Sweetness is an economically important eating quality trait for sweet-corn breeding. To investigate the genetic control of the sweetness trait, we conducted a genome-wide association study (GWAS) in an association panel consisting of 250 sweet corn and waxy corn inbred and recombinant inbred lines (RILs), together with the genotypes obtained from the high-density 600K maize genotyping single-nucleotide polymorphism (SNP) array. GWAS results identified 12 significantly associated SNPs on chromosomes 3, 4, 5, and 7. The most associated SNP, AX_91849634, was found on chromosome 3 with a highly significant p-value of ≤1.53 × 10⁻¹⁴. The candidate gene identified within the linkage disequilibrium (LD) of this marker was shrunken2 (Zm00001d044129; sh2), which encodes ADP-glucose pyrophosphorylase (AGPase), a 60 kDa subunit enzyme that affects starch metabolism in the maize endosperm. Several SNP markers specific to variants in sh2 were developed and validated. According to the validation in a set of 81 inbred, RIL, and popular corn varieties, marker Sh2_rs844805326, which was developed on the basis of the SNP at the position 154 of exon 1, was highly efficient in classifying sh2-based sweet corn from other types of corn. This functional marker is extremely useful for marker-assisted breeding in sh2-sweet corn improvement and marketable seed production.

The impact of increasing drought periods on crop yields as a result of global climate change is a major concern in modern agriculture. Thus, a greater understanding of crop physiological responses under drought stress can guide breeders to develop new cultivars with enhanced drought tolerance. In this study, selected chromosome segment substitution lines of KDML105 (KDML105-CSSL) were grown in the Plant Phenomics Center of Kasetsart University in Thailand under well-watered and drought-stressed conditions. Physiological traits were measured by observing gas exchange dynamics and using a high-throughput phenotyping platform. Furthermore, because of its impact on plant internal gas and water regulation, stomatal morphological trait variation was recorded. The results show that KDML105-CSS lines exhibited plasticity responses to enhance water-use efficiency which increased by 3.62%. Moreover, photosynthesis, stomatal conductance and transpiration decreased by approximately 40% and plant height was reduced by 17.69%. Stomatal density tended to decrease and was negatively correlated with stomatal size, and stomata on different sides of the leaves responded differently under drought stress. Under drought stress, top-performing KDML105-CSS lines with high net photosynthesis had shorter plant height and improved IWUE, as influenced by an increase in stomatal density on the upper leaf side and a decrease on the lower leaf side.

Waxy maize (Zea mays L. var. ceratina) is a special type of maize characterized by a sticky texture when cooked, due to high amylopectin content in the endosperm. Waxy maize is popular in China and Southeast Asia for fresh consumption. Breeding strategies have been used to improve the quality of waxy maize, including hybrid breeding by crossing super sweet maize and waxy maize. However, the lack of a marker has limited the efficiency of breeding for the waxy trait, especially because the waxy allele is recessive. In this study, we conducted a genome-wide association study (GWAS) in an association panel consisting of 213 inbred lines and recombinant inbred lines (RILs) of field maize and waxy maize to identify loci associated with the waxy kernel phenotype. The genotypic data were 155,768 SNPs derived from the high-density 600 K maize genotyping array for single-nucleotide polymorphisms (SNPs). The GWAS results identified the qWx9 locus on chromosome 9 (25.06–25.18 Mb) associated with the trait. Based on the most significantly associated SNP (AX-90613979, −log10(P) = 6.8)), which was located on Wx1, a MassArray marker was developed and validated in a panel of 139 maize lines containing waxy maize and sweet maize with different amylose content. The newly developed marker had a significant association with amylose content (R² value of 0.81, p < 0.001) and clearly distinguished between waxy maize and sweet maize lines that had different amylose content. This marker will be useful for maize breeding programs for the waxy trait, as well as for breeding programs for hybrid maize combining the sweetness and waxy traits. The gene-based SNP markers could aid breeders by eliminating the costs and time required to perform lengthy field trials and help to accelerate sweet maize and waxy maize breeding programs.

