ACCUMULATION AND TRANSLOCATION OF TOMATO YELLOW LEAF CURL VIRUS (TYLCV) IN A LYCOPERSICON-ESCULENTUM BREEDING LINE CONTAINING THE L-CHILENSE TYLCV TOLERANCE GENE TY-1

The major tomato yellow leaf curl virus (TYLCV) tolerance gene, Ty-1, of the wild tomato species Lycopersicon chilense was mapped to chromes ome 6 by using restriction fragment length polymorphism (RFLP) markers and introgressed into the domesticated tomato L. esculentum. Two near ly isogenic breeding lines were obtained. In infected fields, plants f rom line 52, which contained the Ty-1 allele, remained symptomless (to lerant line); plants from line 50, which did not contain the Ty-1 alle le, were all symptomatic (susceptible line). The effect of the Ty-1 ge ne on TYLCV DNA accumulation and translocation was investigated by hyb ridizing plant DNA extracts with a viral DNA probe. After inoculation with a small number of viruliferous whiteflies (three insects per plan t), plants of the tolerant line 52 had barely detectable levels of TYL CV DNA compared with plants of the susceptible line 50. Agroinoculatio n of whole plants showed that similar amounts of TYLCV DNA accumulated in both lines. The long-distance movement of TYLCV was impaired in th e tolerant plants. After inoculation of the youngest leaf on each plan t with 50-70 whiteflies, TYLCV DNA accumulated in the inoculated leave s of plants from both lines, although at a slower rate in plants of li ne 52. In plants from susceptible line 50, the viral DNA moved from th e site of inoculation to the neighboring leaves and to the roots, in c ontrast to plants from the tolerant line, where it remained confined t o the inoculated leaf. Western blot analysis of proteins from the inoc ulated plants with an antisera against TYLCV confirmed that the moveme nt of the capsid protein was associated with that of the viral DNA. Re moval of all leaves except the inoculated youngest leaf hastened the t ransport of virus towards the roots of the susceptible plants but not of the tolerant plants. Plants of line 50 developed symptoms in all ex periments, white plants of line 52 always remained symptomless. Theref ore, the Ty-1 gene is associated with inhibition of disease symptoms; and at low titer inoculum, viral accumulation is significantly reduced in inoculated tissue. At high titer inoculum, viral long-distance tra nslocation is limited.