Early-generation (e.g. F₂–F₄) selection for grain yield itself is frustrated in particular by the small amounts of seed available. However, there has long been an interest in traits related to yield and reasonably faithfully expressed in spaced planting arrangements using little seed; these are potentially useful as indirect selection criteria for yield, with the view to increasing genetic progress per unit cost. This subject is revisited in this review, targeting potential yield (yield in the absence of abiotic and biotic stresses) of small-grain cereals.

A brief assessment of current breeding systems for self-pollinated crops such as wheat reveals that all have some stage during which selection among visually acceptable spaced plants has to, or could, be practiced. The relative performance of different genotypes in such spaced plantings is then explored, highlighting interactions arising from intergenotypic competition as well as from the extra space itself. The theory of indirect selection is presented, along with some practical examples. After a brief survey of possible selection traits and developments in high-throughput measurement, harvest index, fruiting efficiency and stomatal conductance (and its surrogates) are chosen for in-depth review. All three traits show promise, especially in the light of possible new ways of reducing the cost of their measurement in early generations. Remote sensing of foliage temperature for the detection of genotypic differences in stomatal conductance makes this clearly the most promising trait for thorough testing in commercial breeding populations. Such traits could be used directly or they could complement genomic selection in early generations.

High levels of crop productivity cannot be sustained by chemical fertiliser application alone. In order to mitigate this, a 2-year study was conducted to test the effects of combined application of indigenous plant-growth-promoting rhizobacteria (PGPR) and chemical fertilisers on productivity of wheat and soil properties. Ten morphologically distinct indigenous PGPR isolates from wheat roots and rhizosphere were evaluated at Solan, Himachal Pradesh, India, during 2013–14. Three PGPR isolates (B2, SIR1 and BIS2) with maximum PGP traits were screened at different doses of nitrogen (N) and phosphorus (P) (80%, 60% and 40% of recommended fertiliser dose, RFD) under net-house conditions. Two isolates, B2 (Serratia sp.) and SIR1 (Bacillus subtilis), along with the optimum NP dose (i.e. 80% RFD) were selected for field experimentation, which was performed over two consecutive years, 2014–16. Combined application of 80% RDF of NP with PGPR (B2) significantly increased wheat yield by 9.4%, number of tillers per plant by 28.03%, grain number per spike by 19.61%, 1000-grain weight by 10.5%, and biomass by 9.2% relative to the uninoculated control with 100% RFD. Soil properties in the terms of available N, P and potassium, microbial biomass carbon, soil enzyme activities and population of phosphate-solubilising bacteria in the wheat crop were significantly increased by the combined application of bacterial inoculants with 80% RFD of NP in both years over the uninoculated control. Therefore, the results revealed the potential of indigenous PGPR isolates to supplement ∼20% of NP fertilisers without hampering the soil fertility and productivity of wheat.

Male reproductive development in higher plants is highly sensitive to various stressors, including high temperature (HT). In this study, physiological male-sterile plants of wheat (Triticum aestivum L.) were established using HT induction. The physiological changes and expression levels of genes mainly related to carbohydrate metabolism and sporopollenin in male-sterile processes were studied by using biological techniques, including iodine–potassium iodide staining, paraffin sectioning, scanning electron microscopy (SEM) and fluorescent quantitative analysis. Results of paraffin sectioning and SEM revealed that parts of HT male-sterile anthers, including the epidermis and tapetum, were remarkably different from those of normal anthers. The expression levels of TaSUT1, TaSUT2, IVR1 and IVR5 were significantly lower than of normal anthers at the early microspore and trinucleate stages. The RAFTIN1 and TaMS26 genes may contribute to biosynthesis and proper ‘fixation’ of sporopollenin in the development of pollen wall; however, their expression levels were significantly higher at the early tetrad stage and early microspore stage in HT sterile anthers. The recently cloned MS1 gene was expressed at the early tetrad and early microspore stages but not at the trinucleate stage. Moreover, this gene showed extremely significant, high expression in HT sterile anthers compared with normal anthers. These results demonstrate that HT induction of wheat male sterility is probably related to the expression of genes related to carbohydrate metabolism and sporopollenin metabolism. This provides a theoretical basis and technological approach for further studies on the mechanisms of HT induction of male sterility.

