How caterpillar-damaged plants protect themselves by attracting parasitic wasps.

Parasitic and predatory arthropods often prevent plants from being severely damaged by killing herbivores as they feed on the plants. Recent studies show that a variety of plants, when injured by herbivores, emit chemical signals that guide natural enemies to the herbivores. It is unlikely that herbivore-damaged plants initiate the production of chemicals solely to attract parasitoids and predators. The signaling role probably evolved secondarily from plant responses that produce toxins and deterrents against herbivores and antibiotics against pathogens. To effectively function as signals for natural enemies, the emitted volatiles should be clearly distinguishable from background odors, specific for prey or host species that feed on the plant, and emitted at times when the natural enemies forage. Our studies on the phenomena of herbivore-induced emissions of volatiles in corn and cotton plants and studies conducted by others indicate that (i) the clarity of the volatile signals is high, as they are unique for herbivore damage, produced in relatively large amounts, and easily distinguishable from background odors; (ii) specificity is limited when different herbivores feed on the same plant species but high as far as odors emitted by different plant species and genotypes are concerned; (iii) the signals are timed so that they are mainly released during the daytime, when natural enemies tend to forage, and they wane slowly after herbivory stops.

Response of cotton to 2,4-D and related phenoxy herbicides /

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The effect of high temperature on the insecticidal properties of Bt Cotton

Bt transgenic cotton has not shown the same level of resistance to bollworm in China, as in other major Bt cotton growing areas of the world. The objective of this study was to investigate the effects of high temperature on the CryIA insecticidal protein content and nitrogen metabolism, in the leaf of Bt transgenic cotton. The study was undertaken on two transgenic cotton cultivars, one conventional (Xinyang 822) and the other a hybrid (Kumian No. 1), during the 2001 and 2002 growing seasons at the Yangzhou University Farm, Yangzhou, China. In the 2001 study, potted cotton plants were exposed to 37 C for 24 h under glasshouse conditions at three growth stages peak square, peak flowering and peak boll developing periods. Based on the 2001 results, in 2002 the same two cultivars were exposed to the same temperature for 48 h at two growth stages-peak flowering and boll developing periods. The results of the study indicated that the insecticidal protein content of the leaf was not significantly affected by the stress during the square and flowering periods. However, exposure to high temperature for 24h during the boll period reduced the CryIA protein content by approximately 51% in the cultivar Kumian No 1, and 30% in Xinyang 822 in the 2001 study, and by approximately 73 and 63% for 48 h with the same cultivars, respectively, in the 2002 study. Glutamic-pyruvic transaminase (GPT) activity, total free amino acid and soluble protein content, and the activity of protease in the leaf, showed relatively little change in response to high temperature in the flowering period. However, exposure to high temperature in the boll period resulted in the following changes - a reduction of GPT activity, a sharp increase in free amino acid content, a significant decrease in soluble protein content, and significant increases in the activity of protease. The results suggest that high temperature may result in the degradation of soluble protein in the leaf, with a resulting decline in the level of the toxin CryIA. It is believed that this may be the cause of the reduced efficacy of Bt cotton in growing conditions in China, where temperatures during the boll period often reach 36-40° C. © 2004 Elsevier B.V All rights reserved.

Do increases in xylem sap pH and/or ABA concentration mediate stomatal closure following nitrate deprivation?

Stomatal conductance (g(s)) of pepper (Capsicum annuum L.) plants decreased during the second photoperiod (day 2) after withholding nitrate (N). Stomatal closure of N-deprived plants was not associated with a decreased shoot water potential (Psi(shoot)); conversely Psi(shoot) was lower in N-supplied plants. N deprivation transiently (days 2 and 3) alkalized (0.2-0.3 pH units) xylem sap exuded from de-topped root systems under root pressure, and xylem sap expressed from excised shoots by pressurization. The ABA concentration of expressed sap increased 3-4-fold when measured on days 2 and 4. On day 2, leaves detached from N-deprived and N-supplied plants showed decreased transpiration rates when fed an alkaline (pH 7) artificial xylem (AX) solution, independent of the ABA concentration (10-100 nM) supplied. Thus changes in xylem sap composition following N deprivation can potentially close stomata. However, the lower transpiration rate of detached N-deprived leaves relative to N-supplied leaves shows that factors residing within N-deprived leaves also mediate stomatal closure, and that these factors assume greater importance as the duration of N deprivation increases.

