Penetration resistance of second above ground internode in V6–10 stage maize plants confer resistance to stalk boring larvae of Chilo partellus (Swinhoe) in maize

Abstract

Large scale germplasm screening for Chilo partellus resistance in maize is solely based on visual scoring of damage by leaf injury rating (LIR), where the accuracy in judging a genotype comes by experience of the person, who logically integrate certain symptoms such as levels of growth retardation. Since the pest spends more than half of its larval period damaging the stalk, a quantitative phenotyping method that gives weightage to stalk resistance is required. To explore the traits governing stalk resistance, stalk infestation behaviour of C. partellus was studied first. It was found that first instar C. partellus larva is exclusive whorl feeder, second instar is the transition stage which disperse to infest stalk, and third instar onwards are exclusive stalk borers. To access the stalk, larva tends to penetrate the second above ground internode (seventh internode of maize plant) of V6–10 stage maize. Thus, penetration resistance (PR) of seventh internode was hypothesized to be the characteristic resistance trait. Twenty elite maize breeding lines were evaluated for PR of rind (RPR) and pith (PPR) of seventh internode in V6–7, V8–9 and V10–11 stage plants by TA + Di Texture Analyzer. Significant negative correlation of LIR with RPR of all plant stages and with PPR of V6–7 stage plants suggests the ability of seventh internode to resist larval penetration would confer tolerance to C. partellus. The trait was also found a strong predictor of antibiosis, by affecting the biology and behaviour of C. partellus larva. Thus, PR of seventh internode is proposed to be the trait for phenotyping stalk resistance to C. partellus in maize, whose deployment could lead to selection of genotypes which are resistant to stalk lodging also.