Physiological Basis of Fall Armyworm (Lepidoptera: Noctuidae) Resistance in Seedlings of Maize Inbred Lines with Varying Levels of Silk Maysin

Xinzhi Ni, Kedong Da, G. David Buntin, Steve L. Brown

Abstract


To assess both foliage- and ear-feeding insect resistance in the same maize inbred lines, fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) resistance at the seedling stage was examined in 6 corn inbred lines, including 4 CIMMYT maize inbred lines (CML333, CML335, CML 336, and CML338) with varying levels of silk maysin that confers corn earworm, Helicoverpa zea (Boddie), resistance and controls (fall armyworm-resistant Mp708 and susceptible AB24E). Fall armyworm injury rating and chlorophyll content were examined under greenhouse and field conditions. Plant height, plant stem circumference, and photosynthesis-related measurements were recorded on uninfested and infested plants only under greenhouse conditions. Injury ratings on CML333, CML336, and CML338 (with a range of low to high levels of silk maysin) were the same as for the resistant control (Mp708), and were significantly lower than for the susceptible control AB24E and CML335 (without silk maysin). Plant height, plant stem circumference, and chlorophyll content varied among the 6 inbred lines, but were not consistently correlated to resistance at the seedling stage. Photosynthetic rate was negatively affected by injury in AB24E, CML333, CML335, and CML336, but not affected in CML338 and Mp708. The reduction in photosynthetic rate of fall armyworm-susceptible AB24E, and in resistant CML333 and CML336 indicated that insect resistance in CML333 and CML336 might not be related to photosynthetic rate. At the same time, the data suggest that CML338 and Mp708 were tolerant to herbivory because no difference in either photosynthetic rate or photosynthetic capacity was detected in either inbred line between uninfested and injured corn seedlings. Further examination of photosynthetic capacity based on A/Ci and light response curves supported this resistance mechanism categorization. This experiment indicated that corn earworm-resistant corn inbred lines with varying levels of silk maysin could confer resistance to foliage-feeding fall armyworm at its seedling stage.

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