Arsenicais e inseticidas orgânicos sôbre o algodoeiro em terras roxa e arenosa

The authors carried out a series of pots and plots experiments applying arsenical and organic insecticides to cotton plants cultivated in "terra roxa" and in a sandy soil. The first results were presented in 1947, to the la. Reunião Brasileira de Ciência do Solo (First Brazilian Congress of Soil Science); they pointed out the danger resulting from the accumulation of arsenic in soils due to the constant applications of arsenicais to control cotton pests; in the course of the time, the amount of residual arsenic in the soil would determine a decrease in cotton yield caused by its toxic effect on the crop. The following conclusions were drawn from the last three experiments: 1) the field experiment conducted in a sandy soil to which lead arseniate was applied in increasing rates produced a reduction of 50 per cent in the yield (the three highest doses were responsible for this result); by this way, the pot experiment published in 1947 was confirmed); 2) in the pot experiment with "terra roxa" toxic effects appeared only in the plants receiving the last dosis of lead arsenate; this result is explained quite naturally by a considerable absorption of the AsO4 --- ion by "terra roxa" colloidal material; furthermore the CaO, P2O5 and Fe2O3 content and the pH value (higher) would decrease the arsenate solubilization in the soil considered; 3) the pot experiment with organic insecticides applied in the rates usually employed in the control of cotton pests, showed that 10% D.D.TD. and 2.5% Rotenone did not affect cotton plants cultivated in a sandy soil; however we agree with FOSTER (1951), in the point that both mineral and organic insecticides must be applied in the minimum amount as possible; we also think that experiments like those should be carried out with the known insecticides, in several soil conditions and with many crops in order to determine the maximum limits of tolerancy.

Effect of gossypol on survival and reproduction of the zoophytophagous stinkbug Podisus nigrispinus (Dallas)

Effect of gossypol on survival and reproduction of the zoophytophagous stinkbug Podisus nigrispinus (Dallas). Gossypol is a sesquiterpene aldehyde found in cotton plants conferring resistance against herbivory. Although the effect of this sesquiterpenoid on insect pests of cotton is known, the interaction of this compound with zoophytophagous predators such as Podisus nigrispinus (Dallas) (Hemiptera, Pentatomidae) has not been studied so far. Thus, the objective of this study was to evaluate the effect of the purified gossypol on nymphs and adults of P. nigrispinus. Nymphs and adults of this predator were fed on Tenebrio molitor pupae and supplemented with solutions of gossypol at concentrations of 0.00, 0.05, 0.10, and 0.20% (w/v) during the nymphal and adult stages or, only during the adult stage of P. nigrispinus. The nymphal stage of the predator was, on average, two days longer when suplemmented with gossypol. Emerged adults had lower fecundity and egg hatching, especially at the highest gossypol concentration (0.20%) ingested during the nymphal and adult stages. However, this predator was not affected when it ingested the compound only during the adult stage. P. nigrispinus can have delayed nymphal development and lower reproductive performance when ingesting the gossypol during the nymphal and adult stages, but only at higher concentrations of gossypol than that produced by cotton plants.

In situ and genetic characterization of Gossypium barbadense populations from the states of Pará and Amapá, Brazil

The objective of this work was to characterize the populations of Gossypium barbadense in the states of Amapá and Pará, Brazil. In situ characterization was conducted through interviews with the owners of the plants and environmental observations. Leaf or petal tissue as well as seed samples were collected for genetic characterization by single sequence repeats markers and for storage in germplasm banks, respectively. The plants were maintained in dooryards and used mainly for medical purposes. The genetic analysis showed no heterozygous plants at the loci tested (f = 1), indicating that reproduction occurs mainly through selfing. The total genetic diversity was high (He = 0.39); and a high level of differentiation was observed between cotton plants from the two states (F ST = 0.36). Conventional methods of in situ maintenance of G. barbadense populations are not applicable. The conservation of the genetic variability of populations present in the two states could be achieved through germplasm collection and establishing of ex situ seed banks.

