Recent Advances in Legume Crop Protection

The legume family is economically important and is one of the most important sources of starch, protein, oil, and vegetables for human food around the world, playing an irreplaceable role in guaranteeing human food security. However, the frequent occurrence of diseases, pests, and weeds is one of the important factors restricting the high and stable yield of legume crops [1]. Major diseases of legumes include root rots, bacterial blights, and mosaic diseases. In addition, damage caused by malignant weeds, nematodes, and sap-sucking/-chewing insects is also included as a constraint on legume production [2]. This Special Issue is focused on 13 selected topics (12 articles and 1 editorial) from different universities and research institutes. The research fields covered include mechanisms of resistance to pests and diseases, identification and monitoring of diseases, alternative control strategies, weed management, and drone-mounted multispectral imaging technology. Current problems in the prevention and control of legume crop diseases, pests, and weeds are discussed with a view to providing subsequent research and applications of key pest- and disease-monitoring and -control technologies with a reference point.

Disease and insect resistance of soybean cultivars are extremely important and effective measures for controlling soybean diseases and pests [3]. The following four papers cover relevant topics:

Contribution 1: Raza et al. from Junyi Gai’s team used resistant (Kefeng-1) and susceptible (NN1138-2) soybean cultivars inoculated with SMV-SC4, and transcriptional analyses at 0, 6, 24, and 48 h post-inoculation identified 1,201 core differentially expressed genes (DEGs). Most DEGs were activated early in the resistant cultivar. Gene ontology analysis revealed enriched DEGs in three key functional categories contributing to resistance: signal transduction, oxidoreductase activity, and response to auxin. These DEGs exhibited significantly higher differential expressions in Kefeng-1 versus NN1138-2. This study elucidates molecular networks underlying soybean resistance to SMV, providing crucial insights for developing virus-resistant soybean cultivars.

Contribution 2: Antwi-Boasiako et al. utilized two RIL populations, namely ZM6 and MN, to identify quantitative trait loci (QTLs) associated with red crown root resistance in soybeans. In total, 15 and 14 QTLs were found to be related to RCR resistance in ZM6 and MN populations, respectively. Six ‘QTL hotspots’ for resistance to RCR from the ZM6 and MN RIL populations were detected on chromosomes 1, 7, 10, 11, 13, and 18. Through gene annotations, gene ontology enhancement, and RNA sequencing assessment, 23 genes located within six ‘QTL Hotspots’ were found as potential candidate genes that could provide resistance to red crown root in soybeans.

Contribution 3: Murodova et al. used 96 chickpea accessions from ICARDA infected with fusarium wilt (FW). Six pathogenic species (Neocosmospora solani, N. nelsonii, N. falciformis, N. brevis, Fusarium brachygibbosum, and F. gossypinum) were identified by molecular analysis (targeting ITS, *tef1-α*, and tub2 regions). Genetic diversity assessment using 69 polymorphic SSR markers revealed 191 alleles across all markers. Association mapping (employing GLM and MLM approaches) identified five consistent marker–trait associations for FW resistance. This study represents the first association mapping for FW resistance in ICARDA chickpeas, thus identifying key genomic regions for targeted resistance breeding to enhance global chickpea sustainability.

Contribution 4: Soybean ‘Zhengqing’ (or namely stay-green syndrome) is a major issue that causes soybean yield reduction in North China [4]. Wang D. et al. investigated differentially expressed genes (DEGs) in the sensitive soybean variety (HD0702) impacted by/without ‘Zhengqing’ (1,858 DEGs in the pods and 2,814 DEGs in the leaves). The chlorophyll content of the pods increased, soluble sugar levels significantly increased, whereas indole-3-acetic acid and abscisic acid decreased.

The identification and monitoring of soybean diseases have always presented a challenge to producers [5]. Three papers cover topics relevant to this subject, including rot, seed, and foliar diseases.

