Poor Seedling Establishment Research Articles

The use of Groasis Waterboxx devices to improve mineland reclamation efforts by increasing transplant survival and growth of five native woody species

The reclamation of disturbed lands worldwide is a difficult and increasing problem. In the Mountain West region of the United States, mining activities commonly occur in zones dominated by native woody plants. The restoration of woody plants in these areas is challenging, and direct seeding efforts result in poor seedling emergence and establishment. Therefore, seedling transplants are often used, but they frequently experience high mortality during the first year, particularly due to summer stresses. We evaluated if the Groasis Waterboxx device could be used to mitigate drought stress on seedling transplants and improve their establishment on a reclaimed waste rock dump. The Waterboxx device collects precipitation into a polypropylene reservoir and slowly dispenses water onto the soil next to the seedling. To test such a hypothesis, 400 seedlings from five native woody plants (Atriplex canescens, Cercocarpus ledifolius, Pinus edulis, Purshia tridentata, and Rhus glabra) were planted with and without a Waterboxx. The Waterboxx device improved soil water potential, at 40 cm, it took 1 month longer to go below −1 MPa under a Waterboxx. Survival increased 30–65% in four of the five species, and seedling vigor increased for three of the five species. Vigor was higher with all plant species at both planting times and was significantly better in 50% of comparisons. Results support the use of the Waterboxx for improving seedling establishment on mineland overburden sites in the semiarid mountain west. The effectiveness of the Waterboxx device provides merit for future testing where drought challenges seedling establishment.

Morphological, Molecular Identification and Pathogenicity of Rhizoctonia solani Kuhn: A Seed and Soil Borne Pathogen Infecting French Bean

French bean (Phaseolus vulgaris L.), holds significant importance as a both vegetable and pulse crop in India. Root rot disease has become threat for successful french bean cultivation. Fusarium spp., Sclerotium rolfsii, Rhizoctonia sp., Macrophomina, Pythium spp. and Thielaviopsis sp. may incite root rot disease in french bean. The root rot caused by Rhizoctonia soalni Kuhn is one among the root rot causing pathogens, is a major devasticating disease in this crop. The objective of this investigation was to perform the morphological, molecular identification and pathogenicity of R. solani Kuhn infecting french bean root rot. The pathogen was isolated from the naturally infected french bean field with characteristic symptoms like yellowing, drying at the soil level, stunting, poor seedling establishment, uneven growth, chlorosis, and premature defoliation in severely affected cases. It was isolated using standard tissue isolation technique and identified based on morphological traits. The fungus was molecular identified by sequencing ITS region of rDNA by using ITS1 and ITS4 primers. Further, pathogenicity of R. solani was proved according to Koch’s postulates.

Customise the seeds, not the seeder: Pelleting of small-seeded species for ecological restoration

Direct native seed planting is a cost-effective and popular approach for restoring degraded terrestrial ecosystems. However, the handling and precision seeding of multispecies mixes with diverse seed sizes, and shapes is logistically complex, requires highly customised equipment and often results in poor seedling establishment. This issue is accentuated in small-seeded species, where handling difficulties and a lack of precision placement result in seed wastage. The agricultural seed sector relies on the application of external material to small seeds to improve handling via seed pelleting. Yet this method has been rarely tested on small-seeded native species for ecological restoration.We pelleted the seeds of 15 small-seeded Myrtaceae species commonly used for seed-based restoration programs and recorded a range of physical traits. Prior to pelleting, each seed batch was tested for purity and viability and processed to improve quality (Pure Live Seed, PLS%). Seedling emergence from pelleted and control seeds was tested in controlled laboratory conditions and at two field sites in Western Australia. We linked seedling's emergence outcomes to the degree of physical modification achieved via pelleting to understand which trait would be responsible for a potential decrease or delay in emergence.Seed processing improved the average quality (PLS%) across all species from 23.4 ± 4.8% to 83.6 ± 2.3%. Seed pelleting, on average, resulted in a 27-fold increase in volume, a 30-fold increase in weight, and a 26% increase in bulk density. Seedling emergence response to pelleting varied among species, but on average, emergence speed was 3.1 days faster (p < 0.001) for pelleted seeds, while final emergence was not significantly different (p = 0.217).The results show that a combination of seed processing and pelleting can be used to increase and standardise seed physical properties for improved handling and precision seeding, with limited consequences on seedling emergence and faster emergence. This novel approach could enable the use of large-scale agricultural seeding equipment for rapid and cost-effective delivery of multispecies native seed mixes in biodiverse global restoration programs.