Agronomic biofortification by seed treatments is a convenient way to harvest improved yields of micronutrient-enriched grains. This 2-year field study was conducted to evaluate the effects of seed priming with zinc (Zn), boron (B) and manganese (Mn) alone and in combinations on stand establishment, grain yield and biofortification of bread wheat (Triticum aestivum L.). Seeds of wheat cv. Faisalabad-2008 were soaked in aerated solutions of 0.5 m Zn, 0.01 m B and 0.1 m Mn, alone and in different combinations, for 12 h. Seed priming with the micronutrients was quite effective in improving stand establishment, yield-contributing traits, grain yield, and straw and grain micronutrient contents during both years. Best stand establishment was achieved from seed priming with Zn+B, followed by seed priming with Zn+Mn. Grain yield improvement from different seed priming treatments was in the order Zn+B > Zn+Mn > Zn > B > Mn > Zn+B+Mn, with respective increases of 34%, 33%, 21%, 19%, 18% and 8% relative to untreated seeds. Seed priming with Zn, B and Mn alone and in combinations also improved the contents of the respective micronutrients in straw and grain. All seed priming treatments were economically profitable except Zn+B+Mn, which was not cost-effective. The highest benefit : cost ratio accrued from seed priming with Zn+B. In conclusion, seed priming with micronutrients was generally cost-effective in meeting the crop micronutrient requirements, and in improving crop stand, grain yield and grain micronutrient contents in bread wheat. Seed priming with Zn+B was the most effective in this regard.

In tropical conservation agricultural systems, crop yield is limited by soil acidity and root-growth inhibition, especially under intensive crop rotation. This study evaluated the effect of surface applications of lime and phosphogypsum in improving soil fertility and crop yield in a tropical region. Four treatments were evaluated: control (without soil amendment); and application phosphogypsum (2.1 + 2.1 + 2.1 Mg ha^–1), lime (2.7 + 2.0 + 2.0 Mg ha^–1), and a combination of lime and phosphogypsum at the given rates, applied in 2002, 2004 and 2010, respectively. We evaluated the soil chemical properties, root development, plant nutrition, yield components and grain yield of 10 crops over 4 years using five species: maize (Zea mays), crambe (Crambe abyssinica), cowpea (Vigna unguiculata), wheat (Triticum aestivum) and common bean (Phaseolus vulgaris). Our long-term results demonstrate the benefits of surface liming in alleviating subsoil acidity, reducing Al³⁺ toxicity, improving availability of Ca²⁺ and Mg²⁺, and increasing accumulation of soil organic matter in all soil profiles at depths up to 0.60 m. For maize and crambe, adding phosphogypsum increased development of plants and reproductive structures, which increased grain yield. Phosphogypsum exhibited synergistic effects in association with lime for maize and common bean. Phosphogypsum did not have an effect on cowpea and wheat, whereas surface liming was essential to improve plant nutrition, grain yield and wheat grain quality. The combination of both soil amendments is an important tool to reduce the soil acidification process, resulting in the highest levels of Ca²⁺ and Mg²⁺ and the highest base-saturation values in the topsoil layers (0–0.20 m) over time. Our long-term results showed the viability of surface liming plus phosphogypsum for improving tropical soil fertility, which can reflect an increase in grain yield and contribute to the sustainability of agricultural systems under intensive land use in highly weathered areas.

Rooted single leaves of sweet potato (Ipomoea batatas L.) produce and translocate photosynthates, thus representing an ideal model for characterising the source–sink relationships and responses to various environments. A hydroponics culture study was conducted with rooted single leaves of sweet potato to determine intraspecific variation in growth, biomass partitioning, and associated physiological changes in response to variable potassium (K) supply among genotypes Ji22 (low K-use efficiency), Nan88 (high K-uptake efficiency) and Xu28 (high K-use efficiency). Potassium deficiency suppressed biomass accumulation in blades, petioles and roots in all three genotypes. Root length of diameters <0.25 mm and 0.25–0.5 mm was significantly less for K-deficient than K-sufficient roots of all genotypes, but the difference was proportionally greater in the K-inefficient genotype Ji22 than the other two genotypes. Potassium deficiency also severely inhibited net photosynthesis of blades in Nan88 and Ji22, as well reducing photosynthate translocation, increasing starch, hexose and sucrose concentrations, and decreasing K concentration in blades. The genotypes varied in photosynthesis-related responses to the K deficiency. Xu28 had greater blade K concentration and net photosynthesis as well as stable maximum quantum yield of photosystem II (F_V/F_M, with F_V = F_M – F₀) under K deficiency, possibly because of a better source–sink balance and more efficient translocation of photosynthates to roots and K to blade compared with genotypes Ji22 and Nan88. Impaired phloem loading during K deficiency was associated with a decline in photosynthetic rate and decreased carbohydrate supply from blades, resulting in restricted root growth.

