Arbuscular mycorrhizal fungi (AMF) are found to be causing the most abundant symbioses between fungi and roots of terrestrial plants. AMF act as a biofertiliser that stimulate plant growth and increase plant productivity under poor soil fertility. In addition, unbalanced application of zinc (Zn) and the antagonistic relationship with phosphorus (P) also play an imperative role in decreasing crop productivity. It is necessary to synchronise Zn application rate with applied inorganic P and AMF to achieve optimum crop yield. For tha purpose, a pot trial was conducted on Zn-deficient soil with five application rates of Zn, i.e. 0, 30, 60, 90, 120 and 150 mg kg⁻¹. Two levels of inorganic P [0 (P0) and 21 (P1) mg kg⁻¹] were applied with and without AMF inoculation. Results showed that more AMF colonisation was observed under deficient Zn and P conditions. Higher soil Zn (Zn120 and Zn150) significantly decreased the germination rate and plant growth. However, a significant improvement in germination, plant height, biomass, transpiration rate and 100-grain weight validated the productive functioning of AMF over no AMF. AMF inoculation alleviated P-induced Zn deficiency and Zn-induced P deficiency. Application of P0Zn60 and P0Zn30 with and without AMF is a better treatment to maximise wheat growth, yield and gas-exchange attributes in Zn-deficient conditions. It is also recommended to apply low Zn, (30 or 60 mg kg⁻¹ Zn) when AMF is used, with 21 mg kg⁻¹ P, or half of the recommended dose of P.

Context. Defoliation management targets applied to forages under the full sun have not yet been properly evaluated for shaded environments such as occur in integrated crop–livestock systems with the presence of trees.

AimsThis study aimed to determine defoliation targets under full sun and shaded environments for the shade-tolerant perennial summer grass hybrid Axonopus catharinensis (giant missionary grass), widely used in pasture systems of South Brazil and Argentina.

Methods. Four pre-defoliation canopy heights (15, 25, 35 and 45 cm) and four defoliation severities (20%, 40%, 60% and 80% reduction in pre-defoliation canopy height) were evaluated. Plants were grown in 0.15 m³ wooden boxes filled with sand/vermiculite substrate (1:1 v/v) and irrigated with a complete nutrient solution. An artificial shade structure was made with wooden slats, reducing light intensity by 50% for shaded plants.

Key results. Herbage accumulation decreased by 54% in shaded plants compared with those under full sun. Regardless of the light environment, the lowest crude protein content (<150 g/kg dry matter) and the highest neutral detergent fibre content (>650 g/kg dry matter) were observed when the defoliation target height was >35 cm. Both shaded and full sun environments showed decreases in tiller density when defoliation severity was >60% of pre-defoliation canopy heights.

Conclusions. Pre-defoliation canopy heights >35 cm and defoliation severity >60% of pre-defoliation canopy height should be avoided when managing A. catharinensis, regardless of the light environment.

Implications. Recommended targets may be easily implemented by livestock producers and are similar for full sun and shade environments.

Context. Panicum coloratum is a relatively undomesticated small-seeded warm-season forage grass. Seed shattering, an extended reproductive period and non-synchronic seed maturation limit harvested seed yields. Low seed quantity and quality hinder pasture establishment and discourage its use.

Aims. To assess whether seed yield potential could be improved by breeding, we sought to measure variability in traits related to seed production including phenotypic plasticity in response to environmental cues, and estimated narrow-sense heritability, prospective genetic gain after selection and co-heritabilities in seed yield components.

Methods. Seed retention (SR), number of panicles (PN), seed number per panicle (SN) and seed weight (SW) were measured in plants growing in the field. Clonal replicates of 13 genotypes were assessed in 2007 and 2010 and half-sib families derived from these genotypes were measured in 2010.

Key results. Phenotypic variability among genotypes was related to genetic factors for all measured variables. Two broad groups of accessions showing differences in SR were studied. Phenotypic plasticity in SR differed among genotypes and was negatively related to levels of SR, implying that stable high-SR genotypes could be selected in a breeding program. Maximum narrow-sense heritabilities were 0.89 and 0.41 for SN and SR, respectively, with estimated gains after selection around 30%. The best results were achieved if selecting for SR at 3–5 weeks after anthesis. Low genetic correlations and extremely low co-heritabilities between other characters and seed yield components discourage the possibility of indirect selection.

Conclusion. Moderate increases in seed production potential may be achieved after selection for SN, SW and SR in P. coloratum var. makarikariense.

Implications. Improvements in SR and other seed yield components would facilitate harvest, increase yield and consequently increase profitability to growers and stimulate pasture adoption by farmers.

