Thesis (MScAgric)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Low crop productivity in arid and semi-arid regions is a problem caused by water stress as well as associated high levels of soil and water salinity. An increased demand for salt tolerant crops is experienced in these regions. Amaranth is a glycophyte and C4 dicotyledonous crop, well adapted to arid and semi-arid regions. Previous studies on the physiological response of salt-stressed amaranths have indicated that this crop is salt tolerant. As vegetable, amaranths can be harvested by uprooting and by topping. The most common harvesting method is by topping, allowing repeated harvesting. When harvested by topping, the cutting height is an important parameter that may be manipulated to optimise growth rates. In this study, plants were exposed to different salt stress levels and harvesting procedures while yield and quality of Amaranthus tricolor were investigated. Nutrient solutions at four different electrical conducti vi ty (EC) levels were used to fertigate the plants. At high EC levels (4 mS cm-l and 8 mS cm-lj, the length and diameter of main stems, internode lengths, stem weights as well as root weights were reduced, especially with a longer growth period. However, the shoot: root ratio and leaf protein yields increased and flowering was delayed. The best leaf yield was obtained where plants were fertigated at an EC of 4 mS cm-l for 45 days. The cutting height did not affect leaf yield, growth rates and leaf protein yield in plants fertigated at EC levels of 1, 2 and 4 mS cm-l. At an EC of 8 mS cm-l, the growth rate recovered to a value similar to that of plants fertigated with an EC of 2 mS cmonly where plants were topped at 25%. With this less destructive cutting height (topped at 25%), leaf yields, growth rates and ·leaf calcium and protein yields at an EC of 8 mS cm" were superior to that of plants topped at 50%. In plants topped at 25%, the recovered growth rates at EC 8 mS cm-l was probably due to more photosynthetic active tissue left after cuttings, resulting in the accumulation of compatible solutes for osmotic adjustment. / AFRIKAANSE OPSOMMING: Die invloed van soutstremmings en oesprosedures op die groei, ontwikkeling en blaarkwaliteit van Amaranthus trico~or L. Lae produksie van gewasse in ariede en semi-ariede gebiede is 'n probleem wat veroorsaak word deur watertekorte asook geassosieerde hoë peile van grondverbrakking en soute in water. 'n Verhoogde vraag na soutverdraagsame gewasse word in hierdie gebiede ervaar. Amaranthus is 'n glikofiet en dikotiele C4 gewas wat goed in ariede en semi-ariede streke aangepas is. Vorige ondersoeke oor die fisiologiese reaksie van Amaranthus op soutstremmings het daarop gedui dat die gewas soutverdraagsaam is. As groentegewas word dit ge-oes deur dit uit te trek of deur dit gereeld te top. Waar dit getop word is die oes-tophoogte 'n belangrike parameter wat gemanipuleer kan word om die groeitempo te optimaliseer. In hierdie ondersoek is plante aan verskillende peile van soutstremmings en oesprosedures blootgestel terwyl die opbrengs en kwaliteit van Amaranthus tricolor ondersoek is. Voedingsoplossings is teen vier elektriese geleidingspeile (EC) gebruik om plante te voedsproei. Teen hoë EC peile (4 mS cm-l en 8 mS cm-l ), het lengtes en die deursnit van hoofstamme, internode lengtes, stam massas en wortelmassas afgeneem, veral met lang groeiperiodes. Die opbrengs het egter bogroei:wortel verhouding en toegeneem terwyl blomvorming blaarproteien vertraag is. Die beste blaar opbrengs is na 45 dae verkry waar plante teen 'n EC van 4 mS cm-l gevoedsproei is. Oes-tophoogte het nie blaar opbrengs, groeitempo of blaar protei en opbrengs beïnvloed met EC waardes in voedingsoplossings van 1, 2 en 4 mS cm-l nie. Met' n EC van 8 mS cm-l het die groeitempo herstel tot 'n vlak, gelykwaardig aan wat by 'n EC van 2 mS cm-l verkry is, slegs waar teen 25% tophoogtes ge-oes is. Met hierdie minder destruktiewe oesmetode (oes-tophoogte 25%), was blaar opbrengs, groei tempo en blaar kalsium en -proteien opbrengste by 'n EC van 8 mS cm-l betekenisvol beter as waar die oes-topdiepte 50% was. Plante wat met 25% topdieptes ge-oes is se herstel in groetempo teen EC 8 mS cm-1 was waarskynlik te danke aan meer fotosinteties aktiewe materiaal wat na oes op plante gelaat is. Dit kon tot die akkumulasie van oplosbare stowwe en osmotiese aanpassings aanleiding gegee het.

The grain amaranths, Amaranthus cruentus and Amaranthus hypochondriacus have been promoted as grain-bearing plants of possible high productivity in saline or hot arid habitats. To investigate these claims, seeds of both species were germinated at 10, 15, 20, 25, 30, 35 and 40°centigrade. Germination percentage for both species was above 90% after four days at 20, 25, 30, and 35°C. Germination was negligible at 10 and 15°C and very low at 40°C. Seeds were germinated in isotonic solutions of PEG and NaCl at 0.0, -0.2, -0.4, -0.5, -0.6, -0.8, and -1.0 MPa osmotic potential at 30°C. Germination percentage was high in the range 0.0 to -0.4 MPa and dropped rapidly to zero in the -0.6 to -1.0 MPa range. Differences due to chemical effects were significant. Species differences were not. Radicles and hypocotyls were measured after six days in the above media. PEG was more inhibitory of seedling growth than was NaCl and generally inhibited A. cruentus more than A. hypochondriacus. This was also true of NaCl. All growth functions were slightly inhibited at 0.0 to -0.4 MPa and very inhibited above -0.6 MPa. PEG radically increased root/shoot ratio in both species.