AFLP markers differentiate isolates of Colletotrichum gossypii from C. gossypii var. cephalosporioides

Fungal diseases in cotton (Gossypium hirsutum), such as anthracnose caused by Colletotrichum gossypii and ramulose caused by C. gossypii var. cephalosporioides, are responsible for large yield losses. These pathogens are seed borne and morphologically similar although they induce different symptoms, which can lead to misdiagnosis using the blotter testing method. The present study was carried out to assess the viability of using Amplified Fragment Length Polymorphism (AFLP) markers to differentiate these pathogens. Five isolates, for each pathogen, were classified according to pathogenicity on cotton plants, and mycelial growth morphology. Conidial suspensions were sprayed on 30-day-old cotton plants and the symptoms assessed ten and 40 days after inoculation. For growth morphology 200 cottonseeds were inoculated with seven-day-old pure cultures, and the mycelial traits observed under a stereoscopic microscope seven days after inoculation. The DNA for AFLP analysis was obtained from seven-day-old fungal mycelia grown in liquid medium, using the Dneasy Qiagen protocol. Using the AFLP technique 318 polymorphic bands were selected to estimate similarities using Dice's Coefficient. The results clearly distinguished between ramulose and anthracnose isolates, which agreed with morphological and pathogenicity testing.

Diversidade de afídeos na cultura do algodoeiro no município de Campo Verde (MT)

O objetivo deste trabalho foi verificar a diversidade de afídeos (Hemiptera: Aphididae) na cultura do algodoeiro (Gossypium hirsutum L.) no município de Campo Verde (MT). Os afídeos foram amostrados diretamente nas plantas e através de armadilhas tipo Moericke. As amostragens foram realizadas a cada dois dias, até 60 dias após a germinação das plantas. A espécie Aphis gossypii Glover prevaleceu nas amostragens realizadas sobre as plantas. Formas aladas, de ocorrência acidental na cultura, tais como Aphis spiraecola Patch e Rhopalosiphum padi (Linnaeus) também foram observadas. Com as armadilhas tipo Moericke foram capturados 2280 afídeos alados, pertencentes a 13 espécies: R. padi (52,6% do total), A. spiraecola (26,4%), A. gossypii (8,9%), Rhopalosiphum maidis (Fitch) (5,3%), Geopemphigus floccosus (Moreira) (3,1%), Uroleucon ambrosiae (Thomas) (1,5%), Rhopalosiphum rufiabdominalis (Sasaki) (1,3%), Myzus persicae (Sulzer) (0,4%), Sipha flava (Forbes) (0,3%), Pentalonia nigronervosa Coquerel, Tetraneura nigriabdominalis (Sasaki), Lizerius melanocallis (Quednau) e Toxoptera citricidus (Kirkaldy) (0,1% cada uma). Nas amostragens diretamente sobre as plantas foram observados ápteros e alados de A. gossypii e alados de A. spiraecola e R. padi. Nas armadilhas tipo Moericke, as principais espécies capturadas foram R. padi, A. spiraecola, A. gossypii e R. maidis.

