Beatriz da Silveira Pinheiro

Carbon isotope discrimination as a means of evaluating drought resistance in barley, rice and cowpeas

SummaryIn all the crops studied there was variation among genotypes in carbon isotope discrimination (Δ). In trials of barley genotypes there were strong positive correlations between grain yield and Δ, though in trials which were irrigated or received abundant rainfall, this correlation was non-significant or negative. Some of the variation in yield and Δ was related to date of heading, as early varieties in stressed trials had highest yields and had high Δ.In an experiment with 8 early and 10 late flowering rice genotypes there were consistent positive correlations between yield and Δ in the early group, but in the late group the correlations tended to be negative. Among the early group the early genotypes were highest yielding, and may be presumed to have avoided the worst effects of drought and hence had higher Δ. In the late group, there was no correlation between yield and date of flowering.In one experiment with cowpeas, a weak positive correlation between grain yield and Δ was observed, but in a s...

Carbon isotope discrimination and yield of upland rice as affected by drought at flowering

Field experiments involving upland rice genotypes, sown in various dates in late season, were carried out to assess the relationship of carbon isotope discrimination with grain yield and drought resistance. In each one of the three years, one trial was kept under good water availability, while other suffered water shortage for a period of 18-23 days, encompassing panicle emergence and flowering. Drought stress reduced carbon isotope discrimination measured on soluble sugars (Ds) extracted from stem uppermost internode at the end of the imposition period, but had relatively less effect on bulk dry matter of leaves, sampled at the same period, or that of uppermost internodes and grains, sampled at harvest. The drought-induced reduction in Ds was accompanied of reduced spikelet fertility and grain yield. In the three trials subjected to drought, genotypes with the highest yield and spikelet fertility had the lowest Ds. However, this relationship was weak and it was concluded that Ds is not a sufficiently reliable indicator of rice drought resistance to be useful as a screening test in breeding programs. On the other hand, grain yield and spikelet fertility of genotypes which were the soonest to reach 50% flowering within the drought imposition period, were the least adversely affected by drought. Then, timing of drought in relation to panicle emergence and to flowering appeared to be a more important cause of yield variation among genotypes than variation in Ds.

Herança da tolerância à toxidez de alumínio em arroz com base em análise dialélica

Three tolerant (Guarani, Guapore e IAC 25) and three sensitive (CNA 5600, CNA 5615 e IAC 899) genotypes of rice (Oryza sativa L.) and their respective F1 crosses, obtained in a diallel cross system not accounting the reciprocal crosses, were evaluated to study the inheritance of toxicity aluminum (Al) tolerance. The Al concentration in nutritive solution was 20 mg/L. The results showed that the inheritance is oligogenic with the tolerance determined by the dominant alleles. The parents Guarani, Guapore and IAC 25 showed greater dominant allele concentration and CNA 5600, CNA 5615 and IAC 899 more recessive alleles.