Tomato yellow leaf curl virus (TYLCV), a geminivirus transmitted by the tobacco whitefly (Bemisia Tabac.) causes severe damage to tomatoes in the Mediterranean basin. Pilowsky and Cohen (1990) introduced tolerance to TYLCV from L. peruvianum into L. esculentum and developed the F1 hybrid cultivar TY-20.
In this study, we compared viral accumulation rates in TY-20 (TYLCV-tolerant) versus line 1651 TYLCV-susceptible). TYLCV inoculation was carried out by introducing viruliferous whiteflies to tomato seedlings at the two-leaf stage. Single stranded viral DNA was isolated from tomato plants at different intervals after inoculation. The isolated DNA was subjected to quantitative analysis by molecular hybridization using a cloned viral DNA as a probe.
Viral DNA could be detected as early as one day after inoculation and reached a peak 9-11 days later. This level remained stable until the appearance of symptoms, 1-4 days afterwards. Thereafter, DNA level in tolerant and susceptible plants decreased by 20-50% and remained stable for several weeks. During the experiment, DNA accumulation in cv. PY-20 was consistently lower by 50% compared to line 1651. A good correlator was found between severity of symptoms and DNA level, as measured in the top leaf. Both viral DNA accumulation and disease symptom appearance were dependent on plant age at time of inoculation. A delay of about 10 days was recorded in these parameters when plants were inoculated at the six-leaf stage or later.
The data of this experiment as well as preliminary results with various tolerant lines indicate a good correlation between severity of symptoms and viral DNA level.
Literature cited:
Pilowsky, M. and S. Cohen. 1990. Plant Dis. 74:248-250.