Differential acclimation capacity to frost in sugarcane varieties grown under field conditions

In certain sugarcane (Saccharum spp. hybrids) production regions of the world, including South Africa, frost frequently occurs. Great demand exists for frost tolerant sugarcane varieties as production in these areas could become more profitable. Two Louisiana (USA) varieties, known to yield high sugar even when immature (LCP 85-384 and HOCP 96-540), and two South African varieties (N21 and N36) were evaluated in a field trial for frost tolerance. O-J-I-P chlorophyll a fluorescence transients were recorded in youngest fully-expanded leaves of these varieties on several occasions before and following exposure to frost. Analysis of these transients revealed that varieties N36 and LCP 85-384 were capable of cold acclimation following the first frost, while N21 and HOCP 96-540 lacked similar capability. Exposure to further frosts altered the fluorescence transients in a variety-specific fashion, with recovery in N36 and LCP 85- 384 towards baseline kinetics, but with further deterioration in N21 and HOCP 96-540. Between the first frost and harvest, estimated recoverable crystal (ERC) content values in cane stalks of N36 and LCP 85-384 increased by 26% and 20% respectively, while in N21 and HOCP 96-540 ERC content values only increased by 8% and 11% respectively. Consequently, N36 and LCP 85-384 ultimately achieved the highest ERC yields (tons/hectare). The ability to maintain high ERC accumulation capacity for longer following frost could be an important factor determining sugarcane yield performance in frost-prone areas. In addition, O-J-I-P fluorescence rise kinetics show promise as a rapid screening tool for assessment of cold acclimation potential in sugarcane.http://link.springer.com/journal/10725hb201

Chemical ripening of sugarcane with trinexapac-ethyl (Moddus®) – mode of action and comparative efficacy

Chemical ripeners cause growth suppression, thus increasing sucrose accumulation in sugarcane by lowering the growth sink demand for sucrose. Trinexapac-ethyl (Moddus®), the most recent chemical to be introduced as a ripener with a hormonal mechanism, inhibits production of the plant hormone gibberellic acid, which leads to restriction of internode elongation. This study reports novel findings on a dual mode of action, by which Moddus® affects growth processes in both the stalk and leaf canopy above a certain concentration, and how this influences ripening efficacy. In addition the efficacy of Moddus® is compared to Ethephon®, the other ripener with a hormonal mechanism. An irrigated field trial was planted to variety N32 at the South African Sugarcane Research Institute’s research station in Pongola, South Africa. The plant and subsequent three ratoons were used as experimental crops and harvested in April of each year. Replicated treatment plots consisted of 6 cane rows, 16mlong and spaced 1.4mapart. Treatments comprised an unsprayed control, Ethephon® applied according to standard practise, and Moddus® applied at three dosages. Products were applied with CO2-pressurised equipment and a hand-held overhead spray boom. Measurements on the stalks (length, individual internode elongation and juice quality) and leaves (green and dead leaf mass per stalk) were conducted at intervals until harvest. At harvest the cane and sugar yield was determined for each treatment. A novel finding was that Moddus®, above a certain concentration, ripened the crop through a dual mode of action involving restriction of both internode elongation and leaf growth. Characterisation of effects on individual internode elongation and mass of the green leaf canopy, coupled to yield data, provided insights to be considered in future when attempting to explain varietal differences in response to Moddus®. The easy-to-measure plant processes identified in this study as sensitive indicators of ripening efficacy might enable initial pot-based screening of large numbers of varieties for responsiveness to Moddus®, before embarking on more time-consuming and expensive field-based testing. The data acquired in this study could also be used in attempts to simulate Moddus®-induced ripening with mechanistic sugarcane crop models.Syngenta South Africa (Pty) Limitedhttp://www.elsevier.com/locate/fcr2016-09-30hb201

Negative effects of lodging on irrigated sugarcane productivity : an experimental and crop modelling assessment

