Relações hidricas, trocas gasosas e conteudo de acido abscisico e acido 3-indol acetico em laranjeiras pera com clorose variegada dos citros

AUTOR(ES)
DATA DE PUBLICAÇÃO

2001

RESUMO

Pêra sweet orange plants (Citrus sinensis L. Osbeck) grafted on Rangpur lime rootstock (1 yr-old) (Çitrus limonia Osbeck) were inoculated with Xylella fastidiosa, a xylem-limited bacterium pathogen, which causes Citrus Variegated Chlorosis (CVC), by using the spliced approach grafting method. These plants were cultivated in 100,0 L pots under a screen house to prevent CVC-insect-vectors. Six months after inoculation, leaves were assayed by PCR (polymerase chain reaction) to confirm the bacteria in its tissues. Since it was known that water deficiency in the field enhances CVC-effects on the plant, the trees were submitted to three cycles ofwater stress in one year term (March and October, 1998; and April, 1999) and divided in four treatments: healthy plants (HP); water-stressed healthy plants (WSHP); diseased plants (DP) and water-stressed diseased plants (WSDP). The photosynthesis (A) and transpiration (E) rates, and stomatal conductance (g) ofwater-stressed plants decreased in the first and s_cond cycles of water deficiency, as the stress was increasing.The values ôfAfor WSHP and WSDP were near zero after ten days of water deficiency. Diseased plants were more sensitive to the increase in VPDl-air (vapor pressure deficit between the air and the leãI) during the day. The low stomatal conductance verified may be due to the high concentrations of abscisic acid (ABA) found in water-stressed plants. In the first cycle, the concentrations of starch and sucrose were greater in HP when compared with the other treatments (DP, WSHP and WSDP). In the second cycleof water deficiency, starch concentrations in water stressed plants were lower in relation to the irrigated ones; and there were no differences between the healthy and diseased irrigated plants. In the third cycle, values of A, g and E in diseased plants were, usually, lower than the healthy ones. In hea1thy plants, A, g and E showed the same response when these plants were submitted to water deficiency, independently of the cycle. The drop of leaf water potential in healthy plants was faster after irrigation was withheld, because healthy plants transpired more and, therefore, the substrate water content decreased more quickly. WSDP transpired less than the healthy plants, possibly due to the xylem occlusions by gums, tyloses and bacteria aggregates. In plants infected for two years, the photosynthesis rates were lower than the healthy plants, starting fTom the time of the day that temperature, radiation and VPDI-air increased. When the irrigation of WSDP was withheld in the third cycle, it was not possible to detect increases in ABA contents, suggesting that other factors could be acting to diminish the stomatal conductance in these plants. The presence of Xylella fastidiosa did not induce to an increase in indole-3-acetic acid content in the leaves. Afier three cycles ofwater deficiency, the concentrations ofindole-3-acetic acid in WSHP and WSDP were lower than those concentrations in the irrigated controls, on the day water stress was more severe. In the third cycle, the concentrations of starch were lower in diseased plants compared to the healthy ones, independently of water deficiency. This fact could be related to the requirement for reserves in diseased plants, as they showed significant decreases in photosynthesis rates

ASSUNTO(S)

laranja acido abscisico

ACESSO AO ARTIGO

Documentos Relacionados