Incomplete Infection of Secondarily Infected Potato Plants - an Environment Dependent Underestimated Mechanism in Plant Virology.

Lukas Bertschinger,Lukas Bertschinger,Brion Duffy,Urs C Scheidegger,Brice Dupuis,Cesare Gessler,Gregory A Forbes,Paul C Struik,Lukas Bühler,Urs C Scheidegger,Ernst R Keller

doi:10.3389/fpls.2017.00074

Abstract

The common assumption in potato virus epidemiology is that all daughter tubers produced by plants coming from infected mother tubers (secondary infection) will become infected via systemic translocation of the virus during growth. We hypothesize that depending on the prevalent environmental conditions, only a portion of the daughter tubers of a plant that is secondarily infected by viruses may become infected. To test this hypothesis experimental data from standardized field experiments were produced in three contrasting environments at 112, 3280, and 4000 m a.s.l. in Peru during two growing seasons. In these experiments, the percentage of infected daughter tubers produced by seed tubers that were infected with either potato potexvirus X (PVX), potato Andean mottle comovirus (APMoV), potato potyvirus Y (PVY) (jointly infected with PVX) or potato leafroll luteovirus (PLRV) was determined. Incomplete autoinfection was found in all cases, as the percentage of virus infected daughter tubers harvested from secondarily infected plants was invariably less than 100%, with the lowest percentage of infection being 30%. Changing the growing site to higher altitudes decreased autoinfection for all viruses. Therefore, the assumption of complete autoinfection of secondarily infected plants were rejected, while the hypothesis of environmentally dependent incomplete autoinfection was accepted. The findings help explain the occurrence of traditional seed management practices in the Andes and may help to develop locally adapted seed systems in environments of the world that have no steady access to healthy seed tubers coming from a formally certified seed system. The results obtained almost three decades ago are discussed in light of most recent knowledge on epigenetic regulation of host plant – virus interactions which allow for speculating about the underlying biological principles of the incomplete autoinfection. A research roadmap is proposed for achieving explicit experimental proof for the epigenetic regulation of incomplete autoinfection in the pathosystem under study.

Highlights

Potato (Solanum tuberosum L.) seed tubers used for planting can harbor latent pathogens that subsequently reduce emergence, plant vigor, crop quality and/or yield
We report on an experimental test of the hypothesis that environment-driven factors may limit autoinfection with four important potato viruses: PVX, APMoV, potyvirus Y (PVY), and potato leafroll luteovirus (PLRV) and we confront the results of these experiments with most recent findings related with virus propagation
The hypothesis that potato tuber infection by viruses may be limited or even avoided by a mechanism preventing daughter tubers of an infected mother tuber to become infected, is clearly supported by the presented field data. This seemingly simple theory has great practical consequences, since costly, formal seed potato systems in industrialized countries in temperate climates are based on this assumption, supported by evidence under these climates

Summary

Introduction

Potato (Solanum tuberosum L.) seed tubers used for planting can harbor latent pathogens that subsequently reduce emergence, plant vigor, crop quality and/or yield. Seed-borne pathogens have been dealt with in several ways, including selection of better looking mother plants and/or tubers for seed, or acquiring seed from areas known to produce a cleaner product (Young, 1990). Propagation systems for pathogen-free seed tubers have been developed that provide growers in industrialized countries with a readily available source of healthy planting stock (Frost et al, 2013). Progress toward developing similar pathogen-free seed propagation systems in the small-holder potato growing regions of the low-income countries has been slow and represents a major production limitation (Thiele, 1999; Thomas-Sharma et al, 2016). Small-holder farmers in low-income countries still produce their own seed or acquire it locally from other farmers, and this seed represents many field generations that have never passed through a process of pathogen elimination

Methods

Results

Conclusion