Efficiency of Rz1-based rhizomania resistance and molecular studies on BNYVV isolates from sugar beet cultivation in Greece

Abstract

A survey was carried out to investigate the current situation concerning rhizomania disease incidence in sugar beet cultivation of Greece. A systematic field evaluation over locations and years revealed a consistent disease severity pattern according to favourable agroclimatic conditions and pointed to the so far effectiveness of the Rz1 gene-based resistance, as no major disease outbreaks were observed. Molecular analyses aiming at the characterization of the type and genetic diversity of the virus further confirmed the widespread occurrence of BNYVV in the country, as evidenced by RT-PCR amplification of all five known genomic molecules and nested-PCR assays. None of the isolates contained an RNA 5, typically found in pathotype P. On the basis of RFLP patterns, all BNYVV isolates analysed were classified as pathotype A. Sequence determination of the full-length RNA 3-encoded p25 protein, responsible for symptom development, revealed amino acid motifs ACHG/VCHG in the hypervariable region aa [67][68][69][70] . The presence of valine in position 67 did not appear associated with increased pathogenicity and resistance breaking properties, as earlier reported.

Identification of strain types of some Beet necrotic yellow vein virus isolates determined in Northern and Central Parts of Turkey

“…Arosa) in bait plant tests, whereas the isolate 186 showed green vein banding and leaf deformation (Table 1). Similarly, A-type BNYVV have been previously reported in Turkey (Kruse et al 1994;Chiba et al 2011;Kutluk Yilmaz et al 2016) and in its neighboring counties for example Iran (Sohi and Melaki, 2004) and Greece (Kruse et al 1994;Pavli et al 2011). No B-type BNYVV infections were found in tested samples in the region whereas the B-type BNYVV (Sohi and Maleki, 2004) was recorded in Iran.…”

The hrpZ Gene of Pseudomonas syringae pv. phaseolicola Enhances Resistance to Rhizomania Disease in Transgenic Nicotiana benthamiana and Sugar Beet

“…Based on previous characterization, sugar beets used for virus inoculations were infected with A-type BNYVV, with amino acid motif VCHG in the hypervariable region aa 67–70 of RNA 3-encoded p25 [47].…”

“…BNYVV-infected sugar beet plants were used as virus source for inoculation of both transgenic N. benthamiana plants and sugar beet seedlings consisted of a transgenic root system. Based on previous characterization, sugar beets used for virus inoculations were infected with A-type BNYVV, with amino acid motif VCHG in the hypervariable region aa 67–70 of RNA 3-encoded p25 [47] .…”

High Level Resistance against Rhizomania Disease by Simultaneously Integrating Two Distinct Defense Mechanisms

“…In order to evaluate resistance under high infectivity pressure, a previously characterized as highly infectious virus isolate, due to the presence of specific aa at key positions of the BNYVV p25 protein, was used [31].…”

“…However, recent changes in field and molecular BNYVV epidemiology, as manifested by the recent emergence of resistance-breaking mutants for the Rz1 -mediated resistance, resulting from high selective pressure to overcome this gene [1], [13], [24]–[31], probably reflect an ensuing new endemic disease development. Such an evolution would require major adjustments in mainstream breeding programs if they were to keep providing a durable crop protection through the use of appropriate cultivars.…”