Effect of diammonium phosphate application on strigolactone production and Striga hermonthica infection in three sorghum cultivars

Striga hermonthica infection poses a major constraint to sorghum production in sub-Saharan Africa, and low soil fertility aggravates the S. hermonthica problem. Under mineral nutrient deficiency, the sorghum host secretes large quantities of strigolactones, signalling molecules, into the rhizosphere. These induce S. hermonthica seed germination and subsequent infection of the host roots. In a combination of field and glasshouse experiments, we analysed the effect of microdose applied diammonium hydrogen phosphate (DAP) fertiliser on production of strigolactones, S. hermonthica infection and yield of three different African sorghum genotypes (CGM-19/1-1, Lina-3, DouaG). The sorghum cultivars all produced the strigolactones sorgomol and 5-deoxystrigol, albeit in different quantity and ratio. Without fertiliser, high S. hermonthica infection and emergence occurred under both glasshouse and field conditions. DAP application reduced secretion of sorgomol and 5-deoxystrigol and reduced S. hermonthica germination (66–70%), emergence (49–73%) and dry biomass (90–96%) under glasshouse conditions. Under field conditions, DAP microdosing reduced S. hermonthica emergence by 40–84% and increased sorghum grain yield by 47–142%. Thus DAP application reduced secretion of strigolactones into the rhizosphere and S. hermonthica parasitism both under controlled and field conditions. Microdosing of DAP may prove to be an efficient and cost effective option to reduce S. hermonthica damage in sorghum in sub-Saharan Africa, particularly in combination with other control options, such as intercropping, use of organic fertiliser and hand pulling of S. hermonthica at flowering to achieve integrated S. hermonthica management