Contribution 5: As a soil-borne disorder, soybean root rot is driven by a complex of pathogens that threaten soybean production worldwide. The pathogenic fungal strains from Heilongjiang Province were identified as Fusarium oxysporum, F. graminearum, F. asiaticum, Pythium macrosporum, and Rhizoctonia solani, through morphological and molecular identification. Among them, F. oxysporum was the dominant species. The application of fludioxonil and pyraclostrobin had better control effects for F. asiaticum.

Contribution 6: Wang Y. et al. sampled 14 soybean cultivars and profiled their seed-borne microbiota with both conventional assays and high-throughput sequencing. The results indicated that seeds sourced from Jilin Province carried the greatest abundance of fungi and bacteria, followed by those from Liaoning and Heilongjiang Province. Characterizing these microbial communities establishes a foundation for seed quarantine protocols and disease-management strategies.

Contribution 7: Meng et al. found that the green normalized difference vegetation index could be used to monitor the soybean bacterial blight disease using drone-mounted multispectral imaging. The soybean yield loss was significantly higher at disease grade four for this disease. This approach leverages a random-forest model to survey disease classes and predict yield loss, laying the groundwork for future precision plant-protection strategies.

This Special Issue contains five papers that explore selected issues related to the integrated management of soybean diseases, pests, and weeds.

Contribution 8: For the sustained control of soybean root rot, Liu et al. have made breakthroughs. The researchers developed an innovative strategy, where a wheat–straw-fiber-based mulch film coated with carbendazim and chitosan mixture was prepared through a bar-coating technology. This special film achieved the desired physical properties and could effectively inhibit the growth of F. solani and boost soybean growth.

Contribution 9: In the coming period, alternative solutions of chemical control will be investigated, moving from artificially synthesized chemical insecticides to plant-based insecticides. The study by Niu et al. proposed four alternative essential oils (marjoram oil, clary sage oil, perilla leaf oil, and spearmint oil) against an emerging pest, Thrips flavus, in soybean fields in Northeast China. Linalool, isopropyl myristate, limonene, and carvone were the primary chemical constituents of these essential oils. The spearmint oil was significantly attractive to female adults in the olfactory test, indicating its potential for developing a thrips attractant.

Contribution 10: The whitefly (Bemisia tabaci) represents a cryptic species complex and ranks among the world’s most damaging pests, owing to its extensive host range and global reach. Alvarez et al. assessed the development and survival of the Mediterranean biotype on soybean, common bean, cotton, bell pepper, and tomato across multiple temperatures. Their findings show that conditions suitable for this biotype prevail throughout much of Brazil, especially in cropping systems marked by heavy insecticide use. These outcomes are pivotal for forecasting the Mediterranean biotype’s establishment and spread across Brazil’s varied climatic zones.

Contribution 11: Yangui et al. explored the use of discrete choice experiments to analyze farmers’ decision-making preferences in integrated Orobanche management and their willingness to pay for different control measures. It highlights significant variability in farmer acceptance of these measures, influenced by factors such as their financial situation and the severity of Orobanche infestation.

Contribution 12: Pamungkas et al. evaluated the efficacy and selectivity of three pre-emergence herbicides (pendimethalin, s-metolachlor, and flumioxazin) on dominant soybean weeds in Northeast Thailand across rainy (2023) and dry (2024/25) seasons, using two soybean varieties. They proposed that season-specific herbicide selection is critical. CM60 is better adapted for herbicide use under Thai conditions. Manual weeding remains the gold standard, but herbicides like s-metolachlor offer viable alternatives. Cyperus rotundus requires targeted management due to its persistence.

In summary, the 12 articles in this Special Issue collectively underscore the critical need for integrated management of disease, pests, and weeds in legume crops. These findings will provide valuable strategies to improve the productivity of legume crops, from elucidating the identification and monitoring of diseases, mining for resistance genes, to revealing crop resistance mechanisms to pests and diseases, as well as multiple control measures for pests, diseases, and weeds. Given the intensification of crop diseases and pests caused by global climate change and changes in planting structures, the adoption of integrated management theories and methods for diseases, pests, and weeds remains crucial for ensuring food security and the sustainable development of agriculture [6,7].