Call number: LD2668 .T4 1984 I92 / Master of Science

Thesis (MScAgric.)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Experi!11entsin KwaZulu-Natal showed that seed treatment with molybdenum (Mo) could double the yield and increase the protein content by 1.9% of soybeans grown on acidic soils. However, it was also found that soybean yield at five of the localities was reduced on average by 8% after Mo seed treatment. It was surmised that the yield reductions observed after Mo seed treatment were connected to the quality of the seed used for planting. The aim of this project was to assess the relationship between seed quality and Mo seed treatment and find a fast, easy quality assessment test that could be used to adapt Mo treatments according to seed quality. The first investigation entailed assessing the quality of the seed obtained, from various seed lots, for planting. A number of different seed quality testing techniques were performed and they included the accelerated ageing test, tetrazolium test, conductivity test, standard germination test and an emergence . test planted at different depths with incubation at different temperatures. All the test results were compared with the accelerated ageing test results, to find the test most closely correlated to the accelerated ageing test, which is regarded as the most accurate indicator of soybean seed vigour. It was found that the emergence test where the seeds where planted at 10 cm presented a close correlation with the accelerated ageing test. An assessment of seed quality revealed that the four different seed lots provided seed of three significantly different levels of quality, which could be used for further investigations. The second investigation was concerned with the reaction of the seed of different quality levels to Mo seed treatment. Firstly, seeds from four different seed lots were treated with five different concentrations of Mo and planted under acidic conditions. The establishment was monitored up until six weeks, at which point the experiment was terminated. In the second planting, seeds from the four different seed lots were treated with six different concentrations of Mo and planted under optimum pH conditions. Emergence was monitored and after thinning out the remaining plants were left to mature and produce seed. The emergence percentage results from both of these two plantings did not reveal the alleged positive effect Mo seed treatment has produced in the field and no definite relationship between seed quality and Mo seed treatment was observed. The third investigation was concerned with the effect that osmoconditioning had on the reaction of seed to Mo seed treatment. Seeds from two seed lots, one of very poor quality and the other of good quality, were pre-treated with four different levels of poly-ethylene glycol (PEG 6000) and then treated with four concentrations of Mo. They were planted under optimum pH conditions and establishment was monitored. After being thinned out the remaining plants were allowed to mature and produce seed. The emergence percentage results revealed that the PEG pre-treatments greatly improved emergence percentages, especially in the poor quality seed. There were some positive effects of Mo seed treatment observed where the lower concentrations of Mo were used, but again, no definite relationship between seed quality and Mo seed treatment was found. PEG pre-treatment appeared to help make the seeds more "resistant" to the harmful effects of Mo. / AFRIKAANSE OPSOMMING: Navorsing in KwaZulu-Natal het aangetoon dat saadbehandeling met molibdeen (Mo) die opbrengs van sojabone op suurgrond kan verdubbel en die proteieninhoud met tot 1.9% kan verhoog. Daar is egter ook gevind dat sojaboonopbrengs op vyf lokaliteite met gemiddeld 8% gedaal het na saadbehandeling met Mo. "nVermoede bestaan dat die opbrengsverlagings wat voorgekom het na saadbehandeling met Mo verband hou met die kwaliteit van saad wat vir die aanplantings gebruik is. Die doel van die projek was om vas te stel wat die verband tussen saadkwaliteit en Mo saadbehandeling is en om "n vinnige en maklike toets te vind om saadkwaliteit te bepaal om sodoende Mo behandelings aan te pas volgens saadkwaliteit. In die eerste eksperiment is die kwaliteit van verskillende saadlotte wat verkry is, getoets. "n Aantal verskillende tegnieke om saadkwaliteit te bepaal is uitgevoer. Die tegnieke was die versnelde verouderingstoets, tetrazoliumtoets, konduktiwiteitstoets, standaard ontkiemingstoets en "n vestigingstoets waar saad op verskillende dieptes geplant en by verskillende temperature geïnkubeer is. Die resultate van die verskillende toetse is gekorreleer met die resultate van die versnelde verouderingstoets, wat beskou word as die toets wat die beste aanduiding gee van saadgroeikragtigheid. Daar is gevind dat sade wat 10 cm diep in sand geplant is, se opkoms die beste korrelasie met die versnelde verouderingstoets toon en dus as "n goeie aanduiding van die kwaliteit van saad beskou kan word. Daar is gevind dat daar drie saadlotte is met duidelike kwaliteitsverskille wat gebruik kon word in verdere eksperimente. Die tweede eksperiment het die reaksie van saad van verskillende kwaliteitsvlakke teenoor molibdeen saadbehandeling ondersoek. Eerstens is saad van vier verskillende saadlotte behandel met vyf verskillende konsentrasies Mo en onder baie suur toestande geplant. Die vestiging is gemonitor vir ses weke waarna die eksperiment gestaak is. Daarna is saad van dieselfde vier saadlotte behandel met ses verskillende Mo konsentrasies en onder optimum pH toestande geplant. Vestiging is gemonitor en na ses weke is die plante uitgedun en twee plante per pot is gelaat om saad te produseer. Die ~ vestigingspersentasie van beide die eerste en tweede plantings het nie die verwagte positiewe effek teenoor Mo saadbehandeling getoon nie en geen betekenisvolle verwantskap tussen saadkwaliteit en Mo saadbehandeling kon waargeneem word nie. Die derde eksperiment het die invloed van osmokondisionering op die reaksie van saad op Mo saadbehandeling ondersoek. Saad van twee saadlotte, een van goeie kwaliteit en een van swak kwaliteit, is voorafbehandel met poli-etileen glikol (PEG 6000) en daarna met vier konsentrasies van Mo behandel. Die sade is onder optimum pH toestande geplant en die vestiging is gemonitor. Nadat dit uitgedun is, is die oorblywende twee plante gelaat om saad te produseer. Die vestigingspersentasies het getoon dat PEG voorafbehandelings vestiging betekenisvol verbeter, veral in die geval van lae kwaliteit saad. Daar was 'n . positiewe effek van Mo saadbehandeling waar relatief lae konsentrasies molibdeen toegedien is, maar daar kon weereens nie 'n duidelike verwantskap tussen saadkwaliteit en Mo saadbehandeling waargeneem word nie. Dit blyk dat PEG voorafbehandeling die sade meer bestand teen die skadelike invloed van Mo gemaak het.