Regulation of reactive oxygen species and phytohormones in osmotic stress tolerance during seed germination in indica rice.

Climate change due to global warming is now affecting agricultural production worldwide. In rice, one of the most important crops, water limitation due to irregular rainfall in rainfed lowlands during crop growth limits yield. Dry direct-sowing has been proposed as a water-efficient approach to cope with water stress during rice growth, but poor seedling establishment due to drought during germination and emergence is a problem. Here, we germinated indica rice cultivars Rc348 (drought tolerant) and Rc10 (drought sensitive) under osmotic stress induced by PEG to elucidate mechanisms of germination under drought. Rc348 had higher germination rate and germination index under severe osmotic stress of -1.5 MPa, above those of Rc10. Rc348 showed up-regulated GA biosynthesis, down-regulated ABA catabolism, and up-regulated α-amylase gene expression in imbibed seeds under PEG treatment compared to that of Rc10. During germination, reactive oxygen species (ROS) play important roles in antagonism between gibberellic acid (GA) and abscisic acid (ABA). Embryo of Rc348 treated with PEG had significantly greater expression of NADPH oxidase genes and higher endogenous ROS levels, together with significantly increased endogenous GA1, GA4 and ABA contents compared to that of Rc10. In aleurone layers treated with exogenous GA, expression of α-amylase genes was higher in Rc348 than in Rc10, and expression of NADPH oxidase genes was enhanced with significantly higher ROS content in Rc348, suggesting higher sensitivity of GA to ROS production and starch degradation in aleurone cells of Rc348. These results suggest that the osmotic stress tolerance of Rc348 is due to enhancement of ROS production, GA biosynthesis, and GA sensitivity, resulting in a higher germination rate under osmotic stress.

Influence of iron seed priming on seed germination, growth and iron content in rice seedlings

The area under direct-seeded aerobic rice (DSR) is increasing in Indo-gangetic plains due to labor and water scarcity. However, iron (Fe) deficiency is a severe problem in DSR under coarse-textured soils, resulting in poor germination, interveinal chlorosis, and poor seedling establishment. Fe seed priming is a better option to ensure higher seed germination and optimum supply of Fe at initial growth stages. Hence, the experiment was conducted with seven seed priming treatments i.e. Control (hydropriming), 0.5% Fe through ferrous sulfate (FeSO4 7H2O), 1.0% Fe through FeSO4 7H2O, 0.25% Fe through ethylene diamine tetra acetic acid chelated iron (Fe-EDTA), 0.5% Fe through Fe-EDTA, 0.025% Fe through iron oxide nanoparticle (FeO NPs) and 0.05% Fe through FeO NPs. The Fe seed priming showed a significant increase in Fe content of paddy seeds over the hydropriming treatment. Among different treatments, FeSO4.7H2O (1.0% Fe) showed highest germination percentage (91.3%), root length (8.4%) and shoot length (9.4%) followed by FeSO4.7H2O (0.5% Fe) which was significantly higher over the control. But, the treatment involving Fe-EDTA (0.5% Fe) showed adverse effects on germination and seedling growth. Ferrous (Fe2+) iron and total Fe content in rice seedlings showed similar trends to total Fe content in primed seeds treated with different Fe sources. Thus, Fe seed priming of rice with FeSO4.7H2O (1.0%Fe) for 12 h was effective for higher germination percentage, greater iron content at initial growth stages and ameliorated the Fe deficiency in direct seeded aerobic rice.

