An examination of the effects of adding phosphorus to the soil on nodulation and P utilization in Phaseolus vulgaris L. showed a positive response in plant weight to increasing rates of phosphorus ( 32 P) when water tension was low in the pots.The efficiency of the utilization of fertilizer-P was directly influenced by the water content of the soil, showing increasing P accumulation after flowering.A highly positive interaction between P addition, water content and nodulation was observed. Nodules were shown to have a high P requirement, with phosphorus ( 32 P) contributing to an increase in the number and size of nodules.
Soil water content affected the nodulation and N 2 fixation of Phaseolus vulgaris by Rhizobium phaseoli and the utilization of mineral N by plants. Plants grown in wet soil produced twice as much as those grown on dry soils. Nodule weight and activity were five to ten times greater than those from dry soils. At 45 days, N additions inhibited nodulation, but this effect was partially diminished in wet soils.The maximum N utilization from fertilizer to produce dry matter did not correspond to maximum N utilization by pods.
RESUMOVerificou-se o efeito de giberelinas, quando aplicada sob a forma de pulverização das plântulas, no desenvolvimento do algodoeiro cultivar ' IAC-RM3' em condições de casa-de-vegetação.Estudaram-se as concentrações de 0, 2, 20 e 200 ppm do regulador de crescimento; sendo que os tratamentos aumentaram a altura das plantas em 27, 48 e 65%, com relação ao controle.Aplicações de giberelinas nas dosagens de 2 e 20 ppm promoveram aumento na TAL e na RAF do algodoeiro. A TCR foi superior nas plantas tratadas com giberelinas.Verificou-se ainda que giberelinas a 200 ppm promove redução na TAL e variação mínima na RAF, com relação ao controle.
INTRODUÇÃOObservações realizadas no Japão com a doença do arroz denominada "bakanae", levaram ao descobrimento das giberelinas. Esta doença fúngica era provocada por Gibberella fujikwoi, forma sexuada de Fusarium moniliforme. Plantas atacadas mostravam um crescimento excessivo, sendo que KUROSAWA (1926) verificou que o meio no qual o fungo se desenvolvera estimulava o crescimento de plántulas de milho e arroz, não infectadas.YABUTA (1935) cristalizou o composto de extrato de fungo pela primeira vez, dando-lhe a denominação de giberelina; sendo que CROSS (1954) estabeleceu as estruturas moleculares das giberelinas; após MITCHELL & ANGEL (1950) estudaram o efeito do meio de cultura do fungo em feijoeiro.Giberelina é um composto isoprenóide formado de diterpenos, sendo que nas plantas superiores, os precursores imediatos de giberelina parecem ser caureno e esteviol, variando provavelmente com a espécie (WEST et al., 1969).
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