Discovery of a major QTL for root-knot nematode (Meloidogyne incognita) resistance in cultivated sweetpotato (Ipomoea batatas)

Bonny Michael Oloka, Guilherme da Silva Pereira, Victor A. Amankwaah, Marcelo Mollinari, Kenneth V. Pecota, Benard Yada, Bode A. Olukolu, Zhao-Bang Zeng & G. Craig Yencho

Theoretical and Applied Genetics July 2021; vol. 134:1945–1955.

Key message

Utilizing a high-density integrated genetic linkage map of hexaploid sweetpotato, we discovered a major dominant QTL for root-knot nematode (RKN) resistance and modeled its effects. This discovery is useful for development of a modern sweetpotato breeding program that utilizes marker-assisted selection and genomic selection approaches for faster genetic gain of RKN resistance.

Abstract

The root-knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood] (RKN) causes significant storage root quality reduction and yields losses in cultivated sweetpotato [Ipomoea batatas (L.) Lam.]. In this study, resistance to RKN was examined in a mapping population consisting of 244 progenies derived from a cross (TB) between ‘Tanzania,’ a predominant African landrace cultivar with resistance to RKN, and ‘Beauregard,’ an RKN susceptible major cultivar in the USA. We performed quantitative trait loci (QTL) analysis using a random-effect QTL mapping model on the TB genetic map. An RKN bioassay incorporating potted cuttings of each genotype was conducted in the greenhouse and replicated five times over a period of 10 weeks. For each replication, each genotype was inoculated with ca. 20,000 RKN eggs, and root-knot galls were counted ~62 days after inoculation. Resistance to RKN in the progeny was highly skewed toward the resistant parent, exhibiting medium to high levels of resistance. We identified one major QTL on linkage group 7, dominant in nature, which explained 58.3% of the phenotypic variation in RKN counts. This work represents a significant step forward in our understanding of the genetic architecture of RKN resistance and sets the stage for future utilization of genomics-assisted breeding in sweetpotato breeding programs.

See: https://link.springer.com/article/10.1007/s00122-021-03797-z

Figure 1: Histogram and boxplot of the adjusted means of root-knot counts in the TB population. Most of the progeny (75%) reacted like ‘Tanzania’ (< 15 root-knot counts), the resistant parent, while < 1% were more susceptible than ‘Beauregard.’ The boxplot above the histogram shows the statistics of the distribution.