Utilizing Genetic Resources for Agronomic Trait Improvement: Series II

1. Introduction

Genetic resources are a particularly valuable reserve; specifically, in the search for genetic variability in agronomic traits that allow for greater adaptability, tolerance to limiting abiotic conditions, resistance to pathogens, and further traits related to valued qualities (e.g., higher protein or vitamin content) [1]. Over the last 50 years, methods for the conservation and evaluation of genetic resources have been developed to a great extent [2]. Currently, there are about 1750 gene banks worldwide, preserving around 7.4 million accessions, of which 2 million are unique non-duplicate samples [3]. Searching for favorable alleles is key in plant breeding, including for those involved in quantitative traits, the so-called QTLs [4]. Further, these alleles may be found in landraces or crop wild relatives kept at the world’s gene banks. For example, an accession of the wild rice species Oryza nivara provides resistance to the grassy stunt virus disease in almost all tropical rice varieties in Asia [3]. In this context, both molecular markers and genomic selection aid in selecting parents with a better ability to be crossed or backcrossed, and furthermore in predicting the phenotypic value of the offspring’s superior lines [4]. Sequencing genomes of different species and varieties can inform us, for example, about the mechanisms of adaptation to abiotic stresses, such as heat or drought tolerance [3]. This Editorial provides an overview of the content of the second edition of the Agronomy Special Issue ‘Utilizing Genetic Resources for Agronomic Trait Improvement’.

2. An Overview of the Published Articles

In the first study (contribution 1), Cuevas et al. (2023) reported on biofortification in sorghum, increasing the protein content in the grain by selecting landraces with a high protein content from a collection of 228 African accessions. Sixteen landraces (most from Mali, of the guinea race, and with a light or white color of pericarp) presented a higher protein content, which could be used in breeding programs. The second contribution is an article by Cai et al. (2023) focusing on the GmERF54 gene, which confers resistance to the common cutworm (Spodoptera litura Fabricius) in the Chinese soybean cultivar Wanxianbaidongdou. Here, the down-regulated expression of GmERF54 increased the resistance of transgenic soybean hairy roots to this insect, while GmERF54-overexpressed transgenic hairy roots exhibited decreased resistance. In our third article (contribution 3), Elfanah et al. (2023) investigated salinity tolerance, screening a collection of 40 genotypes of bread wheat using pot experiments: differences were found in terms of yield performance. Furthermore, these differences correlated well with spectral reflectance indices such as NDVI. The six more tolerant genotypes were tested again with a lysimeter under diluted seawater stress. Results were promising, and tolerant genotypes can be employed in a breeding program or be recommended for sowing. In our fourth contribution, Perisic et al. (2023) analyzed the silage-making potential of lines from the Germplasm Enhancement of Maize (an international collection). This took place across three years and seven environments in (field) trials in Serbia. Hybrids were compared based on their conversion into animal productivity units: milk yield per hectare (Milk ha⁻¹) and milk yield per ton of silage (Milk t⁻¹). Although broad-sense heritability was moderate (0.24 and 0.31, respectively), some superior hybrids were identified. In another study on salinity tolerance (contribution 5), Fairoj et al. (2023) applied different concentrations of salicylic acid in two bread wheat genotypes to improve salinity tolerance. Salicylic acid improved the relative water content, gas exchange activities, photosynthetic pigments and maintained a lower Na+/K+ ratio and Na+ concentrations. In a different study, Martínez-Moreno et al. (2023) investigated the origin of durum wheat and olive tree landraces in Spain, two important crops in the country and in the Mediterranean Basin (contribution 6). Landraces of both crops are preserved in different gene banks. Most durum wheat landraces originate from the internal circulation of genotypes within the east and south of Spain, and have come from external circulation from northwest Africa and Sicily in the last 500 years. However, olive tree genotype circulation was low, keeping the same landraces in the same place for centuries. Southern olive tree landraces also come from northwest Africa, having probably arrived during the Islamic period in Spain, while eastern landraces come from Italy (either in the Roman or Renaissance times). In a search for new rice genotypes with low amylose content, which is positively correlated with its digestibility, 167 upland rice landraces of Thailand were examined by Srinang et al. (2023) (contribution 7). Regarding glutinous low-amylose genotypes, four accessions released less sugar and had slower starch digestibility than the reference. In the non-glutinous low-amylose group, two accessions presented slower digestion and lower sugar release with respect to the reference. Contribution 8 concerns Septoria tritici blotch, an important durum wheat disease in areas such as the Mediterranean Basin. Here, it is interesting to foresee what may happen in 2070–2099 in relation to the predicted global warming. Inoculations of three cultivars of durum wheat leaves in two different temperature situations were performed by Porras et al. (2023): current (10–24 °C) and elevated (15–30 °C). Interestingly, it seems that the elevated temperature reduced disease incidence, especially at the stages of host penetration and pycnidia formation and maturation. A higher concentration of CO₂ slightly favored fungal development, but its effect was much smaller compared to that of the temperature. Perhaps an intermediate temperature range would provide more clues as to the effect on Septoria tritici blotch development. When examining a collection of 112 black gram (a pulse) accessions from India, Verma et al. (2024) selected for tolerance to pre-harvest sprouting, a common issue in humid tropical regions (contribution 9). Water absorption by pods and seeds, alpha-amylase activity, and seed hardness were conveniently assessed. The accession IC485641 was highly tolerant to pre-harvest sprouting (only 2.75% of the seed germinated in the pod) and might be used as a parent in a breeding program. Oyoque-Salcedo et al. (2024) studied the nutritional content of Polimaize lines (or Polimaize) (contribution 10), a set of pure lines derived from crosses between a local Mexican variety (Native Bue Corn, with a high level of antioxidants and anthocyanins) and 13 elite maize lines from CIMMYT. Although antioxidant and anthocyanin levels did increase in the offspring, the sucrose and tryptophan content decreased. The new lines offer farmers a chance to cultivate high-yield varieties with the added value of nutritionally enhanced kernels. Sea Island cotton (Gossypium barbadense L.) shows great fiber quality. An evaluation by Lin et al. (2024) of a global collection of 240 genotypes for 19 traits affecting mechanical harvesting—showed interesting results (contribution 11). Higher first fruiting branch height and a high defoliation rate positively influence mechanical harvesting; genotypes like MoShi729 were especially suitable for mechanical harvesting. Studying the edible mushroom Shiitake, a Chinese group led by Deng et al. (2024) estimated that 10 fruiting bodies are needed to test the DUS (distinctness, uniformity, and stability) of a particular variety (contribution 12). Notably, the minimum number of testing samples (fruiting bodies) for DUS testing in this species had not yet been described. An evaluation of 12 agronomic traits of 159 accessions of chickpea from the Russian N. Vavilov Plant Genetic Resources’ worldwide collection was carried out by Duk et al. (2024) at two different locations, Kuban and Astrakhan (southwest Russia) (contribution 13). Agronomic data were crossed with genotypic data using the IIIVmrMLM model. While many favorable alleles showed stable effects at the two locations, others were location-specific. Such location-specific effects may be used to enhance chickpea adaptation to particular climatic conditions. Attempting to broaden the spectrum of varieties within the Spanish purple garlic landrace ‘Ajo Morado de Pedroñeras’, Licea-Moreno et al. (2024) selected 23 genotypes after two field trials from an initial population of 360 bulbs of this landrace. This was based on having a purple color, fewer small cloves, and resistance to Fusarium (contribution 14). High genotype × environment interaction affected the performance of the lines, highlighting the necessity of evaluating in different locations. In the final article of this Special Issue, Lou et al. (2024) tried to map the QTLs related to first pod height in faba bean, an important trait for mechanizing faba bean harvest (contribution 15). The genetic linkage map consisted of 3012 SNP markers covering 4089 cM. In total, 19 QTLs were found for the trait on chromosomes 1L, 1S, 2, 3, 5, and 6; many of these QTLs are involved in gibberellin and auxin movement in the plant driving internode elongation.

