Towards management of fertilization to control wheat crown rot caused by Fusarium culmorum.

Wheat crown rot, caused by Fusarium culmorum, is becoming an increasing constraint to Moroccan wheat production for inducing grain yield losses that vary between 12 and 17%. This project was initiated in 2014 with the objective to develop a fertilizer management package to control this disease in durum wheat. The management strategy is based on the use of different combinations of nitrogen (N) fertilizer, ammonium nitrate (AN) or urea, in combination with with phosphorus (P) and potassium (K). Field experiments were established in November 2016 at three locations: two under rain-fed conditions (Sidi El Aidi and Jemaat Shaim) and one under supplemental irrigation (Khemis Zemamra). The experimental design was a strip plot with four blocks, where treatments included two levels of inoculation (Fusarium-inoculated or non-inoculated seeds). The inoculation treatment was crossed with six fertilizer treatments: 1) diammonium phosphate (DAP); 2) DAP + potassium sulfate (KS); 3) DAP +AN; 4) DAP + urea; 5) DAP + KS + AN; and 6) DAP + KS + urea.

Disease severity index (DSI) results for Jemaat Shaim found significantly lower values for treatments receiving DAP+KS, DAP+KS+AN, or DAP+KS+urea, with the average value being 0.24. The average DSI was 0.42 for DAP alone, DAP+AN, and DAP+Urea. The trend was similar for the number of whiteheads at Khemis Zemamra. A significant effect of fertilization was observed on the grain yield at Sidi El Aidi. The lowest yield was 0.74 t/ha for DAP+KS+AN and the highest yield was 1.2 and 1.3 t/ha for DAP+AN and DAP+KS, respectively. In contrast, K fertilization at planting reduced the thousand kernel weight (TKW) at Sidi El Aidi where disease severity had a significant impact, especially for DAP+KS and DAP+KS+AN that registered a TKW of 28 and 20 g, respectively. The grain quality, measured as vitreousness, was found to be dependent on N and K application.

A pooled data analysis, based on a qualitative regression analysis of grain yield with grain yield components, fertilization treatments and wheat crown rot disease components revealed that the important factors to consider were number of grains per ear, number of ears/m², disease severity, TKW, and number of whiteheads in order of importance. In this linear relationship, disease severity and number of whiteheads impacted grain yield negatively.