic correlations between fruit diameter (FD) and fruit height, FD and mean fruit weight, and number of fruits ha-1 and fruit yield.

Effect of humic substances and weather conditions on leaf biochemical changes of fertigated guava tree, during orchard establishment

In São Francisco Valley, Northeast Brazil, humic substances have been used by growers in fertigated fruit crops, due to its improvements on soil conditions and in plant nutrient uptake, metabolism and growth, reported from different growing places and crops. Nevertheless, little information about plant response to humic substance usage for local soil, weather and cropping system conditions is known. Hence, the metabolic response of guava tree during the orchard establishment to fertigation with humic substances and its correlation to the weather conditions were evaluated in Petrolina, State of Pernambuco. The treatments were manure application in soil combined with mineral fertilizers and humic substances applied through water of irrigation. The results showed that the fertigation treatments and plant age did not present conclusive effects in guava leaf contents of carbohydrates, proteins and amino acids. On the other side, the leaf contents of these compounds were influenced by the weather conditions.

The effects of inter-crop cultivation Between rows of citrus crop on spreading of Guignardia citricarpa Ascospores and in the citrus black spot occurrence

This study highlighted the effect of planting coast-cross grass and forage peanut cv. Amarilis between rows of Natal oranges on spreading of Guignardia citricarpa ascospores and consequent citrus black spot control. Treatments evaluated were: 1- conventional cultivation, free of fungicides; 2- conventional cultivation, using protective fungicides; 3- inter-crop cultivation of coast-cross grass between rows of citrus crops and; 4- inter-cropping cultivation of forage peanut between the rows of citrus crops. Quest Volumetric Spore SystemTM traps were set in order to determine the number of ascospores released. A total of 33 inspections were conducted weekly, from the end of August until early September the following year. A diagrammatic scale was used to determine the severity of the disease as well as the percentage of fruits having a commercial standard. The coast-cross grass was more effective in reducing the number of ascospores produced, whose average statistics were lower than in the conventional treatments, free-fungicides. The inter-crop and conventional cultivation method coupled with fungicide treatment was more effective in reducing the severity of citrus black spot symptoms, and differs statistically from the fungicide-free control method. These methods also resulted in a higher percentage of fruits of a commercial standard, ranging from the 89% through the 91% percentile, and the cultivation, free of fungicides, fell within the 73%.

Investigation of the occurrence of pesticide residues in rural wells and surface water following application to tobacco

In this work the exposure of wells and surface water to pesticides, commonly used for tobacco cropping, was assessed. Water consumption wells and surface water flows were sampled at different times. After a preconcentration step with solid phase extraction (SPE), the selected pesticides were determined by gas chromatography with electron capture detection (GC-ECD) or high performance liquid chromatography with diode array detection (HPLC-DAD). No pesticides were detected in the well water samples and surface water flow in the winter season. However, in the spring and summer higher concentrations of chlorpyrifos and imidacloprid were found in the water source samples. Atrazine, simazine and clomazone were also found. The occurrence of pesticides in collected water samples was related with the application to tobacco.

Cultural practices and genetic resistance as factors affecting soybean stem canker and plant yield in the Cerrado

Field experiments were conducted in the 1995-96 soybean (Glycine max) growing season to evaluate the effects of cultural practices and host genetic resistance on the intensity of soybean stem canker, caused by Diaporthe phaseolorum f.sp. meridionalis (Dpm). Experiments were conducted in a commercial field severely infected in the previous (1994-95) season. In one study, minimum tillage (MT) and no-tillage (NT) cropping systems were investigated for their effects on disease development and on plant yields in cvs. FT-Cristalina (susceptible) and FT-Seriema (moderately resistant). Another study evaluated the effects of plant densities (8, 15, 21 and 36 plants/m) on disease development in cvs. FT-Cristalina, FT-101 (moderately resistant) and FT-104 (resistant). Disease incidence and severity were consistently lower in NT than in MT, and plant yields were increased by 23% and 14% in the NT system for the susceptible and moderately resistant cultivars, respectively, compared to the yields in the MT system. The Gompertz and Logistic models described well the disease progress curves in all situations. For both susceptible and moderately resistant cultivars, disease severity increased proportionately to the increase in plant densities. At the end of the season, 100% of the plants of cv. FT-Cristalina were infected by Dpm, at all plant densities. Disease levels on cv. FT-101 were intermediate while only very low disease levels were recorded on cv. FT-104. There was a consistent negative correlation between stem canker severity and yield. Some practices demonstrated potential for direct application in disease control, and could be combined considering their additive effects.

Progress of soybean charcoal rot under tillage and no-tillage systems in Brazil

The increase in incidence of charcoal rot caused by Macrophomina phaseolina on soybeans (Glycine max) was followed four seasons in conventional and no-till cropping systems. In the 1997/98 and 2000/01 seasons, total precipitation between sowing and harvest reached 876.3 and 846.9 mm, respectively. For these seasons, disease incidence did not differ significantly between the no-till and conventional systems. In 1998/99 and 1999/00 precipitation totaled 689.9 and 478.3 mm, respectively. In 1998/99, in the no-till system, the disease incidence was 43.7% and 53.1% in the conventional system. In 1999/00 the final incidence was 68.7% and 81.2% for the no-till and conventional systems, respectively. For these two seasons, precipitation was lower than that required for soybean crops (840 mm), and the averages of disease incidence were significantly higher in the conventional system. The concentration of microsclerotia in soil samples was higher in samples collected in conventional system at 0 - 10 cm depth. However, analysis of microsclerotia in roots showed that in years with adequate rain no difference was detected. In dry years, however, roots from plants developed under the conventional system had significantly more microsclerotia. Because of the wide host range of M. phaseolina and the long survival times of the microsclerotia, crop rotation would probably have little benefit in reducing charcoal rot. Under these study conditions it may be a better alternative to suppress charcoal rot by using the no-till cropping system to conserve soil moisture and reduce disease progress.