Protection between strains of Papaya ringspot virus: type w in zucchini squash involves competition for viral replication sites

Abstract

A mild strain of Papaya ringspot virus -type W (PRSV-W), named PRSV-W-1, has proved to be very effective in the control of the disease in zucchini squash plants under greenhouse and field conditions. The aim of this work was to obtain additional information on the protection mechanism between PRSV-W-1 and a severe homologous strain (PRSV-W-C) in Cucurbita pepo L. cv. Caserta. Protective inoculation with the mild strain was made on the cotyledons and the challenge inoculation with the severe strain was applied on the first true expanded leaf, and vice-versa. Plants were challenged at three, six or nine days later, respectively. Plants infected with either the mild or the severe strain alone served as controls. Evaluations were based on the recovery test and specific RT-PCR to detect the challenge strain from challenge inoculated and newly developed leaves of the testplants. Symptoms evaluation was made 30 days after the challenge inoculation. Regardless of the site of the protective inoculation it seems there are some infectable sites available for superinfection with the severe strain. When the challenge inoculation was performed three days after the protective inoculation, a systemic superinfection occurred in some plants. All plants became protected against the expression of symptoms induced by the severe strain when the challenge inoculation was made six and nine days after protective inoculation. However, the severe strain was still detected in the inoculated and upper leaves of a few test-plants, eight days after the challenge inoculation. These data showed that competition for viral replication sites plays a role in the protection between strains of PRSV-W. Key words: Cucurbita pepo, Potyvirus, cross protection, preimmunization PROTEÇÃO ENTRE ESTIRPES DO Papaya ringspot virus -TIPO W EM ABOBRINHA DE MOITA ENVOLVE COMPETIÇÃO POR SÍTIOS DE REPLICAÇÃO VIRALRESUMO: Uma estirpe fraca do vírus do mosaico da abobrinha (Papaya ringspot virus -type W), denominada PRSV-W-1, tem se mostrado altamente eficiente na proteção de algumas cucurbitáceas contra estirpes severas do vírus. O objetivo deste trabalho foi avaliar se a competição por sítios de replicação pode estar envolvida na proteção entre a estirpe PRSV-W-1 e a estirpe severa homóloga PRSV-W-C em plantas de abobrinha-de-moita (Cucurbita pepo L. cv. Caserta). Plantas inoculadas com a estirpe fraca na primeira folha verdadeira expandida foram desafiadas nos cotilédones e vice-versa. A inoculação de desafio com a estirpe PRSV-W-C foi feita aos três, seis ou nove dias após a inoculação de proteção. As plantas inoculadas separadamente com as duas estirpes serviram de controles. As avaliações da proteção foram feitas por meio do teste de recuperação da estirpe desafiante e detecção desta por RT-PCR, aos oito dias após o desafio. Avaliações de sintomas foram feitas 30 dias após o desafio. Os resultados mostraram que, independente do local onde foi realizada a inoculação de proteção, de uma maneira geral há alguns sítios livres para a superinfecção com a est...

First report and molecular characterization of an isolate of papaya ringspot virus (PRSV-W) detected in pumpkin in Cuba

“…Caserta plants at 16 days after the inoculation of the Cuba-PR isolate. During plant development, the symptoms became stronger in the young leaves, causing leaf reduction and malformation ( Figure 1A and 1C), as observed by other authors in cucurbit plants infected with PRSV-W (PURCIFULL and HIEBERT , 1979 ;PEREIRA et al, 2007;FREITAS and REZENDE, 2008). In contrast, even after five repetitions of mechanical inoculation, papaya plants did not become infected.…”

“…The disease symptoms in pumpkin are characterized by an intense mosaic, a drastic reduction of the leaves and vegetative development and a reduction in production and fruit quality, resulting in losses of up to 100%, depending on the age at which the plants are infected and also of the spread in the areas in which it occurs. The fruits may also present deformation and changes in color (PEREIRA et al, 2007;FREITAS andREZENDE, 2008, RAHMAN et al, 2010).…”

Facilitative and antagonistic interactions between plant viruses in mixed infections

“…Since the discovery of the phenomenon by McKinney in 1929 (after Zaitlin and Palukaitis, 2000), cross‐protection has been applied with greater or lesser success to protect cultivated plants against detrimental viral diseases (e.g. Freitas and Rezende, 2008; Fulton, 1986; Gal‐On and Shiboleth, 2005; Hanssen et al ., 2010; Lecoq and Raccah, 2001; Nakazono‐Nagaoka et al ., 2009; Singh and Singh, 1995; Walkey, 1992). Success in virus control by this method depends on whether the attenuated virus isolate can invade the plant and displace the virulent virus (Zhang and Holt, 2001).…”

Inheritance of Resistance to Papaya Ringspot Virus-Watermelon Strain in Watermelon

“…Most of the time, PRSV-W outbreaks result in losses through a reduction in growth, yield, and fruit quality. There are two pathotypes of this potyvirus: PRSV-P (papaya strain) that infects papaya (Carica papaya) and most of the cucurbitaceous crops (Cucurbitaceae), and PRSV-W (watermelon strain) that exclusively infects cucurbitaceous crops (Cucurbitaceae) (Freitas and Rezende, 2008;Romay et al, 2014). The virus can be transmitted in a nonpersistent, noncirculative manner by several aphid species (Aphididae), and also by mechanical inoculation, but not via seeds (Tiwari and Rao, 2014).…”

“…Type W isolates are reported to infect 38 species in 11 genera of Cucurbitaceae, and two species of Chenopodiaceae, with squash (Cucurbita spp. ), watermelon (C. lanatus), cucumber (Cucumis sativus), and melon (Cucumis melo) among the commercially important natural hosts (Freitas and Rezende, 2008). The virus is not seed transmitted.…”