Agricultural Sciences: Techniques and Innovations Vol. 12

Heterotic Grouping in Maize: Critical Narrative Review of Conceptual Foundations, Classification Methods and Genomic Prospects

Sudhir Kumar Injeti — 2026-08-20

Heterotic grouping is central to maize hybrid breeding because it structures parental pools, guides tester choice and concentrates crossing effort on combinations with a higher probability of superior performance. Yet the term is frequently used imprecisely, and molecular clusters, pedigree classes and combining-ability groups are often treated as interchangeable even though they capture different biological and operational signals. This critical narrative review evaluates the conceptual basis, regional development, classification methods and genomic future of heterotic grouping in maize. Literature published principally from 1990 to 31 May 2026 was selected through live searches of accessible scholarly indexes and DOI metadata sources, supplemented by citation chaining and verification against official article records. The evidence indicates that a heterotic group is best understood as a breeding population defined by repeatable cross-performance relationships, not as a taxonomic unit or a neutral-marker cluster. Long-established temperate patterns, including Stiff Stalk versus non-Stiff Stalk in North American dent maize and Dent versus Flint in Europe, show comparatively strong alignment among pedigree, genomic differentiation and hybrid performance because recurrent selection and germplasm recycling have reinforced those divisions. In tropical, subtropical and recently assembled breeding material, agreement is weaker: genetic distance can describe ancestry and avoid close relatives, but it does not consistently predict heterosis or specific combining ability. Testcross evidence remains the most direct basis for operational assignment, although results depend on tester choice, target environment, maturity, stress regime and trial precision. Heterotic group-specific and general combining ability methods can improve classification in some populations, while genomic prediction generally offers greater practical value than simple marker distance when adequate training relationships and multi-environment data are available. The most defensible strategy is therefore integrative and dynamic: combine pedigree and genomic structure with replicated testcross performance, update assignments as programmes evolve, and manage within-group diversity as deliberately as between-group divergence.

Ecological Management of the Brinjal Insect-Pest Complex: Integrating Natural Enemies and Plant Diversification

Rudra Narayan Borkakati — 2026-08-20

Brinjal, or eggplant, supports a persistent insect-pest complex in which internal feeders, sap feeders, mites and defoliators impose different ecological and operational demands on pest management. The fruit and shoot borer is usually the principal yield-limiting species in South Asian production, but whiteflies, leafhoppers, aphids, thrips, mites and leaf-feeding beetles can become locally dominant, particularly when insecticide use disrupts natural regulation. This critical narrative review evaluates how natural enemies and plant diversification can be combined to build more durable pest management rather than applied as isolated components. Literature was selected through transparent searches of accessible scholarly indexes and verified journal records, with emphasis on field evidence, mechanistic relevance, methodological quality and consistency across production systems. The evidence indicates that plant diversification can reduce pest colonisation, alter host-finding, provide food and refuge for beneficial arthropods, and improve yield stability; nevertheless, outcomes depend strongly on companion identity, spatial arrangement, crop ratio, phenology and landscape context. Natural enemies contribute most reliably when interventions are matched to pest biology: parasitoids and egg-stage tactics must act before fruit and shoot borer larvae enter plant tissue, whereas predator-parasitoid assemblages can exert stronger continuous pressure on exposed sucking pests. Higher natural-enemy abundance does not automatically produce lower pest density or damage, and broad-spectrum insecticides, intraguild interactions, alternative prey, poor synchrony and inadequate habitat resources can weaken expected benefits. The strongest strategy is therefore an adaptive architecture that couples sanitation, monitoring and selective interventions with purpose-designed intercrops, flowering resources, semi-natural habitat and compatible biological products. Current evidence is limited by short experimental durations, small plots, inconsistent outcome reporting and geographical concentration. Future research should use factorial, multi-season and landscape-aware trials that measure pest suppression, natural-enemy function, yield, profitability, pesticide displacement and farmer feasibility together.

Nutrient Delivery to Woody Plants by Stem Injection: A Critical Appraisal of Transport Mechanisms, Agronomic Efficacy and Physiological Cost

