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 par tellus) damage parameters and grain yield reduction on maize (Zea mays L.) will aid in elucidation of the most important damage parameters t hat reduce yield, and may consequently lead to development of function al criteria to quantify tolerance and resistance. Correlations, stepwi se multiple regressions and path coefficient analyses were used to stu dy the interrelationship among the three damage parameters (foliar les ions, dead heart and stem tunnelling) and their contribution to grain yield reduction using three separate groups of genotypes in trials con ducted between 1990 and 1991. Foliar lesions and stem tunnelling were positively correlated. Reduction in the number of ears harvested due t o larval infestation was the primary cause of grain yield loss. The co mbined effect of both number of ears and stem tunnelling accounted for 34%, 37% and 43% of yield reduction in the three groups of entries, w hile the additional contribution of any other trait was a maximum of 2 %. Using path analysis, the direct effect of ear number and stem tunne lling on yield loss was consistently large and the direct effect of fo liar lesion or dead heart was secondary when compared to that of stem tunnelling. When the effects of only the damage parameters were consid ered, foliar lesions, acting primarily via stem tunnelling, had the hi ghest total indirect effects in all groups of entries. In effect, yiel d loss caused by the spotted stem borer is primarily due to stem tunne lling of the plants.