The biochemical changes taking place during soybean seed development and gennination, and some aspects of desiccation tolerance were assessed with reference to lipid peroxidation and antioxidant systems. During nonnal seed development, fresh weight and dry weight increased between 20 and 50 days after flowering (DAF), concomitant with the accumulation of triacylglycerols and sugar reserves, after which dry weight remained almost unchanged, and fresh weight decreased. Seed moisture content decreased rapidly during the last stages of development. High levels of lipid peroxidation were evident between 20 and 45 DAF, and decreased thereafter. An examination of antioxidant systems revealed that whereas total glutathione levels accumulated continuously throughout the 80 days of seed development, both dehydroascorbic acid (DHA) reductase and ascorbate free radical (AFR) reductase increased concurrently with the increase in total ascorbate content, and the overall levels did not decrease markedly during maturation drying. Ascorbate peroxidase (ASC POD) activity was high during the period ofgreatest ascorbate accumulation. Both catalase (CAn and superoxide dismutase (SOD) activities increased progressively during early seed development (20-40 DAF), but showed variable patterns of change during maturational drying, in marked contrast to ASC POD which declined from 40 DAF to undetectable levels at 70 DAF. An assessment of the relationship between the antioxidant systems and lipid peroxidation was made during imbibition and gennination, as it has been suggested that controlling free radicals was a critical event in early imbibition. Unexpectedly, lipid peroxidation increased progressively in both seeds and isolated axes, and were eight-fold higher at 48 hours of imbibition compared to dry tissues. A progressive, and co-ordinated, increase in CAT, total glutathione, total ascorbate pool, guaiacol POD, ASC POD, and SOD appeared to parallel the rise in lipid peroxidation in both whole seeds and axes. Variable responses were evident between seeds and axes for the enzymes AFR reductase and DHA reductase In order to gain a further insight into the dynamics of desiccation-tolerance and desiccationsensitivity, imbibing seeds were subjected to an unscheduled dehydration treatment, and then rehydrated for up to 24 hours. During these hydration-dehydration-rehydration (H-D-R) treatments, changes in lipid peroxidation and antioxidant systems were measured. Concurrent with the loss of viability in the axes of seeds dehydrated after 24 and 36 hours of imbibition, there were increases in both lipid peroxidation and solute leakage. Unscheduled drying was seen to be a critical stage, as intolerant axes showed four- to eightfold increases in lipid peroxidation, which were only partially reduced on subsequent rehydration. Tolerant axes, on the other hand, were able to maintain low, basal levels of lipid hydroperoxides on drying. The relationship between these observations and the antioxidant systems showed that the antioxidant enzymes CAT, ASC POD, AFR reductase, DHA reductase, guaiacol POD and SOD declined markedly during the unscheduled drying, whereas GSH and ASC declined only slightly. On rehydration, most of the enzymes, total glutathione, and total ascorbate pool increased, the only exception being the loss of ASC POD activity. ORA reductase, which was seen to decrease as a part of nonnal gennination, declined progressively also in H-D-R treatments. These results suggested that loss of viability was not attributable to a decline of the antioxidant systems but rather to the combined deleterious effects of increased lipid peroxidation, and a generalized and moderately compromised antioxidant system. These studies have indicated that the occurrence of lipid peroxidation can be seen as a nonnal part of seed development and gennination. The H-D-R studies, on the other hand, supported the concept that the balance between peroxidation reactions and the protective systems was critical to the development of desiccation tolerance. / Thesis (Ph.D.)-University of Natal, Durban, 2003.