Insect resistance in sweetpotato plant introductions

One hundred U.S. sweetpotato [Ipomoea batatus (L.) Lam.] plant introduction s (PIs) and four control cultivars were screened for insect injury in 1993, Of the least injured by insects, 56 and 31 were tested again in 1994 and 1 995, respectively. Among control cultivars, the most highly resistant was ' Regal' (moderately resistant), followed by 'Beauregard' (susceptible), 'Cen tennial' (susceptible), and 'Jewel' (susceptible). Stem and root injury by the sweetpotato weevil (SPW) [Cylas formicarius elegantulus (Summers)] and root injury by the wireworm (Conoderus sp.)-Diabrotica sp. (cucumber beetle )-Systena sp. (flea beetle) (WDS) complex were measured. SPW stem injury wa s less severe (P less than or equal to 0.05) in 1994 and 1995 in PIs 508523 , 531116, and 564107 than in control cultivars, PIs 508523 and 531116 also suffered less SPW root injury than did 'Regal', In the six PIs with least S PW root injury, PIs 538354, 564149, 508523, 538286, 531116, and 564103, 70% to 85% of the roots were not injured compared with 36% in 'Regal' and 6% i n 'Jewel', SPW root injury scores (0 = no injury; 5 = severe injury) in tho se PIs averaged 0.5 vs. 2.3 for 'Regal', Only in PI 538286 was WDS injury t o roots less than in 'Regal' over 2 years. However, eight additional access ions suffered less WDS injury; than 'Regal' in 1995 and four of those were among the six with least SPW injury. The lower levels of combined insect in jury found in these four PIs (compared to 'Regal') show that PIs have poten tial use for increasing insect resistance in sweetpotato improvement progra ms.