The effect of the combination of salinity and waterlogging may be additive, or alternatively, more or less detrimental than effects of them separately. Our objective was to evaluate the effects of waterlogging, salinity and the combination of both on seedlings of Panicum coloratum, a subtropical forage grass. Seedlings of cultivars Kapivera INTA (KA) and Klein (KL) were exposed to treatments in a controlled hydroponic experiment and several morphological and physiological variables evaluated.The effect of hypoxia was almost null when the plants were already in salinity. KA showed lower reduction than KL in shoot biomass. Both varieties showed synergistic effect of stresses, indicating that biomass production was less affected under the combined treatment than predicted from them separately. Root length, tips, forks and volume were reduced by saline exposure, while no differences in root architecture was noticeable between cultivars. Plants of KA increased leaf temperature in salinity. Nonenzymatic oxidative response and the activity of antioxidant enzymes increased in saline conditions and were lower in KA than in KL. Oxidative damage was equivalent between cultivars and among stress conditions. Proline content was comparable to control in hypoxia but increased significantly in saline conditions, with a higher response in KL than in KA. Increases in Na + (over 900%) and decreases in K + (50%) tissue concentration in salinity occurred only in KA. In general, P. coloratum proved more tolerant to hypoxia than to salinity or their combination, KA being more tolerant than KL. Findings provide basis to deepen research into tolerance mechanisms.
Context Panicum coloratum is a relatively undomesticated small-seeded warm-season forage grass. Seed shattering, an extended reproductive period and non-synchronic seed maturation limit harvested seed yields. Low seed quantity and quality hinder pasture establishment and discourage its use. Aims To assess whether seed yield potential could be improved by breeding, we sought to measure variability in traits related to seed production including phenotypic plasticity in response to environmental cues, and estimated narrow-sense heritability, prospective genetic gain after selection and co-heritabilities in seed yield components. Methods Seed retention (SR), number of panicles (PN), seed number per panicle (SN) and seed weight (SW) were measured in plants growing in the field. Clonal replicates of 13 genotypes were assessed in 2007 and 2010 and half-sib families derived from these genotypes were measured in 2010. Key results Phenotypic variability among genotypes was related to genetic factors for all measured variables. Two broad groups of accessions showing differences in SR were studied. Phenotypic plasticity in SR differed among genotypes and was negatively related to levels of SR, implying that stable high-SR genotypes could be selected in a breeding program. Maximum narrow-sense heritabilities were 0.89 and 0.41 for SN and SR, respectively, with estimated gains after selection around 30%. The best results were achieved if selecting for SR at 3–5 weeks after anthesis. Low genetic correlations and extremely low co-heritabilities between other characters and seed yield components discourage the possibility of indirect selection. Conclusion Moderate increases in seed production potential may be achieved after selection for SN, SW and SR in P. coloratum var. makarikariense. Implications Improvements in SR and other seed yield components would facilitate harvest, increase yield and consequently increase profitability to growers and stimulate pasture adoption by farmers.
Panicum coloratum var. coloratum is a subtropical grass for potentially increasing forage production in lowly productive environments where cattle-raising activities have been relocated. Heritability was estimated for characters related to salinity tolerance under saline and non-saline conditions to explore the possibility of improving tolerance by selection. From a base germplasm collected in a very harsh environment, heritability and gain after selection were calculated using 2 recombination units: individual and phenotypic family mean (PFM). Heritability estimates were very low for all characters both in saline and non-saline conditions, suggesting a complex genetic control of salinity tolerance, with a high proportion of non-additive genetic effects. Estimates were higher using individual selection than with PFM and expected genetic gains were higher for individual selection. When compared in both saline and non-saline conditions, predicted means were greater than for plants of cv. Klein, the most common cultivar in use. It appears that the analyzed germplasm would be a valuable source of genes to be included in breeding programs to increase salinity tolerance in Panicum coloratum.
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