Floret Sterility Research Articles

Influence of Wheat Cultivars, Infection Level, and Climate after Anthesis on Efficacy of Fungicide for Control of Fusarium Head Blight in the Huang-Huai-Hai Plain of China

Fusarium head blight (FHB), caused by the Fusarium graminearum species complex, causes significant losses in grain yield and quality of wheat (Triticum aestivum) by inducing floret sterility. Grains become contaminated with mycotoxins, especially deoxynivalenol (DON), making them unsuitable for consumption. To clarify the impact of wheat cultivar resistance, infection level, and climate after anthesis on the efficacy of a fungicide for the control of FHB, we treated two moderately susceptible cultivars and 11 susceptible cultivars with fungicide (48% phenamacril + tebuconazole) at anthesis over two years. FHB incidence (INC), disease severity index (DSI), Fusarium-damaged kernels, DON contamination, thousand-kernel weight, and yield were evaluated under artificially inoculated and naturally infected field trials in 2018 and 2021. The results of multi-factor variance analysis show that the control efficacy with respect to INC and DSI is affected by cultivar, fungicide, infection level, and climatic conditions including the average daily temperature, average daily relative humidity, and total rainfall from anthesis to 21 days after anthesis (p < 0.01). Notably, cultivar resistance (deviance = 13.34, 9.55, and 11.22) is more important than fungicide (deviance = 5.77, 6.66, and 6.69) to control the efficacy of INC, DSI, and DON. The results also suggest that infection level appears to be more important than cultivars and fungicide to control the efficacy of INC, and more important than fungicide to control the efficacy of DSI. Total rainfall is more important than other climatic factors. Our results reveal that fungicide is more effective in moderately susceptible cultivars (‘Zhengmai 9023’ and ‘Xinong 979’, 89.5%~98.9%) and some susceptible cultivars than in other susceptible cultivars (‘Zhengmai 7698’ and ‘Zhoumai 27’, 51.9%~67.2%). Thus, integrating cultivar resistance with fungicide application can be an effective strategy for the management of FHB and DON in winter wheat in the Huang-huai-hai Plain of China.

Field screening for heat-stress tolerance of floret fertility in wheat (Triticum aestivum and T. durum)

Context As global temperatures increase, heat waves of >30°C for at least 3 days are projected to become more frequent during reproductive development of wheat, causing reductions in grain yield. Breeding for tolerance is difficult under field conditions owing to the unpredictable timing and intensity of natural heat events and the narrow developmental windows of sensitivity. Aims We report on a series of experiments designed to explore genetic variability for floret sterility induced by natural heat waves in the field by targeting a sensitive development stage. Methods Our method involved sowing late, and the use of auricle distance to identify main tillers exposed to heat events at a sensitive developmental stage (booting). Key results Substantial genetic variation was found for tolerance of grain set to natural heat waves, with a broad-sense heritability estimate of 0.94 for heat-exposed stems compared with 0.72 for non-stressed controls. An auricle distance of 1–3 cm was established as a phenotypic marker for tagging stems at the sensitive stage of development, and the optimal number of spikes to assess was determined as 10–15 per plot. A validation study with durum lines previously classified as tolerant/intolerant under glasshouse conditions showed agreement in ranking of genotypes at the extremes of tolerance. Conclusions We demonstrate that it is possible to screen wheat genotypes for stage-specific tolerance to natural heat waves in the field. Implications The protocol described could provide a low-cost method for evaluating heat tolerance in wheat, with relevance to commercial field production conditions. The approach allows tolerance to be assessed at a single stage of reproductive development, which should allow greater heritability in field assessments.

Estimating Effects of Radiation Frost on Wheat Using a Field-Based Frost Control Treatment to Stop Freezing Damage.

