Evaluation of resistance to six races of southern root-knot nematode in 87 sweetpotato cultivars in laboratory tests

Abstract

We evaluated resistance of 87 sweetpotato cultivars to 6 races (SP1, SP2, SP3, SP4, SP6-1, and SP6-2) of the southern root-knot nematode (SRKN) using a 5-point scale based on the number of egg masses (NEM) formed in laboratory tests. NEM values for all 6 races showed highly skewed distributions. Significant differences in resistance were observed among the 6 races, with resistance to SP1, SP2, and SP3 generally higher than or equal to that observed for SP4, SP6-1, and SP6-2. Laboratory resistance evaluations for the 6 races were significantly correlated with field test results from Miyakonojo, Yawara, Katori, and Hamaoka. No significant differences in laboratory resistance were observed among cultivars grouped by their 3 major primary usages, nor between resistance evaluations for 5 of the 6 races (SP2 being the exception) and production area ranks. However, cultivars registered after 1970 exhibited higher or equal resistance compared to those registered before 1970 and landrace cultivars, suggesting that although higher SRKN resistance in a cultivar did not correlate with an expansion of its production area, breeding for SRKN resistance across various usages intensified from the 1960s. These results provide valuable insights for breeding SRKN-resistant sweetpotato cultivars.