Problemas na premunização de melancia para o controle do mosaico causado pelo Papaya ringspot virus

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...

Section: Introductionmentioning

confidence: 99%

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

Freitas

Rezende²

2008

“…In Brazil, this technology has been utilized quite successfully for over three decades, for the control of citrus tristeza (Citrus tristeza virus -CTV) (Müller & Costa, 1968;Müller & Carvalho, 2001). It has also been proved to be efficient for control of mosaic caused by the Papaya ringspot virus -type W (PRSV-W) in some cucurbit species Rezende & Pacheco, 1998;Rezende et al, 1999;Dias & Rezende, 2000).…”

Section: Introductionmentioning

confidence: 99%

Selected mild strains of Passion fruit woodiness virus (PWV) fail to protect pre-immunized vines in Brazil

Novaes

Rezende

2003

The Passion fruit woodiness virus (PWV) is the most important virus affecting passion fruit (Passiflora edulis f. flavicarpa Deg.) crops in Brazil. The main purpose of this work was to select mild strains of PWV and to evaluate their protective effect against a severe strain of the virus. Three mild strains were selected from outstanding plants found in orchards severely affected by the virus (F-101, F-102 and F-103) and three others were obtained from blisters formed in passion fruit vine leaves showing mosaic (F-99, F-144 and F-145). The protective effect of the mild strains was evaluated for vines under greenhouse and field conditions. Plants pre-immunized with mild strains F-101, F-102 and F-144, in a greenhouse, had partial protection against the severe strain PWV-SP. In a first field experiment, all passion fruit vines pre-immunized with the six selected mild strains showed severe symptoms of the disease, approximately four months after the challenge inoculation with the PWV-SP strain. Results from a second field experiment, with vines preimmunized with strains F-101 and F-144, followed by a quantitative evaluation of the mild strains in different leaves of the protected plants, indicated that breakdown in protection seems to be related to the low concentration and/or irregular distribution of the mild strains in leaves, which allows the existence of infection sites available for the establishment of the severe strain. Pre-immunization was not an appropriate alternative for the control of the passion fruit woodiness disease.

“…In California, studied on the protection of 'TopMark' melon plants with ZYMV-WK showed that 75% of total fruit yielded was classified as marketable (Perring et al, 1995). In Brazil, 16.2% of fruits harvested from Tetsukabuto (Takayama) hybrid pumpkin plants infected with mild strain PRSV-W-1 were unmarketable (Dias & Rezende, 2000).…”

Section: Resultsmentioning

confidence: 99%

“…The use of squash plants preimmunized with mild strains of the viruses has been investigated for more than ten years in Brazil, and has proven effective in controlling PRSV-W and ZYMV in some cucurbit species, especially C. pepo cv. Caserta (Rezende & Pacheco, 1998;Rezende et al, 1999;Dias & Rezende, 2000).…”

Section: Introductionmentioning

confidence: 99%

Yield of varieties of Cucurbita pepo preimmunized with mild strains of Papaya ringspot virus - type W and Zucchini yellow mosaic virus

Bonilha¹,

Giória

Kobori

et al. 2009

Papaya ringspot virus -type W (PRSV-W) and Zucchini yellow mosaic virus (ZYMV) are the most prevalent viruses in cucurbit crops in Brazil and responsible for frequent yield losses. Diseases caused by these viruses are difficult to control. The objective of this work was to evaluate the effects of mild strains PRSV-W-1 and ZYMV-M on the yield of Cucurbita pepo L. cvs. Samira, Novita Plus, AF 2847, and Yasmin, under plastic greenhouse and field conditions. Plants infected with ZYMV-M and grown in a plastic greenhouse did not exhibit typical leaf symptoms or significant alterations in quantitative and qualitative fruit yield. However, when infected with PRSV-W-1, or PRSV-W-1 + ZYMV-M, the plants exhibited severe leaf mosaic symptoms and reduced fruit quality, although there were no changes in the number and mean fruit weight harvested from these plants. When these plants were infected with PRSV-W-1 and studied simultaneously in the field and plastic greenhouse, intensification of symptoms in the fruits and leaves was more pronounced under the greenhouse conditions. Quantitative yield did not change. Environmental factors seem to influence symptoms induced by PRSV-W-1.