Crop phenotyping experiments have long struggled to have a reliable control treatment that excludes frost and associated freezing damage to plants. Previous attempts used a barrier, such as a removable shelter or cloth to exclude frost. However, these methods were labour intensive and varied in their effectiveness. An automated diesel heater was used to protect field plots of wheat (Triticum aestivum L.) from frost damage. In 2018 and 2019 there were 22 and 33 radiation frost events from July to October at the field site. The heater maintained canopy air temperature above freezing (>0 °C) for the duration of the frost (~6–8 h). Heated plots had 2–3 °C warmer minimum canopy air temperatures. Cold and chilling damage was still present in heated plots and represented 20–30% floret sterility; freezing damage in non-heated plots accounted for an additional 10–30% floret sterility. Grain mapping revealed: grain set in the apical spikelets is most affected by frost damage; proximal florets (G1 and G2) contribute the most to grain yield, but distal (G3 and G4) are important contributors to grain yield when sterility in proximal florets occurs. These results demonstrate that a plot heater is a useful tool to study frost-induced freezing damage in cereal crops, by way of preventing freezing damage in heated field plots for direct comparison to naturally frosted plots. This approach could be used to develop improved damage functions for crop simulation models through a dose and timing-response experiment for natural frost incidence on cereal crops in field plots.

Analyses of MADS-box Genes Suggest HvMADS56 to Regulate Lateral Spikelet Development in Barley.

MADS-box transcription factors are crucial regulators of inflorescence and flower development in plants. Therefore, the recent interest in this family has received much attention in plant breeding programs due to their impact on plant development and inflorescence architecture. The aim of this study was to investigate the role of HvMADS-box genes in lateral spikelet development in barley (Hordeum vulgare L.). A set of 30 spike-contrasting barley lines were phenotypically and genotypically investigated under controlled conditions. We detected clear variations in the spike and spikelet development during the developmental stages among the tested lines. The lateral florets in the deficiens and semi-deficiens lines were more reduced than in two-rowed cultivars except cv. Kristina. Interestingly, cv. Kristina, int-h.43 and int-i.39 exhibited the same behavior as def.5, def.6, semi-def.1, semi-def.8 regarding development and showed reduced lateral florets size. In HOR1555, HOR7191 and HOR7041, the lateral florets continued their development, eventually setting seeds. In contrast, lateral florets in two-rowed barley stopped differentiating after the awn primordia stage giving rise to lateral floret sterility. At harvest, the lines tested showed large variation for all central and lateral spikelet-related traits. Phylogenetic analysis showed that more than half of the 108 MADS-box genes identified are highly conserved and are expressed in different barley tissues. Re-sequence analysis of a subset of these genes showed clear polymorphism in either SNPs or in/del. Variation in HvMADS56 correlated with altered lateral spikelet morphology. This suggests that HvMADS56 plays an important role in lateral spikelet development in barley.

Effects of high temperature and organic fertilizer on growth of several varieties of rice (Oryza sativa L) during the flowering stage

Climate change significantly increased the occurrence of high temperatures. High temperature significantly reduces rice yield and quality due to induced floret sterility in rice. Organic manure is one of the nutrients that is expected to maintain the soil temperature of rice. The study aims to determine the effect of application organic fertilizer in high temperature during the flowering stage in several varieties of rice (Oryza sativa L.). This research was conducted in a greenhouse with an average temperature of 28–34 0C from July to December 2020. The experiment consisted of 3 factors, namely: Varieties of Rice, V (IR64 and Gogo); Application of Organic Fertilizer, O (with and without organic fertilizer); and High Temperature, T (35 and 40°C). The treatments were arranged in a completely randomized design with 4 replicates. Growth parameters observed were rice plant height, number of tillers, and rice biomass. The result showed that Interaction on varieties, application of organic fertilizer at a high temperature significantly reduce the rice plant height and rice biomass. The estimation of the global warming impact of rice growth can be predicted by this information and mitigating for it.

Factors determining the occurrence of floret sterility in rice in a hot and low-wind paddy field in Jianghan Basin, China

