Growth and Physiological Response of Seven Amaranth Species to Soil Water Deficit

Abstract

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.