Browsing by Author "Moller, Leandra"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    The effect of different soil yeasts on the growth and physiology of lupin and wheat
    (Stellenbosch : Stellenbosch University, 2018-03) Moller, Leandra; Botha, Alfred; Valentine, Alexander J.; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: Leguminous plants are often used in break-crop and crop rotation systems to fix atmospheric di-nitrogen (N2), thereby reducing the need for nitrogen (N) fertiliser input during cereal production. In these systems, wheat (Triticum aestivum L.) yield increases following blue lupin (Lupinus angustifolius L.) cultivation. Yields can also be increased by plant growth promoting microorganisms such as yeasts. These plant growth promoting yeasts (PGPY) enhance seed germination, produce plant growth promoting (PGP) factors, and partake in beneficial tripartite and quadripartite symbioses with their host plant and its root symbionts. Despite the importance of blue lupin in agriculture, it was unclear how tripartite and quadripartite interactions involving PGPY affect this legume’s biological N2 fixation (BNF) and growth. In addition, the effect of a single PGPY on germination and growth of plants used in break-crop or crop rotation systems, such as blue lupin and wheat, was unknown. To address these aspects, the impact of a rhizosphere yeast and mycorrhizal fungi on growth and nutrition of nodulated blue lupin was firstly evaluated. The ability of this rhizosphere yeast to affect a break-crop or crop rotation system was subsequently assessed by studying the yeast’s influence on the germination and developmental physiology of blue lupin and wheat. Papiliotrema laurentii (syn. Cryptococcus laurentii) was isolated from the rhizosphere of blue lupin. Nodulated blue lupin seedlings, treated with either P. laurentii CAB 91 (PL), or mycorrhizal fungi (MF), or with both symbionts (PLMF), were then cultivated in a glasshouse, after which the plants’ biomass parameters, symbiotic colonisation, and mineral nutrition were analysed. The PGP traits of PL were subsequently evaluated by comparing them to that of two other rhizosphere yeasts, i.e. Hannaella zeae CAB 1119 (HZ) and Saitozyma podzolica CAB 1199 (SP). The yeasts were used to coat seeds of blue lupin and wheat, where after their influence on the germination of these seeds was assessed under controlled conditions. The cold test was used to evaluate the influence of the three yeast strains on the vigour of both plants. To determine the effect of HZ, PL, and SP on growth and photosynthesis of nodulated blue lupin and wheat, plants were cultivated under glass house conditions. It was found that the MF treatment had no effect on blue lupin seedlings under glass house conditions. Improved growth of PL treated seedlings was underpinned by increased BNF efficiency, while greater nodulation and efficient growth on N resources supported the increased biomass of PLMF treated plants. Subsequent trials with the three rhizosphere yeasts mentioned above, indicated that of these three yeasts only PL can be used to coat the seeds of both blue lupin and wheat, since this yeast increased the germination of blue lupin and the vigour of wheat. Additionally, under glass house conditions PL promoted higher relative growth rates during the early developmental stages of both plants. The latter coincided with enhanced photosynthetic metabolism and water relations. These findings indicate that PL may potentially serve as an efficient bio-fertiliser of blue lupin and wheat to benefit breakcrop and crop rotation systems.
  • Thumbnail Image
    Item
    Soil yeasts, mycorrhizal fungi and biochar: their interactions and effect on wheat (Triticum aestivum L.) growth and nutrition
    (Stellenbosch : Stellenbosch University, 2012-03) Moller, Leandra; Botha, Alfred; Valentine, Alexander J.; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: In order to test the effect of different plant growth-promoting strategies on Triticum aestivum L. (wheat), we investigated the ability of biochar and a grain-associated soil yeast, to improve the growth of this crop. Our first goal was to study the effect of biochar amendments to sandy soil on the growth and nutrition of wheat in the presence of mycorrhizal fungi. This was accomplished by amending soil with 0%, 1%, 2.5%, 5% and 10% (w/w) biochar and cultivating wheat plants in these soil-biochar mixtures. After harvesting, plant growth and mycorrhizal colonization of roots were measured. In addition, we studied the nutritional physiology of these plants with regards to nitrogen (N), phosphorous (P) and potassium (K) concentrations, as well as the growth efficiencies and uptake rates of these nutrients. We found that wheat growth was improved by biochar amendments to soil, probably as a result of elevated K levels in the plant tissues supplied by the biochar amendments. The second goal of this study was to obtain a soil yeast from the rhizosphere of another monocot in the family Poaceae, i.e. Themeda triandra Forssk. (red grass), and then evaluate this isolate for its ability to improve wheat performance. Three different Cryptococcus species were isolated from the rhizosphere of wild grass, i.e. Cryptococcus zeae, Cryptococcus luteolus and Cryptococcus rajasthanensis. Since C. zeae was previously isolated from maize, an isolate representing this species was selected to be used in further experimentation. With the ultimate goal of testing the ability of this yeast to improve wheat growth, its effect on wheat germination was investigated and compared to that of two other soil yeasts, i.e. Cryptococcus podzolicus CAB 978 and Rhodotorula mucilaginosa CAB 826. These three yeasts were subsequently tested for their ability to improve wheat growth in pot cultures in a greenhouse. After one and two months of growth, the culturable yeasts present in the rhizosphere and bulk soil were enumerated. The effects of these yeasts were elucidated by measuring wheat growth in terms of dry weight, as well as root and shoot relative growth rates (RGR). Changes in wheat nutrition were evaluated by determining the concentrations, growth efficiencies and uptake rates for P, K, zinc (Zn) and iron (Fe). During this study, it was found that only C. zeae CAB 1119 and C. podzolicus CAB 978 were able to enhance seed germination. Similarly, it was shown that C. zeae CAB 1119 was able to improve wheat growth during the first and second month of cultivation, whereas C. podzolicus CAB 978 only improved growth during the first month, and R. mucilaginosa CAB 826 had no effect on growth. This improved growth could be attributed to C. zeae CAB 1119 improving the P, K, Zn and Fe growth efficiency of wheat, which positively influenced the root and shoot RGR, and subsequently wheat growth. Our final goal was to test whether C. zeae CAB 1119 could affect wheat growth and nutrition when cultivated in sandy soil, which contained natural microbial consortia and 10% (w/w) biochar. Plants treated with viable or autoclaved cells of C. zeae CAB 1119, were subsequently cultivated in soil only or soil amended with biochar. After one month, plants were harvested and growth was measured with regards to dry weight, root RGR and shoot RGR. In addition, the concentrations of P, K, Zn and Fe were analyzed for these plants, where after the growth efficiencies and uptake rates were calculated for these four nutrients. Results indicated that plants growing in soil amended with biochar, and treated with viable C. zeae CAB 1119, showed the best growth. The increased root and shoot RGR witnessed in these plants was probably due to increased concentrations of P and K in the plants. This study opens new avenues of research with regards to the bio-fertilizers of wheat.