The genetic basis of physiological responses to drought and its association with productivity, persistence and summer dormancy is not clear in orchardgrass (Dactylis glomerata L.). Thirty-six orchardgrass genotypes were evaluated under water stress and non-stressed conditions during 2 years (2013–14). High genotypic variation was observed for all of the agronomic and physiological traits. Water stress reduced dry matter yield, relative water content and chlorophyll content while significantly increasing carotenoids, water-soluble carbohydrates, proline and chlorophyll a : b ratio. The results indicated that carotenoids and proline accumulation could not be used for discriminating drought-tolerant genotypes of orchardgrass, whereas water-soluble carbohydrates may be used to achieve this purpose. Moreover, the results showed that the stable genotypes that have lower changes in productivity from normal to water-stress environments also have more persistence. No association was found between summer dormancy and drought tolerance measured by both physiological and yield-based drought-tolerance indices. Some of the drought-tolerant genotypes had relatively high persistence and better autumn recovery, a characteristic useful for the development of new synthetic varieties.

The key agricultural species of Urochloa P.Beauv. (signal grass), important as tropical forage grasses, are characterised by asexual seed formation (apomixis), and this presents a challenge for breeding programs. Biotechnological approaches could be an option to develop improved cultivars. We evaluated the regenerative potential from three commercial genotypes, U. brizantha cv. Marandu, U. decumbens cv. Basilisk and U. ruziziensis cv. Ruziziensis, by using leaf-base segments as explants. We tested two auxins (2,4-D and picloram) and one cytokinin (TDZ) at four concentrations (1, 2, 3 and 4 mg L^–1). Seeds were scarified, peeled and disinfected before inoculation on half-strength MS media in the dark for 14 days. Leaf-base explants were sectioned in thin slices and inoculated into the media. We analysed the number of primary calluses, number of calluses with shoots clusters and the average of regenerated plants. The lowest concentration of auxins tested (1 mg L^–1) yielded the highest number of regenerated plants for Marandú and Basilisk, whereas the optimum for Ruziziensis was 2 mg L^–1. Medium with higher concentrations of TDZ (4 mg L^–1) was required to produce high frequency of plants for all genotypes. Explants cultured on media with TDZ produced very few calluses. These results indicate that the auxins and cytokinin tested can induce plant regeneration from Urochloa leaf-base segments, and may be used to produce transgenic plants in genetic transformation studies.

Salt stress is known to hamper steady-state water flow, which may reduce plant growth. This research was aimed to study the roles of leaf turgor, osmotic adjustment and cell wall elasticity under saline conditions which may reduce biomass production in Phragmites karka (Retz.) Trin, ex. Steud. (a marsh grass). Plants were grown in 0, 100 and 300 mM NaCl and harvested on 3, 7, 15 and 30 days to observe periodic changes in growth and water relations. Leaf number, relative growth rate, and relative elongation rates were higher in the non-saline control than in the plants grown under saline conditions. Plants showed a rapid decline in leaf growth rate (7–15 days) in 300 mM NaCl compared with a delayed response (15–30 days) in 100 mM NaCl. Leaf water potential decreased with increases in salinity after the third day of exposure whereas osmotic potential decreased after the fifteenth day. Low leaf turgor (Ψ_p) on the third day indicated an initial phase of osmotic stress under saline conditions. Plants maintained higher Ψ_p in 0 and 100 mM than in 300 mM NaCl. Differences between mid-day and pre-dawn water potential and water saturation deficit were higher in 300 mM NaCl than with other treatments. Water potential and hydraulic capacitance at turgor loss point decreased whereas bulk elastic modulus increased in 300 mM NaCl. Maintenance of turgor and growth at 100 mM NaCl could be related to efficient osmotic adjustment (use of K⁺ and Cl^–), higher WUE_i, and lower bulk elasticity whereas poor growth at 300 mM NaCl may have been a consequence of low turgor, decreased cell hydraulic capacitance and higher bulk elastic modulus.