Adelson Paulo Araújo

Phosphorus efficiency of wild and cultivated genotypes of common bean (Phaseolus vulgaris L.) under biological nitrogen fixation

Abstract Production of common bean (Phaseolus vulgaris L.) in the tropics is often limited by low soil P availability, and P deficiency is therefore a major nutritional constraint to N2 fixation of legumes. Two experiments were conducted in 4 kg pots with a sandy loam soil, to evaluate the efficiency of P absorption and utilization of wild and cultivated genotypes of common bean under biological nitrogen fixation. In Experiment 1, 20 wild and 7 cultivated genotypes were grown at two soil P levels (20 and 80 mg P kg−1 soil); in Experiment 2, 4 wild and 27 cultivated genotypes were grown at the same P levels. The higher P supply increased the number of leaves, leaf area, and dry weight of all plant parts, particularly nodule dry weight. The cultivated genotypes exhibited fewer leaves but greater leaf dry weight, and also lower specific leaf area and leaf area ratio, thereby producing larger and thicker leaves probably with higher photosynthetic activity. The cultivated genotypes presented greater root dry weight and root-to-shoot ratio, suggesting that bean selection could have resulted in plants which invest preferentially in root production, a valuable trait in low P soils. The means of shoot dry weight and P content of wild and cultivated groups were similar in both P levels, although there were distinctions within each group. The wild genotypes presented a lower efficiency of P utilization, as attested by smaller P utilization index and higher shoot P concentration at the lower P level. These results indicate that wild bean genotypes are not more tolerant to low P soils, but the genotypic variation observed suggests these materials as a source of genetic diversity for nutritional breeding programs.

Nitrogen and phosphorus harvest indices of common bean cultivars: Implications for yield quantity and quality

Breeding for yield in common bean (Phaseolus vulgaris L.) should consider the efficiency of biomass and nutrient partitioning to grains. In field experiments, 9 and 18 bean cultivars were cultivated in 1998 and 1999, respectively, to identify the genotypic variability of harvest index (HI) and N and P harvest indices (NHI and PHI), and to evaluate the relationships between these indices and grain yield. Cultivars differed for grain yield, HI, NHI and PHI in both years, but these indices varied less than grain yield. Growth habit markedly influenced HI, with prostrate cultivars possessing higher HI, NHI and PHI than erect cultivars; hence selection for HI should be performed within each phenological group. Grain yield was strongly associated with grain N and P contents, and positively but weakly correlated to HI, NHI and PHI; the indices were highly correlated among themselves. Multiple-regression analysis showed that most genotypic variation of grain yield was associated with the amount of N and P accumulated by the crop at maturity, and some yield variation was associated with seed nutrient concentration, particularly P concentration, whereas NHI and PHI had a minor role. Combined analysis of both experiments showed that grain yield diminished by 57% from 1998 to 1999, whereas HI remained almost stable and NHI and PHI decreased slightly, but the significant year × cultivar interaction revealed different degrees of phenotypic plasticity of biomass partitioning among cultivars. Selection solely for increased HI would scarcely result in improved grain yield, raising concomitantly NHI and PHI and probably reducing grain P concentration.

Ontogenetic variations on absorption and utilization of phosphorus in common bean cultivars under biological nitrogen fixation.

An experiment was conducted to evaluate the effect of plant ontogeny on traits associated with absorption and utilization of P by common bean (Phaseolus vulgaris L.) cultivars under biological N2 fixation through plant growth analysis. Eight cultivars were grown in pots at two levels of applied P (20 and 80 mg P kg−1 soil) and harvested at three growth stages (third trifoliate expanded, plentiful flowering, pod setting). The development of nodulation differed among cultivars and depended on P supply; some cultivars showed an intense decline in nodule number after flowering. There were different patterns of root growth: Some cultivars increased root area after flowering mainly by increasing root mass, whereas others by decreasing root radius. Despite the overall drift of reducing P influx into roots over time, some cultivars maintained P influx almost stable after flowering. Cultivars with greater root area had lower influx, whereas cultivars with smaller root area had higher influx, denoting a compensatory mechanism between root growth and P influx, such mechanism presenting ontogenetic variations associated to patterns of root area production. The cultivars differed in specific P utilization rate at low but not at high soil P level; hence P utilization seems an important physiological component for screening bean genotypes under limited P supply. High correlation between net assimilation rate and specific P utilization rate suggests that P utilization is strongly related to photosynthetic activity. Despite, the wide variation among cultivars on root growth, nodulation and rates of P absorption and utilization, the genotypic variability for total dry mass and P content was narrow by pod setting. Owing to growth constraints caused by a possible inefficient symbiosis, the concomitant selection of bean genotypes for tolerance to low P and high N2 fixation activity should prioritize traits related to the root system and to N2 fixation over total dry matter. The ontogenetic variations of traits associated with P absorption and utilization in common bean cultivars require evaluations at different plant growth stages.