Evolving Promising Redgram (Cajanas cajan L.) Transplanting Techniques for Better Crop Establishment under Resource Constraint Dryland Areas of Southern India

Background: Redgram a predominant dryland crop is vulnerable to the whims of rainfall at initial stages of crop growth. Moreover, the wider spacing promotes transplanting over conventional method but, appropriate nursery technique is yet to be standardised to prevent root coiling which leads to poor plant stand under main field conditions. Methods: A field experiment was conducted during 2020-21 at Agricultural College and Research Institute, Tamil Nadu Agricultural University, Madurai to identify suitable nursery techniques for raising redgram seedlings. Redgram was raised in poly bag, 98 cone protray, 50 cone protray and high density poly ethylene (HDPE) woven fabric mat for 20 and 30 days before transplanting. The experiment was laid out in randomized block design replicated thrice. Result: The results revealed that, raising redgram seedlings in HDPE woven fabric mat and transplanting at 20 DAS resulted in lesser root length, root volume but with lesser root coiling coefficient which is highly favourable. Moreover, after being transplanted the seedlings recorded higher plant height, leaf area index with increased photosynthetic activity, respiration andchlorophyll content. Similarly, higher yield and benefit cost ratio was attained over the conventional line sowing. Therefore, raising red gram seedlings in HDPE woven fabric mat can be considered as a cost-effective technology to attain higher yields and with the possibility to gap fill under poor seedling establishment without differential harvest maturity under the dry land tracts of southern Tamil Nadu, India.

Seed Germination and Early Seedling Growth Responses to Drought Stress in Annual Medicago L. and Trifolium L. Forages

Climate change in the Mediterranean-like regions of South Africa has resulted in increased rainfall variability, a delayed start to the wet winter season, and increased occurrences of out-of-season summer rainfall events. These changes in bioclimatic conditions are predicted to become more pronounced and, therefore, could result in poor seedling establishment and false breaks from the soil seed bank, followed by seedling desiccation in annual medic and clover pastures. This study therefore aimed to quantify and compare the responses of three annual Medicago species and five annual Trifolium species to drought stress imposed at the seed germination, seedling establishment, and early seedling growth stages. Three separate controlled trials were conducted. Firstly, the seeds were germinated in seed germination chambers at constant temperatures ranging from 5 to 30 °C, in 5 °C increments, with five osmotic treatments within each temperature, and germination was recorded daily. For the second experiment, seeds were planted at 100, 70, 50, and 30% of the soil’s moisture-holding capacity without subsequent watering, and emergence was recorded daily. For the third experiment, one-month-old seedlings were subjected to two water-limitation periods (15 or 30 days), and their subsequent morphological responses were measured. The results from these experiments indicated that the species differed significantly in their responses to drought, and the best-performing species often differed when drought was imposed at different development stages. Five species—M. polymorpha L., M. truncatula Gaertn., T. alexandrinum L., T. vesiculosum Savi., and T. subterraneum L. ssp. subterraneum—were able to tolerate incidences of drought better than other species and, thus, should be prioritized for further research into the variation in drought tolerance between cultivars within these species.

Mapping QTLs for anaerobic tolerance at germination and bud stages using new high density genetic map of rice.