• High temperature (<36.5 °C) and low wind induced floret sterility in the paddy field. • High temperatures increased the sterility through processes after pollen germination. • Wind lessened the sterility through stable pollination and probably via cooling. • Positive effects of low and erect panicle, and short anther were newly demonstrated. • Positive effects of long basal anther dehiscence and early flowering were confirmed. Global warming may increase the occurrence of heat-induced floret sterility (HIFS) in rice. The effects of meteorological factors and plant traits on the occurrence of floret sterility have only been examined independently and under controlled or simplified conditions. The aim of this study was to comprehensively clarify the role and impact of these factors in HIFS in rice under practical field conditions. We observed pollination and seed set of 12 rice cultivars with wide variation in traits potentially related to HIFS for 3 years in a paddy field in the Yangtze Valley in China where HIFS sometimes occurs. Floret sterility increased as temperature increased under moderately high temperatures (32–36.5 °C) and low-wind conditions (<3.5 m s −1 at flowering time). Path analysis with multiple regression revealed that high temperatures increased the occurrence of floret sterility through processes after pollen germination on the stigma and that wind lessened the occurrence of floret sterility; the magnitude of the wind effect was equivalent to that of high temperature. Multiple regression analysis estimated that low and erect panicles, and short anthers have positive effects on tolerance to HIFS and known heat tolerance traits, e.g., long anther dehiscence at the base of the anther and early morning flowering. The results clarified the factors that control HIFS in the paddy field and identify the processes and traits that scientists and breeders should focus on to mitigate HIFS under global warming.

The WtmsDW Locus on Wheat Chromosome 2B Controls Major Natural Variation for Floret Sterility Responses to Heat Stress at Booting Stage.

Heat stress at booting stage causes significant losses to floret fertility (grain set) and hence yield in wheat (Triticum aestivum L.); however, there is a lack of well-characterized sources of tolerance to this type of stress. Here, we describe the genetic analysis of booting stage heat tolerance in a cross between the Australian cultivars Drysdale (intolerant) and Waagan (tolerant), leading to the definition of a major-effect tolerance locus on the short arm of chromosome 2B, Wheat thermosensitive male sterile Drysdale/Waagan (WtmsDW). WtmsDW offsets between 44 and 65% of the losses in grain set due to heat, suggesting that it offers significant value for marker-assisted tolerance breeding. In lines lacking the WtmsDW tolerance allele, peaks in sensitivity were defined with reference to auricle distance, for various floret positions along the spike. Other (relatively minor) floret fertility response effects, including at the Rht-D1 dwarfing locus, were considered likely escape artifacts, due to their association with height and flowering time effects that might interfere with correct staging of stems for heat treatment. Heat stress increased grain set at distal floret positions in spikelets located at the top of the spike and increased the size of spikelets at the base of the spike, but these effects were offset by greater reductions in grain set at other floret positions. Potentially orthologous loci on chromosomes 1A and 1B were identified for heat response of flowering time. The potential significance of these findings for tolerance breeding and further tolerance screening is discussed.

How panicle angle and panicle position in the canopy determine pollination and seed set in rice (Oryza sativa L.)

ABSTRACT We examined the effect of panicle position relative to canopy and of panicle angle on pollination and floret sterility in rice at anthesis in a paddy field. We set panicles of pot-grown rice at the flowering stage either upright (0°) or inclined (30°), either above or at canopy height (Experiment 1) and either beneath or at canopy height (Experiment 2), in three replications each. In Experiment 1 and Experiment 2, panicle inclination at 30° increased the percentage of florets with <20 total pollen grains on the stigma (TP20) by 21% and 27%, increased the percentage of florets with <10 germinated pollen grains on the stigma (GP10) by 21% and 30%, and increased floret sterility by 10% and 26%, respectively. Floret sterility was correlated with GP10 in all trials. GP10 was correlated with TP20. The effect of position on floret sterility was not significant. We conclude that panicle inclination at 30° significantly increased floret sterility even under the canopy condition. Uprightness of panicles should be an important objective in rice breeding and production. Abbreviations TP20, percentage of florets with <20 total pollen grains on the stigma; GP10, percentage of florets with <10 germinated pollen grains on the stigma.

Dependence of pollination and fertilization in rice (Oryza sativa L.) on floret height within the canopy

We examined changes in rice (Oryza sativa L.) floret sterility and pollination as a function of vertical position of florets in the canopy at anthesis in paddy fields to clarify the ideal panicle height. Flowering pot-grown rice plants were placed in the rice canopy at different heights to position their florets at different depths below the canopy surface. The percentage of floret sterility was approximated as Y = 0.000335 X12 + 0.0296 X1 – 0.0451 X2 + 0.0152 X1X2 – 0.0468 (R2 = 0.921), where Y is the logit-transformed floret sterility (%), X1 is floret depth at anthesis (cm), and X2 is wind speed above the canopy (m s–1). The percentage of florets with fewer than 20 pollen grains on the stigma after flowering was approximated well by Y = 0.000554 X12 – 0.235 X22 + 0.5346 (R2 = 0.892), where Y is the logit-transformed percentage. The floret sterility (%) was correlated with the percentage of florets with <10 germinated pollen grains and with the percentage with <20 total pollen grains. Thus, there exists an optimal flowering depth and an ideal panicle position with respect to the canopy surface that stabilizes pollination and fertilization, and the optimal position for fertilization deepens with increasing wind strength.