Variability of traits associated with phosphorus efficiency in wild and cultivated genotypes of common bean

Genetic variation in plant growth under limited phosphorus (P) supply is necessary to obtain more productive cultivars on low P-available soils. Two pot experiments were conducted to evaluate the variability of some traits associated with efficiency of P absorption and utilization in wild and cultivated genotypes of common bean (Phaseolus vulgaris L.) under biological N2 fixation. At two P levels (20 and 80 mg P kg-1 soil, P1 and P2, respectively), 20 wild and 6 cultivated genotypes were grown in Experiment 1, and 4 wild and 27 cultivated genotypes were grown in Experiment 2. Plants were harvested at flowering, but in Experiment 1 wild accessions that did not flower were harvested at the beginning of leaf senescence. In Experiment 1, part of the genotypic variability of wild accessions was attributed to a less homogeneous ontogenetic stage at harvest, whereas in Experiment 2 some variation in biomass production was due to distinct phenologies of cultivated genotypes. Wild lines did not seem more tolerant to low P conditions, but the genotypic variation observed suggests these materials as a source of genetic diversity. Part of the variation in the root area and root efficiency ratio (total P content:root area) was compensatory, resulting in narrow genotypic differences in the total P content. The total P content and root efficiency ratio presented a wider amplitude of variation at P2 than at P1, and P uptake was more influenced by P supply than root production. Since the genotype × P level interaction was not significant for shoot biomass and shoot P concentration in Experiment 2, P utilization efficiency may be a useful selection criterion for cultivars between limited and adequate P supply. Within the sample of genetic diversity evaluated herein, there was large genotypic variability for traits related to P efficiency among wild and cultivated genotypes of common bean.

Growth and yield of common bean cultivars at two soil phosphorus levels under biological nitrogen fixation

The genotypic differences on growth and yield of common bean (Phaseolus vulgaris L.) in response to P supply were evaluated in a field experiment under biological N2 fixation. Eight cultivars were grown at two levels of applied P (12 and 50 kg ha-1 of P ¾ P1 and P2 respectively), in randomized block design in factorial arrangement. Vegetative biomass was sampled at three ontogenetic stages. The effects of genotype and phosphorus were significant for most traits, but not the genotype ´ phosphorus interaction. The cultivars presented different patterns of biomass production and nutrient accumulation, particularly on root system. At P1, P accumulation persisted after the beginning of pod filling, and P translocation from roots to shoots was lower. The nodule senescence observed after flowering might have reduced N2 fixation during pod filling. The responses of vegetative growth to the higher P supply did not reflect with the same magnitude on yield, which increased only 6% at P2; hence the harvest index was lower at P2. The cultivars with highest yields also presented lower grain P concentrations. A sub-optimal supply of N could have limited the expression of the yield potential of cultivars, reducing the genotypic variability of responses to P levels.

Inheritance of root traits and phosphorus uptake in common bean (Phaseolus vulgaris L.) under limited soil phosphorus supply

Scarce information about genetic control of root traits in common bean (Phaseolus vulgaris L.) impedes a more effective exploitation of the reported variability for plant breeding. This work investigated the inheritance of traits related to the root system and P absorption of common bean grown under limited soil P supply. Two experiments were carried out, each one involving one family of crosses comprising six populations (two parental cultivars, F1, F2, and two backcrosses). One plant was grown per pot with 3 kg of soil (7 mg P kg−1 Mehlich-1) and harvested at pod setting. Root samples provided the root surface area and root length by digital image analysis. Considerable additive genotypic effects were detected in both experiments; additive × additive epistases were significant only in the second experiment, whereas dominance effects were seldom significant. Estimated broad-sense heritabilities were 0.55 and 0.51 for root area, 0.50 and 0.47 for root length, 0.51 and 0.61 for root mass, and 0.51 and 0.43 for the total P content, in the first and second experiments, respectively. High genotypic correlation between root mass and root area justifies screening genotypes based solely on root mass. Phenotypic and genotypic correlations between shoot mass and root mass, and shoot mass and total P content, were highly significant, indicating that direct selection for higher shoot growth of bean plants under limited soil P supply would result in increased root mass and P uptake. A scheme for root breeding in common bean towards improving P efficiency should include: matching cultivars with favourable alleles; advance until later generations without any selection; selection of resultant genotypes under low soil P supply via shoot growth; evaluation of promising lines for root growth and agronomic performance.

Effect of seed phosphorus concentration on nodulation and growth of three common bean cultivars

Abstract An experiment was conducted in the greenhouse to evaluate the effects of seed phosphorus (P) concentration on growth, nodulation, and nitrogen (N) and P accumulation of three common bean (Phaseolus vulgaris L.) cultivars. Seeds were produced under low or high soil P levels, and soaked, or not, in 200 mM KH2PO4 solution. The experiment had a 3×3×2×2 factorial block design: three cultivars (ICA Col 10103, Carioca and Honduras 35), three levels of applied P (15, 30 and 45 mg P kg−1 soil), two native seed P concentrations, and two seed soaking treatments. Plants were harvested at flowering. Soaked seeds increased the number, dry mass and P content of nodules, but did not affect plant growth. Plants originated from seeds with high native P concentration presented higher shoot dry mass and nodule number and mass at every soil P level, and were less responsive to increased soil P supply, than plants from low seed P. In plants from seeds with high P, soil P levels did not alter significantly root dry mas...

