COMPARISON OF SEVERAL METHODS FOR THE ASSESSMENTOF Cylas INFESTATION OF SOME ADVANCED SWEET POTATO (Ipomoea batatas (L.) Lam.) BREEDING LINES IN NIGERIA.

Field trials were conducted at three locations in Nigeria to assess the levels of Cylas infestation of some advanced sweet potato (Ipomoea batatas (L.) Lam) breeding lines at pre-release stage using several methods. These locations include: Nyanya, Makurdi and Umudike. Sweet potato genotypes were planted in a randomized complete block design (RCBD) with three replicates at each location. At four months maturity, sweet potato roots were harvested and assessed for Cylas spp. infestation using four methods. Of the four methods used, two distinguished between clean and infested roots, while two took into consideration the extent of individual root damage. Significant difference (P<0.01) in levels of infestation expressed as percentage clean yield was observed but a nonsignificant difference was observed in extent of individual root damage expressed as Cylas mean scores. Comparison of these methods was done using correlation and regression analysis tools. Correlation studies showed significant associations (P<0.01) among all the methods. Whereas methods A and D were positively correlated (R2=0.627) methods B and C showed negative correlation (R2=-0.737). Comparison of both methods A and B however showed positive correlation with a lower R2=0.475 and methods C and D showed negative and significant correlation with the value of R2=-0.477. This indicates a stronger correlation between methods A and D/B and C and a lesser correlation between methods A and B/C and D. Thus, the more rapid method A can be used as an approximation of the more time-consuming method D. And with the limitation of time, methods A, B or C would be appropriate in assessing Cylas spp. damage in sweet potato roots.