Claudio Mario Mundstock

Wheat root growth as affected by soil strength

SUMMARY Soil compaction is a common problem that affects several soil properties and plant growth. In order to assess the effects of soil strength expressed by its mechanical resistance on roots, a growth chamber experiment was conducted at the Universidade Federal do Rio Grande do Sul, Porto Alegre, in 1994, during 35 days (530 GDD, 0oC base temperature) on a typical Paleudult soil. Treatments, using pots arranged in a completely randomized design, consisted of soil compactions that resulted in resistances of 1.0, 2.0, 3.5 and 5.5 MPa. A combination of soil gravimetric moisture and densities was used in order to minimize possible effects due to lack of water and oxygen supply to the roots under the treatments. As soil resistance increased, roots showed a reduced length, surface and dry matter, but a higher radius. As less soil was explored under high resistances, shoot and root dry matter decreased but the latter suffered the most. This study shows that soil mechanical resistance itself, is an important factor restricting plant growth, with its effects being detected very early in the plant development.

Regulação da absorção e assimilação do nitrogênio nas plantas

A presente revisao tem por objetivo discutir os mecanismos de regulacao da absorcao e assimilacao do nitrogenio nas plantas, de modo que a eficiencia de uso desse nutriente seja aumentada. O nitrogenio e absorvido nas raizes sob a forma de NO3 ou NH4 , sendo entao incorporado em aminoacidos na propria raiz ou na parte aerea. A taxa e a quantidade de nitrogenio absorvido e assimilado durante o ciclo da planta dependem da presenca de carregadores especificos na membrana plasmatica, da atividade das enzimas envolvidas no seu ciclo, da disponibilidade de energia necessaria para os processos de absorcao e assimilacao e do estadio de desenvolvimento da planta. Inumeros grupos de pesquisa tem centrado esforcos na identificacao dos pontos mais limitantes do metabolismo do nitrogenio nas plantas. Os limitadores tem sido relacionados com: a) a afinidade dos carregadores pelo nitrato e amonio; b) o suprimento de carboidratos as raizes; c) o nivel de aminoacidos no floema radicular; d) a atividade das enzimas redutase do nitrato (RN), sintetase da glutamina (GS) e sintase do glutamato (GOGAT); e) a fonte de N suprida as plantas (NO3 ou NH4 ); f) o local de assimilacao do N (raiz ou parte aerea). Esses estudos tem mostrado que o metabolismo do N e multiregulado e integrado ao metabolismo geral da planta. A identificacao de pontos metabolicos especificos que sao mais limitantes para o incremento da produtividade e complexa. A perspectiva e que a clonagem dos transportadores de N podera auxiliar os programas de melhoramento genetico na obtencao de plantas mais eficientes na absorcao do nitrogenio.

A qualidade da luz afeta o afilhamento em plantas de trigo, quando cultivadas sob competição

O presente trabalho foi conduzido com o objetivo de verificar os efeitos da mudanca na qualidade da luz sobre a emissao de afilhos e na sua acumulacao de massa seca. A cultivar de trigo EMBRAPA 16 foi cultivada em comunidades de aproximadamente 400p- /m2, em condicoes naturais de radiacao durante o inverno, no Sul do Brasil. No primeiro experimento (baixa qualidade de luz), utilizaram-se filtros verde e vermelho entre as linhas, entre os estadios Haun de 1.0 a 3.1. No segundo experimento (melhor qualidade de luz), as plantas foram suplementadas durante o dia com luz vermelha (V) (660nm), entre os estadios Haun 1.0 e 3.1. Ja no terceiro experimento (baixa qualidade de luz), as plantas foram suplementadas durante o dia com luz vermelha extrema (Ve) (730nm), entre os estadios Haun 1.0 e 3.1. A qualidade da luz afetou a emissao de afilhos, sua massa seca e sua distribuicao entre o colmo principal e os afilhos. A baixa qualidade da luz (filtros verde e vermelho e luz Ve) induziu as plantas a emitir menos afilhos com menos massa seca/afilho. A baixa qualidade da luz priorizou o colmo principal sob condicoes de comunidades, antes que tivesse sido estabelecida a competicao pela quantidade total de luz recebida pelas plantas. A melhor qualidade de luz (luz V) teve efeito oposto. Os afilhos foram emitidos em maior numero e a alocacao de massa seca foi menos priorizada para o colmo principal do que nos tratamentos com baixa qualidade.