Análise de variância dos dados primários na análise de crescimento vegetal

(2) Abstract - Plant growth analysis presents difficulties related to statistical comparison of growth rates, and the analysis of variance of primary data could guide the interpretation of results. The objective of this work was to evaluate the analysis of variance of data from distinct harvests of an experiment, focusing especially on the homogeneity of variances and the choice of an adequate ANOVA model. Data from five experiments covering different crops and growth conditions were used. From the total number of variables, 19% were originally homoscedastic, 60% became homoscedastic after logarithmic transformation, and 21% remained heteroscedastic after transformation. Data transformation did not affect the F test in one experiment, whereas in the other experiments transformation modified the F test usually reducing the number of significant effects. Even when transformation has not altered the F test, mean comparisons led to divergent interpretations. The mixed ANOVA model, considering harvest as a random effect, reduced the number of significant effects of every factor which had the F test modified by this model. Examples illustrated that analysis of variance of primary variables provides a tool for identifying significant differences in growth rates. The analysis of variance imposes restrictions to experimental design thereby eliminating some advantages of the functional growth analysis.

Crescimento e acumulação de nitrogênio de plantas de feijoeiro originadas de sementes com alto teor de molibdênio

Sementes de feijoeiro (Phaseolus vulgaris) com alto teor de molibdenio podem garantir o suprimento adequado desse nutriente para a cultura. Foram realizados dois experimentos em casa de vegetacao, com o objetivo de avaliar o efeito de sementes enriquecidas com Mo, obtidas em plantas que receberam adubacao foliar, no crescimento e acumulacao de N do feijoeiro. O substrato foi horizonte A de Argissolo em vasos de 3,5 kg, que receberam calagem e nutrientes, exceto Mo. O primeiro experimento teve arranjo fatorial 3 x 2 x 2 com cinco repeticoes: tres cultivares de feijoeiro, duas concentracoes de Mo na semente e duas epocas de coleta. Plantas originadas de sementes com alto teor de Mo, dos tres cultivares, apresentaram maior acumulacao de biomassa e N na parte aerea, nas duas epocas de coleta. Sementes com alto teor de Mo aumentaram a massa de nodulos dos cultivares Manteigao e Rio Tibagi aos 30 dias pos-emergencia (DAE), mas reduziram a massa e o numero de nodulos dos cultivares Carioca e Manteigao aos 45 DAE. O maior teor de Mo nas sementes aumentou a atividade da nitrogenase aos 30 DAE e a atividade especifica da nitrogenase aos 45 DAE. O segundo experimento teve arranjo fatorial 2 x 2 x 4 com cinco repeticoes: dois cultivares, dois niveis de Mo na semente e quatro epocas de coleta. Plantas oriundas de sementes com alto teor de Mo apresentaram maior massa de parte aerea aos 47 e 59 DAE, e maior acumulacao de N na parte aerea aos 59 DAE. O maior teor de Mo nas sementes nao afetou a nodulacao ate os 45 DAE, mas reduziu o numero de nodulos aos 59 DAE. A reducao na nodulacao no estadio de enchimento de vagens observada nos dois experimentos, nas plantas oriundas de sementes com alto teor de Mo, pode ser atribuida ao maior crescimento dessas plantas, que teria antecipado a translocacao de assimilados para as vagens. Pode-se concluir que sementes enriquecidas com Mo, colhidas em plantas que receberam adubacao foliar, podem estimular a atividade da nitrogenase e aumentar a acumulacao de biomassa e N do feijoeiro.

Effects of the size of sown seed on growth and yield of common bean cultivars of different seed sizes

A field experiment was conducted to evaluate the effects of planting different sizes of seed of the same cultivar on biomass accumulation and grain yield of common bean (Phaseolus vulgaris L.) cultivars of different seed sizes. A 6 X 2 split-plot factorial design with four replicates was employed, with six bean cultivars as main plots and two seed sizes (small and large, the latter twice as heavy as the former) of the same cultivar as subplots. Eight weekly samplings of biomass were performed, and yield components were measured at maturity. Large seeds increased the leaf area index and the shoot and root biomass of bean cultivars, particularly at the beginning of the growth cycle, but they did not affect the pod biomass. Improved growth associated with the large seed was more intense for erect than for prostrate cultivars. Plants originating from small seed presented a higher relative growth rate and net assimilation rate than plants from large seed. Large seed did not affect grain yield, but reduced the number of seeds per pod, increased the 100-seed mass, and reduced the harvest index. The results indicate that sowing larger seeds of a bean cultivar can improve early-season plant growth, which might be advantageous for crop establishment in stress environments. However, some compensatory effect, associated with delayed leaf senescence, higher net assimilation rate, or greater number of seeds per pod, allows plants originating from small seed to achieve similar grain yield. Lack of consistent effects of the seed size on grain yield indicate that the extra costs of sowing only the largest seed would not be profitable, but large seed resulted in larger grains at harvest which usually attain better market price.