Juan Andrés Cardoso

Morpho-anatomical adaptations to waterlogging by germplasm accessions in a tropical forage grass

Brachiaria humidicola, a tropical forage grass, is recognized for its tolerance to temporary waterlogging. Waterlogged soils are characterized by slow movement of gases and oxygen defficiency. B. humidicola accessions showed adaptations common to wetland species, including a ventilation system (aerenchyma) from shoot to root that might facilitate O2 transport and the escape of gases that usually accumulate in roots under waterlogging. Of 12 accessions tested, one accession (CIAT 26570) showed greater aerenchyma formation. Quicker growth under waterlogging of CIAT 26570 might be associated with greater aerenchyma formation.

Waterlogging-induced changes in root architecture of germplasm accessions of the tropical forage grass Brachiaria humidicola

Brachiaria humidicola, a tropical forage grass, develops aerenchyma in nodal roots to adapt to waterlogging. A large body of work has focused on the functional role of aerenchyma in nodal roots under waterlogged soil conditions. On the other hand, quantification of responses of lateral roots to waterlogging has been often overlooked in past work. Our data indicated that although waterlogging reduced the overall proportion of lateral roots, its proportion significantly increased in the top 10 cm of the soil. This suggests that soil flooding increases lateral root proliferation of B. humidicola in upper soil layers. This may compensate the reduction of root surface area brought by the restriction of root growth at depths below 30 cm into waterlogged soil.

Contrasting strategies to cope with drought conditions by two tropical forage C4 grasses

The study provided an overview of the dynamics of growth, water uptake and water use of two tropical C4 forage grasses: Napier grass (Pennisetum purpureum) and Brachiaria hybrid cv. Mulato II. This in combination with the observations of leaf rolling scores suggested that Napier grass and Mulato fall respectively into contrasting “water spending/water saving” models of water use. As such, Napier grass might be targeted for areas with intermittent and short periods of drought, whereas Mulato II might be a better option for areas with longer drought spells.

Non-destructive Phenotyping to Identify Brachiaria Hybrids Tolerant to Waterlogging Stress under Field Conditions

Brachiaria grasses are sown in tropical regions around the world, especially in the Neotropics, to improve livestock production. Waterlogging is a major constraint to the productivity and persistence of Brachiaria grasses during the rainy season. While some Brachiaria cultivars are moderately tolerant to seasonal waterlogging, none of the commercial cultivars combines superior yield potential and nutritional quality with a high level of waterlogging tolerance. The Brachiaria breeding program at the International Center for Tropical Agriculture, has been using recurrent selection for the past two decades to combine forage yield with resistance to biotic and abiotic stress factors. The main objective of this study was to test the suitability of normalized difference vegetation index (NDVI) and image-based phenotyping as non-destructive approaches to identify Brachiaria hybrids tolerant to waterlogging stress under field conditions. Nineteen promising hybrid selections from the breeding program and three commercial checks were evaluated for their tolerance to waterlogging under field conditions. The waterlogging treatment was imposed by applying and maintaining water to 3 cm above soil surface. Plant performance was determined non-destructively using proximal sensing and image-based phenotyping and also destructively via harvesting for comparison. Image analysis of projected green and dead areas, NDVI and shoot biomass were positively correlated (r ≥ 0.8). Our results indicate that image analysis and NDVI can serve as non-destructive screening approaches for the identification of Brachiaria hybrids tolerant to waterlogging stress.

The Effect of Pre-Harvest Methyl Jasmonate Treatment on the SelectedVolatile Compounds and Endogenous Hormones Contends in the Pulp ofGrape Berries

Grapevine is one of the most valued and widely cultivated fruit crop worldwide, with their pleasant flavor and valuable health effects. During the consequent ripening at ambient temperature, the volatile compounds of table grape often decreased, to affect their sensory evaluation. The development of new and effective methods to increase the volatile compounds of berries is necessary. Present study was carried out to investigate the pre-harvest methyl jasmonate (MeJA) treatment on the selected volatile compounds and endogenous hormones content from ‘Shine Muscat’ berries pulp. The results indicated that, pre-harvest application of MeJA (0.1 mM or 0.01 mM) on grape berries generally enhanced the production of terpenes, like nerol, linalool, alpha-terpineol; While some C6 compounds were reduced, such as (E)-2-hexenol, hexanol, (Z)-3-hexenol, hexanal and (E)-2-hexenal. The endogenous hormones like IAA (indole acetic acid), ABA (abscisic acid) and JA (jasmonate acid) content were also changed after MeJA treatment. We also observed that MeJA palys a key role in fruit endogenous hormones level and volatile compounds by increasing the expression level of several related genes, such as aroma-related genes Vvter, Vv-syn and hormone-related genes VvOPR3, VvAuI, VvEth, VvNCED1. We hypothesize that, MeJA as an effective elicitor affects the volatile compounds by altering endogenous hormones level in berries pulp of ‘Shine Muscat’.

Effect of endophyte association with Brachiaria species on shoot and root morpho-physiological responses under drought stress

A greenhouse experiment was conducted at the International Centre for Tropical Agriculture in Colombia to evaluate effects of the fungal endophyte, Acremonium implicatum, on growth and physiological responses of five Brachiaria cultivars. Plants were grown under well-watered (WW) and drought-stressed (DS) conditions, with (E+) and without (E-) endophyte; and their morpho-physiological responses were determined. Significant two-way and three-way interactions produced variable effects on leaf area, number of tillers, shoot elongation, shoot biomass, total root diameter, diameter of cortex, area of stele and diameter of xylem vessel. Main effect of endophyte significantly increased leaf stomatal conductance and reduced diameter of xylem. Smaller leaf area was found in endophyte-infected than control plants of three cultivars, both under WW and DS conditions, which indicates a cost of endophyte infection to the host cultivars. Large root diameter and area of stele under WW conditions, as well as small diameter of xylem vessels in some cultivars suggests that endophyte may improve efficiency for water uptake and use under different water regimes. Less Root Cortical Aerenchyma (RCA) was observed in endophyte-infected plants of Tully and Cayman than the control, which may influence plant capacity for resource acquisition in Brachiaria. Genotype-specific variation among hosts generally segregated the cultivars in terms of their shoot and root responses, based on presence (E+) or absence (E-) of endophyte. However, future studies should examine how association of A. implicatum with Brachiaria grass affects capacity for water uptake and carbon accumulation, and the role of RCA in these processes.