Potassium application alleviates grain sterility and increases yield of wheat (Triticum aestivum) in frost-prone Mediterranean-type climate

Frost is a major risk factor for grain production in Australian farming systems and appears to be increasing in severity and occurrence due to changing climate. In this study we assessed the role of potassium (K) and micronutrients in alleviating floret sterility (FS) and yield loss in wheat crops subject to frost. Field experiments with K application in 2015 and 2016 were conducted in frost-prone, low soil K fields in the grain belt of Western Australia. Following frost events the heads reaching anther dehiscence were tagged and FS was measured 5–6 weeks later. We also measured leaf K concentration, photosynthesis and antioxidant activity, and grain yield. In 2015 K supply decreased FS from 32% at nil K to 24% at 80 kg K ha−1. In 2016 the FS values varied from 30 to >95%. Although there was no effect of K on FS at extreme frosts (FS >95%), applying 20–80 kg K ha−1 reduced FS by 10–20% and increased yield by 0.2–0.4 t ha−1 at less severe frosts. The decrease in FS was associated with increasing leaf K concentrations in the range 1.5–2.6%, higher photosynthesis and less oxidative stress at anthesis, but K supply did not provide extra protection from frost damage at leaf K > 2.6%. Foliar micronutrients at booting and heading did not affect FS in either year due to adequate micronutrient levels in the topsoil. Improved plant K status can increase grain set and yields in wheat under frost, likely by maintaining physiological functions such as cell osmoregulation, plant photosynthesis and anti-oxidant systems. Plant K requirement in frost prone parts of the landscape is greater than in the areas with low risk of frost damage.

Involvement of CAT in the detoxification of HT-induced ROS burst in rice anther and its relation to pollen fertility.

HT-induced ROS burst in developing anther is closely related to the lowered CAT activity as the result of the markedly suppressed OsCATB transcript, thereby causing severe fertility injury for rice plants exposed to HT at meiosis stage. The reproductive stage of rice plants is highly sensitive to heat stress. In this paper, different rice cultivars were used to investigate the relationship of HT-induced floret sterility with reactive oxygen species (ROS) detoxification in rice anthers under well-controlled climatic conditions. Results showed that high temperature (HT) exposure significantly enhanced the ROS level and malondialdehyde (MDA) content in developing anther, and the increase in ROS amount in rice anther under HT exposure was closely associated with HT-induced decline in the activities of several antioxidant enzymes. For various antioxidant enzymes, SOD and CAT were more susceptible to the ROS burst in rice anther induced by HT exposure than APX and POD, in which SOD and CAT activity in developing anther decreased significantly by HT exposure, whereas APX activity was relatively stable among different temperature regimes. HT-induced decrease in CAT activity was attributable to the suppressed transcript of OsCATB. This occurrence was strongly responsible for HT-induced increase in ROS level and oxidative-damage in rice anther, thereby it finally caused significant reduction in pollen viability and floret fertility for the rice plants exposed to HT during meiosis. Exogenous application of 1000µM salicylic acid (SA) may alleviate HT-induced reduction in pollen viability and floret fertility, concomitantly with the increased CAT activity and reduced ROS level in rice anther.

Progress in decoding the impact of abiotic stress on spikelet fertility in rice

Recent research progress in the impact of abiotic stress on florets sterility was summarized in this review to reveal key processes in determining the floret sterility resulted from abiotic stress and their coherent connections. The spikelet fertility was mainly determined by four key processes, including behavior of tapetum, anther dehiscence and pollen release, pollen germination and fertilization. Abiotic stress affected these processes and led to the spikelet sterility. Abnormal changes at the early-stage of anther growth could impact the development of germ cell and fertilization. Damages of floret fertility caused by abiotic stress could be mitigated via some practices such as spraying exogenous plant growth substances or silicon fertilizer. Some research topics were suggested for future investigation, including the interactions of multiple stress factors on fertility, morphological and physiological effects on floral organ formation, differential responses of rice varieties to abiotic stress, and molecular mechanism of abiotic stress on floral organ development.

