Identification and Breeding of High-Quality, Disease-Resistant, and High-Producing Varieties

1. Introduction

Developing varieties that combine high productivity, desirable quality, and resistance to diseases and environmental stresses remains a central goal of plant breeding. Combining these traits is challenging because yield potential, resistance, and adaptation depend on genetic background, growing conditions, and crop management. Breeding strategies must therefore address both productivity and the consistency of performance across relevant production environments [1].

Genetic diversity provides the foundation for crop improvement [2]. Translating this diversity into improved varieties requires breeders to identify useful genetic resources, select suitable parents, and evaluate whether desirable traits are maintained across growing conditions. Field trials, phenotypic screening, and genomic information provide complementary evidence to guide selection [3].

This Special Issue of Agronomy, entitled “Identification and Breeding of High-Quality, Disease-Resistant, and High-Producing Varieties”, brings together 11 contributions on genetic improvement and the evaluation of agricultural biological resources. The studies encompass maize (Zea mays L.), barley (Hordeum vulgare L.), soybean (Glycine max (L.) Merr.), potato (Solanum tuberosum L.), rice (Oryza sativa L.), forage mulberry (Morus alba L.), cannabis (Cannabis sativa L.), the woody oil-bearing species Idesia polycarpa Maxim., and the edible fungus Rhodotus palmatus (Bull.) Maire. Together, they address germplasm utilization, variety development, agronomic performance, resistance to biotic stresses, and evaluation methods for specialized production systems.

2. Genetic Resources and the Development of Improved Varieties

Effective use of genetic resources requires selection criteria that link desirable traits to breeding objectives and end uses. Two contributions illustrate this principle through the evaluation of maize germplasm with contrasting breeding applications.

Călugăr et al. evaluated 56 maize hybrids developed by crossing 14 dent and semi-dent inbred lines with four flint lines. Across two years, A478 × D328, A480 × B330, and A480 × D328 combined favorable yield, flowering synchronization, stay-green characteristics, and a high proportion of unlodged plants. The maternal lines A478 and A480 were identified as useful breeding resources, and A478 × D328 was proposed for further registration testing. These findings support the development of productive hybrids that retain grain characteristics valued for food uses.

In a related study, Călugăr et al. evaluated hybrids derived from Iodent and Iodent-mixed maternal lines from 2020 to 2025. Hybrids derived from A452 exceeded the trial mean in all six years, whereas those derived from E390 exceeded it in five years. Two hybrids tested during the earlier years of the program, Turda 380 and Turda 350, were subsequently registered in 2022 and 2025, respectively. The study illustrates both the breeding value of parental germplasm and the progression of selected hybrids toward registration.

Geng et al. developed the forage mulberry variety ‘Fengyuan No. 1’ through the evaluation of 31 accessions, parental selection, and testing of hybrid families. In multi-location trials, it produced 14.20% more leaf dry matter and 13.36% more branch–leaf biomass than the reference variety ‘Fengchi’. Leaf crude protein content reached 30.87% of dry matter. Favorable responses to cold and saline conditions further supported its forage potential in the environments evaluated.

Luo et al. selected a strain of the edible mushroom Rhodotus palmatus for commercial cultivation. Strain ZJGWG001 had a 23-day production cycle, an average yield of 177.43 g per cultivation bag, and a biological efficiency of 59.1%. It was designated ‘Zhongjunguoweigu No. 1’ and received provincial-level certification in China. Although fungal strain selection differs from plant breeding, the study illustrates how biological resources can be characterized and developed for a defined production purpose.

These contributions demonstrate the value of aligning germplasm selection with the intended product, its quality requirements, and the production system.

3. Agronomic Performance, Quality, and Environmental Adaptation

High yield in a single season does not establish reliable agronomic performance. Evaluations across years and locations help determine how environmental variation affects yield, quality, and adaptation.

Vasilescu et al. evaluated 50 two-row and six-row winter barley genotypes over three growing seasons at a single location in southeastern Romania. The measured traits included phenology, grain yield, thousand-grain weight, protein content, and starch content. Among the two-row genotypes, Idra and Sandra combined favorable yield and quality characteristics, whereas the six-row genotypes SU-Ellen and LG Zebra showed high productivity. Because the trials were conducted at one location, the stability assessment reflects variation among seasons rather than adaptation across geographic locations.

Jia et al. evaluated the soybean cultivar Heike 60 at seven locations over four growing seasons in northeastern China, representing 28 location–year combinations. Heike 60 outperformed the regional check Heihe 43 across the evaluated locations and seasons. Its maturity period was approximately 110 days, and reported mean seed protein and fat contents were 39.59% and 20.46%, respectively. Hundred-seed weight and pod number were important predictors of yield. The findings support further evaluation of Heike 60 for cold-temperate production and illustrate the value of multi-environment cultivar testing.

