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Background C:N:P homeostasis in plants guarantees optimal levels of these nutrients in plant metabolism. H However, one of the causes to the effects of deficit irrigation is the loss of C:N:P homeostasis in leaves and stems that causes reduction in the growth of sugarcane. Being able to measure the impact of water deficit on C:N:P homeostasis in plants from the stoichiometric ratios of the concentrations of these nutrients in leaves and stems. This loss causes a decrease in nutritional efficiency, but can be mitigated with the use of silicon. Silicon favors the homeostasis of these nutrients and crop productivity. The magnitude of this benefit depends on the absorption of Si by the plant and Si availability in the soil, which varies with the type of soil used. Thus, this study aims to evaluate whether the application of Si via fertigation is efficient in increasing the absorption of Si and whether it is capable of modifying the homeostatic balance of C:N:P of the plant, causing an increase in nutritional efficiency and consequently in the production of biomass in leaves and stems of sugarcane ratoon cultivated with deficient and adequate irrigations in different tropical soils. Results Water deficit caused biological losses in concentrations and accumulation of C, N, and P, and reduced the nutrient use efficiency and biomass production of sugarcane plants cultivated in three tropical soils due to disturbances in the stoichiometric homeostasis of C:N:P. The application of Si increased the concentration and accumulation of Si, C, N, and P and their use efficiency and reduced the biological damage caused by water deficit due to the modification of homeostatic balance of C:N:P by ensuring sustainability of the production of sugarcane biomass in tropical soils. However, the intensity of attenuation of such deleterious effects stood out in plants cultivated in Eutrophic Red Oxisols. Si contributed biologically by improving the performance of sugarcane ratoon with an adequate irrigation due to the optimization of stoichiometric ratios of C:N:P; increased the accumulation and the use efficiency of C, N, and P, and promoted production gains in biomass of sugarcane in three tropical soils. Conclusion Our study shows that fertigation with Si can mitigate the deleterious effects of deficient irrigation or potentiate the beneficial effects using an adequate irrigation system due to the induction of a new stoichiometric homeostasis of C:N:P, which in turn improves the nutritional efficiency of sugarcane cultivated in tropical soils.

Background In many regions of the world, K is being depleted from soils due to agricultural intensification a lack of accessibility, and the high cost of K. Thus, there is an urgent need for a sustainable strategy for crops in this environment. Si is an option for mitigating stress due to nutritional deficiency. However, the underlying effects of Si in mitigating K deficiency C:N:P homeostasis still remains unknown for bean plants. This is a species of great worldwide importance. Thus, this study aims to evaluate whether i) K deficiency modifies the homeostatic balance of C, N and P, and, if so, ii) Si supply can reduce damage caused to nutritional stoichiometry, nutrient use efficiency, and production of dry mass in bean plants. Results K deficiency caused a reduction in the stoichiometric ratios C:N, C:P, and P:Si in shoots and C:N, C:P, C:Si, N:Si, and P:Si in roots, resulting in a decrease in K content and use efficiency and reducing biomass production. The application of Si in K-deficient plants modified the ratios C:N, C:Si, N:P, N:Si, and P:Si in shoots and C:N, C:P, C:Si, N:Si, N:P, and P:Si in roots, increasing the K content and efficiency, reducing the loss of biomass. In bean plants with K sufficiency, Si also changed the stoichiometric ratios C:N, C:P, C:Si, N:P, N:Si, and P:Si in shoots and C:N, C:Si, N:Si, and P:Si in roots, increasing K content only in roots and the use efficiency of C and P in shoots and C, N, and P in roots, increasing the biomass production only in roots. Conclusion K deficiency causes damage to the C:N:P homeostatic balance, reducing the efficiency of nutrient use and biomass production. However, Si is a viable alternative to attenuate these nutritional damages, favoring bean growth. The future perspective is that the use of Si in agriculture in underdeveloped economies with restrictions on the use of K will constitute a sustainable strategy to increase food security.

