Susceptibility of Prunus rootstocks to natural infection of Plum pox virus and effect of mineral oil treatments

Abstract

The use of rootstocks that are less susceptible or resistant to natural Plum pox virus (PPV) infection and/or the application of mineral oil treatments are two possible strategies to reduce viral incidence in nursery plots. We evaluated the susceptibility of Prunus rootstocks used in the Spanish stone fruit industry and the effect of mineral oil treatment (Sunspray Ultrafine at 1%) on the spread of the virus at two different localities in Valencia, Spain, under different natural PPV inoculum pressures (high inoculum pressure, 2006–08; low inoculum pressure, 2006–07). Samples from both plots were analysed by double‐antibody sandwich indirect enzyme‐linked immunosorbent assay (DASI‐ELISA) and spot real‐time RT‐PCR. Under high inoculum pressure, the assayed rootstocks exhibited significant differences in their susceptibility to natural infection. The most susceptible rootstocks at the end of the experiment were Adesoto 101 and Mariana GF8‐1. Cadaman and Garnem rootstocks presented the fewest PPV‐infected plants; these infections could be detected only by spot real‐time RT‐PCR. No differences among the assayed rootstocks were found under low PPV inoculum pressure. Aphid species were monitored using Moericke yellow water traps and sticky‐plant methods at both localities in May 2006 and 2007. Aphis spiraecola was the most abundant aphid species monitored by both methods at both localities. The average percentage of A. spiraecola carrying PPV PCR‐amplifiable targets was 30.37% in the plot with high PPV inoculum pressure and only 7.98% in the plot with low inoculum pressure. We found significant differences in PPV incidence between Mariana GF8‐1 plots that were treated with mineral oil and those that were not treated after one year under natural conditions and high PPV inoculum pressure.

Epidemiology of Citrus tristeza virus in nursery blocks of Citrus macrophylla and evaluation of control measures

“…The total number of aphid individuals caught by both monitoring methods was different, with the higher number of aphid individuals caught using the Moericke yellow traps. Similar results were reported by Hermoso de Mendoza et al (1997) and Marroquín et al (2004) in citrus orchards and by Avinent et al (1993) and Vidal et al (2010) in orchards and nursery blocks of Prunus, respectively. However, the most prevalent aphid species Vidal et al (2010) in nursery blocks of Prunus rootstocks.…”

“…Similar results were reported by Hermoso de Mendoza et al (1997) and Marroquín et al (2004) in citrus orchards and by Avinent et al (1993) and Vidal et al (2010) in orchards and nursery blocks of Prunus, respectively. However, the most prevalent aphid species Vidal et al (2010) in nursery blocks of Prunus rootstocks. These differences in the proportion of A. spiraecola caught by the different monitoring methods may be explained by the yellow colour of the Moericke traps, which attracts certain aphid species, including A. spiraecola (Hermoso de Mendoza et al, 1998).…”

“…This is the first time that this technique has been used to estimate the number of CTV-viruliferous aphids in a specific area, though it was previously used for PPV (Plum pox virus) epidemiological studies with a similar purpose (Vidal et al, 2010). Therefore, the estimated number of CTV-viruliferous aphids that would visit a nursery block established at Moncada during May (maximum peak of aphid population) would range from 2,440,000 to 4,880,000 aphids ha -1 (depending on the planting pattern).…”

“…The complete plants were collected and processed to identify the aphid species present and to estimate their numbers, as described by Marroquín et al (2004) and Vidal et al (2010).…”

“…Furthermore, insects generally do not develop resistance to these treatments because of their physical action. The epidemiological studies on the use of oils as a control strategy has been mainly conducted with non-persistently aphid-transmitted viruses (Perring et al, 1999), including under nursery blocks conditions (Vidal et al, 2010). Furthermore, the use of mineral oil treatments has also been successfully tested against semi-persistent and persistent viruses (Allen et al, 1993;Perring et al, 1999;Asjes & Blom-Barnhoorn, 2001), including CTV (Powell et al, 1997).…”