Behavior of new entries and developed tomato hybrids carrying Ty-2 genes

Tomato yellow leaf curl disease (TYLCD) is a serious problem hampering tomato production worldwide. In the Mediterranean Basin, disease incidence and severity are higher in the dry season increasing whitefly (Bemisia tabaci) populations. Effectiveness of resistance to Tomato yellow leaf curl virus (TYLCV) depends on both tomato host resistance and TYLCV complex species. So far, six different Ty tomato resistance genes have been identified. Two main TYLCV complex species, Tomato yellow leaf curl virus-Israel (TYLCV-Is) and Tomato yellow leaf curl Sardinia virus (TYLCSV), have been identified in Tunisia. The present work aimed to evaluate entries heterozygous for Ty-2 gene to help predict hybrid performance. Two tomato entries homozygous for the Ty-2 TYLCV resistance gene, one tomato hybrid homozygous for Ty-2 and two heterozygous hybrids were included, besides two susceptible tomato entries. Resistance response to TYLCD was recorded based on disease incidence and severity levels. Data analysis was performed according to presence/absence of Ty-2 gene and taking into account homozygosity and heterozygosity of Ty-2. Generalized linear model analysis was applied to check significance of individual factors' effects (i.e. effect of tomato entries or tomato groups of entries based on presence or absence of homozygous/heterozygous Ty-2 gene, block unit within the field trial and the year of the trial) on the dependent variables (disease incidence and severity). Further multicomparison tests gave evidence on significant effect of Ty-2 homozygous gene tomato entries on TYLCD incidence and severity levels. The results were discussed with special focus on the relevance use of heterozygous hybrid tomato varieties.