Root-knot nematodes (RKNs), Meloidogyne spp., are the most economically important plant parasites with a worldwide distribution and a very wide host spectrum. The use of rhizobacteria for biocontrol has seen a marked increase in recent years, with particular emphasis on members of the Bacillaceae family in Brazil. This work reports on five years of experience using Bacillus-based products as nematicides, including both commercial and experimental formulations. Trials on cotton (200–300 mL/100 kg of seeds) against M. incognita race 3 produced inconsistent results: one trial achieved approximately 50% control, while another showed no significant effect. In soybean, Bacillus-based biological products (200–300 mL/100 kg) were able to reduce the final population of M. javanica and M. incognita by an average of approximately 30%, although in some cases, no effect was observed. The use of different doses of a product containing the RTI 545 strain (B. thuringiensis) resulted in control efficiencies of approximately 60–80% at a dose of 500 mL/100 kg, when applied as a seed treatment in soybean. This dose is too high to employ in field conditions. In tomato crop, strain S2538 of Priestia aryabhattai and strain RTI 545 (150 mL/100 kg) reduced the final population of M. incognita by 45–50%, confirming the results obtained in previous trials. Additionally, microscopic observations of Bacillus spp. against Meloidogyne spp. in soybean were made during histopathological studies. The bacteria were found to colonize root tissues early, including the cortex and vascular cylinder, probably producing chemical compounds and later disrupting giant cells. This microscopic observation suggests a mechanism aligned with induced resistance. Currently, biological products must be used in integrated management, such as resistant varieties, crop rotation, and other agronomic practices that aim to balance the physical, chemical and biological conditions of soils.

The Mi- 1.2 gene confers resistance to a wide range of Meloidogyne species, being the most important resistance factor employed in tomato breeding so far. However, many aspects related to the interaction of Mi- 1.2-carrying tomato cultivars and virulent/avirulent Meloidogyne populations have not yet been clarified. Herein, comparative histopathological analyses were carried after inoculation of the homozygous ( Mi -1.2/ Mi -1.2) tomato rootstock ‘Guardião’ and the susceptible cultivar ‘Santa Clara’ ( mi -1.2/ mi -1.2) with virulent and avirulent populations of M. javanica. In the susceptible control, it was possible to visualize second stage juveniles (J2) of avirulent population and feeding sites from 2 to 30 days after infection (DAI) with females reaching maturity at 24-34 DAI. In the resistant rootstock, the Mi- 1.2 gene-mediated resistance was related mainly to early defense responses (pre-infection and hypersensitive reaction), which led to an immunity-like phenotype that completely prevented the reproduction of the avirulent Meloidogyne population. On the other hand, J2s of the virulent M. javanica population were able to penetrate roots much more than the avirulent population, migrated and developed normally, showing intense and similar pattern of penetration from 4 to 34 DAI in the root tissues of both resistant and susceptible tomato genotypes. The total numbers of J2, J3, J4, and females counted in ‘Santa Clara’ for the virulent population of M. javanica were higher than in ‘Guardião’.

Potassium (K) deficiency affects physiological performance and decreases vegetative growth in common bean plants. Although silicon (Si) supplied via nutrient solution or foliar application may alleviate nutritional stress, research on the bean crop is incipient. Thus, two experiments were carried out: initially, a test was performed to determine the best source and foliar concentration of silicon. Subsequently, the chosen Si source was supplied in nutrient solution via roots or foliar application to verify whether Si supply forms are efficient in alleviating the effects of K deficiency. For these purposes, a completely randomized 2 × 3 factorial design was used, with two levels of K: deficient (0.2 mmol L −1  of K) and sufficient (6 mmol L −1  of K); and Si: in nutrient solution via roots (2 mmol L −1  of Si) or foliar application (5.4 mmol L −1  of Si) and control (0 mmol L −1  of Si). Our findings revealed that Si supplied via foliar spraying using the source of sodium silicate and stabilized potassium at a concentration of 5.4 mmol L −1 was agronomically viable for the cultivation of bean plant. K deficiency, when not supplied with silicon, compromised plant growth. Moreover, root-and-foliar-applied Si attenuated the effects of K deficiency as it increased chlorophylls and carotenoids content, photosynthetic activity, water use efficiency and vegetative growth. For the first time, the role of Si to mitigate K deficiency in the bean crop was evidenced, with a view to further research on plants that do not accumulate this beneficial element.