Perdas de rendimento de grãos de soja causadas por interferência de picão-preto e guanxuma

The level of reciprocal interference between weeds and crops is affected by the competing species and plant populations involved. This research was conducted in order to evaluate the possibility of using the retangular hyperbolic model for predicting soybean grain yield losses caused by beggarticks (Bidens spp.) and arrowleaf sida (Sida rhombifolia L.) infestations. To accomplish this, there were carried out two field experiments in Eldorado do Sul, RS, Brazil, during the 1999/00 and 2000/01 growing seasons. Treatments consisted of beggarticks and arrowleaf densities, which were located according to naturally ocurring population levels in the research area. Was detected that grain yield losses due to increasing densities of these weeds increased non-linearly. The retangular hyperbolic model suits better adjustments when is used grain yield losses than using soybean dry matter at flowering stage or biological yield losses. Through comparison of the parameters estimated for the adjusted model, it is concluded that beggarticks exerts greater interference in soybean than arrowleaf sida.

Modelo para estimativa do potencial produtivo em trigo e cevada por meio do sensor GreenSeeker

Areas with different yield potential within a field need to be managed separately as for nitrogen application in small grain cereals. Terrestrial remote sensing-based equipment such as the GreenSeeker sensor is one of the tools available to handle different management zones. To do this, the sensor allows the definition of classes to estimate yield potential. A model which correlated the Normalized Difference Vegetation Index (NDVI) to shoot dry biomass at the 6-leaf-stage was developed for estimating yield potential classes for wheat and barley. The model eliminated differences between species and cultivars as no correction for these factors is necessary. The effects of surface background (corn or soybean crop residues) were considered in this model. When readings are carried out before or after the recommended period, the model can be adjusted for under or overestimation. Spatial variability analysis may evaluate if yield potential zones estimated by the NDVI classes proposed in the model are related to spatial variability of shoot biomass, N rates applied and grain yield.

O afilhamento da aveia afetado pela qualidade da luz em plantas sob competição

Oat plants grown in communities can change their morphology at early stages of development because of differential light absorption on the red and far-red wavelengths. This was studied in open air experiments with oat cultivar UFRGS 15, sown from 300 to 350 plants/m2, under natural radiation conditions, in wintertime, in Southern Brazil. In the first experiment, blue filters were placed between plant rows in order to decrease light quality, between Haun stages 1.1 and 3.1. For second experiment, low fluence of red (660nm) e far-red (730nm) light were supplemented during the day to increase (red) and decrease (far-red) respectively the light quality. This was done between Haun stage 1.1 to 3.1, at two distances from the plants. In the third experiment, red and far-red light were also supplemented but for two different periods: emergence to Haun stage 2.1 and Haun stage 2.1 to 4.1. The blue filters and far-red supplementation (expts 1 and 2) induced plants to emit less tillers and tillers with less dry mass but was not seen in experiment 3, when soil chemical conditions were better than the other experiments. With red supplementation, plants emitted more tillers with more dry mass. Under these conditions, the mass ratio mainstem/tiller was less proeminent than under blue filters and far-red supplementation.

Conceito de ideotipo e seu uso no aumento do rendimento potencial de cereais

This review has the purpose of presenting some important traits to be incorporated in cereals through the integration of physiology, biochemistry and plant breeding. Several plant attributes were modified during the selection process to improve grain yield of different plant species. This paper intends to discuss the validity of aggregating some of the se traits in new cultivars and to pinpoint the possible consequences of using those individual characteristics rather than grain yield per se to bred the old genotypes. Discussion about crop ideotipes grows in importance with the fast evolution of genetic variability techniques because if a model plant to increase grain yield is not defined all the new genetic technology available may have a narrow practical utilization. This ideotipe was formulated integrating severa! characteristics that have been analyzed individually in the past. Its main proposed features are: (a) higher initial growth and greater communal phytomass, which are both important to improve solar radiation use, particularly during early stages of development, (b) an increase in photosynthetic capacity through the enhancement of sink strength with a probable effect on harvest index. The collective influence of the suggested traits must be evaluated on different genotypes to analyze the response level obtained.