Due to its low cost and convenience, direct seeding is an efficient technique for the production of rice in different rice growing areas. However, anaerobic conditions are a major obstacle to the direct seeding of rice and result in poor seedling establishment, which leads to yield losses. We constructed a collection of recombinant inbred lines (RIL) comprising 275 lines derived from the H335 and CHA-1 cross by the method of single seed descent. Via a genotyping-by-sequencing (GBS) strategy, a high-density genetic map containing 2498 recombination bin markers was constructed, the average physical distance between the markers was only 149.38 Kb. After anaerobic treatment, 12 phenotypes related to both the coleoptile at germination and seedling quality at budding were evaluated. There were no significant correlations between seedling and bud traits. Genetic mapping of quantitative traits was performed for these traits across two cropping seasons. A total of 20 loci were detected, named locus 1~20. Three of them were repeatedly detected across both seasons. Six loci overlapped with those in previous reports, and nine loci were associated with multiple traits at both stages. Notably, locus 3, which is located on chromosome 2 (26,713,837 to 27,333,897 bp), was detected for both the germination and bud traits. By focusing on the locus 3 interval and by combining gene annotation and expression analyses, we identified a promising candidate gene, trehalose-6-phosphate phosphatase (OsTPP1, LOC_Os02g44230). Furthermore, RILs (G289, G379, G403, G430 and G454) that have superior phenotypes and that pyramid elite alleles were recognized. The findings of present study provide new genetic resources for direct-seeding rice (DSR) varieties for molecular breeding strategies and expand our knowledge of genetic regulation of seedling establishment under anaerobic conditions.

Increasing the appropriate seedling density for higher yield in dry direct-seeded rice sown by a multifunctional seeder after wheat-straw return

Dry direct-seeded rice (DDR) sown using a multifunctional seeder that performs synchronous rotary tillage and sowing has received increased attention because it is highly efficient, relatively cheap, and environmentally friendly. However, this method of rice production may produce lower yields in a rice–wheat rotation system because of its poor seedling establishment. To address this problem, we performed field experiments to determine the rice yield at five seedling density levels (B1, B2, B3, B4, and B5=100, 190, 280, 370, and 460 seedlings m−2, respectively) and clarify the physiological basis of yield formation. We selected a representative high-quality rice variety and a multifunctional seeder that used in a typical rice–wheat rotation area in 2016 and 2018. The proportion of main stem panicle increased with increasing seedling density. There was a parabolic relationship between yield and seedling density, and the maximum yield (9.34−9.47 t ha−1) was obtained under B3. The maximum yield was associated with a higher total spikelet number m−2 and greater biomass accumulation from heading to maturity. The higher total spikelet number m−2 under B3 was attributed to an increase in panicle number m−2 compared with B1 and B2. Although the panicle numbers also increased under B4 and B5, these increases were insufficient to compensate for the reduced spikelet numbers per panicle. Lower biomass, smaller leaf area, and lower N uptake per plant from the stem elongation stage to the heading stage were partially responsible for the smaller panicle size at higher seedling density levels such as B5. The higher biomass accumulation under B3 was ascribed to the increases in the photosynthetic rate of the top three leaves m−2 of land, crop growth rate, net assimilation rate, and leaf area index. Furthermore, the B3 rice population was marked by a higher grain–leaf ratio, as well as a lower export ratio and transport ratio of biomass per stem-sheath. A quadratic function predicted that 260−290 seedlings m−2 is the optimum seedling density for achieving maximum yield. Together, these results suggested that appropriately increasing the seedling density, and thereby increasing the proportion of panicles formed by the main stem, is an effective approach for obtaining a higher yield in DDR sown using a multifunctional seeder in a rice–wheat rotation system.

Management and environmental factors associated with simulated restoration seeding barriers in sagebrush steppe

