Prunus necrotic ringspot virusEarly Invasion and Its Effects on Apricot Pollen Grain Performance

Abstract

The route of infection and the pattern of distribution of Prunus necrotic ringspot virus (PNRSV) in apricot pollen were studied. PNRSV was detected both within and on the surface of infected pollen grains. The virus invaded pollen during its early developmental stages, being detected in pollen mother cells. It was distributed uniformly within the cytoplasm of uni- and bicellular pollen grains and infected the generative cell. In mature pollen grains, characterized by their triangular shape, the virus was located mainly at the apertures, suggesting that PNRSV distribution follows the same pattern as the cellular components required for pollen tube germination and cell wall tube synthesis. PNRSV also was localized inside pollen tubes, especially in the growth zone. In vitro experiments demonstrated that infection with PNRSV decreases the germination percentage of pollen grains by more than half and delays the growth of pollen tubes by approximately 24 h. However, although PNRSV infection affected apricot pollen grain performance during germination, the presence of the virus did not completely prevent fertilization, because the infected apricot pollen tubes, once germinated, were able to reach the apricot embryo sacs, which, in the climatic conditions of southeastern Spain, mature later than in other climates. Thus, infected pollen still could play an important role in the vertical transmission of PNRSV in apricot.

Vertical transmission of Prunus necrotic ringspot virus: hitch-hiking from gametes to seedling

“…We have already demonstrated that PNRSV invades apricot reproductive organs, including the pollen mother cell (PMC) stage, early in development (Amari et al, 2007). In that work, we showed that the virus reduces pollen fitness, causing poor germination and delayed growth inside the pistil.…”

“…Ten flower buds, ovaries and seeds were fixed by immersion in a freshly made mixture of 4 % paraformaldehyde and 2.5 % glutaraldehyde in 0.1 M phosphate buffer (pH 7.2), at 4 uC for 4 h and embedded in paraffin (Paraplast Plus) as described previously (García-Castillo et al, 2001;Amari et al, 2007). The same probe used for dot-blot hybridization was used for in situ hybridization.…”

“…It causes serious economic damage (Uyemoto & Scott, 1992), decreasing tree growth by up to 30 % and their yield by 20-56 %; PNRSV infection also makes infected trees very susceptible to chilling damage. PNRSV belongs to the genus Ilarvirus and has , 1982;Hamilton et al, 1984;Kelley & Cameron, 1986;Aparicio et al, 1999;Amari et al, 2007), which contributes to its rapid spread in stone fruit trees (Mink, 1992). The seed transmission rate for PNRSV varies among the infected species.…”

“…In situ hybridization was performed at 55 uC overnight. Slide pre-treatments, hybridization and colourigenic detection were carried out as described previously (García-Castillo et al, 2001;Amari et al, 2007). Sections were examined and photographed with a Leica DC 500 digital camera using a DMRB Leitz microscope.…”

Study of main grapevine viruses transmission in breeding programs

“…It has been demonstrated also that seed transmission is related to the ability of the virus to infect flower organs, especially the meristematic reproductive tissue, during early developmental stages [34]. Similarly, Amari et al [35] have demonstrated that Prunus necrotic ringspot virus (PNRSV) invades apricot reproductive organs, including the pollen mother cell stage, early in development, and after that PNRSV infects all parts of the seed, including embryo, endosperm and testa, shedding light on the vertical transmission of PNRSV from gametes to seedlings [1]. Also the wide natural incidence of the nepovirus Cherry leaf roll virus (CLRV) is believed to have occurred mainly by seed transmission, in fact vertical transmission of CLRV by seed and pollen has been reported to occur naturally by embryo invasion in different works [36][37][38].…”