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Description:
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Greenbug is one of two key insect pests of sorghum , and biotype evolution hinders the long -term usefulness of resistant sorghums . The current study sought to identify plant resistance mechanisms , plant damage characteristics , and greenbug fitness in sorghum /greenbug interactions . Choice tests were conducted to elucidate resistance mechanisms displayed by four sorghum genotypes towards several greenbug biotypes and isolates . Results indicated all three resistance modalities (antibiosis , antixenosis , tolerance ) were identified in sorghums , with some genotypes displaying two or more modalities towards some biotypes . This suggests some sorghum genotypes do not select for greenbug biotypes , and the sorghum genotypes cultivated may have relatively long -term resistance . Non -choice tests were used to determine plant damage associated with greenbug feeding . Four sorghum genotype , Johnson grass , and five greenbug biotype combinations were used to elucidate plant characteristics associated with visible plant damage . Fluid loss and plant stunting were significantly associated with visible plant damage , and were also observed in some plants not incurring heavy visible damage . Additionally , some biotypes avirulent to cultivated sorghum caused significant damage to Johnson grass . These results suggest visible plant damage , routinely used in damage studies , reflects underlying causes that could lead to poor agronomic performance . Additionally , Johnson grass may harbor greenbug biotypes not commonly found in sorghum fields . Greenbug colony and individual fitness were determined by reproduction rates of five biotypes on four sorghum genotypes and Johnson grass in non -choice tests . Generally , colony and individual fitness estimates were not different within genotype /biotype combinations . Also , biotypes did best on more susceptible and worst on more resistant sorghum genotypes . Colonies and individuals of all biotypes had lowest fitness on Johnson grass . These results suggest virulent biotypes may have a fitness advantage over avirulent ones , at least in the presence of the cultivated host . The results presented herein reflect the diversity of sorghum /greenbug interactions , and underscore the need for further understanding of the nature of greenbug biotypes , and how they interact with cultivated and non -cultivated host plants . |