Adverse weather conditions, particularly freezing or drought, are often associated with poor seedling establishment following restoration seeding in drylands like the Great Basin sagebrush steppe (U.S.A.). Management decisions such as planting date or seed source could improve restoration outcomes by reducing seedling exposure to weather barriers. We simulated the effects of management and environmental factors on seedling exposure to post‐germination barriers for bottlebrush squirreltail (Elymus elymoides), Sandberg bluegrass (Poa secunda), and bluebunch wheatgrass (Pseudoroegneria spicata). We combined germination timing models with daily soil moisture and temperature estimates to calculate yearly germination favorability and post‐germination freezing and drought barriers for three planting dates (15 October, 15 November, and 15 March) and three seed sources or cultivars per species for 5,000 sites in each of 40 years (water years 1980–2019). We tested the effects of site environmental variables (elevation, mean annual precipitation, heat load, and clay content) and management choices (seed source and planting date) on germination favorability and barrier occurrence (mean) and variability (coefficient of variation). Seedling exposure to barriers was strongly linked to management decisions in addition to site mean precipitation and elevation. Later fall plantings and seed sources with slower germination (lower mean germination favorability) were less likely to encounter freezing and drought barriers. These results suggest that management actions can play a role comparable to site environmental variables in reducing exposure of vulnerable seedlings to adverse weather conditions and subsequent effects on restoration outcomes.

Screening Direct Seeding-Related Traits by Using an Improved Mesocotyl Elongation Assay and Association between Seedling and Maturity Traits in Rice

Direct seeding (DS) of rice gained much attention due to labor scarcity and unavailability of water. However, reduced emergence and poor seedling establishment are the main problems of DS which causes significant yield losses. Herein, DS-associated seedling traits of three major rice groups, i.e., Indica (Ind), Japonica (Jap), and aus-type (Aus), were evaluated by using an improved mesocotyl elongation assay. The associations among different traits at the seedling and maturity stage were also studied. Significant variation was observed among the cultivars of different rice groups. The Aus group cultivars showed higher mean values for coleoptile (C, 3.85 cm), mesocotyl (MC, 4.17 cm), shoot length (SL, 13.64 cm), panicle length (PL, 23.44 cm), tillers number (T, 15.95), culm length (CL, 105.29 cm), and plant height (PH, 128.73 cm), while the Indica and Japonica groups showed higher mean values of grain length (GL, 8.69 mm), grain length/width ratio (GL/WR, 3.07), and grain width (GW, 3.31 mm), with 1000 grain weight (TGWt, 25.53 g), respectively. Pairwise correlation analysis showed that MC, C, and SL were positively correlated among themselves and with PL, CL, and PH. Moreover, based on principal component analysis (PCA), C, MC, SL, CL, and PH were identified as the major discriminative factors in the rice cultivars. This study describes the development of desired DS rice variety with long MC and semidwarf in height and suggests that Aus group cultivars can be used as the donor parents of favorable DS-associated traits in rice breeding programs.

Seedling Establishment and Yield Performance of Dry Direct-Seeded Rice after Wheat Straw Returning Coupled with Early Nitrogen Application

Dry direct-seeded rice sown by multifunctional seeders (MS-DDSR) has received increased attention for its high efficiency. Wheat straw returning is widely used as an important agricultural practice because it is the simplest and quickest approach to dispose of wheat straw and also improve soil quality. The study determined whether MS-DDSR after wheat straw returning could obtain a high yield and whether early nitrogen (N) application could compensate for the negative effects caused by returned wheat straw. Field experiments were performed in a split-plot design. Main plots were comprised without wheat straw returning (S0) and wheat straw returning (S1). Split plots consisted of three plots with early N application treatment: 65 (N1), 95 (N2), and 125 (N3) kg N ha−1 at 0 and 20 days after sowing. S1 reduced yield, N uptake, and biomass accumulation in MS-DDSR compared to S0 because S1 negatively affected the seedling roots growth, seedling establishment, and tillering capacity of MS-DDSR. The positive interaction between wheat straw returning and early N on yield, biomass accumulation, and N uptake was likely related to the positive interaction on spikelet number per panicle, total spikelet number, and biomass accumulation after the stem elongation stage. These findings demonstrate that wheat straw returning led to poor seedling establishment and yield loss for MS-DDSR, but these negative effects could be compensated for by an appropriate increase in early N application, based on the locally recommended N application protocols.

Growth of Deciduous and Evergreen Species in Two Contrasting Temperate Forest Stands in Korea: An Intersite Experiment.

