The effect of different soil yeasts on the growth and physiology of lupin and wheat

Thesis (PhD)--Stellenbosch University, 2018.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.AFRIKAANSE OPSOMMING: Peulplante word dikwels gebruik in breekgewas- en wisselboustelsels om atmosferiese stikstof (N2) te bind, wat die behoefte aan stikstof (N) kunsmis-insette tydens graanproduksie verminder. In hierdie stelsels word die opbrengs van koring (Triticum aestivum L.) verhoog na die verbouing van blou lupiene (Lupinus angustifolius L.). Opbrengste kan ook verhoog word deur plant-groei-bevorderende mikroörganismes, soos giste. Hierdie plant-groei-bevorderende giste (PGBG) verbeter saadontkieming, produseer plant-groei-bevorderende (PGB) faktore en is betrokke by voordelige drie- en vierledige simbiosis met hul gasheerplant en sy wortelsimbionte. Ten spyte van die belangrikheid van blou lupien in die landbou bedryf, was dit onduidelik hoe drie- en vierledige interaksies waarby PGBG betrokke is, die biologiese N2-fiksering (BNF) en groei van die peulplant beïnvloed. Daarbenewens was die effek van 'n enkele PGBG op ontkieming en groei van plante wat in breekgewas- of wisselboustelsels gebruik word, soos blou lupiene en koring, onbekend. Om hierdie aspekte aan te spreek, is die impak van 'n rhisosfeergis en mikorisas op die groei en voeding van blou lupiene in die teenwoordigheid van wortelknoppie-bakterieë in hierdie studie geëvalueer. Vervolgens is die vermoë van hierdie rhisosfeergis om 'n breekgewas- of wisselboustelsel te beïnvloed, beoordeel deur die gis se invloed op die ontkieming en ontwikkelingsfisiologie van blou lupiene en koring te bestudeer. Papiliotrema laurentii (sinoniem Cryptococcus laurentii) is vanuit die rhisosfeer van blou lupiene geïsoleer. Blou lupiene-plantjies, gekoloniseer deur wortelknoppie bakterieë, is behandel met óf P. laurentii CAB 91 (PL), óf mikorisas (MF), óf met beide simbionte (PLMF). Die plantjies is daarna in 'n glashuis gekweek, waarna die plante se biomassa-veranderlikes, simbiotiese kolonisasie en minerale voeding geëvalueer is. Die PGB-eienskappe van PL is vervolgens geëvalueer deur die eienskappe te vergelyk met dié van twee ander rhisosfeergiste, nl. Hannaella zeae CAB 1119 (HZ) en Saitozyma podzolica CAB 1199 (SP). Die giste is as saadbedekking van blou lupiene en koring gebruik, waarna hul invloed op die ontkieming van hierdie sade onder beheerde toestande beoordeel is. Die koue toets is gebruik om die invloed van die drie gisstamme op die groeikragtigheid van albei plantsoorte te evalueer. Die plante is onder glashuistoestande gekweek om die effek van HZ, PL en SP op die groei en fotosintese van blou lupiene en koring te bepaal. Daar is gevind dat die MF-behandeling geen invloed op blou lupiene-plantjies onder glashuis-toestande gehad het nie. Verbeterde groei van PL-behandelde saailinge is ondersteun deur verhoogde BNF-doeltreffendheid, terwyl meer wortelknoppies en doeltreffende groei op N-bronne die verhoogde biomassa van PLMF-behandelde plante ondersteun het. Daaropvolgende proewe met die drie bogenoemde rhisosfeergiste het aangedui dat slegs PL as 'n saadbedekking vir beide blou lupiene en koring gebruik kan word, aangesien hierdie gis die ontkieming van blou lupiene en die groeikragtigheid van koring verbeter het. Verder, onder glashuistoestande het PL albei plante se relatiewe groeitempo tydens die vroeë ontwikkelingsfases verhoog. Laasgenoemde het gepaard gegaan met verbeterde fotosintetiese metabolisme en water verbruik. Hierdie bevindinge dui daarop dat PL moontlik aangewend kan word as 'n doeltreffende bio-kunsmis vir blou lupiene en koring, om breekgewas- en wisselboustelsels te verbeter.Doctora