Biologia de aphis gossypii em plantas infectadas pelo vírus do mosaico das nervuras do algodoeiro

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Efeito da época de inoculação do vírus do mosaico das nervuras por Aphis gossypii Glover (Hemiptera: Aphididae) no desenvolvimento e na produção do algodoeiro

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Eficiência de ninfas e adultos de Aphis gossypii Glov. na transmissão do vírus do mosaico das nervuras do algodoeiro

O objetivo deste trabalho foi avaliar a eficiência de transmissão do vírus do mosaico das nervuras, por ninfas e adultos de Aphis gossypii Glov., em duas cultivares de algodoeiro e registrar a evolução dos sintomas da doença. O trabalho foi realizado em casa de vegetação do Departamento de Fitossanidade da FCAV/UNESP, em Jaboticabal (SP). Ninfas e adultos ápteros criados em plantas infectadas da cultivar CNPTA ITA 90 foram transferidos para as plantas de algodoeiro das cultivares Coodetec 402 e CNPA ITA 90, com dois pares de folhas verdadeiras, onde permaneceram por 96 e 48 horas respectivamente. Para verificar a evolução da doença nas plantas, os sintomas foram avaliados até 60 dias após o confinamento dos afídeos, baseando-se numa escala de notas visuais. Os sintomas da doença foram inicialmente observados 25 dias após a inoculação pelos afídeos e se intensificaram com o desenvolvimento das plantas. A transmissão do vírus foi realizada mais eficientemente pelos adultos ápteros, do que pelas ninfas.

Efeito de cultivares de algodoeiro sobre a biologia e capacidade predatória de Orius Insidiosus (say, 1832) (hemiptera: anthocoridae) predando Aphis Gossypii Glover, 1877 (Hemiptera: Aphididae)

The objective of this research was to determine the survival, reproduction and predaceous capacity of Orius insidiosus on cotton aphid Aphis gossypii. Cotton plants of Antares, CNPA7H and Acala 90 cultivars (respectively, without tricome, medium tricome density and high tricome density) were individualized and infested with 15 third/fourth instar nymphs of A. gossypii, and then first-instar nymphs of O. insidiosus were released on the plants. The evaluations were made daily, quantifying survival and nymphal development; the number of cotton aphids A. gossypii per day and total; the number of eggs and the population of the predator (number of insects by female); and the conversion efficiency of A. gossypii predaceous. The nymphal development did not differ according to the cotton cultivars. The Antares cultivar favored a higher daily predation rate for the 1st, 2nd and 4th instars and adults of O. insidiosus. The number of eggs and nymphs was smaller when O. insidiosus females were confined on the Acala 90 cultivar. According to the predation rate of O. insidiosus, the efficiency of alimentary conversion was determined for the Antares, CNPA7H and Acala 90 cultivars, being respectively, 4.28, 3.00 and 2.75 cotton aphid predation for each egg of the predator.

DEFICIÊNCIAS MINERAIS NO CULTIVAR DE ALGODÃO IAC-22

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Sensibilidade de cultivares de algodoeiro ao cloreto de mepiquat

O objetivo deste trabalho foi avaliar a sensibilidade de cultivares de algodoeiro ao cloreto de mepiquat e verificar se ela está relacionada ao ciclo ou à arquitetura da planta. Foi realizado um experimento em casa de vegetação com seis cultivares de algodoeiro - FiberMax 966, FiberMax 977, Delta Penta, Delta Opal, FMT 501 e FMT 701 - e quatro doses do regulador vegetal à base de cloreto de mepiquat - 0, 7,5, 15 e 22,5 g ha-1 de i.a. -, em delineamento de blocos ao acaso, com arranjo fatorial 6x4 e quatro repetições. As parcelas experimentais foram constituídas por vasos de 12 L com duas plantas em cada um. As doses do regulador vegetal foram aplicadas sem adjuvante, no estádio de aparecimento dos botões florais, aos 34 dias após a emergência das plântulas. Paralelamente ao experimento com doses, a retenção do regulador pelas folhas das cultivares foi quantificada. O crescimento em altura das plantas de algodoeiro é diminuído com a aplicação do regulador vegetal, e esse efeito se intensifica com o aumento da dosagem aplicada. Existe diferença entre as cultivares estudadas quanto à sensibilidade ao cloreto de mepiquat, sendo que as mais precoces são mais sensíveis. Além da sensibilidade diferenciada, a arquitetura das plantas pode possibilitar maior ou menor deposição do regulador sobre as folhas.