Potassium (K) deficiency in maize plants damages the nutritional functions of K. However, few studies have investigated the influence of K on C:N:P stoichiometry, the nutritional efficiency of these nutrients, and whether the mitigating effect of Si in plants under stress could act on these nutritional mechanisms involved with C, N, and P to mitigate K deficiency. Therefore, this study aimed to evaluate the impact of K deficiency in the absence and presence of Si on N and P uptake, C:N:P stoichiometric homeostasis, nutritional efficiency, photosynthetic rate, and dry matter production of maize plants. The experiment was conducted under controlled conditions using a 2 × 2 factorial scheme comprising two K concentrations: potassium deficiency (7.82 mg L −1 ) and potassium sufficiency (234.59 mg L −1 ). These concentrations were combined with the absence (0.0 mg L −1 ) and presence of Si (56.17 mg L −1 ), arranged in randomized blocks with five replicates. Potassium deficiency decreased stoichiometric ratios (C:N and C:P) and the plant’s C, N, and P accumulation. Furthermore, it decreased the use efficiency of these nutrients, net photosynthesis, and biomass of maize plants. The results showed that Si supply stood out in K-deficient maize plants by increasing the C, N, and P accumulation. Moreover, it decreased stoichiometric ratios (C:N, C:P, N:P, C:Si, N:Si, and P:Si) and increased the efficiencies of uptake, translocation, and use of nutrients, net photosynthesis, and dry matter production of maize plants. Therefore, the low nutritional efficiency of C, N, and P caused by K deficiency in maize plants can be alleviated with the supply of 56.17 mg L −1 of Si in the nutrient solution. It changes C:N:P stoichiometry and favors the use efficiency of these nutrients, which enhances the photosynthesis and sustainability of maize.

Very effective genetic control of some root-knot nematode (RKN) species (Meloidogyne spp.) is obtained by the employment of the tomato (Solanum lycopersicum L.) dominant Mi-1.2 gene. However, the phenotypic expression conferred by the Mi-1.2 gene may be impaired by high soil temperatures (above 28 °C) and by previously reported virulent RKN species and/or populations. Here, a putative Mi-1.2 gene-virulent RKN population was found inducing severe gall symptoms in roots of the tomato rootstock ‘Guardião’ (a homozygous Mi-1.2 hybrid of S. lycopersicum × S. peruvianum) under protected crop conditions in Southern Brazil. Females were extracted from severely infected roots displaying large galls and used for biochemical characterization of α-esterase (EST) and confirmed by SCAR markers. Additional pathogenicity assays were carried out in order to confirm the virulence (= resistance-breaking) feature of this RKN population by employing other or the same Mi-1.2 gene-carrying rootstocks. This virulent RKN population was identified as M. javanica (EST J3 and J2). The pathogenicity tests confirmed that this M. javanica population can overcome the Mi-1.2 resistance gene, and it is able to induce severe root-gall symptoms and to reproduce in two dominant resistant rootstocks (‘Muralha’ and ‘Guardião’) under greenhouse conditions. In addition, an initial inoculum of 2000–7000 eggs was considered ideal for future studies with the virulent M. javanica population. It is the first report of a Mi-1.2 gene-virulent M. javanica population in Brazil, which may represent a potential threat to the tomato agribusiness sector.