3. Conclusions

Within this Special Issue, fifteen articles across a diverse range of topics have been published. The most important subjects (present in two articles) were the adaptation to mechanical harvesting (cotton and faba bean), salinity tolerance (bread wheat), and improving quality in the edible purple part of varieties of maize and garlic. All showed that genetic resources are a potential reservoir of desirable allelic variants of valuable traits and could therefore help both in the enrichment of biodiversity and in the stabilization of crop production under changing climatic conditions. Fortunately, a global collection of thousands of landraces and wild relatives of the most important crops are preserved in seed banks and in situ collections. Studies such as those presented here are essential to unlock the potential of these resources for plant breeding. One final thought concerns the current use of plant genetic resources. The Standard Material Transfer Agreements (SMTAs) of the Nagoya protocol of 2010 [5], ratified in 2022 by 137 states, have allowed for a portion of any monetary benefits derived from the commercialization of products from gene-bank materials to be put into a fund supporting conservation and the sustainable use of crop genetic resources. This has had both positive and negative consequences. Breeding companies, institutions related to genetic research, and seed banks themselves currently have problems accessing and exchanging plant material, notwithstanding the huge amount of paperwork they have to fill out. To some extent, plant genetic resources now seem further away from us than before. For many breeding companies within the European Union, restrictions on genetic modifications and this near restriction of the use of plant genetic resources have led them, in many instances, to return to mutagenesis + tilling techniques to obtain their own alleles. With this, a simpler method to facilitate access to plant genetic resources—such as a fixed tax to access to any plant material and the elimination of the SMTA—might be beneficial to all parties involved in this complex field.