Ramularia leaf spot and Boll rot are affected differently by organic and inorganic nitrogen fertilization in cotton plants

Abstract

Background: In this work, the interaction among nitrogen fertilization using bovine manure, poultry manure, Jatropha curcas seed cake and urea, and the diseases Ramularia leaf spot (RLS) and Boll rot (BR), caused by Ramulariopsis pseudoglycines and Diplodia gossypina, respectively, on cotton plants (Gossypium hirsutum L.), was studied under field conditions. The intensity (incidence and severity in percentage) of RLS and the incidence (%) of BR were evaluated six times, starting in the reproductive stage B1 (first visible flower bud). A randomized complete block experimental design with a 4x4 factorial arrangement (fertilizers x dose), totaling 16 treatments were used. The disease progress was analyzed with the nonlinear Logistic and Gomperts models, obtaining the initial disease's epidemiological parameters (Y0) and progress rate (r). Results: Cotton plants fertilized with 100 kg N ha-1 of J. curcas seed cake and poultry manure with 100 and 200 kg N ha-1 showed an incidence between 16 and 21% of RLS. In contrast, plants fertilized with bovine manure presented the highest incidence of ramularia leaf spot (33%). Regarding factor B (dose), cotton plants fertilized with 50 kg N ha-1, showed a higher percentage of BR incidence, being different from those fertilized with the other doses. In the analysis of the interaction corresponding to the BR incidence, no response pattern was found in the doses for each fertilizer. No correlation was observed between the three health variables analyzed, finding probabilities between 0.002 and 0.892. In the temporal progress of RLS incidence, it was shown that fertilization with J. curcas seedcake and poultry manure was lower than the rest. In severity, the plants were fertilized by J. curcas seedcake concerning the rest. The progression curve of RLS severity temporarily increased similarly, observing that plants fertilized with higher doses reached a lower final proportion of the disease.Regarding the modeling of epidemics using the nonlinear Logistic and Gompertz models, the first model better represented the RLS, except for factor B, where none of the curves was significant. In the Logistic model, a lower amount of initial disease was found (Y0) of RLS, both in incidence (0.259) as in severity (0.081), in plants fertilized with J. curcas seed cake and poultry manure, compared to the rest. For the case of BR incidence, none of the nonlinear models used could be represented.Conclusions: Plants fertilized with 50 kg N ha-1, presented an incidence twice higher than those obtained with other fertilizers. The Logistic model better fits RLS, but no model was adapted to BR. Only the RLS epidemiological parameters were affected differently in this experiment compared to BR disease.