Growth temperature and plant age influence on nutritional quality of &lt;i&gt;Amaranthus&lt;/i&gt; leaves and seed germination capacity&lt;sup&gt;#&lt;/sup&gt;

At Modi

doi:10.4314/wsa.v33i3.49118

Abstract

As a leafy vegetable, Amaranthus can be harvested at different stages of plant growth, ranging from young seedlings to the late juvenile stage, but data on the changes in leaf nutritional value with plant age are scanty. The objective of this study was to determine the effect of growth temperature on Amaranthus leaf yield and nutritional quality at different stages of plant growth. Five species, A. hybridus var. cruentus, A. hypochondriacus, A. tricolor, A. thunbergii and A. hybridus were compared for their response to hot (33/27oC), warm (27/21oC) and cool (21/15oC) temperature regimes (day/night) in separate glasshouses. Plants were harvested at 20, 40 and 60 d after sowing and leaf yield, minerals (Ca, P and Fe), total protein content, amino acid (methionine and lysine) content and antioxidant activity (inhibition of linoleic acid oxidation) were determined. Seed yield and germination capacity, during two years of after-ripening, were also determined. Results showed that leaf protein content differed significantly (P The phosphorus content of leaves was not significantly affected by temperature and stage of plant development, and there were also no significant differences between species. However, the amounts of both calcium and iron changed significantly (P leaves increased consistently with plant age and there were significant (P < 0.01) differences between stages of plant development and growth temperature. Warm temperature regimes were most favourable (P < 0.01) for biomass accumulation in all species. Seed production under cool and hot temperatures significantly (P < 0.01) decreased seed germination capacity for all species, but germination improved in response to after-ripening. It is recommended that for greater nutritional benefit, Amaranthus should be grown under warm conditions and younger leaves are preferable.

Highlights

The maturity stage of a conventional vegetable is universally defined, and a crop is normally harvested and consumed at a known stage of plant development, irrespective of environmental conditions for plant growth
Leaf protein content differed significantly (P < 0.01) between species, with Amaranthus thunbergii consistently showing a higher amount of leaf protein than the other species, regardless of plant age and growth temperature (Fig. 1)
From the perspective of human and animal nutrition, the results shown in Table 1 suggest that more calcium and iron would be found in the leaves of older Amaranthus plants that grow under warm to hot conditions than those which grown under cool conditions

Summary

Introduction

The maturity stage of a conventional vegetable is universally defined, and a crop is normally harvested and consumed at a known stage of plant development, irrespective of environmental conditions for plant growth. Data on the nutritional content of conventional vegetables can be reasonably associated with a specific stage of plant development. There is no documented information about the stage of plant development to define harvest maturity for wild leafy vegetables. Data on their nutritional value is likely to vary widely (Guarino, 1997; Jansen van Rensburg et al, 2004; Kruger et al, 1998), due to influences of plant age and the environmental conditions during plant growth. It is likely that for some wild leafy vegetables there is a preferred stage of plant development when flavour and palatability are favourable for human consumption

Objectives

Results

Conclusion