2020-05-31 Factors influencing inhibition of glutamine synthetase enzyme in grass weeds by glufosinate ammonium under different temperatures

Mucheri, Tendai (2019-12)

Thesis (PhDAgric)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Evolution of weed resistance emphasized the need to implement integrated weed management strategies, however, farmers still immensely rely on chemical weed management. Glufosinate ammonium is an alternative herbicide that can replace or be used in rotations with herbicides such as glyphosate and paraquat, but it poses a problem due to its inconsistencies in controlling weeds. Studies in this dissertation aimed to investigate the influence of temperature on glufosinate ammonium efficacy. Chapter 3 of this dissertation investigated the influence of temperature on ryegrass cuticle thickness, phenolic acid concentration and calcium accumulation, and subsequently, the effect of the afore-mentioned factors on glufosinate ammonium efficacy. Ryegrass was grown at 10/15, 15/20, 20/25, and 20/30 °C (night/day) temperatures and treated with 0, 1.5, 3, 4.5, 6 and 7.5 L ha-1 glufosinate ammonium dosage rates. The grass was treated six weeks after planting and assessment was done four weeks after glufosinate application. Control of ryegrass decreased with increasing temperature. Results indicated that cuticle thickness and calcium content increased as temperatures increased, probably due to production of phenolic compounds responsible for plant defence mechanisms against herbicide stress, hence resulting in poor control of ryegrass under warmer temperatures. Chapter 4 investigated ammonia accumulation, glutamine synthetase, glutamate dehydrogenase, nitrate reductase activity and ryegrass photosynthesis in roots and leaves of control (0 L ha-1) and treated ryegrass (4.5 L ha-1) harvested 24 hours after glufosinate ammonium application. There was a significant increase in glutamine synthetase enzyme activity with increasing temperature after glufosinate ammonium application. Better control of ryegrass under cooler temperatures with glufosinate ammonium was mainly attributed to the plants’ inability to produce adequate glutamate and α-ketoglutarate, which form the carbon skeleton for transamination processes. Response of glutamine synthetase to glufosinate ammonium was significantly higher at warmer temperatures, such that the use of an alternative glutamate dehydrogenase pathway was not vital. The significant increase in glutamine synthetase activity in ryegrass under warm temperatures was able to circumvent photosynthetic inhibition. A comparative study to investigate the response of different grass weed species to glufosinate ammonium was conducted on ryegrass (Lolium spp.), ripgut brome (Bromus diandrus L.) and wild oats (Avena fatua L) in Chapter 5. The grasses were grown at 10/15, 15/20, 20/25, and 20/30 °C (night/day) temperatures and treated with 0, 1.5, 3, 4.5, 6 and 7.5 L ha-1 glufosinate ammonium dosage rates. The study observed that glufosinate ammonium control differed among weed species. Control of ryegrass increased with decreasing temperature. Temperature had no effect on wild oats. Control of ripgut brome was initially poor at 10/15 °C then increased at 15/20 and 20/25 °C and finally decreased again at 25/30 °C. Such differences in the grass response to glufosinate ammonium, even after being grown under the same conditions, was attributed to their differences in morphological characteristics such as cuticle thickness, calcium accumulation and photosynthesis after herbicide application. Increase in cuticle thickness decreased mortality of all grasses. The study perceived that negative effects of calcium on mortality can only be noticed if the cytosolic and mitochondrial calcium is mobile and active, thus, allowing it to react with glufosinate ammonium. A possible solution to mitigate problems arising from calcium level, cuticle thickness and phenolic compounds was investigated in Chapter 6. The study investigated