Abstract
The influence of different nitrogen and potassium ratios on mineral nutrition and resistance of tomato plants to leafminer fly attack was evaluated. Tomato variety Alambra F1 was grown to conduct the experiment in a randomized block design, with 4 repetitions, in a 5 × 5 factorial scheme, being 5 doses of nitrogen and 5 doses of potassium at levels 0, 50, 100, 150, and 200% for each nutrient and in a 5 × 5 factorial design, being 0, 0.5, 1, 1.5, and 2 for each ratio between nitrogen and potassium (N/K) in the analyses on the leafminer fly. For infestation, the 3rd or 4th leaf was selected and covered with a Voile-type cloth bag with 10 leaf fly adults for 24 hours. The confinement test took place on the 3rd or 4th leaf, where nitrogen and potassium contents, larval and pupal duration and viability, longevity and sex ratio of the adults were also analyzed. The tomato plants showed increasing levels of nitrogen and potassium as their respective levels increased in the combinations studied. The N/K 1/1 ratio showed unfavorable averages for the insect as egg viability and/or larval development of Liriomyza sativae, indicating a possible induced resistance of the tomato plants to the leafminer fly.
Highlights
An increase in N contents was observed on the response surface as an increase in the combinations of nitrogen and potassium was obtained up to the highest level studied for both nutrients
Silva et al (2016) stated that when potassium fertilization is insufficient, this can cause increased NH4+ adsorption by the soil, negatively influencing N availability to plants. These findings are due to the fact that K+ competes with NH4+ for soil exchange complex sites, and higher levels of potassium in the soil would leave more NH4+ free in solution for uptake by the tomato plant
Another fact that may have contributed to the influence of potassium levels on nitrogen contents was that the amount of nitrogen found in the leaf dry mass (g kg-1) was lower than the amount of K in the leaf dry mass (g kg-1), indicating that, proportionally, there was a greater uptake of potassium and this may have resulted in a greater influence of this nutrient on nitrogen
Summary
Potassium is taken up in larger amounts when compared to other nutrients, and together with nitrogen, which has a prominent role in protein production, contribute directly to fruit yield and quality (Felix et al, 2015) and has a prominent role as an enzyme activator (Butzke, 2019). The unbalanced supply of these nutrients to tomato plants favors, to some degree, that their tissues become food for phytophagous insects (Becker et al, 2016). Under these conditions, the leafminer fly feeds on the leaves of the tomato plant, reducing its photosynthetic capacity, affecting the entire plant. As a consequence of this attack, the severely attacked leaves dry out and fall, exposing the fruit to solar radiation, decreasing its commercial viability, affecting the quality of its production (Oliveira, 2014)
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