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N and K interactions in cucumber plants artificially inoculated with P. cubensis

Background: The use of fungicides in order to manage plant diseases can potentially pose a risk to the environment which could lead to adverse impacts to human health. An alternative practice for efficient plant protection need to be found. Nevertheless, the positive effect of host nutrition to disease incidence is well documented for many crops. This study examined the efficacy of N and K fertilization compared to fungicide applications in controlling downy mildew of cucumber plants. The relationship between disease intensity, soil nutrients’ and cucumber leaves was also assessed. Methods: Cucumber plants grown in pots were treated with two N levels (200 and 300 ppm) and three levels of K (200, 300 and 400 ppm) along with two applications of Aliette 80 WG (protective and curative action) in a randomized block design. Inoculation of cucumber leaves with Pseuperonospora cubensis was carried out. Downy mildew development assessed at various intervals along with soil and leaf nutrient status of the plants. Experimental data were submitted to ANOVA. Results: The results demonstrated that downy mildew declined with increasing rates of K when N applied in low levels while at high N dose disease was elevated as K was increased. High disease severity was observed in cucumber plants grown under low levels of N and K, at early growth of the pathogen while at late disease stage, high rates of both N and K exhibited increased infection. Even though the preventative fungicide application gave best control of downy mildew, its effectiveness on inhibition of P. cubensis growth did not differ from the impact of fertilization with low N and high K doses, as disease was spreading. Conclusion: This work concluded that the application of N and K through inorganic fertilizers to cucumber plants had a suppressing effect on downy mildew disease. The positive impact of the correct management of nutrients could make integrative plant nutrition an essential component in sustainable agriculture.