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  • Author or Editor: Boyett Graves x
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Twenty-four half-sib sweetpotato families were field tested for freedom from injury by sweetpotato weevil and other soil inhabiting, injurious insects (WDS). Three pairs of adult male and female weevils were applied to the crown of each plant at the beginning of storage root enlargement. Naturally occurring numbers of WDS were high enough for considerable injury from those insects. WDS injury free roots ranged from 19% in Centennial, the suceptible control, to 57% in Regal, the resistant control. The highest family mean for percent non-injured by WDS was 55%. Weevil injury free roots ranged from 67% in Centennial to 90% in Regal with 3 families producing mean weevil non-injured roots of 89%. The genetic correlation between weevil injury free and WDS injury free roots was 0.69 ± 0.28. That estimate is preliminary and based on data from one environment. Evaluations will be repeated in 1994 for estimates of GXE to derive genetic correlation estimates with less environmental interactions.

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Nitrogen treatments (0–134 kg N/ha) were applied on a sandy loam over 11 growing seasons to establish critical soil and tissue N levels, and to evaluate the effects of seasonal precipitation on annual variability in response of ‘Painter’ and ‘Centennial’ sweet potatoes [Ipomoea batatas (L.) Lam.] to applied N. Critical concentrations of soil NO3-N at 29 days after transplanting (DAT) and laminal N at 72 DAT were determined to be 37 μg N/g soil and 5% (dry weight), respectively. Correlation between soil NO3-N at 29 DAT and leaf N at 72 DAT was highly significant. Multiple regression analyses predicted a quadratic relationship between root yield and applied N and predicted a yield maximum at 88 kg N/ha. Inclusion of annual precipitation during the fallow season (1 Oct. – 31 May) in the N model significantly improved the prediction of response to applied N. Fallow season precipitation provided an index of N carry-over in sandy loam soils and could be used to improve estimates of N fertilizer requirements for sweet potatoes.

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