Legume-Colonising Aphids as Potential PNYDV-Vectors: Reproduction and Infestation Dynamics in Two Different Field Bean Varieties

Faba bean can be infected by Pea necrotic yellow dwarf virus (PNYDV), a novel pathogen throughout Europe, and transmitted persistently by several legume-colonising aphid species. Recent field screenings in Austria and Germany of different faba bean varieties were encouraging as consistently the lowest viral symptom development in the variety ‘GL Sunrise’ was reported. However, our own greenhouse experiments revealed that ‘GL Sunrise’ was not resistant to PNYDV but showed a similar susceptibility such as other common varieties, for example, ‘Fuego’. Therefore, we suspected varietal host traits were affecting the reproductive potential of virus vector species with reduced virus transmission, probably explaining the empirical superior health status in the field. Under greenhouse conditions, vector-specific intrinsic rates of increase (r_m) for Acyrthosiphon pisum Harris Aphis fabae Scopoli and Megoura viciae Buckton were similar for both varieties, except for a particular A. pisum-biotype derived from field pea, with a significantly reduced r_m and fecundity in ‘GL Sunrise’. Furthermore, vector abundance assessments in multisite varietal showed A. pisum as the predominant species. In overall cross-year and -site evaluation, early aphid census in ‘GL Sunrise’ at growth stage BBCH 61–65 indicated significantly lower primary A. pisum-infestation pressure (factor 0,43 relative to ‘Fuego’). This lower infestation level in ‘GL Sunrise’ was kept until BBCH 77–79 but the difference had diminished down to the non-significant factor of 0,74 A. pisum-density relative to ‘Fuego’ in the late census, respectively. Based on our findings of (i) basic PNYDV susceptibility, (ii) similar reproductive vector performance of key aphid species, together with (iii) a significantly weaker initial A. pisum-infestation levels in the field, we hypothesise ‘GL Sunrise’-specific additional antixenosis/antibiotic traits, must influence host recognition and settling behaviour of alighting (viruliferous) migrants and/or apteres, which finally determine the superior PNYDV-health status in ‘GL Sunrise’ at field conditions.