Context. The genus Sehima is an important component of grasslands worldwide and is the dominant grass of Sehima–Dichanthium grasslands of India. It is an excellent fodder and a good source of lignocellulosic material and several industrially important biomolecules.

Aims. We aimed to characterise and conserve locally adapted diverse germplasm of S. nervosum, collected from different agro-climatic zones, for effective utilisation.

Methods. Morphological and nutritive traits were measured and statistically analysed for diversity in a germplasm collection of S. nervosum genotypes from diverse agro-climatic conditions of India, and a representative core subset was created.

Key results. Morphological traits and nutritive parameters such as crude protein content and digestibility showed wide variability among accessions. Principal component analysis established that plant height, number of tillers per tussock and number of nodes per tiller accounted for half of the variation present. Tiller internode length, stem diameter, and leaf blade length and width also contributed >5 unit points each to the cumulative proportion of variance accounted for.

Conclusions. The set of germplasm, possessing substantial variability, is a valuable genetic resource for developing new cultivars. Genotypes identified with high protein content could be used as forage, and those with high cellulose and hemicelluloses as a biofuel resource.

Implications. Genotypes can be separately identified for forage and biofuel, and the core subset can effectively be used for evaluation and selection of genotypes in target environments. Additionally, the core subset can be used to establish and rejuvenate sustainable pastures by allowing natural selection.

Context. Crop production in Eastern Himalaya is constrained by combined effects of soil acidity and moisture deficit during post monsoon under a changing climate.

Aim. This study aimed to identify potential buckwheat genotypes and stress mechanisms in hill environments of Meghalaya (India).

Method. Field and microcosm experiments were conducted to study field performance, genotypic variability and physio-morphological efficiency in buckwheat.

Key results. Substantial genetic variability for shoot length (30.3–110 cm), crop canopy distribution (3.0–7.5 number of primary branches), leaf area retention (15.7–60.2 cm²/two leaves), 1000 seed weight (16.2–34.7 g) and seed yield (0.088–1.31 metric tonne (MT)/ha) was observed. Mean grain yield of buckwheat genotypes was 0.446 MT/ha whereas IC13411, IC24298 and IC37305 produced significantly higher seed yield (1.31, 1.28 and 1.14 MT/ha, respectively) accounting to 1.93, 1.87 and 1.67 times higher than average yield (0.680 MT/ha). Genotypes like IC42416, EC323730 and EC218784 have lower crop yields (0.8, 1.02, 0.93 MT/ha respectively). Interestingly, few high yielders (IC13411 and IC24298) exhibited higher photosynthetic rate (46.1 and 32.3 μmol/m².s), increased stomatal conductance (311.0 and 326.2 mmol/m².s), leaf chlorophyll (2.47 and 2.55 mg/g fresh weight (FW)) and carotenoids (95 and 106.3 μg/g FW). Chlorophyll a and b ratio (3.3 and 3.0) and total chlorophyll to carotenoids (4.2 and 4.0) were higher in high yielders (IC13411 and IC24298) compared to other low yielders.

Conclusions. Robust root systems, stomatal structure and higher cuticle wax ideally enhanced water use efficiency (WUE) and drought tolerance in high-yielding buckwheat genotypes.

Implications. IC13411 and IC24298 are promising for enhanced productivity in the mountainous ecosystem of Meghalaya.

Context. Soybeans (Glycine max. (L.) Merr.) are a major source of phospholipids, which are vital to human and animal nutrition, as well having many pharmaceutical and industrial applications. Identification of quantitative trait loci (QTLs) is a prerequisite for the development of high-phospholipid soybean genotypes through marker-assisted breeding.

Aims. We aimed to identify QTLs associated with biosynthesis of four phospholipids in soybean.

Methods. We developed two F₂ populations comprising 233 and 254 plants, respectively, from two crosses (JS20-34 × AVKS215 and JS20-98 × AVKS215), and used 208 polymorphic simple sequence repeat markers found common to both F₂ populations for linkage map construction. QTLs associated with four phospholipids, phosphatidylethanolamine (PE), phosphatidic acid (PA), phosphatidylinositol (PI) and phosphatidylcholine (PC), were analysed via inclusive composite interval mapping of additive QTLs using QTL IciMapping software.

Key results. In the respective F₂ populations, we identified seven and six QTLs for PE, seven and nine QTLs for PA, and nine and eight QTLs for PC. Six QTLs were associated with PI in each population. Five QTLs for each of PA and PC, three QTLs for PE, and four QTLs for PI were found common to both F₂ populations.

