INTERRELATIONSHIP AMONG CHILO-PARTELLUS (SWINHOE) DAMAGE PARAMETERS AND THEIR CONTRIBUTION TO GRAIN-YIELD REDUCTION IN MAIZE (ZEA-MAYS L)

Understanding the relationship among the spotted stem borer (Chilo partellus) damage parameters and grain yield reduction on maize (Zea mays L.) will aid in elucidation of the most important damage parameters that reduce yield, and may consequently lead to development of functional criteria to quantify tolerance and resistance. Correlations, stepwise multiple regressions and path coefficient analyses were used to study the interrelationship among the three damage parameters (foliar lesions, dead heart and stem tunnelling) and their contribution to grain yield reduction using three separate groups of genotypes in trials conducted between 1990 and 1991. Foliar lesions and stem tunnelling were positively correlated. Reduction in the number of ears harvested due to larval infestation was the primary cause of grain yield loss. The combined effect of both number of ears and stem tunnelling accounted for 34%, 37% and 43% of yield reduction in the three groups of entries, while the additional contribution of any other trait was a maximum of 2%. Using path analysis, the direct effect of ear number and stem tunnelling on yield loss was consistently large and the direct effect of foliar lesion or dead heart was secondary when compared to that of stem tunnelling. When the effects of only the damage parameters were considered, foliar lesions, acting primarily via stem tunnelling, had the highest total indirect effects in all groups of entries. In effect, yield loss caused by the spotted stem borer is primarily due to stem tunnelling of the plants.