Caracterização morfofisiológica radicular relacionada aos mecanismos de aquisição de fósforo em sorgo

• Autor(a) principal: Rocha, Michel Castellani da
• Data de Publicação: 2008
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/4489
• topic: Sorgo; Fósforo; Eficiência; Sorghum; Phosphorus; Efficiency; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOTECNIA

Low availability of phosphorus in the soil is one of the principal limiting factors in plant development and plant production. Plants have developed adaptive mechanisms for these environments that vary between species and between genotypes within a species. The capacity of plants to explore the soil, transform unusable forms to usable forms, develop relationships with mycorrhiza fungi, etc., influence the efficiency of plants in these environments. The objective of this study was to evaluate morphophysiological root characteristics related to mechanisms of phosphorus acquisition in sorghum lines of the sorghum improvement program at Embrapa Maize and Sorghum. Nine lines were used to study the root system in a soil with two levels of phosphorus (5 and 20 mg dm-3), and four lines were used to study the composition of strigolactone derivatives of root exudates. No significant interactions were found between genotypes and phosphorus level in the soil for the root morphological characteristics studied. Significant differences for the root characteristics: total root length (CTR), total root surface area (ATR), mean root diameter (DMR), number of root branches (NR), very fine root length (CRMF), root surface area of very fine roots (ARMF), root dry weight (MSR), dry weight root/plant dry weight ratio (MSR/MSPA) specific root length (CE), fineness of root (FR) and root tissue density (DeTR) between high and low phosphorus levels were observed. Significant differences between genotypes independently of the phosphorus level were observed for: DMR, length of thick roots (CRG), surface area of thick roots (ARG), surface area of fine roots (ARF), plant dry weight (MSPA), MSR, total plant dry weight (MST) and root fineness FR. Significant differences among the line in the plots with high phosphorus were observed for DMR, CRG, ARG, MSPA, MSR, MST, and FR, but not in the plots with low phosphorus. Significant differences between genotypes in the low phosphorus plots were only observed for CTR, ATR, NR, CRMF, CRF, ARMF, and ARF. Genetic variability was observed CTR, CRMF, CRF, ATR, ARMF, ARF e NR at low phosphorus levels and could be useful parameters for selection in sorghum improvement programs. Root length and root surface area appear to be more important for plant adaptation to low levels of phosphorus than root volume and root diameter. Different mechanisms of phosphorus acquisition may be occurring in environments with low and high phosphorus availability. Root tissue density was one of the most useful parameters related to plant productivity at low phosphorus. Four lines were characterized for root exudation components at low phosphorus. High performance liquid chromatography (HPLC) and coupling gas chromatography to mass spectrometry were used to analyze the compost isolated from root exudates from each line. Differences were observed between lines for what appears to be sorgolactone (strigolactone), a substance that is associated with signaling the colonization of mycorrhiza fungi. BR0007B, one of the four lines evaluated, had the highest quantity of total exudates, being 2.8 times greater than the line SC283, with the least amount. These physiological differences between the lines grown in a medium without phosphorus strongly support the presence of genetic variability in sorghum for the ability of the plant to induce (signal) mycorrhiza colonization.