Hussein J. Shareef — 2026-08-20

Nutrient disorders in perennial woody crops and amenity trees are frequently refractory to soil fertilisation because calcareous or alkaline substrates immobilise applied micronutrients, and to foliar sprays because several elements move poorly once deposited on the leaf surface. Stem injection, the direct introduction of solutions into functional xylem through a port in the trunk, has been proposed for more than nine decades as a way of bypassing both bottlenecks. Interest has intensified as injection hardware developed for pesticide and antibacterial delivery has become commercially available, yet the nutritional application has never been subjected to the same critical scrutiny as the plant-protection application. This review examines the physiological basis, delivery technology, agronomic evidence and physiological cost of stem injection used specifically for nutrient delivery. Literature was identified through structured searching of scholarly bibliographic indexes accessible during preparation, supplemented by backward citation searching, and appraised for design adequacy, controls, measurement validity and generalisability rather than scored with a formal instrument. Four conclusions emerge with differing degrees of confidence. Correction of iron deficiency chlorosis by injected ferrous sulphate is the best-supported application, replicated across several genera and reported to persist for more than one season, although most trials are small, short and conducted on severely chlorotic trees. Evidence for zinc, manganese and boron is thinner, is often confounded with co-injected fungicidal compounds, and includes documented failures to reach critical leaf concentrations. Macronutrient delivery is constrained by a mass-balance problem that no reported injection protocol resolves, and the single well-documented magnesium trial found the approach ineffective. Injection ports impose a reproducible wound whose consequences depend on host compartmentalisation capacity, dose and pressure, and are rarely followed for long enough to quantify cumulative cost under repeated annual use. The dominant unresolved question is not whether injected nutrients enter the tree, which is well established, but whether the delivered dose reaches deficient tissue in a spatially uniform and physiologically meaningful quantity at acceptable cost to the stem.

Polyhalite and Soil Health: Mechanisms, Evidence Boundaries and Implications for Sustainable Agriculture

K. Balagangathar — 2026-08-20

Polyhalite is a naturally occurring hydrated sulphate mineral that supplies potassium, sulphur, calcium and magnesium in a fixed stoichiometric association. Its increasing agronomic use has generated claims extending from balanced crop nutrition to improved soil health and lower environmental impact. This critical narrative review evaluates those claims by separating demonstrated nutrient-delivery effects from plausible but incompletely tested soil-health mechanisms. Literature published from 1 January 1991 to 5 June 2026 was identified through accessible scholarly indexes, bibliographic databases, journal platforms, institutional repositories and citation searching, with foundational mineralogical studies included where necessary. Evidence was appraised for comparator adequacy, nutrient-rate equivalence, duration, soil and crop representativeness, measured soil-health domains, independence of funding and consistency across studies. Polyhalite is an effective source of potassium and sulphate sulphur, while its calcium and magnesium can contribute to crop uptake and exchangeable pools under responsive conditions. Its slower dissolution than highly soluble potassium salts can moderate nutrient-release peaks, but release remains strongly dependent on particle form, moisture, soil texture and rainfall. Crop responses are generally positive relative to nutrient-omission controls, yet superiority over balanced conventional fertilisation is inconsistent. Direct evidence for durable improvement of soil structure, organic carbon, biodiversity or multifunctionality remains limited; most studies assess post-harvest nutrient concentrations, pH, electrical conductivity or short-term enzyme and microbial indicators. The product’s chloride-free composition is useful for chloride-sensitive crops and some salinity contexts, but does not establish universal agronomic or environmental superiority. A substantial share of the evidence base involves manufacturer funding or authorship, reinforcing the need for independent, long-term, nutrient-balanced trials. Polyhalite can support sustainable agriculture when selected through soil testing, crop demand, rainfall risk and whole-rotation nutrient budgets, preferably as part of blended and adaptive nutrient management rather than as a stand-alone soil-health intervention.

Synthetic Seed and Encapsulation Technologies for Plant Propagules: A Critical Review of Biological Design, Storage Performance and Translational Readiness

Sananda Mondal — 2026-08-20

Synthetic seed technology seeks to convert clonally propagated plant material into discrete, handleable propagules that can be stored, transported and established with some of the operational advantages of true seed. The concept began with encapsulated somatic embryos but has expanded to shoot tips, axillary buds, nodal segments, microshoots, protocorm-like bodies and other regenerable tissues. This critical narrative review evaluates how that expansion has altered the biological meaning, engineering requirements and practical expectations of the technology. Literature from 1982 to 10 June 2026 was identified through accessible scholarly sources and citation tracing, with emphasis on peer-reviewed studies whose bibliographic identity and relevance could be verified. Evidence indicates that calcium-alginate encapsulation remains the dominant platform because ionotropic gelation is mild, inexpensive and readily adjustable, yet a capsule that is morphologically satisfactory is not necessarily biologically competent. Conversion depends jointly on propagule developmental state, matrix composition, mineral nutrition, plant growth regulator history, gas and water exchange, storage environment and the need for post-encapsulation rooting. Somatic embryos retain the closest functional analogy to zygotic seeds, whereas non-embryogenic propagules broaden genotype coverage but frequently preserve dependence on tissue-culture steps. Short- to medium-term storage is feasible in many species, but optimum temperature is not consistently low, and long-duration retention of conversion capacity remains strongly species- and protocol-dependent. Molecular-marker studies generally report clonal similarity after encapsulation, although reliance on limited RAPD or ISSR sampling constrains conclusions about genomic and epigenomic stability. The principal translational weakness is therefore not the ability to form beads, but the absence of standardised quality attributes linking capsule mechanics, physiological state, conversion probability, storage life, sanitation and cost. Future progress requires quality-by-design experiments, sensitive stability assays, non-sterile or direct-sowing validation, automation, and multi-laboratory performance testing. Synthetic seeds are best regarded as a configurable clonal propagule-delivery system rather than a universal replacement for botanical seed.