Lodging lowers the productivity of sugarcane through a reduction in radiation use efficiency and stalkdamage. However, there are few reports of experiments specifically designed to quantify effects of lodg-ing in sugarcane. Efforts to model onset and progression of lodging, and the impact on crop productivity,have not been attempted. The objectives of this paper were to quantify effects of lodging on sugarcaneand to develop modeling capability in terms of predicting lodging onset, progression and impact. Fieldexperiments with irrigated ratoon crops were conducted at Pongola, South Africa. In one treatment thecane in each plot was allowed to grow through bamboo frames that prevented lodging. In the othertreatment, the cane was not supported and could lodge at any stage. The degree of lodging was capturedweekly by a rating that ranged from 1 to 9, where 1 = fully erect cane and 9 = completely lodged cane.At harvest estimated recoverable crystal percent (ERC %) of stalks and yield (cane and ERC) was mea-sured for each plot. Lodging resulted in decreased ERC yields of up to 20.6%. An algorithm for simulatinglodging when aboveground biomass (including rainfall and irrigation water retained on it) exceeds avariety-specific threshold, and which also considers wind speed and soil water content, was evaluatedfor predicting the extent and impact of lodging in the Pongola experiments, as well as for four deficitirrigation treatments of a field experiment conducted in Komatipoort, South Africa. The study showedthat the onset of lodging was simulated reasonably well for various soil/crop/atmospheric conditions,while the extent of lodging at harvest was simulated very accurately for all crops. Simulated lodging wasprimarily driven by crop size and lodging events were triggered by rainfall that added weight to the aerialmass of the crop, and reduced the anchoring ability of the soil through saturation of the top soil. Moreaccurate simulation of lodging, and its impacts on yield, will improve the accuracy of yield predictionsby crop models, increasing their value in applications such as crop forecasting, climate change studiesand exploring crop improvement and management options.South African Sugarcane Research Institute.http://www.elsevier.com/locate/fcr2016-08-31hb201

Reduction of dark chilling stress in N₂‐fixing soybean by nitrate as indicated by chlorophyll <i>α</i> fluorescence kinetics

Sub‐optimal night temperatures below 15°C (dark chilling) frequently reduce soybean [Glycine max (L.) Merrill] production. Nitrate application is known to alleviate some of the negative effects of low root zone temperatures, probably by counteracting the inhibition caused by decreased symbiotic nitrogen fixation (SNF). Under field conditions, however, dark chilling is frequently not accompanied by low root zone temperatures. The possibility that nitrate might increase dark‐chilling tolerance under these conditions is still largely unexplored. In addition to quantifying vegetative development by means of the plastochron index, O–J–I–P (O–I1–I2–P) chlorophyll α fluorescence transients were recorded in soybean genotypes of contrasting chilling tolerance during and following exposure to dark chilling in the absence of low root zone temperatures. Plants, inoculated with the N2‐fixing bacteria, Bradyrhizobium japonicum , were grown with and without nitrate supplementation. The recorded O–J–I–P chlorophyll α fluorescence transients were analysed by the so‐called JIP‐test which translates stress‐induced alterations in these transients to changes in biophysical parameters that quantifies the energy flow through photosystem II (PSII). One of these parameters, the performance index (PIABS ), combines the three main functional steps (light energy absorption, excitation energy trapping, and conversion of excitation energy to electron transport) of photosynthetic activity by a PSII reaction centre complex into a single multiparametric expression. By using the PIABS we could convincingly show that nitrate supplementation considerably enhances dark‐chilling tolerance and recovery capacity of plants in the absence of low root zone temperatures. This was especially true for the chilling‐sensitive genotype (‘Java 29’), suggesting that the response of SNF to dark chilling might be an important factor contributing towards genotypic differences in chilling tolerance. Our results corroborated previous reports about the superior chilling tolerance of ‘Maple Arrow’, a chilling‐tolerant genotype. The results obtained indicated that the PIABS is a far more sensitive indicator of dark‐chilling stress than the maximum quantum yield of primary photochemistry (FV/FM).</p

Promoting adoption of soil health related regenerative agriculture practices amongst small-scale sugarcane grower communities in South Africa