the role of adjuvants in increasing glufosinate ammonium efficacy. Ryegrass was grown at 20/25 °C and treated with 0, 1, 2, 3 and 4 L ha-1 glufosinate ammonium. Glufosinate ammonium was applied solo and in tank mixtures with Velocity Super™ (ammonium sulfate, L 9603), Summit Super (nitrogen solution/non-ionic surfactant, L 8539) and Class act NG™ (ammonium sulfate plus a non-ionic surfactant, L 10477). Better control of ryegrass was observed when treated with glufosinate ammonium in a tank mixture with Class act NG™ and Velocity Super™ than its solo application as well as in a tank mixture with Summit Super. Ammonium sulfate exhibits surfactant and humectant properties and it facilitates movement of glufosinate ammonium into the plant while non-ionic surfactants aim to reduce water surface tension only. This explains better control observed with glufosinate ammonium in tank mixture with adjuvants containing ammonium sulfate than with Summit Super. The study suggests that adjuvant Class act NG™ and Velocity Super™ can be used to mitigate the defensive response of phenolic compounds after glufosinate ammonium application, hence, increasing its efficacy. The practical relevance of glasshouse observations in Chapter 3, 4, 5 and 6 was confirmed in Chapter 7. The study was conducted under rainfed conditions at Langgewens and Roodebloem farms in 2018 and 2019. Glufosinate ammonium was applied at different times of the day (8:00 am, 12:00 pm and 5:00 pm). The dosage rates applied were 0, 2.5, 5 and 7.5 L ha-1. The study observed that morning (8:00 am) and evening (5:00 pm) applications showed better control of ryegrass than mid-day application provided relative humidity during application time was greater than 75%. Application at mid-day (when temperatures were higher than morning temperatures) showed good control only if relative humidity was recorded above 80%, however, higher dosage rates of 5 or 7.5 L ha-1 were required to achieve greater than 90% control.

AFRIKAANSE OPSOMMING: Die ontwikkeling van onkruiddoderweerstand het die belang van geïntegreerde onkruidbeheermaatreëls beklemtoon maar produsente is nog steeds afhanklik van chemise onkruidbestuurstrategieë. Glufosinaat ammonium is ‘n alternatiewe onkruiddoder wat glifosaat en parakwat kan vervang of afwissel maar wisselvallige werking veroorsaak probleme. Die hoofdoelwit in hierdie studie was om die invloed van temperatuur op die effektiwiteit van glufosinaat ammonium te ondersoek. In Hoofstuk 3 van hierdie proefskrif is die effek van temperatuur op die kutikuladikte, fenoliese suur konsentrasie en kalsiumopeenhoping, en voortspruitend daaruit, effektiwiteit van glufosinaat ammonium op raaigras ondersoek. Raaigras is gekweek in glashuise wat by temperature van 10/15, 15/20, 20/25 en 20/30 °C (nag/dag) gestel was en die raaigras is behandel met glufosinaat ammonium dosisse van 0, 1.5, 3, 4.5, 6 en 7.5 L ha-1. Die gras is ses weke na plant behandel en evaluasie is vier weke na toediening van glufosinaat ammonium gedoen. Beheer van raaigras het verlaag met verhoogde temperature. Resultate het aangedui dat kutikuladikte en kalsiuminhoud verhoog het met verhoogde temperature, waarskynlik as gevolg van produksie van fenoliese verbindings wat verantwoordelik is vir beveiliging van die plant teen onkruiddoderstremming en dus veroorsaak het dat swak beheer van raaigras verkry is onder warmer toestande. In Hoofstuk 4 is opeenhoping van ammoniak, die aktiwiteit van glutamien sintetase, glutamaat dehidrogenase en nitraatreduktase asook fotosintese in wortels en blare van kontrole raaigras (0 L ha-1) en behandelde raaigras (4.5 L ha-1) wat 24 uur na glufosinaat ammonium toediening ge-oes is, bepaal. Daar was ‘n beduidende toename in aktiwiteit van die glutamien sintetase ensiem met toenemende temperatuur na toediening van glufosinaat ammonium. Beter beheer van raaigras met glufosinaat ammonium by koeler temperature is toegeskryf aan die plant se vermoë om genoeg glutamaat en α-ketoglutaraat, wat