Vector and graft inoculations of Potato yellow mosaic virus reveal recessive resistance in Solanum pimpinellifolium

Transmission of Potato yellow mosaic virus (PYMV) (bipartite begomovirus) to tomato by 50 Bemisia tabaci biotype B individuals was observed when the acquisition access period (AAP) was at least 3 h and the inoculation access period (IAP) at least 30 min. The transmission efficiency increased with the access period to reach 92% transmission after a 48‐h IAP and 48‐h AAP. The transmission efficiency decreased when whiteflies were fed on PYMV non‐host plant between AAP and IAP. According to these results, we inoculated nine Solanum accessions with 50 whiteflies (48‐h APP and 48‐h IAP) to assess their resistance level. Four of these accessions with various levels of resistance were graft inoculated with PYMV. Although none of the accessions were immune, we observed a high level of resistance to PYMV in Solanumpimpinellifolium LA2187‐5 (no symptoms after vector or graft inoculation) and in Solanum chilense LA1969 (no symptoms after vector inoculation and one plant with symptoms after graft inoculation). Inheritance of LA2187‐5 resistance, investigated in F1 and F2 populations, appeared to be recessive. Fewer plants were infected by PYMV in S. pimpinellifolium LA1478 after vector inoculation than after graft inoculation. We hypothesised that this was because of vector resistance, which could also be effective against other begomoviruses.     

Insect-screened cultivation to reduce the invasion of tomato crops by Bemisia tabaci: modelling the impact on virus disease and vector

1 In two experiments carried out in Guadeloupe, barriers were used to reduce the entry of the virus vector Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) to tomato plots. The barriers erected around the crop were of insect‐proof cloth fences (<50 mesh), 1.5 m in height, in the first experiment with a deltamethrin‐treated, insect‐attracting strip facing inwards, and, in the second, with the barrier but no insecticide‐treated strip. 2 A mathematical model of epidemic development was fitted to the symptom data from the treated and control (unprotected) tomato plots. There were two viruses present, tomato yellow leaf curl and potato yellow mosaic; specific detection confirmed that symptoms gave an accurate indication of infection and that the two virus diseases had similar progress curves. 3 Parameter estimates obtained by model‐fitting suggested that the barriers reduced vector immigration by approximately 12‐fold but that B. tabaci retention within the plots was also increased slightly despite the mortality caused by the insecticide‐treated strips. Disease establishment was delayed by approximately 2 weeks. The results obtained in the second experiment involving barriers deployed without insecticide‐treated strips could be explained by a large increase in B. tabaci retention within the barriers resulting in more rapid virus disease progress than in controls. The results of mathematical modelling indicate that partial insect barriers can be worse than none because sufficient whiteflies can enter to establish a population and, at the same time, large numbers are retained in the barrier plot, with the net effect being a more rapid population increase than in the absence of barriers.