Path coefficient and regression analysis of the effects of leaf and panicle blast on tropical rice yield

Abstract

Three lowland field experiments were conducted to assess the effects of blast on rice growth, yield components and yield loss. Different levels of blast epidemics were obtained by application of different amounts of inoculum, environment manipulation and fungicide applications. The leaf blast (LB) severity obtained ranged from 0 to 16% actual lesion area and panicle blast (PB) incidence ranged from 0 to 97%. Analysis of blast effects on rice growth indicated that both LB and PB had a stronger negative effect on plant height than other measured plant parameters and that PB had a stronger influence than LB in increasing the percentage of unfilled grains, to reduce grain yield. Both LB and PB had significant effects on yield. High LB severity almost always resulted in high PB incidence; however, even when LB severity was low, high PB incidence could still be obtained provided that favourable conditions for blast infection were present. Under field conditions, yield loss due to blast can be estimated with > 70% confidence by knowing the percentage diseased leaf area at maximum tillering and the PB incidence at harvest.