Physico-chemical bases of resistance in maize against shoot fly, Atherigona naqvii Steyskal during spring season in north India

Host plant resistance is one of the most promising alternatives to insecticides to manage the shoot fly, Atherigona naqvii Steyskal, which is a major biotic constraint to spring sown maize in northern India. In present studies, Nineteen maize inbreds selected from diverse sources were characterized for resistance traits against shoot fly under its natural infestation using moistened fishmeal. Though the antixenosis to shoot fly for oviposition was not observed in the test genotypes. But, the presence of significant variation in the deadhearts incidence revealed the existence of relative amount of resistance among the test genotypes. The Tolerance (measured in the terms of less proportion of deadhearts out of total shoot fly incidence (leaf injury + deadhearts)) and Antibiosis (in terms of larval and pupal weight, duration and survival) were recognized as key mechanisms of this resistance. Tolerance to shoot fly was significantly more in resistant inbreds, SO1SHYQBBB13B, HK12-6-2-4, DMSC 28, CM 143 and Winpop 8 (29.46–36.56%) in comparison to the susceptible genotypes SE 563 and LM 16 (46.31–47.44%). The correlation and stepwise regression analyses revealed that the more seedling vigor, less leaf area, less number of leaves and thin stem had significant impact on the shoot fly deadhearts incidence and provided resistance against this pest. The total soluble sugars (TSS), proteins and amino acids were significantly higher in the susceptible inbreds; whereas, total phenols and tannins; and activities of defensive enzymes viz. phenylalanine ammonia lyase (PAL) and polyphenol oxidase (PPO) were significantly higher in resistant inbreds. Further, the stepwise regression revealed that the larval period, per cent pupation, pupal weight female, pupal weight male and adult emergence of shoot fly were significantly influenced by PAL activity, which explained 71.5, 82.9, 47.0, 29.8 and 39.9% of their total variation, respectively. PPO activity significantly influenced the pupal period (R² = 59.7%) whereas, the larval weight was significantly influenced by amino acids (R² = 56.9%), proteins (R² = 10.2%) and TSS (R² = 7.7%). So, the correlation and regression analyses revealed that these physico-chemical characters of the maize inbreds can be utilized as reliable markers traits to identify resistant sources to develop shoot fly resistant maize hybrids.