Segregation of Hydroxycinnamic Acid Esters Mediating Sweetpotato Weevil Resistance in Storage Roots of Sweetpotato.

Milton O Anyanga,G C Yencho,Robert O M Mwanga,Philip C Stevenson,Benard Yada,Gorrettie N Ssemakula,Agnes Alajo,Dudley I Farman

doi:10.3389/fpls.2017.01011

Abstract

Resistance to sweetpotato weevils (Cylas spp.) has been identified in several sweetpotato (Ipomoea batatas) landraces from East Africa and shown to be conferred by hydroxycinnamic acids that occur on the surface of storage roots. The segregation of resistance in this crop is unknown and could be monitored using these chemical traits as markers for resistance in F1 offspring from breeding programs. For the first time in a segregating population, we quantified the plant chemicals that confer resistance and evaluated levels of insect colonization of the same progeny in field and laboratory studies. We used a bi-parental mapping population of 287 progenies from a cross between I. batatas ‘New Kawogo,’ a weevil resistant Ugandan landrace and I. batatas ‘Beauregard’ a North American orange-fleshed and weevil susceptible cultivar. The progenies were evaluated for resistance to sweetpotato weevil, Cylas puncticollis at three field locations that varied climatically and across two seasons to determine how environment and location influenced resistance. To augment our field open-choice resistance screening, each clone was also evaluated in a no choice experiment with weevils reared in the laboratory. Chemical analysis was used to determine whether differences in resistance to weevils were associated with plant compounds previously identified as conferring resistance. We established linkage between field and laboratory resistance to Cylas spp. and sweetpotato root chemistry. The data also showed that resistance in sweetpotato was mediated by root chemicals in most but not all cases. Multi-location trials especially from Serere data provided evidence that the hydroxycinnamic acid esters are produced constitutively within the plants in different clonal genotypes and that the ecological interaction of these chemicals in sweetpotato with weevils confers resistance. Our data suggest that these chemical traits are controlled quantitatively and that ultimately a knowledge of the genetics of resistance will facilitate management of these traits, enhance our understanding of the mechanistic basis of resistance and speed the development of new sweetpotato varieties with resistance to sweetpotato weevil.

Highlights

Sweetpotato (Ipomoea batatas (L.) Lam) is a globally important crop (Scott et al, 1999; Andrade et al, 2009)
An F1 population of 287 progenies from a bi-parental cross between an African landrace that is resistant to Sweetpotato weevils (SPW), I. batatas ‘New Kawogo’ (NK) (Stevenson et al, 2009; Muyinza et al, 2012; Anyanga et al, 2013) and a susceptible North American orange-fleshed variety I. batatas ‘Beauregard’ (B), was generated at the National Crops Resources Research Institute (NaCRRI), Namulonge, Uganda
Fresh roots of the 287 different progenies obtained from the field sites located at Ugandan Agricultural Ministry Research Stations: Ngetta Zonal Agricultural Research and Development Institute (NgeZARDI), National Semi Arid Resources Research Institute, Serere (NaSARRI) and National Crops Resources Research Institute, Namulonge (NaCRRI) and the two parents were cleaned of loose soil and left to air dry at room temperature

Summary

Introduction

Sweetpotato (Ipomoea batatas (L.) Lam) is a globally important crop (Scott et al, 1999; Andrade et al, 2009) It is important in sub-Saharan Africa where it contributes to food security and income generation for marginalized farmers. The major damage reported is caused by feeding from both SPW adults and larvae which tunnel inside the storage roots and induce production of sesquiterpenes that appear not to affect the insect but make it unfit for sale or human consumption (Uritani et al, 1975; Sato and Uritani, 1981). Farmers typically use cultural practices such as field sanitation, hilling up and timely planting and harvesting before drought to enable escape but the current practice is not cost effective or consistently implemented (Stathers et al, 2003)

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