Detection of Ralstonia solanacearum phylotype II, sequevar 1 in seasonal weed plants associated with potato cultivations in Egypt

Abstract

Weed plants were randomly sampled from different potato fields in some Egyptian villages and were examined for the presence of Ralstonia solanacearum. A total of (1609) plants were sampled over two year's period (2017/2018 and 2018/2019). These weeds were found belonging to almost (50) species affiliated to (20) families associated more or less with the potato fields near Al-Kalubeiah, El-Behira, El-Giza, El-Gharbeya, El-Ismailia and El-Menofiya governorates at different village (Digwa, El-Saadany, Al-Rifai, Kafr-Yaqoub, Abu Sawyer and Talia, respectively). The pathogen was successfully recovered from the crown area of 272 plant weeds belonging to 25 plant species of 13 families. The weeds in concern, 70 days after planting potato, were found latently infected and mostly symptomless at the time of sampling. The rates of positive isolation from these weeds were generally low, and account for 16.9%. All isolates of R. solanacearum from weeds were confirmed as phylotype II, sequevar 1 (race 3, biovar 2) via PCR. Data revealed that, the highest infection percentage of weed plants were shown from El-Gharbeya and Al-Kalubeiah, governorates (44.7 and 31.7 % respectively) followed by El-Behira governorate (16.1%), whereas the lowest percentage (11.5%) was observed in El-Menofiya governorate. On the other hand, both El-Giza and El-Ismailia governorates showed almost similar percentage of infected weeds (12.7 and 13.9% respectively). The winter annual weeds were the most affected weeds and included 11 different species of weeds (e.g. Amaranthus ascendens Lois, Amaranthus cruentus, Chenopodium album and Chenopodium mural) followed by the summer annual weeds that included 7 different species (e.g. Portulaca oleracea L. and Solanum nigrum L.). While the perennial weeds included 4 species (e.g. Convolvulus arvensis and Dicanthium annulatum), the biennial, however, weeds included only two species of infected weeds (Beta vulgaris L. and Centaurea calcitrapa L.). The results denoting that symptomless weeds might be a serious masked source of latent infection for either weeds or exported potato crop and it may be considered as an attractive overwintering hosts of R. solanacearum.