Poor seedling establishment and growth can be a result of the limitation of light and soil resources in the forest understory. Here, we investigate the interacting effects of stand and soil characteristics on the seedling growth of deciduous species (Fraxinus rhynchophylla and Zelkova serrata) and evergreen species (Pinus koraiensis) through a 3-year intersite experiment in two contrasting forest stands. Seedlings were grown in both oak and pine stands using two different soil types, i.e., gray-brown forest soil (GB) and red-yellow forest soil (RY). Soil physicochemical properties, light intensity, tree-seedling height, root-collar diameter (RCD), and biomass growth were analyzed between two stands and/or soil types. Light availability was generally more abundant in the pine stand (mean: 1074.08 lx or 20.25%) than the oak stand (mean: 424.33 lx or 9.20%) throughout the year. The height and RCD growth of fast-growing and deciduous F. rhynchophylla and Z. serrata were higher in the pine than in the oak stand, particularly in GB soil. The growth of the slow-growing and evergreen P. koraiensis was not affected by the forest stand, except for its higher root growth in the oak stand and RY soil. Therefore, abundant light availability can enhance the growth and seedling establishment of F. rhynchophylla and Z. serrata in the pine-stand understory. Contrarily, P. koraiensis may be planted in the understory regardless of light condition, but with a slower growth rate.

Seedball technology enhances pearl millet yield in a Sahelian subsistence production system

Pearl millet (Pennisetum glaucum (L.) R.Br.) is the major staple crop produced by subsistence farmers in the West African Sahel, but its panicle yield is low because of poor seedling establishment in low-nutrient soils. Seedball is a cheap seed-pelleting technique that combines sand, loam, seeds and optionally wood ash or mineral fertiliser as an additive to enhance early growth of pearl millet under infertile soil conditions. The aim of this study was to investigate the effects of seedball technology on pearl millet crop establishment and panicle yield on-farm under Sahelian subsistence conditions. Over 2000 on-farm (2015–18) trials were conducted in 65 villages of the Maradi region in Niger. Conventionally sown and seedball-derived pearl millet crops were grown by using ‘farmer-optimised’ simple split-plot designs with three treatments: (i) farmers’ practice as control; and seedballs (2.0 cm diameter, made from 80 g sand + 50 g loam + 25 mL water + 2.5 g seeds as standard recipe) that contained either (ii) 3 g wood ash or (iii) 1 g mineral fertiliser (nitrogen, phosphorus, potassium; NPK) as effective nutrient compounds. In 2016–18, participating farmers could opt for one of the seedball treatments. Panicle as well as stover yield data were collected and compared with respect to seedball type (wood ash vs NPK), sowing depth (shallow vs deep), sowing time (wet vs dry), weed management (complete vs partial), local soil type (texture range sand to loamy sand), cropping system (sole vs mixed), and farmer. Results showed that seedballs do not suppress seedling emergence. Seedball treatments produced fewer but longer and denser panicles. Wood ash-amended seedballs showed a higher panicle yield increase relative to their site controls than NPK-amended seedballs. However, the average panicle yield of NPK-amended seedballs was higher than that of the wood ash-amended seedballs. The treatment factors wet sowing, partial weeding, sole cropping and farmers showed higher panicle yield. The seedball technology increases pearl millet panicle yield by ∼30% in the Sahel; it is simple and based on local materials.

Salicylic acid seed priming boosts germination in Brassica rapa ssp pekinensis under cold stress

In Korea, the seeds of Brassica rapa ssp. pekinensis are sown in the winter and spring months. Cold stress can result in irregular seed germination and poor seedling establishment in some cases. Priming seeds with salicylic acid (SA) can reduce the likelihood of poor seedling establishment when exposed to cold stress conditions, which is beneficial for many plant species. The present study was carried out to determine the effectiveness of seed priming with SA on seed germination and seedling establishment in B. rapa ssp. pekinensis under cold stress conditions. Seeds were soaked in different SA concentrations (0.5 and 1.0 mM) for 12 and 24 hours, respectively, and then both primed and unprimed seeds germinated at 5 oC. Using SA treatment, seed germination was improved, as was root and shoot length, which were both longer in SA primed seeds than in unprimed seeds. Based on the findings, it is possible to use SA priming as one of the most effective ways to maintain productivity in B. rapa ssp. pekinensis while it is exposed to low temperatures.