Studies with silicon (Si) in sugarcane indicate a greater response in productivity in plants under stress, and the underlying mechanisms of Si in the crop are poorly reported. In this context, the benefits of Si in the crop’s stem production are expected to occur at the C:N:P stoichiometry level in plant tissues, benefiting plants with and without stress. However, the extension of this response may vary in different soils. Thus, this research aimed to evaluate if fertigation with Si modifies the C:N:P stoichiometry and if it can increase sugarcane’s nutritional efficiency and vegetative and productive parameters. Therefore, three experiments were installed using pre-sprouted seedlings to cultivate sugarcane in tropical soils belonging to the Quartzarenic Neosol, Eutrophic Red Latosol, and Dystrophic Red Latosol classes. The treatments comprised a 2 × 2 factorial scheme in each soil. The first factor was composed without water restriction (water retention = 70%; AWD) and with water restriction (water retention = 35%; PWD). The second factor presented Si concentrations (0 mM and 1.8 mM) arranged in randomized blocks with five replications. Fertigation with Si increases the Si and P concentration, the C and N efficiency, the C:N ratio, and the dry mass production. However, it decreases the C and N concentration and the C:P, C:Si, and N:P ratios in sugarcane leaves and stems regardless of the water regime adopted in the three tropical soils. Cluster and principal components analysis indicated that the intensity of the beneficial effects of Si fertigation on sugarcane plants varies depending on the cultivation soil and water conditions. We found that Si can be used in sugarcane with and without water stress. It changes the C:N:P homeostasis enough to improve the nutritional efficiency of C, P, N, and, consequently, the dry mass accumulation on the stems, with variation in the different cultivated soils.

Root-knot nematodes (RKNs), Meloidogyne spp., represent a serious threat to coffee production in Brazil. Although Meloidogyne exigua is widely spread in southern Minas Gerais, a major region of coffee production, no major yield losses have been reported for this nematode. Due to the risk of introducing other more aggressive nematode species into coffee fields, such as M. incognita and M. paranaensis, a survey for Meloidogyne spp. in coffee fields was carried out in this region. Based on esterase phenotypes and SCAR markers, RKNs were detected in 37.7% of samples, of which M. exigua and M. incognita were present in 31.1% and 2.2% of samples, respectively. Mixed populations were observed in 4.4% of samples, i.e. M. exigua + M. incognita + M. paranaensis, or M. exigua + M. incognita. Meloidogyne exigua was the most prevalent species and occurred in majority of counties. Using SCAR markers, M. incognita is reported for the first time in coffee fields located in three counties (Três Pontas, Coqueiral and Aguanil) in southern Minas Gerais. Nematode containment strategies are recommended for this region.

Seven root-knot nematodes (RKN), including Meloidogyne exigua, M. incognita, M. paranaensis, M. enterolobii, M. arabicida, M. izalcoensis and M. arenaria are major pathogens of coffee crop in the Americas. Species-specific primers for their identification have been developed for five of them and constitute a fast and reliable method of identification. Here we report a PCR-based assay for specific detection of M. arabicida and M. izalcoensis. Random Amplified Polymorphic DNA fragments specific for these two species were converted into sequence characterized amplified region (SCAR) markers. PCR amplification using the SCAR primers produced a specific fragment of 300 bp and 670 bp for M. arabicida and M. izalcoensis, respectively, which were absent in other coffee-associated Meloidogyne spp. tested. SCAR primers also allowed successful amplification of DNA from single second-stage juveniles (J2), males and females. In addition, these primers were able to unambiguously detect the target species in nematode suspensions extracted from soil and roots samples, in different isolates of the same species or when used in multiplex PCR reactions containing mixtures of species. These results demonstrated the effectiveness of these SCAR markers and their multiplex use with those previously developed for M. exigua, M. incognita, M. paranaensis, M. enterolobii and M. arenaria constitute an essential detection tool. This diagnostic kit will contribute for specific J2 identification of the major RKN infecting coffee from field samples in the Americas.