Effect of plant age at inoculation on expression of genetic resistance to tomato yellow leaf curl virus

Abstract

To determine the effects of plant age on the expression of genetic resistance to tomato yellow leaf curl virus (TYLCV), six TYLCV-resistant and two susceptible tomato varieties were inoculated at 14, 28 or 45 days after sowing (DAS). Inoculation at 14 and 28 DAS was performed in the greenhouse, and the plants were transplanted to the field at 30 DAS. Inoculation at 45 DAS was performed in the field, by covering the target plants with polypropylene ("Agril") sheets and releasing viruliferous whiteflies under them. Resistance was assayed mainly by comparing yield components of inoculated plants to those of control, non-inoculated plants of the same variety. Symptom severity and plant height were also followed. Plant age at inoculation had no effect on disease-severity scores of the susceptible varieties, and little or no effect on those of the resistant varieties. In contrast, plant age at inoculation had a significant effect on the yield of all varieties tested. All varieties suffered a significant yield reduction due to inoculation with TYLCV; the lowest yield was produced by plants inoculated at 14 DAS. A smaller TYLCV-induced yield reduction (yield increase of 50 to 100%, depending on the variety's resistance level), was achieved following inoculation at 28 DAS. A further reduction in yield loss (yield increase of 30 to 40%) was achieved following inoculation at 45 DAS. Our results clearly demonstrate the occurrence of age-related (or mature-plant) resistance in tomato plants to TYLCV.