Scielo RSS <![CDATA[Scientia Agricola]]> vol. 71 num. 1 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[<b>Process-based simple model for simulating sugarcane growth and production</b>]]> Dynamic simulation models can increase research efficiency and improve risk management of agriculture. Crop models are still little used for sugarcane (Saccharum spp.) because the lack of understanding of their capabilities and limitations, lack of experience in calibrating them, difficulties in evaluating and using models, and a general lack of model credibility. This paper describes the biophysics and shows a statistical evaluation of a simple sugarcane processbased model coupled with a routine for model calibration. Classical crop model approaches were used as a framework for this model, and fitted algorithms for simulating sucrose accumulation and leaf development driven by a source-sink approach were proposed. The model was evaluated using data from five growing seasons at four locations in Brazil, where crops received adequate nutrients and good weed control. Thirteen of the 27 parameters were optimized using a Generalized Likelihood Uncertainty Estimation algorithm using the leave-one-out cross-validation technique. Model predictions were evaluated using measured data of leaf area index, stalk and aerial dry mass, and sucrose content, using bias, root mean squared error, modeling efficiency, correlation coefficient and agreement index. The model well simulated the sugarcane crop in Southern Brazil, using the parameterization reported here. Predictions were best for stalk dry mass, followed by leaf area index and then sucrose content in stalk fresh mass. <![CDATA[<b>Correlations of visual scores, carcass traits, feed efficiency and retail product yield in Nellore cattle</b>]]> The growing use of visual scores (VS) and ultrasound (US) for carcass evaluation in breeding programs, calls for a knowledge of the relationships between these traits and other relevant characteristics, such as feed efficiency and production of commercial cuts. The objective of this study was to evaluate correlations between body visual scores and carcass traits identified by ultrasound (US) and feed efficiency (FE), carcass weight (HCW), dressing percentage (DP) and retail product yield (RPY) in beef cattle. Nellore cattle (male), 42 non-castrated [NCAST] and 44 castrated [CAST]) were evaluated by both VS and US, at the postweaning (15-month old) and finishing phases (21-month old). Visual scores of conformation (C), precocity (P) and muscling (M) were assessed and the backfat thickness (UBFT), rump fat thickness (URFT) and ribeye area (UREA) were measured by ultrasound. Gain-to-feed (G:F) ratio and residual feed intake (RFI) were measured in feedlot. Hot carcass weight, DP and RPY were determined at harvest. Non-castrated cattle had greater HCW and RPY but lower UBFT and URFT than CAST. Postweaning VS and US were poorly correlated with FE in both sexual conditions. Finishing VS were negatively correlated with G:F in CAST and finishing URFT was negatively correlated with RPY in NCAST. The relationship of VS and US with feed efficiency and meat yield is affected by age at the date of evaluation and by castration. Feed efficiency is not related to the yield of meat cuts in Nellore cattle <![CDATA[<b>Forage yield and nutritive value of <i>Panicum maximum</i> genotypes in the Brazilian savannah</b>]]> The narrow genetic variability of grasslands and the incidence of new biotic and abiotic stresses have motivated the selection of new Panicum maximum genotypes for use as forage for beef cattle in the Brazilian savannah. This study aimed to evaluate forage yield and nutritive value of P. maximum genotypes including 14 accessions (PM30 to PM43), four intraspecific hybrids (PM44 to PM47) and six cultivars (Aruana, Massai, Milênio, Mombaça, Tanzania and Vencedor), examining 24 genotypes over two years (2003 and 2004). Milênio cultivar was the genotype with the highest dry matter yield (DMY) in both years (18.4 t ha-1 and 20.9 t ha-1, respectively) although it presented a high proportion of stems (~ 30%). Genotypes that showed higher Leaf DMY in both years were the accession PM34 (14.7 t ha-1) and the hybrid PM46 (14.0 t ha-1), while Mombaça and Tanzania yielded 12.5 and 11.0 t ha-1, respectively. Leaf organic matter digestibility and leaf DMY for PM40 and PM46 genotypes exceeded the mean (> 656 g kg-1 and > 11.7 t ha-1, respectively). For this reason, PM40 and PM46 can be considered promising P. maximum genotypes for use as forage for grazing systems in the Brazilian savannah. <![CDATA[<b>Critical points on growth curves in autoregressive and mixed models</b>]]> Adjusting autoregressive and mixed models to growth data fits discontinuous functions, which makes