Conclusions. The results showed that some genomic regions such as Sat_341–Satt331 on chromosome 10, and Satt325–Sat_387 and Sat_229–Satt510 on chromosome 13, were associated with all four phospholipids in both F₂ populations. QTLs associated with phospholipids were also found to be annotated with genes involved in phospholipid biosynthesis.

Implications. The QTLs identified may be useful in marker-assisted breeding for the development of soybean genotypes with high levels of phospholipids of interest and for identifying functional genes involved in phospholipid biosynthesis.

Context. Sulfur deficiency is a limiting factor of cereal crops, causing significant crop losses associated with a decrease in the number of grains. In barley (Hordeum vulgare L.) crops, grain number (and grain yield) is associated with spike biomass at anthesis, which is related to crop growth rate during the period preceding anthesis (i.e. the ‘critical period’) when spike growth occurs. These relationships have been established for various cultivars under varying radiation intensity and in different locations, and have been confirmed in crops grown under nitrogen and phosphorus deficiencies.

Aims. The objective of this study was to determine, for malting barley, whether the effects of sulfur, nitrogen and their interaction on the number of grains per unit area could be explained by changes in crop growth rate or photothermal quotient (ratio of intercepted photosynthetically active radiation to temperature) during the critical period.

Methods. Three field experiments were conducted in the Pampean region of Argentina to evaluate the effects of sulfur fertilisation under three levels of nitrogen availability on the number of grains per unit area.

Key results. Changes in grain number were associated with crop growth rate or photothermal quotient during the critical period. This association was maintained when sulfur fertilisation changed grain number. Crop growth rate during the critical period varied mainly as a result of changes in accumulated intercepted radiation.

Conclusions. Sulfur fertilisation increases grain number and grain yield by increasing radiation interception during the critical period, probably as a consequence of increased leaf area.

Implications. The determination of grain number under sulfur deficiency is similar to that observed under deficiencies of other nutrients.

Context. Most maize breeding is conducted under high-input conditions, with nitrogen supply being crucial due to its impact on yield.

Aims. This study aimed to investigate broad-sense heritability, and general and specific combining ability variances of physiological traits defining grain yield under contrasting soil nitrogen supply.

Methods. A six-parent full diallel cross was analysed under high (fertilised with 200 kg N/ha) and low (unfertilised control) nitrogen supply in two seasons. We measured kernel number per plant and kernel weight, the associated traits of plant growth during the critical and grain-filling periods, and source–sink relationships in both periods.

Key results. Heritabilities of traits ranged from 0.54 to 0.88, and general surpassed specific combining ability for most traits. At low nitrogen (1) the relative importance of general combining ability estimated by Baker’s ratio increased across traits (low nitrogen: 0.90 vs high: 0.85) because the decrease in combining ability variance was larger for specific than general (–78% vs −39%), and (2) source–sink relationship during grain filling had the highest Baker’s ratio (0.96) and heritability (0.78). Plant growth rates during the critical period and kernel number increased substantially at high nitrogen (40 and 34%, respectively), and they had the highest heritability (0.79 and 0.88) and Baker’s ratio (>0.90).

Conclusions. Low nitrogen environments increased the relative importance of general combining ability effects, and high yield can be obtained by improving the source–sink relationship during grain filling, whereas high nitrogen increased yield by improving plant growth rate during the critical period and kernel number.

Implications. Knowledge of source–sink relationship during effective filling period, plant growth during the critical period and kernel number may result in a more targeted selection program.

Context. Defensive action of plants against biotic and abiotic stresses has been augmented by silicon (Si). Spinach (Spinacia oleracea L.) is a nutritious leafy vegetable that is a cold-tolerant but heat-sensitive crop.

Aims and methods. The ability of exogenous application of Si (0, 2, 4 and 6 mmol L⁻¹ in the form of K₂SiO₃) to alleviate heat stress in spinach cv. Desi Palak was investigated. After an acclimatisation period, plants were grown with or without heat stress for 15 days, followed by Si treatment for 25 days. Plant growth and physiology were assessed at 65 days after sowing.

Key results. Heat stress significantly inhibited plant growth, water status and photosynthesis, soluble sugar and protein contents, and osmolyte status in spinach leaves, but increased electrolyte leakage, activities of antioxidant enzymes, and proline content. Application of Si alleviated heat stress by enhancing water status, photosynthetic pigments, soluble proteins and essential minerals, and by reducing damage of the plasma membrane. The accumulation of osmolytes counterbalance the osmotic stress imposed by heat.

Conclusions. Silicon plays a vital role in alleviating effects of heat stress by improving water status and photosynthetic rate, and accruing osmoprotectants other than proline.

Implications. Exogenous application of Si is an efficient strategy to boost tolerance of spinach plants to heat stress, having significant impact on growth and productivity of spinach at higher temperatures.