Reproductive biology of Ophiorrhiza caudata C.E.C.Fisch. (Rubiaceae), an endemic and endangered creeping perennial herb of the Western Ghats, India

Ophiorrhiza caudata is a creeping, perennial herb distributed along wet and shady areas. The species is distylous with two distinct floral morphs: pin and thrum. Flowering usually occurs during the monsoon season. No particular difference was noticed in the flowering phenology of the two morphs. Presently the species is self-incompatible, however, it shows a tendency towards intramorph compatibility. Fruit set is above 60% in open pollination and intermorph pollination. Bees and butterflies are the major pollinators. The pollen flow between the two floral morphs varies depending upon floral morphology and pollinators. Fruit is a bi-valved capsule which dehisces by a splashing drop mechanism. The seeds are very minute. The rate of seed germination and seedling establishment in the wild condition is very poor due to adverse climatic factors. Ophiorrhiza caudata is struggling for survival in its natural habitat, where habitat fragmentation, climatic factors and poor seedling establishment could account for its narrow distribution.

High light-induced photoinhibition is not limiting seedling establishment at abrupt treeline ecotones in New Zealand.

Seedlings of New Zealand's treeline-forming Fuscospora cliffortioides (Hook.f.) perform poorly beyond the established canopy, limiting treeline advance. To test the long-standing assumption that photoinhibition impairs regeneration in the subalpine belt of New Zealand's Southern Alps, we assessed photosystem II (PSII) performance of seedling-sized individuals and microclimate variation. We performed diurnal, non-invasive chlorophyll-a-fluorescence measurements on exposed and canopy-sheltered individuals at two sites in New Zealand's Southern Alps during summer and winter. Diurnal recordings of the effective (ΦPSII) and optimal (Fv/Fm) photosynthetic quantum yield were supplemented with light response curves and micro-temperature recordings. ΦPSII returned to near-optimal values around 0.8 after 30min of shading, which rules out accumulative or long-term photoinhibition effects. The maximum electron transport rate derived from rapid light curves was significantly higher (+12%) in exposed compared with canopy-shaded individuals. Summer temperature fluctuated widely on the scree (-0.5 to 60.5°C) and near seedlings (-2 to 26.5°C). Our results revealed a remarkable level of light adaptation and contradict previous studies hinting at high light-induced photoinhibition as a treeline-limiting factor in the Southern Alps. By linking low ΦPSII on winter mornings, and large, sudden temperature drops in summer, we suspect that cold-induced photoinhibition might occur but the rapid recovery of ΦPSII seen across a wide temperature range makes lethal photo-oxidative damage rather unlikely. Given the demonstrably low summer frost tolerance of F. cliffortioides, cold-related damage resulting from frost events during the growing season or embolism induced by frost drought may offer more plausible explanations for the poor seedling establishment. Duration and frequency of these events could diminish with global warming, which may promote treeline advance.

Genetic variability for and tolerance to anaerobic germination in rice (Oryza sativa L.)