Adubação nitrogenada em estádios fenológicos em cevada, cultivar "MN 698"

The yield component contribution in the grain yield in barley is affected to growth stage for nitrogen supplementation. The objective of present study was to determine the critical growth stages for nitrogen fertilization in barley, cultivar MN 698. Four field experiments were carried out in Eldorado do Sul, Encruzilhada do Sul and Victor Graeff (RS), Brazil, in 2000 and 2001. Two N rates (30/40kg ha-1 and 60/80kg ha-1) were applied in six growth stages of main shoot (MS): (a) plant emergence, (b) 2nd/3rd leaf emergence, (c) 4th/5th leaf emergence, (d) 6th/7th leaf emergence, (e) 8th/9th leaf emergence and, (f) boot stage. Grain yield and yield components were analyzed. For low soil organic matter the better grain yield were observed when the N was applied at 3rd to 9th leaf emergence. The 3rd and 7th leaf emergence stages, correspondent to begging and final tiller emergence, were critical to nitrogen fertilization in barley plants. For medium soil organic matter, the time of supplementation of N not affected sensibly the grain yield.

DISPONIBILIDADE DE NITROGÊNIO E SUA RELAÇÃO COM O AFILHAMENTO E O RENDIMENTO DE GRÃOS DE AVEIA

Nitrogen shows a strong influence on oat growth and development, mainly on early stages of plant cycle. Oat tiller number and survival and grain yield as affected by nitrogen supply was studied in five field experiments at Estacao Experimental Agronomica/UFRGS (Eldorado do Sul, RS), from 1993 through 1998, with cultivars UFRGS 10 and UFRGS 15. Treatments consisted in applying N in different plant stages (emergence to booting) or in different levels at plant emergence. In all situations, treatments received or not an extra N-supply at the 7th leaf stage. Tillering was stimulated mainly by N applied at plant emergence for tiller emission and by N applied at the 7th leaf stage which reduced tiller mortality and mantained synchrony between main stem and tiller development. The best grain yields were obtained when N was available from emergence up to 7th leaf stage. Late N application (booting stage) resulted in no yield increase. When soil nitrogen supply is restricted, N should be applied at sowing and 7th leaf emission.

Sistema vascular e controle do desenvolvimento de perfilhos em cereais de estação fria

Vascular system and tiller bud development control in small-grain cereals). The reasons for tiller absence and/or low survival were studied by analyzing vascular connections between the tiller and other plant parts. Experiments were conducted on open air and growth chamber conditions with wheat genotypes, IPF- 49865 (uniculm), EMBRAPA-16 and BR-23 (multiculm); oats, UFRGS-10 and UFRGS-15; and barley, FM-519. Analyses were made on main culm and primary tiller foliar development, number of primary and secondary tillers and vascularization and tiller vascular connection with the rest of the plants. Vascular connections did not explain tillering inhibition, since all tillers were vascularly connected to the plant. RESUMO - (Sistema vascular e controle do desenvolvimento de perfilhos em cereais de estacao fria). As causas da ausencia e/ou baixa sobrevivencia dos perfilhos foram estudadas pela conexao vascular entre os perfilhos e o resto da planta. Foram conduzidos ensaios em telado e câmara de crescimento com genotipos de trigo, IPF-49865 (unicolmo), EMBRAPA-16 e BR-23 (multicolmo), de aveia, UFRGS-10 e UFRGS-15 e de cevada, FM-519. Avaliaram-se o desenvolvimento foliar do colmo principal e dos perfilhos primarios, o numero de perfilhos primarios e secundarios, o numero de perfilhos ferteis e a vascularizacao e conexao vascular dos perfilhos com o resto da planta. A conexao vascular poderia explicar a inibicao dos perfilhos, pois todos estavam conectados vascularmente com o resto da planta.