Nitrogen use efficiency (NUE) is important for the growth and development of rice and is significant in reducing the costs of rice production. OsNRT1.1b is involved in nitrate assimilation, and the alleles at position 21,759,092 on chromosome 10 clearly separate indica (Pathum Thani 1 (PTT1) and Homcholasit (HCS)) and japonica (Azucena and Leum Pua (LP)) rice varieties. Rice morphological and physiological traits were collected at three nitrogen levels (N0 = 0 kg ha⁻¹, N7 = 43.75 kg ha⁻¹, and N14 = 87.5 kg ha⁻¹). Leaf and tiller numbers in PTT1 and HCS at N7 and N14 were two to three times higher than those at N0. At harvest, the biomass yield in PTT1 was the highest, while the total grain number in HCS was the maximum. The leaf widths and total chlorophyll contents (SPAD units) of Azucena and LP increased with nitrogen application as well as photosynthetic pigment parameters; for example, plant senescence reflectance indices (PSRIs), structure-insensitive pigment indices (SIPIs), and modified chlorophyll absorption ratio indices (MCARIs) were highly related in the japonica varieties. PTT1 and HCS, both carrying the A allele at OsNRT1.1b, had better NUE than Azucena and LP with the G allele. HCS, overall, had better NUE than PTT1. The translation to grain yield of assimilates was remarkable in PTT1 and HCS compared with Azucena and LP. In addition, HCS converted biomass for a 75% higher yield than PTT1. The ability of HCS to produce high yields was achieved even at N7 nitrogen fertilization, manifesting efficient use of nitrogen.

Callus induction (CI) is a critical trait for transforming desirable genes in plants. A genome-wide association study (GWAS) analysis was conducted on the rice germplasms of 110 Indica rice accessions, in which three tissue culture media, B5, MS, and N6, were used for the CI of those rice panels’ mature seeds. Seven quantitative trait loci (QTLs) on rice chromosomes 2, 6, 7, and 11 affected the CI percentage in the three media. For the B5 medium, one QTL (qCI–B5–Chr6) was identified on rice chromosome 6; for the MS medium, two QTLs were identified on rice chromosomes 2 and 6 (qCI–MS–Chr2 and qCI–MS–Chr6, respectively); for the N6 medium, four QTLs were identified on rice chromosomes 6, 7, and 11 (qCI–N6–Chr6.1 and qCI–N6–Chr6.2, qCI–N6–Chr7, and qCI–N6–Chr11, respectively). Fifty-five genes were identified within the haplotype blocks corresponding to these QTLs, thirty-one of which showed haplotypes associated with different CI percentages in those media. qCI–B5–Chr6 was located in the same region as qCI–N6–Chr6.2, and the Caleosin-related family protein was also identified in this region. Analysis of the gene-based haplotype revealed the association of this gene with different CI percentages in both B5 and N6 media, suggesting that the gene may play a critical role in the CI mechanism. Moreover, several genes, including those that encode the beta-tubulin protein, zinc finger protein, RNP–1 domain-containing protein, and lysophosphatidic acid acyltransferase, were associated with different CI percentages in the N6 medium. The results of this study provide insights into the potential QTLs and candidate genes for callus induction in rice that contribute to our understanding of the physiological and biochemical processes involved in callus formation, which is an essential tool in the molecular breeding of rice.

Bacterial wilt, caused by Ralstonia solanacearum, is a major constraint to tomato production globally. To uncover resistance loci and develop efficient molecular tools for breeding, we conducted disease phenotyping over two growing seasons, which revealed consistent variation in resistance and moderate broad-sense heritability (H² = 0.22–0.28), suggesting a genetic basis. A genome-wide association study (GWAS) was performed on a diverse panel of 267 tomato accessions, evaluated against two R. solanacearum strains. A major resistance locus was identified on chromosome 12, with the strongest association observed at SNP S12_2992992, located within a gene encoding a leucine-rich repeat (LRR) receptor-like protein. Haplotype analysis indicated that the resistance-associated allele is relatively rare (~13.5%) in the population, underscoring its potential value in breeding programs. Functional validation in an F₂ population derived from a cross between the susceptible ‘Seedathip6’ and the resistant ‘Hawaii 7996’ confirmed that the TT genotype at S12_2992992 was significantly associated with enhanced resistance. A Kompetitive Allele Specific PCR (KASP) marker was developed for this SNP, facilitating cost-effective and high-throughput selection. Collectively, these findings establish S12_2992992 as a robust and functionally informative marker, offering a valuable tool for accelerating bacterial wilt resistance breeding in tomato through marker-assisted selection.