The barley study identifies promising breeding material within a diverse panel, while the soybean study evaluates a specific cultivar across locations and seasons. Both emphasize the need to assess yield, quality, and environmental responses together.

4. Resistance to Diseases and Pests

Biotic stresses threaten both yield and product quality. Three contributions address disease and insect resistance using field trials, controlled inoculation, and genome-wide association analysis.

Șopterean et al. evaluated 12 maize hybrids at four sowing dates over three growing seasons in the Transylvanian Plain of Romania. The latest sowing treatment had the lowest mean Fusarium ear rot incidence (59.1%) and severity (2.5%), together with the highest mean grain yield (9.1 t ha⁻¹). Turda 380, HST 149, and Turda 2020 showed greater tolerance than several other hybrids. These results highlight the combined importance of genotype and sowing date in disease management, although the sowing-date response requires confirmation under other environmental conditions.

Iribar et al. screened 336 potato genotypes, comprising 295 commercial varieties and 41 breeding clones, following artificial inoculation with Fusarium sambucinum under postharvest conditions. No genotype was fully resistant, but susceptibility differed among genotypes. The study also evaluated a resistance-scoring scale, providing a basis for consistent comparisons and the identification of germplasm for subsequent breeding.

Chiu et al. conducted parallel genome-wide association analyses of resistance to brown planthopper and white-backed planthopper in rice. They reported six candidate loci for brown planthopper resistance and five for white-backed planthopper resistance, including a promising region on chromosome 9 for the latter. These associations require further validation, and the study did not establish a definitive shared genetic basis for resistance to the two pests.

These studies demonstrate the complementary roles of field, inoculation, and genomic approaches. Field trials characterize disease responses under agronomic conditions, controlled inoculation enables comparisons of susceptibility, and association analyses identify genomic regions for further investigation. Their breeding applications depend on appropriate validation of the observed responses and candidate loci.

5. Variety Evaluation and New Opportunities for Agricultural Improvement

Selection criteria must also reflect the intended use of a crop or biological resource. Contributions on cannabis and Idesia polycarpa highlight the importance of suitable evaluation protocols and a sound understanding of species biology.

Vonlanthen et al. conducted two field trials to inform the development of a Value for Cultivation and Use (VCU) protocol for Cannabis sativa varieties grown for flowers. Proposed evaluation traits included branch number, flower and leaf yield, harvest index, and raceme compactness. Measured tetrahydrocannabinol (THC) levels varied with trial year and sampling procedures, including sampling time and the number of plants sampled. The study provides a foundation for protocol development, with further testing needed before a standardized system can be established.

Huang et al. reviewed the biology and utilization of the woody oil-bearing species Idesia polycarpa and conducted a bibliometric analysis of 109 publications from 2005 to 2025. The analysis identified three main research themes: natural products and biological activities; fruit-oil evaluation and utilization; and genomic, developmental, and reproductive research. The authors emphasized the need for functional validation of molecular findings and closer integration of reproductive biology, germplasm evaluation, and oil-quality research.

These contributions show how improved characterization, relevant testing criteria, and knowledge of species biology can establish a stronger foundation for the improvement of specialized crops and biological resources.

6. Conclusions and Future Perspectives

The 11 contributions span diverse species, methods, and production goals, yet highlight several shared priorities. The first is to translate genetic diversity into demonstrated breeding value through purposeful selection and rigorous evaluation. The maize and mulberry studies illustrate this process in plants, while the mushroom study extends the principle to cultivated fungi.

A second priority is to assess productivity and quality in the environments relevant to the intended production system. The barley and soybean studies illustrate the distinct information gained from trials across seasons and across locations. Additional field evaluation is needed when evidence is restricted to a limited range of environments.

A third priority is to connect reliable phenotyping with appropriately validated genetic information. The maize, potato, and rice studies identify useful disease responses or candidate resistance loci while defining the need for further testing. The cannabis and Idesia contributions similarly demonstrate that suitable evaluation methods and knowledge of species biology underpin effective improvement.

Future research should evaluate promising genotypes across additional environments, improve the consistency of resistance screening, validate candidate genomic regions, and refine evaluation protocols for specialized uses. Breeding priorities and methods should reflect each species, its intended product, and its production conditions. Progress depends on demonstrating that improvements in yield, quality, resistance, and adaptation are reproducible and useful under relevant production conditions.