数種のインド型イネにおける開花期高温障害抵抗性に関する葯裂開，受粉，花粉発芽の寄与評価

数種のインド型イネにおける開花期高温障害抵抗性に関する葯裂開，受粉，花粉発芽の寄与評価

Quantifying pearl millet response to high temperature stress: thresholds, sensitive stages, genetic variability and relative sensitivity of pollen and pistil.

The objectives were to (1) quantify high temperature (HT) stress impacts at different growth stages (season long, booting to seed-set and booting to maturity) on various yield components; (2) identify the most sensitive stage(s) to short episodes of HT stress during reproductive development; (3) understand the genetic variations for HT stress tolerance based on cardinal temperatures for pollen germination; and (4) determine relative sensitivity of pollen and pistil to HT stress and associated tolerance or susceptible mechanisms in pearl millet. High temperature stress (≥36/26°C) imposed at different stages and durations caused decrease in number of seeds, individual seed weight and seed yield. Two periods (10-12days and 2-0days before anthesis) were identified as most sensitive to short episodes of stress, causing maximum decreases in pollen germination percentage and seeds numbers. HT stresses of ≥36/26°C results in floret sterility. Pistils were relatively more sensitive than pollen grains, causing decreased number of seeds and seed yield. HT stress increased the reactive oxygen species contents and decreased the activity of the antioxidant enzymes in both pollen and pistils. Under HT stress, pistils had relatively higher reactive oxygen species and lower antioxidant enzymes activity compared with pollen grains, which explains greater susceptibility of pistils.

Rice sensitivity to saline irrigation in Southern Spain

Losses of productivity of flooded rice in Southern Spain may occur due to the use of saline water coming from the existent tidal regime in the marshes of Guadalquivir River, and the sensibility of the plants is variable according to its stage of development. The aim of this research was to evaluate the production of rice grains and its components, spikelet sterility and the phenological development of rice at different levels of salinity and in different periods of its cycle. In the conditions of the trial, the productive potential of rice based on the electrical conductivity (EC) of the irrigation water can be estimated by using the equation “Percentage of grain yield=100−12.0 (EC – 0.92)”. It was estimated that from 1.6–1.7dSm−1 salt content affects rice grain yield. Salinity also had a negative impact on a number of yield components including panicles per surface unit, tillers and spikelets per plant; floret sterility; and even delayed heading. Individual grain size was scarcely affected by salinity increase. The vegetative and reproductive phases were significantly more sensitive to salinity than grain filling and maturation phase. Irrigation management practices should be adopted to minimize salinity during these critical growth stages.

温室内水田を利用した開花期高温障害抵抗性に関する葯裂開,受粉,花粉発芽の寄与評価

温室内水田を利用した開花期高温障害抵抗性に関する葯裂開,受粉,花粉発芽の寄与評価

Diaspore heteromorphism in the invasive Bromus tectorum L. (Poaceae): Sterile florets increase dispersal propensity and distance

Within a species, the distance travelled by a particular diaspore depends on its morphology. In Poaceae, the presence of terminal sterile florets can lead to diaspore heteromorphism, which may influence dispersal. We tested the hypothesis that the presence of sterile florets favored dispersal in Bromus tectorum L., an invasive grass in the Western US.We used field and controlled experiments to study the dispersal of caryopses with and without sterile florets attached (respectively complex and simple diaspores), as well as pieces of inflorescence that detached from the mother plants. We considered both primary and secondary dispersal, as well as abiotic and biotic dispersal agents. The distance travelled by the diaspores and their attachment to animal fur were related to the presence and number of sterile florets.Abiotic agents moved diaspores over relatively short distances, both in terms of primary and secondary dispersal. A significant proportion of diaspores attached to fur, suggesting a potential for dispersal over long distances. Complex diaspores were better dispersers than simple ones (and pieces of inflorescence), and this pattern was consistent across the study. However, among complex diaspores, the number of sterile florets had little or no influence.Considering primary and secondary dispersal by abiotic and biotic agents provided a general picture of the dispersal ecology of B. tectorum. For all the dispersal steps and dispersal agents we studied, the presence of sterile florets favored dispersal. These results highlight the functional significance of diaspore heteromorphism induced by floret sterility in the dispersal of Poaceae.