This paper was presented at the XXXI Congress of International Society for Sugar Cane Technologists, 20-23 February, 2023 at Hyderabad, India.The term ‘regenerative agriculture’ describes a rehabilitation and conservation approach to farming, which aims to enhance the sustainability of production. The approach consists of an array of practices that focus on the maintenance and rehabilitation of soil health. In the South African sugar industry, major soil related problems include: (a) soil erosion; (b) compaction; (c) acidification; and (d) soil salinity/sodicity. While regenerative practices to guide growers have been developed at the South African Sugarcane Research Institute (SASRI), the remediation of poor soil health in the industry has generally been hampered by low levels of adoption of these practices. The importance of the small-scale grower (SSG) sector to economic development has been recognised as a key element of the South African Sugarcane Value Chain Master Plan to 2030, which aims to ensure the long-term sustainability of the industry. To understand the barriers to adoption, SASRI conducted a survey of a small-scale grower community. This revealed that conventional knowledge exchange methods were ineffective with SSGs. Consequently, SASRI is developing and implementing knowledge exchange approaches which are founded on: (a) networks of demonstration plots where regenerative practices can be showcased and (b) participative research methodologies which aim to empower SSGs in discovering their own practical solutions to production challenges. Complementing these is an initiative to upskill extension specialists and agricultural advisors in soil health regenerative practices supported by regular radio broadcasts and newsletters. In the short term, the impact of these knowledge exchange tactics is being monitored through analysis of SSG production and economic data by SASRI, in collaboration with stakeholders from the local grower associations and mills. To date, data from the small-scale grower community study indicated that the implementation of the demonstration plot methodology focused on matching variety to soil type has had a positive impact on SSG livelihoods.https://link.springer.com/journal/123552025-02-13hj2024Plant Production and Soil ScienceSDG-02:Zero Hunge

Dark chilling effects on soybean genotypes during vegetative development: parallel studies of CO₂ assimilation, chlorophyll α fluorescence kinetics O‐J‐I‐P and nitrogen fixation

The effects of dark chilling on CO 2 assimilation, chlorophyll a fluorescence kinetics and nitrogen fixation were compared in two Glycine max (L.) Merr. genotypes. The aim was to elucidate the mechanisms by which photosynthesis was inhibited as well as identification of selection criteria for dark chilling tolerance. Seedlings were dark chilled (8°C) for 9 consecutive nights but kept at normal day temperatures (28°C). CO 2 gas exchange analysis indicated that photosynthesis in Maple Arrow was inhibited largely as a result of stomatal limitation, while in Fiskeby V, it indicated inhibition of the mesophyll reactions. Increased intercellular CO 2 concentration and decreased carboxylation efficiency suggested loss of Rubisco activity in Fiskeby V, although no effect on the K M (CO 2 ) of Rubisco was observed. Quantification and deconvolution of the Chl a fluorescence transients into several phenomenological and biophysical parameters (JIP‐test) revealed large genotypic differences in the response of PSII to dark chilling. These parameters differentially changed in the two genotypes during the progression of the chilling treatment. Among them, the performance index, reflecting several responses of the photochemical apparatus, provided the best preliminary overall assessment of the genotypes. In contrast, the quantum yield of primary photochemistry ϕ Po (F V /F M ) was quite insensitive. The recovery of most of the JIP‐test parameters in Maple Arrow after 6 and 9 nights of dark chilling was a major genotypic difference. Genotypic differences were also observed with regard to the ureide response and N 2 fixation appeared to be more sensitive to dark chilling than CO 2 assimilation. The JIP‐test provided information consistent with results derived from CO 2 assimilation and N 2 fixation studies suggesting that it can substitute the much more time‐consuming methods for the detection of chilling stress and can well satisfy the requirements of a rapid and accurate screening method. </p

Sugarcane yield and juice quality as affected by harvest age and chemical ripeners in Central Rift Valley of Ethiopia