it difficult to determine critical points. In this study we propose a new approach to determine the critical stability point of cattle growth using a first-order autoregressive model and a mixed model with random asymptote, using the deterministic portion of the models. Three functions were compared: logistic, Gompertz, and Richards. The Richards autoregressive model yielded the best fit, but the critical growth values were adjusted very early, and for this purpose the Gompertz model was more appropriate. <![CDATA[<b>Morphological phenotypic dispersion of garlic cultivars by cluster analysis and multidimensional scaling</b>]]> Multivariate techniques have become a useful tool for studying the phenotypic diversity of Germplasm Bank accessions, since they make it possible to combine a variety of different information from these accessions. This study aimed to characterize the phenotypic dispersion of garlic (Allium sativum L.) using two multivariate techniques with different objective functions. Twenty accessions were morphologically characterized for bulb diameter, length, and weight; number of cloves per bulb; number of leaves per plant; and leaf area. Techniques based on generalized quadratic distance of Mahalanobis, UPGMA (Unweighted Pair Group Method with Arithmetic Mean) clustering, and nMDS (nonmetrric MultiDimensional Scaling) were applied and the relative importance of variables quantified. The two multivariate techniques were capable of identifying cultivars with different characteristics, mainly regarding their classification in subgroups of common garlic or noble garlic, according to the number of cloves per bulb. The representation of the phenotypic distance of cultivars by multidimensional scaling was slightly more effective than that with UPGMA clustering. <![CDATA[<b>Constitutive overexpression of GmDof17-1, a putative DOF transcription factor from soybean causing growth inhibition in tobacco</b>]]> The Dof proteins belong to a large family of plant transcription factors that share a single highly conserved zinc finger and play an important role in many physiological processes. To elucidate the function of Dof in soybean, GmDof17-1 was cloned from soybean (Glycine max (L.) Merr); the open reading frame (ORF) of GmDof17-1 is 846 bp and encodes a putative protein that includes 281 amino acids. Using qRT-PCR, the expression profiles of GmDof17-1 were obtained for various parts of the soybean plant. GmDof17-1 was primarily expressed in the roots and pods at various stages of pod development. The gene was ectopically expressed in tobacco under the control of the 2 × CaMV35S promoter to study the functions of the gene product. The transgenic tobacco plants showed to be dwarf, and the indole-3-acetic acid (IAA) content was decreased, whereas the sulfur-containing amino acid content of the seeds increased. These results provide new insight into the function of GmDof17-1 in seed development. <![CDATA[<b>Improvement in yield and fruit size and quality of the main Italian table olive cultivar 'Nocellara del Belice'</b>]]> Olive (Olea europaea L.) shows alternate bearing, with unreliable cropping patterns and inconsistent fruit size and quality every year. In many countries, thinning with naphthaleneacetic acid (NAA) is used to minimise alternate bearing behavior in olives. However, in Italy, growers are reluctant to employ this practice and no detailed knowledge is available for specific cultivars. We evaluated the effects of spraying NAA on various dates on the productive and vegetative characteristics of the main Italian table olive cultivar'Nocellara del Belice'. Trunk cross-sectional area, fruit set, fruit drop, fruit size, pit size, yield per tree, crop density and flesh to pit ratio were analysed. The NAA treatment applied on the earliest of the dates selected increased fruit weight and flesh to pit ratio, by reducing crop density and enhancing the leaf to fruit ratio, without reducing yield. Two distinct negative relationships were found between fruit weight and crop density during "on" and "off" years, but a unique relationship between pit weight vs. crop density in both years, suggested that the pit is the strongest sink. Fruit size and quality of'Nocellara del Belice' can be enhanced by NAA application, thereby increasing economic returns in the "on" year. <![CDATA[<b>Do soil fertilization and forest canopy foliage affect the growth and photosynthesis of Amazonian saplings?</b>]]> Most Amazonian soils are highly weathered and poor in nutrients. Therefore, photosynthesis and plant growth should positively respond to the addition of mineral nutrients. Surprisingly, no study has been carried out in situ in the central Amazon to address this issue for juvenile trees. The objective of this study was to determine how photosynthetic rates and growth of tree saplings respond to the addition of mineral nutrients, to the variation in leaf area index of the forest canopy, and to changes in soil water content associated with rainfall seasonality. We assessed the effect of adding a slow-release fertilizer. We determined plant growth from 2010 to 2012 and gas exchange in the wet and dry season of 2012. Rainfall seasonality led to variations in soil water content, but it did not affect sapling growth or leaf gas exchange parameters. Although soil amendment increased phosphorus content by 60 %, neither plant growth nor the photosynthetic parameters were influenced by the addition of mineral nutrients. However, photosynthetic rates and growth of saplings decreased as the forest canopy became denser. Even when Amazonian soils are poor in nutrients, photosynthesis and sapling growth are more responsive to slight variations in light availability in the forest understory than to the availability of nutrients. Therefore, the response of saplings to future increases in atmospheric [CO2] will not be limited by the availability of mineral nutrients in the soil. <![CDATA[<b>Breeding new sugarcane clones by mixed models under genotype by environmental interaction</b>]]> Sugarcane (Saccharum spp.) is one of the most important crops cultivated in the tropics and subtropics and plays a significant economic and environmental role in Brazil. Twentyfour new clones were evaluated in different locations as potential models for recommendation as new varieties. The mixed model methodology, using the harmonic mean of the relative performance of genetic values (MHPRVG), facilitated the analysis of genotypic stability and adaptability, culminating in the recommendation of clones for each location. MHPRVG ranked clones RB92579, RB867515, SP81-3250, RB947520 and RB931530 as the best five, and, additionally, clones with greater genotypic potential were identified for each test in the six localities. <![CDATA[<b>Eradicant and curative treatments of hexanal against peach brown rot</b>]]> Brown rot, caused by Monilinia spp. , is one of the most important peach (Prunuspersica (L.) Batsch) diseases and the main cause of postharvest losses. Currently, alternative methods for postharvest disease control, such as the use of volatiles, are under investigation. The objective of this study was to determine the effects of hexanal on the in vitro development of Monilinia fructicola and M. laxa and on monocyclic components of brown rot on peaches. To evaluate the effect on pathogen development in vitro, a single dose of 215 µL of liquid hexanal was placed on glass jars in closed plastic containers (4.3 L) at the moment of fungi transfer, 24 or 48 h after transferring to Petri dishes. After hexanal application, the Petri dishes were kept inside the containers that were closed for 24 h at 20 ºC. Mycelial growth was measured seven days after hexanal removal. For in vivo assays, inoculated fruits were kept in closed plastic containers, and hexanal was applied at the moment of fruit inoculation or 24 hours thereafter. The monocyclic components infection frequency, expressed as brown rot incidence, lesion diameter and lesion sporulation, were assessed daily for seven days. Overall, hexanal was more effective in inhibiting mycelial growth when applied at the moment of pathogen transfer. Hexanal did not prevent pathogen infection, but reduced lesion diameter and completely inhibited spore production on the fruit for both treatments. Hexanal provides a promising alternative for chemical control and can be used in postharvest handling systems. <![CDATA[<b>Introducing the term 'Biocontrol Plants' for integrated pest management</b>]]> Studies of interactions between crops, additional plants, pests and beneficial organisms already exist as well as studies of natural enemy preference, dispersal, and abundance. However, these studies focus on tri-trophic interactions from an "arthropod" point of view. We think that in order to optimize crop protection methods we need to understand the effects that plant structures have on the various arthropods and on subsequent tri-trophic interactions. Although studies and reviews describing the role of secondary plants in Integrated Pest Management (IPM) exist, to date a general term which encompasses all plants added to a cropping system with the aim of enhancing IPM strategies has yet to be formulated. Therefore, we suggest a new term, "biocontrol plants", which we define as plants that are intentionally added to a crop system with the aim of enhancing crop productivity through pest attraction and/or pest regulation; a term that will promote the use of biocontrol services, and can ultimately lead to an increase in the sustainability of cropping systems.