Mechanism of whorl feeding resistance to fall armyworm among converted sorghum accessions

Abstract

AbstractField studies were conducted in 1989 to evaluate selected converted sorghum (Sorghum bicolor [L.] Moench) accessions for resistance to whorl‐stage feeding by larvae of the fall armyworm (Spodoptera frugiperda J. E. Smith) and to determine the mechanism of resistance. The sorghum was infested in the whorl 26 days after planting (DAP) in experiment 1 and 33 DAP in experiment 2. In experiment 1, the plant accessions ‘IS7273C,’ ‘IS7444C,’ ‘IS12573C,’ ‘IS12678C,’ and ‘IS12679C’ were more resistant (rating < 3) to damage by S. frugiperda larvae than the resistant check CIMMYT (CM) 1821 (rating 6.2) at 14 days after infestation (DAI). These genotypes were also more resistant (ratings ≤ 4 at 7 DAI and < 3 at 14 DAI) than the resistant check CM1821 (ratings 5.6 at 7 DAI and 8 at 14 DAI) in experiment 2. The number of larvae that established/plant on IS7273C, IS7444C, IS12573C, or IS12679C was significantly less compared with establishment on the resistant check CM1821 at 14 DAI in experiment 1 and at 7 and 14 DAI in experiment 2. Resistance in IS7273C, IS7444C, IS12573C, and IS12679C was mainly due to their rapid rate of growth which induced a quick change in the plant morphology from the whorl‐ to the panicle‐stage and did not permit a sustained colonization of larvae. This new type of resistance could be referred to as ‘morphological non‐preference’ as apposed to chemical non‐preference where non‐preference is due to plant chemical factors. These genotypes had a significantly shorter cycle than the other sorghum genotypes. Host evasion, a type of pseudoresistance, was the basis for resistance in ‘IS7794C’ and ‘IS7947C’. Tolerance was the major mechanism of resistance in the resistant check CM 1821.