SUPPLEMENTARY MATERIAL : FIGURE S1. Monthly total rainfall (mm) (RF), relative humidity (RH), the mean maximum (Tmax), and minimum (Tmin) temperature (°C) during the study period at Metahara in the late (A), Kessem in the late (B) and Kessem in the early (C) periods. TABLE S1. Dates of planting, application of ripeners, and harvesting. TABLE S2. Main effects of variety and age of harvesting by ripener combination on stalk height and stalk weight of sugarcane at Metahara and Kessem sugarcane plantations. TABLE S3 Main effects of variety and age by ripener combination on cane yield, sucrose content and sucrose yield at Metahara and Kessem sugarcane plantations. TABLE S4 Main effects of variety and age by ripener combination on sucrose content and sucrose yield at Metahara and Kessem sugarcane plantations.TABLE S5 Partial budget analysis for sucrose yield of four harvest ages in the late (June) period harvesting at Metahara sugarcane plantation.Chemical ripening is a promising technology at Metahara and Kessem sugarcane plantations where conditions are not optimal for natural ripening in the early and late period of sugarcane processing. However, the harvest age at which sucrose yield could be maximized with application of ripeners has not been established. Thus, field experiments were conducted to determine the effects of harvest age and chemical ripeners on yield and juice quality of sugarcane. The experiments were conducted in the late period (June) harvesting at Metahara, and in the early (October) and late period (June) harvesting at Kessem. A split plot design with three replications was used where the main plot treatments were two sugarcane varieties, viz. B52-298 and SP70-1284, and the sub-plot treatment consisted of combinations of four harvest ages (10, 12, 14 and 16 months) and two ripener treatments [Moddus™ at 250 g ai ha−1 + Fusilade Forte™ (M + FF) at 25.6 g ai ha−1 combination sequentially sprayed and unsprayed control]. The results showed significant difference between the varieties for stalk height and stalk weight in early period study at Kessem with variety SP70-1284 being superior as compared to variety B52-298. Furthermore, harvest age and ripener combination significantly affected all yield and quality parameters, while there was a significant cane and sucrose yield response at Kessem at both sites and seasons. The highest cane yield was recorded in the unsprayed 16-month harvest age treatment, while the highest sucrose yield was recorded in the M + FF ripener combination 12-month harvest age treatment in all the studies. The economic analysis showed the highest marginal rate of return and net revenue in the M + FF ripener combination 12-month harvest age treatment and represents the best cane quality management practice for varieties B52-298 and SP70-1284 at these plantations.Ethiopian Sugar Corporation.https://link.springer.com/journal/400032024-08-10hj2023Plant Production and Soil ScienceSDG-15:Life on lan

Regulation of Respiration and the Oxygen Diffusion Barrier in Soybean Protect Symbiotic Nitrogen Fixation from Chilling-Induced Inhibition and Shoots from Premature Senescence1[W][OA]

Symbiotic nitrogen fixation is sensitive to dark chilling (7°C–15°C)-induced inhibition in soybean (Glycine max). To characterize the mechanisms that cause the stress-induced loss of nodule function, we examined nodule structure, carbon-nitrogen interactions, and respiration in two soybean genotypes that differ in chilling sensitivity: PAN809 (PAN), which is chilling sensitive, and Highveld Top (HT), which is more chilling resistant. Nodule numbers were unaffected by dark chilling, as was the abundance of the nitrogenase and leghemoglobin proteins. However, dark chilling decreased nodule respiration rates, nitrogenase activities, and NifH and NifK mRNAs and increased nodule starch, sucrose, and glucose in both genotypes. Ureide and fructose contents decreased only in PAN nodules. While the chilling-induced decreases in nodule respiration persisted in PAN even after return to optimal temperatures, respiration started to recover in HT by the end of the chilling period. The area of the intercellular spaces in the nodule cortex and infected zone was greatly decreased in HT after three nights of chilling, an acclimatory response that was absent from PAN. These data show that HT nodules are able to regulate both respiration and the area of the intercellular spaces during chilling and in this way control the oxygen diffusion barrier, which is a key component of the nodule stress response. We conclude that chilling-induced loss of symbiotic nitrogen fixation in PAN is caused by the inhibition of respiration coupled to the failure to regulate the oxygen diffusion barrier effectively. The resultant limitations on nitrogen availability contribute to the greater chilling-induced inhibition of photosynthesis in PAN than in HT

Redox regulation of peroxiredoxin and proteinases by ascorbate and thiols during pea root nodule senescence

Groten K, Dutilleul C, van Heerden PDR, et al. Redox regulation of peroxiredoxin and proteinases by ascorbate and thiols during pea root nodule senescence. FEBS LETTERS. 2006;580(5):1269-1276.Redox factors contributing to nodule senescence were studied in pea. The abundance of the nodule cytosolic peroxiredoxin but not the mitochondrial peroxiredoxin protein was modulated by ascorbate. In contrast to redox-active antioxidants such as ascorbate and cytosolic peroxiredoxin that decreased during nodule development, maximal extractable nodule proteinase activity increased progressively as the nodules aged. Cathepsin-like activities were constant throughout development but serine and cysteine proteinase activities increased during senescence. Senescence-induced cysteine proteinase activity was inhibited by cysteine, dithiotreitol, or E-64. Senescence-dependent decreases in redox-active factors, particularly ascorbate and peroxiredoxin favour decreased redox-mediated inactivation of cysteine proteinases. (c) 2006 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved