Frequencies of Seed Infection and Transmission to Seedlings by Potato Spindle Tuber Viroid (A Pospiviroid) in Tomato

Abstract

Potato spindle tuber viroid (PSTVd) is an emerging pathogen that primarily affects members of the Solanaceae. The distribution of this pathogen is expanding rapidly with several countries reporting new infections in recent years. This pathogen is of phytosanitary concern because infected seed is thought to be one of the factors contributing to the spread of this disease. Thus we developed a qRT-PCR method to determine the seed infection frequency of PSTVd in tomato, as well as a RT-PCR method to determine the frequency of transmission of this pathogen to tomato seedlings. Infection frequency of PSTVd in tomato seeds from infected plants (cv. 'Beefsteak') ranged from 62.3-69% and frequency of PSTVd transmission to tomato seedlings was 50.9%. Germination of the infected seed was significantly lower (53%) than the parent seed (98%), and we also determined that viroid titers in the infected seeds were significantly lower (average 173 ng/μl) than in the infected seedlings (785 ng/μl). Interestingly ~60% of the infected seedlings did not display any observable symptoms of PSTVd until the second or third week; however, plants that were grown to maturity developed severe symptoms, suggesting that a grow-out assay might not be an accurate method for detection of this pathogen.

International Trade and Local Effects of Viral and Bacterial Diseases in Ornamental Plants

“…Questions remain over the relative risk to food crops from asymptomatic pospiviroid infections of ornamentals, compared to other potential sources such as commodity seeds of tomato and pepper (24,25,39,112), and there are conflicting reports of the relative importance of ornamentals in outbreaks in commercial tomato and pepper crops (142,144).…”

Pospiviroides de importância para hortaliças e ornamentais: panorama dos aspectos fitopatológicos e dos riscos para os sistemas agrícolas brasileiros

“…Ao adotar um padrão de menos de 1 infecção por 30.000 mudas (<0,0033%) para pospiviroides em tomate, os lotes de semente de tomate devem ter uma prevalência de contaminação não superior a cerca de uma em 22.500 sementes (0,0044%). Permitindo uma taxa de transmissão de 75%, pode-se prever que as mudas resultantes seriam então infectadas a uma taxa não superior a 0,0033%, ou seja, 1 em 30.000 plantas (SIMMONS et al 2015). Em estudos de transmissão por sementes de tomate e pimentão, cálculos estatísticos empregando distribuições binomiais mostraram que tamanhos de amostra de 3.000 e 9.400 sementes permitiram a detecção de prevalências de viroides tão baixas quanto 0,1% e 0,032%, respectivamente, com 95% de confiança.…”