Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 13, 2009
Publication Date: October 1, 2009
Citation: Ni, X., Wilson, J.P., Buntin, G. 2009. Differential responses of forage pearl millet genotypes to chinch bug (Heteroptera:Blissidae) feeding. Journal of Economic Entomology. 102:1960-1969. Interpretive Summary: In the southeastern and mid-south regions of the United States, pearl millet is grown as a forage, cover and promising alternative feed-grain crop because it is tolerant to drought and acidic soil, and it has a short (about 100-d) crop cycle. The grain has been used as a poultry ration ingredient due to its grain nutritional quality and minimal processing costs. Pearl millet is most widely used as a summer forage crop and is of particular importance in years with severe drought. In the southeastern states, the key insect pest on both forage and grain pearl millet is the chinch bug, which cause significant plant injury and loss of seedling stands. Twenty-nine forage pearl millet genotypes were assessed for chinch bug resistance using stunt and necrosis ratings in combination with quantitative measurements of chlorophyll content and leaf photosynthetic rate measurements. When the 29 pearl millet genotypes were examined for chinch bug resistance, seven genotypes were identified as the most resistant to chinch bug feeding, while another six entries and the susceptible control (Tift 23DB) were identified as the most susceptible to chinch bug feeding. The rest of the genotypes expressed intermediate resistance to chinch bug feeding according tot the six parameters examined. This research demonstrated that visual stunt and necrosis rating methods in combination with chlorophyll and photosynthesis measurements could be used in screening forage pearl millet for chinch bug resistance and deciphering the underlying resistance mechanisms. Using Tift 383 as the chinch bug resistance control for the study, the research has also demonstrated that significant progress was made toward developing new forage pearl millet genotypes that confer chinch bug resistance.
Technical Abstract: Chinch bug, Blissus leucopterus leucopterus (Say) (Heteroptera: Blissidae), is one of the most important insect pests on forage pearl millet (Pennisetum glaucum L. R. Br.) production in the southeastern US. Twenty-nine forage pearl millet genotypes were assessed for chinch bug resistance using stunt and necrosis ratings in combination with quantitative measurements of chlorophyll content and leaf photosynthetic rate. Plant stunt (P = 0.03) and leaf sheath necrosis (P = 0.0001) ratings, and chlorophyll content in flag leaves (P = 0.04) differed among the 29 genotypes. Photosynthetic rate differed both among the non-infested control (P = 0.04) and among the chinch bug-infested plants (P = 0.005). The chinch bug-infested plants had lower photosynthetic rate than the non-infested control plants (P = 0.0001). Inbreds with resistance superior to that of Tift 23DB were identified for hybrid development. When the 29 pearl millet genotypes were assessed by the six parameters using cluster analysis, genotypes 07F-1226, 07F-1229, 07F-1231, 07F-1235, 07F-1238, 07F-1239, and 07F-1240 were the most resistant, whereas the genotypes 07F-1220, 07F-1221, 07F-1225, 07F-1227, 07F-1232, 07F-1246, and Tift 23DB were the most susceptible to chinch bug feeding. The rest of the genotypes expressed intermediate responses to the four parameters. To differentiate the physiological impact of chinch bug feeding on light and dark reactions of plant photosynthesis, photosynthesis capacity was assessed using light and CO2 (A/Ci) response curves on non-infested and chinch bug-infested plants of genotypes 07F-1246, 07F-1223, and 07F1245, which expressed low, intermediate, and high chlorophyll content, respectively. Based on the A/Ci curves, photosynthesis capacity of injured leaves was suppressed in 07F-1223 and 07F-1246, while the chinch bug-injured 07F-1245 leaves showed an increase of photosynthetic rate compared to the non-infested plants. In contrast, light response curves were suppressed in the chinch bug-injured plants compared to the non-infested plants of all three genotypes, irrespective of their variations in insect injury ratings. This research demonstrated that visual stunt and necrosis rating methods in combination with chlorophyll and photosynthesis measurements could be used in screening forage pearl millet for chinch bug resistance and deciphering the underlying resistance mechanisms.