Quantification of the relationship between strigolactones and Striga hermonthica infection in rice under varying levels of nitrogen and phosphorus

Strigolactone exudation, as well as Striga hermonthica germination and attachment, was studied under different levels of nitrogen (N) and phosphorus (P) in two cultivars of rice (IAC 165 and TN 1). Exudation of strigolactones by rice was the highest under mineral-deficient conditions, whereas increasing N and P dose reduced the amount of strigolactones in the exudates. Deficiency of P led to the highest strigolactone exudation, when compared with N or NP deficiency. Production of strigolactones differed strongly between the two cultivars. IAC 165 produced about 100-fold higher amounts than TN 1 of 2'-epi-5-deoxystrigol, orobanchol and three new strigolactones. Across all N and P treatments, a positive relationship was found between the amount of strigolactones in the exudates of both cultivars and in vitro S. hermonthica germination. These results show that the positive effect of fertiliser application in S. hermonthica control is, at least partly, because of the suppression of strigolactone production and hence of S. hermonthica germination and subsequent attachment. This warrants further research into practical application. Maintaining suitable N and P nutrient status of soil through fertiliser use might be a promising strategy to reduce damage in cereals by this notorious weed.