Phytohormone Signaling of the Resistance to Plum pox virus (PPV, Sharka Disease) Induced by Almond (Prunus dulcis (Miller) Webb) Grafting to Peach (P. persica L. Batsch).

Azam Dehkordi,Alfonso Albacete,Nadali Babaeian,Pedro Martínez-Gómez,Manuel Rubio

doi:10.3390/v10050238

Abstract

Plum pox virus (PPV, sharka) is a limiting factor for peach production, and no natural sources of resistance have been described. Recent studies, however, have demonstrated that grafting the almond cultivar “Garrigues” onto the “GF305” peach infected with Dideron-type (PPV-D) isolates progressively reduces disease symptoms and virus accumulation. Furthermore, grafting “Garrigues” onto “GF305” prior to PPV-D inoculation has been found to completely prevent virus infection, showing that resistance is constitutive and not induced by the virus. To unravel the phytohormone signaling of this mechanism, we analyzed the following phytohormones belonging to the principal hormone classes: the growth-related phytohormones cytokinin trans-zeatin (tZ) and the gibberellins GA3 and GA4; and the stress-related phytohormones ethylene acid precursor 1-aminocyclopropane-1-carboxylic acid (ACC), abscisic acid (ABA), salicylic acid (SA), and jasmonic acid (JA). PPV inoculation produced a significant increase in GA3 and ABA in peach, and these imbalances were related to the presence of chlorosis symptoms. However, grafting “Garrigues” almond onto the PPV-inoculated “GF305” peach produced the opposite effect, reducing GA3 and ABA contents in parallel to the elimination of symptoms. Our results showed the significant implication of SA in this induced resistance in peach with an additional effect on tZ and JA concentrations. This SA-induced resistance based in the decrease in symptoms seems to be different from Systemic Acquired Resistance (SAR) and Induced Systemic Resistance (ISR), which are based in other reactions producing necrosis. Further studies are necessary, however, to validate these results against PPV-D isolates in the more aggressive Marcus-type (PPV-M) isolates.

Highlights

Plum pox virus (PPV, sharka disease) is a threat to the production of stone fruits (Prunus) in affected areas
PPV inoculation produced a significant increase in GA3 and abscisic acid (ABA) in peach, and these imbalances were related to the presence of chlorosis symptoms
The study of the hormonal balance in the control “GF305” peach and the “GF305” peach inoculated with a PPV-D isolate, both grafted and not grafted with the almond cultivar “Garrigues”, showed the important differences between treatments

Summary

Introduction

Plum pox virus (PPV, sharka disease) is a threat to the production of stone fruits (Prunus) in affected areas. M (Marcus) is very aggressive, while D (Dideron) is a less aggressive type Another isolate, El Amar, has been reported, which some authors claim belongs to type M and others identify as type D. El Amar, has been reported, which some authors claim belongs to type M and others identify as type D Another isolate has been reported in cherry in Moldavia (PPV-SC), and has been sequenced, characterized, and classified as a new type C. PPV-D and PPV-M, are the most widely distributed strains of plum pox worldwide. These strains are only partially differentiable by their biological or epidemiological properties. PPV-M is the only strain reported to transmit the virus through seed [1,3]

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Conclusion