ABSTRACT Poor germination and seedling establishment under flooded conditions is a major bottleneck in the direct-seeding system of rice. The objectives of this study were to determine the genetic variability for traits associated with anaerobic germination and identify tolerant genotypes. One hundred rice genotypes were screened. Data were collected on survival percentage, shoot length, root length, length of plant above water, and seedling vigor index. Six clusters, which were generally related to the ability of the genotypes to tolerate anaerobic germination, were detected. The first two principal components accounted for 91.1% of the total variation, with survival percentage, seedling vigor index and shoot length being the main discriminatory traits. Genotypic coefficient of variation ranged from 18.21% for shoot length to 50.89% for seedling vigor index. Shoot length and seedling vigor index recorded high broad-sense heritability estimates (>60%), with accompanying high genetic advance as percent of mean (>20%); the latter ranged from 23.12% for root length to 82.21% for seedling vigor index. The high heritability, along with high genetic advance, particularly for shoot length and seedling vigor index, indicated that selection for these traits should be effective in improving tolerance to anaerobic germination. Five tolerant genotypes (OBOLO, ART68-12-1-1-B-B, ART64-31-1-1-B-B, CRI-1-21-5-12, and CRI-Enapa) with high survival percentage (≥70%) under anaerobic conditions were identified. These genotypes could be used to improve commercial rice varieties for tolerance to anaerobic germination.

Role of antioxidative defense system in amelioration of cadmium-induced phytotoxic effects in germinating seeds of maize (

Context Anthropogenic activities are increasing Cd concentration in soil and environment that limits seed germination capacity and causes poor seedling establishment. Aims The effect of different Cd concentrations on seed germination and seedling growth of two maize cultivars (C-20 and EV-1098) was tested in this study. Methods Maize seeds were sown in Petri dishes lined with double filter paper. The seedlings were grown in a growth chamber, applied with different Cd concentrations (0, 2, 4, 6, 8 and 10 μM), and harvested 12 days after germination. Key results Seeds applied with higher levels of Cd showed a significant decrease in seed germination percentage (GP), seed emergence index (EI) and germination energy (GE). A significant delay in seed germination was observed at the highest Cd treatment in terms of increased mean emergence time (MET), days to 50% germination (T 50) and coefficient of uniformity of emergence (CUE). A marked decline in leaf K, Ca, Na, and P was observed, whereas root K, Ca and P increased with an increase in external Cd concentration. The roots and leaves of maize C-20 showed greater activities of superoxide dismutase (SOD) than did those of EV-1098. In contrast, peroxidase (POD) activity was reasonably high in roots and leaves, whereas catalase (CAT) was high only in roots of EV-1098. Non-enzymatic antioxidants such as phenolics and ascorbicacid (AsA) also significantly increased, accompanied with substantially lowermalondialdehyde (MDA) contents in the roots and leaves of EV-1098 than of C-20. Conclusions The differential modulation of the activities of enzymatic and non-enzymaticanti-oxidative defense system in roots and leaves played a critical role intolerance of both cultivars to Cd stress. Implications The findings of this study are helpful in improving seed germination capacity and seedling growth of maize in Cd contaminated soils.

Influence of Salt Stress on Growth of Spermosphere Bacterial Communities in Different Peanut (Arachis hypogaea L.) Cultivars.

Background: Exposure of seeds to high salinity can cause reduced germination and poor seedling establishment. Improving the salt tolerance of peanut (Arachis hypogaea L.) seeds during germination is an important breeding goal of the peanut industry. Bacterial communities in the spermosphere soils may be of special importance to seed germination under salt stress, whereas extant results in oilseed crop peanut are scarce. Methods: Here, bacterial communities colonizing peanut seeds with salt stress were characterized using 16S rRNA gene sequencing. Results: Peanut spermosphere was composed of four dominant genera: Bacillus, Massilia, Pseudarthrobacter, and Sphingomonas. Comparisons of bacterial community structure revealed that the beneficial bacteria (Bacillus), which can produce specific phosphatases to sequentially mineralize organic phosphorus into inorganic phosphorus, occurred in relatively higher abundance in salt-treated spermosphere soils. Further soil enzyme activity assays showed that phosphatase activity increased in salt-treated spermosphere soils, which may be associated with the shift of Bacillus. Conclusion: This study will form the foundation for future improvement of salt tolerance of peanuts at the seed germination stage via modification of the soil microbes.