Effect of potash fertilization on Helminthosporium leaf blight severity in wheat, and associated increases in grain yield and kernel weight

Helminthosporium leaf blight (HLB), caused by Cochliobolus sativus and/or Pyrenophora tritici-repentis, is a serious disease of wheat (Triticum aestivum L.) in the warm lowlands of South Asia. A field study was conducted using three wheat varieties (Bhrikuti, BL1473, and Kanchan) during the 2002 and 2003 wheat seasons at Rampur, Nepal, where HLB is a serious problem every year. The objective was to determine the effect of different levels of potassium (K) on reducing HLB severity on wheat and the associated increases in grain yield and thousand-kernel weight (TKW). The experiment was conducted in a split-split-plot layout in a randomized block with three replicates. Main, sub-, and sub-sub-plots consisted of three levels of K (0, 30, and 60 kg ha−1 of K2O), fungicide spray (protected and non-protected), and three wheat varieties, respectively. Multiple HLB scores were recorded to calculate the area under the disease progress curve (AUDPC). Application of 30 and 60 kg ha−1 of K2O reduced AUDPC by 43 and 51%, respectively. These reductions in AUDPC increased grain yield by 53 and 61% in 2002 and 78 and 125% in 2003. The corresponding gains in TKW were 46 and 42% in 2002 and 27 and 45% in 2003. Seed infection went from 38 to 21% in 2002 due to potash application; the reduction in 2003 was non-significant. All three wheat varieties showed reductions in disease severity due to K application in both years, which resulted in increased grain yield and TKW. Applying 30 kg ha−1 of K2O produced grain yields comparable to those in fungicide-protected plots without K. This underlines the importance of applying K2O to reduce grain yield losses due to HLB when fungicide is either unavailable or too costly, a situation frequently encountered by resource-poor farmers in the Eastern Gangetic Plains of South Asia. These findings may be useful in developing an integrated HLB management strategy in South Asia, and elsewhere, as part of a holistic crop management approach.