RESUMO -Avaliou-se neste trabalho a influência de herbicidas nas características fisiológicas de três cultivares de cana-de-açúcar. O experimento foi conduzido no delineamento em blocos ao acaso, com três repetições, no esquema fatorial 3 x 8. O fator A foi composto por três cultivares de cana-de-açúcar (RB867515, RB855156 e SP80-1816), e o B, pelos herbicidas (tembotrione, MSMA, diuron + hexazinone, sulfentrazone, trifloxysulfuron-sodium, tebuthiuron, clomazone) e uma testemunha sem uso de herbicidas. A taxa transpiratória das plantas do cultivar RB867515 foi afetada negativamente quando foram aplicados os herbicidas sulfentrazone, tebuthiuron e clomazone em comparação à testemunha. Com relação à eficiência do uso da água, não se observaram diferenças entre os cultivares e a aplicação de herbicidas. A condutância estomática dos cultivares RB867515 e SP80-1816 não foi alterada pelos herbicidas aplicados. Apenas o cultivar RB867515 apresentou taxa fotossintética menor quando se aplicou o sulfentrazone. Os herbicidas testados afetam de forma diferenciada as características fisiológicas nos três cultivares avaliados. O cultivar RB867515 foi o que apresentou menor variação na taxa fotossintética na presença dos produtos testados, em relação à testemunha.Palavras-chave: taxa fotossintética, Saccharum spp., seletividade a herbicidas.ABSTRACT -This work aimed to evaluate the influence of herbicides on the physiological characteristics of three sugarcane cultivars. The experiment was conducted in a randomized block design with three replications in a factorial design 3 x 8. Factor A was constituted of three sugarcane cultivars (RB867515, RB855156, and SP80-1816), and factor B of the herbicides tembotrione, MSMA, diuron + hexazinone, sulfentrazone, trifloxysulfuron-sodium, tebuthiuron, clomazone, and a treatment without herbicide (control). The transpiration rate of cultivar RB867515 plants was negatively affected when sulfentrazone, clomazone, and tebuthiuron were applied,compared to the control. Regarding water use efficiency, no differences were observed between the cultivars and the herbicides. Stomatal conductance of cultivars RB867515 and SP80-1816 was not affected by the herbicides. Only cultivar RB867515 presented lower photosynthetic rate when sulfentrazone was applied. The herbicides tested had distinct effects on the physiological characteristics of the three cultivars evaluated. Cultivar RB867515 showed the least variation in photosynthetic rate in the presence of the products tested, as compared to the control.

Neste trabalho avaliou-se o acúmulo de nutrientes em plantas jovens de café e em plantas daninhas cultivadas em competição com a cultura. Mudas de café arábica cultivar Mundo Novo no estádio de quatro a cinco pares de folhas completamente expandidas foram transplantadas para vasos contendo 25 dm³ de substrato. Utilizou-se o delineamento de blocos casualizados em esquema fatorial (4 x 4), com quatro repetições. Os tratamentos foram compostos por quatro espécies de plantas daninhas: Digitaria horizontalis, Brachiaria decumbens, Brachiaria plantaginea e Mucuna aterrima, em quatro densidades de infestação (zero, duas, quatro e seis plantas por vaso), em convivência por 90 dias com uma planta de café. Para determinação dos teores foliares dos nutrientes das plantas de café e das plantas daninhas, realizou-se coleta de folhas na parte mediana das plantas de café e das plantas daninhas. Todas as espécies de plantas daninhas, quando em convivência com o café, proporcionaram menor teor de nutrientes nas folhas da cultura, principalmente com o incremento da densidade de plantas, exceto para as concentrações de N nas folhas do cafeeiro que conviveram com M. aterrima. Os teores de nutrientes nas folhas das plantas daninhas diferiram por espécie, indicando capacidade diferenciada de ciclagem de nutrientes. As espécies daninhas destacaram-se com maior teor foliar de alguns nutrientes, sendo D. horizontalis em P e Fe, B. plantaginea em P, Mg, Mn e Zn e M. aterrima em N, Ca e Zn, independentemente da densidade de infestação.

Bodensamenbank und andere populationsdemographische Parameter der Sommerwurz Orobanche crenata Forsk, in Bestdnden der Acker-Bohne (Vida faba L.) Bei einer Untersuchung der Populationsdynamik der Sommerwurz Orobanche crenata Forsk. in Bestanden der Acker-Bohne {Vicia faba L.) an 2 Orten tiber 8 Jahre hin nahm die Bodensamenbank in der Pfiugzone von 20 cm Tiefe jedes Jahr zu, bis sie rund 4 Millionen Samen m^^ erreichte. Die Lebensfahigkeit der Samen lag bei 53 bis 68%, etwa die Halfte war dormant. Ungefahr 3x10"^ % kamen mit den Bohnenwurzeln in Berlihrung. Nur 9 % davon entwickelten sich und wuchsen heran, worin vielleicht der hohe Grad intraspezifischer Konkurrenz zum Ausdruck kommt. Die hochste Zahl gebildeter Samen eines Sommerwurebestands von 53 Pflanzen m"^ war rund 4Millionen. Etwa 43 % der gebildeten Samen gelangten nicht in den Boden, wahrscheinlich weil sie zerstOrt oder verweht wurden.relationship with the infestation severity and to illustrate an overall demographic analysis of O. crenata in faba bean.

Field studies were conducted at nine locations in southern Spain during 2 yr to develop models of nodding broomrape competition with sunflower and to establish economic thresholds. At each location, 30 to 35 small plots, each consisting of three sunflower plants, were chosen at random. The infection severity (BIS, no. of emerged broomrapes per sunflower plant) varied from 0 to 35. Plots were harvested at maturity to assess several sunflower and broomrape population variables. The percent sunflower yield reduction averaged over locations due to broomrape was estimated by the equation: % SYR = 1.7 x BIS (r2= 0.92). Crop yield loss per BIS unit increased with the expected yield and was estimated to be about 25, 50, and 75 kg ha−1for yields of 1000, 2000, and 3000 kg ha−1, respectively. A consistent relationship could be established between broomrape-infected sunflower yield, crop and broomrape biomass, and BIS parameters: SSYI= 0.2259 x PoBio/(1 + 0.0687 x BIS) (r2= 0.7820). The BIS economic threshold was about 1.5 and 3.5 for control treatment cost of $ 40 ha−1and potential yields of 2000 and 1000 kg ha−1, respectively.

Plant water-use efficiency (WUE) describes the ratio of carbon gain to water loss during photosynthesis. It has been shown that WUE varies among crop genotypes, and crops with high WUE can increase agricultural production in the face of finite water supply. We used measures of leaf carbon isotopic composition to compare WUE among 24 cultivars of Persea americana Mill (avocado) to determine genotypic variability in WUE, identify potentially efficient cultivars, and to better understand how breeding for yield and fruit quality has affected WUE. To validate carbon isotope measurements, we also measured leaf photosynthetic gas exchange of water and carbon, and leaf and stem functional traits of cultivars with the highest and lowest carbon isotope composition to quantify actual WUE ranges during photosynthesis. Our results indicate large variation in WUE among cultivars and coordination among functional traits that structure trade-offs in water loss and carbon gain. Identifying cultivars of subtropical tree crops that are efficient in terms of water use is critical for maintaining a high level of food production under limited water supply. Plant functional traits, including carbon isotopes, appear to be an effective tool for identifying species or genotypes with particular carbon and water economies in managed ecosystems.

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