die koolstofskelet vir die transaminasieproses vorm, te produseer. Reaksie van glutamien sintetase teenoor glufosinaat ammonium was beduidend hoër by hoër temperature, tot so ‘n mate dat die gebruik van ‘n alternatiewe glutamaat dehidrogenase weg nie noodsaaklik was nie. Die beduidende toename in glutamien sintetase aktiwiteit in raaigras in warmer toestande het fotosintetiese onderdrukking omseil. ‘n Vergelykende studie om die reaksie van verskillende grasspesies op die toediening van glufosinaat ammonium te ondersoek is in Hoofstuk 5 uitgevoer op raaigras (Lolium spp.), predikantsluis (Bromus diandrus L.) en wildehawer (Avena fatua L). Die grasse is in glashuise by 10/15, 15/20, 20/25 en 20/30 °C (nag/dag) temperature laat groei en behandel met dosisse van 0, 1.5, 3, 4.5, 6 en 7.5 L ha-1 glufosinaat ammonium. Die studie het aangetoon dat die beheer van glufosinaat ammonium verskil het tussen spesies. Beheer van raaigras het toegeneem met verlaagde temperature. Temperatuur het geen effek gehad op die beheer van wildehawer nie. Beheer van predikantsluis was swak by 10/15 °C waarna dit toegeneem het by 15/20 en 20/25 °C en toe weer afgeneem het by 25/30 °C. Die verskille tussen die grasspesies se reaksie op glufosinaat ammonium, selfs nadat hulle onder dieselfde omstandighede gegroei het, was toegeskryf aan verskille in morfologiese eienskappe soos kutikuladikte, kalsium opeenhoping en fotosintese na toediening van die onkruiddoder. Toename in kutikuladikte het mortaliteit van die grasse verlaag. Die studie het ook aangetoon dat die negatiewe effek van kalsium op mortaliteit slegs waargeneem kan word as die sitosoliese en mitochondriale kalsium aktief en mobiel is en dit dus met glufosinaat ammonium reageer. Moontlike oplossings vir die probleme wat deur kalsiumvlakke, kutikuladikte en fenoliese verbindings veroorsaak is, is in Hoofstuk 6 ondersoek. Die studie het die rol wat bymiddels kan speel om effektiwiteit van glufosinaat ammonium te verbeter, ondersoek. Raaigras is laat groei by temperature van 20/25 °C en behandel met 0, 1, 2, 3 and 4 L ha-1 glufosinaat ammonium. Glufosinaat ammonium is alleen en in tenkmengsels met Velocity Super™ (ammonium sulfaat, L 9603), Summit Super (stikstof oplossing/nie-ioniese benatter, L 8539) en Class act NG™ (ammonium sulfaat plus ‘n nie-ioniese benatter, L 10477) toegedien. Beter beheer van raaigras is waargeneem waar glufosinaat ammonium in ‘n tenkmengsel met Class act NG™ en Velocity Super™ toegedien is as wanneer dit alleen of in ‘n tenkmengsel met Summit Super toegedien is. Ammonium sulfaat vertoon benattings en humectant eienskappe en fasiliteer absorpsie van glufosinaat ammonium deur die plant terwyl nie-ioniese benatters ten doel het om net wateroppervlakspanning te verminder. Dit verklaar die beter beheer wat glufosinaat ammonium behaal in tenkmengsels met bymiddels wat ammonium sulfaat bevat as in tenkmengsels met Summit Super. Die studie impliseer dat die bymiddels Class act NG™ en Velocity Super™ gebruik kan word om die verdedigingsreaksie van fenoliese verbindings teen te werk na toediening van glufosinaat ammonium en sodoende sy effektiwiteit kan verbeter. Die praktiese belang van die glashuis bevindings in Hoofstukke 3, 4, 5 en 6 is bevestig in Hoofstuk 7. Die studie is uitgevoer onder droëlandtoestande op die Langgewens en Roodebloem proefplase in 2018 en 2019. Glufosinaat ammonium is op verskillende tye van die dag (8:00 vm, 12:00 nm and 5:00 nm) toegedien op raaigras. Die dosisse wat toegedien is, was 0, 2.5, 5 and 7.5 L ha-1. Die studie het getoon dat oggend (8:00 vm) en aand (5:00 nm) toedienings beter beheer van raaigras as middag toedienings tot gevolg gehad het, mits humiditeit tydens toediening hoër as 75% was. Middag toedienings (wanneer temperature hoër was as in die oggende of aande) het goeie beheer verkry slegs as relatiewe humiditeit bo 80% was, maar hoër dosisse van 5 of 7.5 L ha-1 was nodig om meer as 90% beheer te verkry.

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