Growth and Physiological Response of Seven Amaranth Species to Soil Water Deficit
Abstract/ Overview
Soil water deficit is a principal abiotic factor that limit plant growth and development in dry
areas. Insufficient moisture contribute to soil water deficit and some negative effects on
plants such as reduced growth, yield, altered biomass allocation, reduced photosynthesis and
decreased plant survival. Differences in soil water deficit responses of plants may be a
consequence of different physiological and morphological adaptations. In arid and semi-arid
areas, water shortage is becoming an increasing problem because of the unreliable and
limited rainfall and it significantly contributes to food shortage especially in Kenya.
Amaranth species are among the most popular and widely consumed micronutrient rich
African indigenous leafy vegetables in Kenya; however, published information is limited
conceming growth and physiological response of amaranth species to soil water deficit. This
researchwas therefore designed to evaluate the response of seven widely cultivated amaranth
speciesin Kenya:- Amaranthus blitum (L), Amaranthus retrojlexus (L), Amaranthus spinosus
(L),Amaranthus albus (L), Amaranthus cruentus (L), Amaranthus hypochondriacus (L) and
Amaranthus tricolor (L). to soil water deficit in relation to their growth and physiology. The
experimentwas carried out at Kenya Agricultural and Livestock Research Organisation, Kisii
Centre. The experiment was laid out as completely randomized design, consisting of four
treatments, seven species and three replications. The treatments were: watering daily (TI),
watering every 3
rd and 6
th day (T2), watering every 9
th day (T3) and watering every lih day
(T4). Seeds of the seven amaranth species were grown in 20 litre plastic pots in loam moist
soils having a pH of around 4.6 to 5.4 in a glasshouse condition. Data collections commenced
on the twelfth day before initiating treatments and were collected after every twelve days.
Growth parameters measured included; shoot height, stem diameter and root to shoot ratio.
Gas exchange parameters were determined from one leaf per plant per treatment per
replication and this included, stomatal conductance, net carbon (iv) oxide assimilation rate,
intercellular carbon (iv) oxide concentration and transpiration rate by use of a portable
infrared gas analyzer. Leaf water potential, chlorophyll fluorescence, chlorophyll a, band
total chlorophyll concentrations were determined. Data was subjected to analysis of variance
and separation of means using the Least Significant Difference at 5% level. The seven
species of amaranth were significantly (pSO.05) affected by soil water deficit. Growth
parameters decreased with increase in water deficit and reduced significantly (pSO.05)with
further increase in soil water deficit. Root to shoot ratio increased with increase in soil water
deficit. CO2 assimilation rate decreased significantly with increase in water deficit while
intercellular CO2 decreased with increasing soil water deficit. Water deficit caused a
significant decrease in stomatal conductance. Leaf transpiration decreased significantly with
increase in water deficit, while leaf water potential increased with an increase in water deficit.
The relative leaf water content showed a significant reduction with increase in water deficit.
Chlorophylls a, b and total chlorophyll decreased with increasing soil water deficit. There
was a significant interaction between soil water deficit treatments and amaranth species.
From the results obtained, it can be concluded that among the seven species of amaranth,
Amaranthus albus, and A. hypochondriacus are more adaptive to soil water deficit and
therefore can be grown in water deficient regions.