Nitrogen rate and timing effects on growth and yield of drill-sown rice

Eight rice experiments were established at two sites in the Riverina district of south-eastern Australia in the 2012–13 and 2013–14 seasons. Two semi-dwarf rice varieties were drill-sown and nitrogen (N) fertiliser (urea) was applied at different rates at the 4-leaf stage before permanent water (pre-PW) and at panicle initiation (PI). The research assessed the impact of timing of N application on grain yield, compared the apparent N recovery of N fertiliser applied at the two stages, and determined an application strategy for N to obtain consistently high grain yields for current, semi-dwarf rice varieties when drill-sown. The apparent N recoveries achieved were 59% for N applied pre-PW and 25% for N applied at PI, averaged across years, sites, varieties and N rates. Grain yield increased significantly with increased rate of N applied at both stages, but the rate of increase from N applied at PI decreased as the rate of N applied pre-PW increased. The grain yield increase for N applied pre-PW was due to increased number of panicles at maturity and increased number of florets per panicle. Nitrogen applied at PI increased dry matter at maturity and number of florets per panicle. Application of N at PI increased grain yield over that when no N was applied; however, at low PI N-uptake levels, application of N at PI is not enough to achieve high grain yields. Therefore, sufficient N should be available to the crop from a combination of soil- and pre-PW-applied N for the crop to reach a level of N uptake at PI whereby high yields can be achieved. Nitrogen applied at PI did not appear to increase the potential for cold-induced floret sterility as much as pre-PW-applied N. Further research is required to confirm this in other seasons and for other rice varieties.

Lower-Than-Expected Floret Sterility of Rice under Extremely Hot Conditions in a Flood-Irrigated Field in New South Wales, Australia

Rice florets are susceptible to high-temperature damage at anthesis, but rice production remains stable in the Riverina region of Australia even when the air temperature during flowering exceeds 40°C. To identify the mechanism that supports rice production under these conditions, we examined sterility and pollination in relation to microclimate and panicle temperature in an extremely hot paddy field in the Riverina region of New South Wales. In windy > 40°C weather, the panicle temperature was > 38°C at the windward edge of the crop but around 35°C inside the crop, probably because of strong transpirational cooling due to the extremely dry wind (15% RH). Pollen from the windward edge of the crop showed extremely poor germination, yet that from inside the crop showed sufficient germination for fertilization. Moreover, sterility inside the crop was significantly lower than that at windward edge. We concluded that the wind with large vapor pressure deficit enabled stable rice production under the extreme heat during flowering.

Influence of Soil Type on Severity of Straighthead in Rice

Straighthead is a physiological disorder of rice (Oryza sativa) that causes symptoms including deformed florets and panicles, floret sterility, and reduced grain yield. Naturally occurring straighthead is very erratic in its expression, hampering efforts to determine its cause and effect. A greenhouse experiment was conducted using soils from four rice fields with variable histories of straighthead occurrence. The experiment included incorporation of zero or 20 t ha–1 of wheat straw and used two rice varieties of varying tolerances to straighthead, Doongara (susceptible) and Jefferson (tolerant). Relationships between straighthead severity and soil and plant nutrients were investigated. There was a large difference between soils in the rate of soil redox potential decline after flooding, rice growth and yield, and the presence and severity of straighthead. Straighthead score was significantly correlated with decreased grain yield and increased floret sterility. The incorporation of 20 t ha–1 straw significantly reduced grain yield and increased floret sterility and straighthead scores in three of the four soils. Plant copper (Cu) and magnesium (Mg) were positively and iron (Fe) and molybdenum (Mo) negatively correlated with straighthead score. There were no consistent relationships among soil properties, plant nutrients at panicle initiation, and straighthead severity. The results indicate that no one soil mineral/nutrient is controlling the severity of straighthead but a combination of soil chemical factors may be involved. It is recommended that only straighthead-tolerant rice varieties be grown on soils that have a history of straighthead and the incorporation of stubble prior to rice growing should be avoided in these fields. Further research needs to be conducted into ranking Australian rice varieties on their tolerance to straighthead so farmers can choose the most suitable variety for their field.