The objective of this study was to evaluate chlorophyll a fluorescence as a stress indicator in Calophyllum brasiliense Cambess seedlings grown with different concentrations of abscisic acid (ABA) under intermittent water deficit condition: daily irrigation without ABA (I); daily irrigation + 10 μM ABA (I 10); daily irrigation + 100 μM ABA (I 100); suspension of daily irrigation without ABA (SI); suspension of daily irrigation + 10 μM ABA (SI 10) and  suspension of daily irrigation + 100 μM ABA (SI 100). The intermittent water deficit reduces water status and impairs the photochemical apparatus functioning and seedling quality. The fluorescence measurements helped identify the stress condition of water deficit in the cultivation of C. brasiliense and the beneficial effect of the application of 10 μM of ABA in minimizing stress and facilitating the recovery of seedlings after re-irrigation, while maintaining the integrity and function of the photosynthetic apparatus.

Silicon (Si) is a beneficial element that can mitigate effects of water stress on photosynthetic metabolism and plant growth. Thus, the aimed was to evaluate the effect of Si in mitigating the stressful effect of water deficit and flooding in Eugenia myrcianthes Nied. seedlings. The seedlings received three silicon doses (0, 2, and 4 mmol) and were subjected to two water regimes (I – continuous irrigation and S – water fluctuation, characterized as water stress obtained by two cycles of water regimes: irrigation suspension and flooding). Each cycle was ended when the seedlings had a photosynthetic rate close to zero (P0) when the stressful irrigation condition was normalized until the photosynthetic rate reached the values of the control seedlings (REC). The evaluations were carried out in five periods: T0 – initial seedling condition; 1st and 2nd P0; and 1st and 2nd REC. The E. myrcianthes seedlings reached P0 at 22 and 50 days under water deficit and flooding, respectively. Water stress caused damage to photochemical activities in photosystem II. E. myrcianthes is a species sensitive to water stress, but capable of adjusting to water fluctuation, and the application of 2 mmol Si contributed to the regulation of gas exchange, photochemical yields, and growth of this species at the deficit and flooding phases. We emphasize that E. myrcianthes seedlings have potential for resilience due to physiological plasticity, regardless of the silicon application.

This study aimed to evaluate the effect of exogenous application of salicylic acid on the photosynthetic metabolism and quality of Eugenia myrcianthes seedlings under water deficit and their recovery potential after rehydration. Two water regimes were evaluated, as follows: control - plants irrigated daily (I) and water deficit (S), with and without the application of 400 mg L–1 of salicylic acid (SA), totaling four treatments. Seedlings were evaluated at three times: at the beginning of the experiment (T0), that is, when the irrigation was interrupted; when the photosynthetic rate reached values close to zero (P0 - 15 days after irrigation interruption), that is, when irrigation restarted; and when the photosynthetic rate was recovered (REC). Eugenia myrcianthes seedlings were negatively affected when subjected to water restriction; salicylic acid attenuated the damage to the photosynthetic apparatus by acting positively on the relative water content in the leaves, SPAD index, photosynthetic metabolism, superoxide dismutase and peroxidase enzyme activity, and seedling growth in P0. Eugenia myrchiantes presented potential for recovery after resumption irrigation. The application of SA contributed to the maintenance of gas exchanges, photochemical processes and quality of E. myrcianthes seedlings during and after water deficit, suggesting the promotion of plant resistance induction.

Intermittent water defi cit decreased plant water status and gas exchange. Application of ABA preserved the photosynthetic apparatus. Antioxidant activity increased depending on the enzyme, ABA concentration and plant part.

In South America, maize (Zea mays L., Poaceae) crops are commonly infested with larvae of Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), known as voracious leaf feeders, as well as by larvae of Diabrotica speciosa (Germar) (Coleoptera: Chrysomelidae), a pest that destroys maize root systems. Despite the relevance of these insects to maize fields, there is no information available about the effects of these herbivores on one another. Therefore, this study aimed to evaluate in different maize varieties: (1) the influence of previous leaf consumption by S. frugiperda on D. speciosa larval weight and survival, (2) effects of previous root attack by D. speciosa on S. frugiperda larval weight and survival, and (3) the relationship between peroxidase and superoxide dismutase (resistance-related enzymes) and maize resistance to the pests. One fifth instar S. frugiperda was released per potted maize plant at vegetative stage 4 (V4), and 24 h later plants were infested with 25 D. speciosa larvae. One set of plants was infested with D. speciosa only, and 16 days later whorl leaf sections were brought to the laboratory and offered to S. frugiperda neonate larvae. Performance of both insect pests was determined based on larval weight and survival. Uninfested plants of variety Maisena were susceptible to both herbivores. However, plants of this variety pre-infested with S. frugiperda disfavored D. speciosa larval survival. Similarly, plants of variety Maisena pre-infested with D. speciosa adversely affected S. frugiperda larval growth. Nevertheless, this induction of resistance was inhibited when the plant was also pre-infested with S. frugiperda. In most cases, peroxidase and superoxide dismutase did not seem to play a role in mediating resistance to the pests. Overall, variety Maisena appears as a template for the development of maize genotypes expressing induced resistance. The potential of some varieties regarding constitutive resistance is also discussed.