Segregation of Ty-1 and Ty-3a by Molecular markers
Ty-1 gene;
Although three different allels (allel 1 at 400 pb, allel 2 at slightly larger than 400 pb and allel 3at 500 pb) for TY-1 gene; were identified by [19], in our research the individuals of segregating populations and parents had two allels. Also, allel at 500 bp were dominant over allel at 400 bp.
Ty-3a gene;
The individuals of segregating populations carried three different allelic forms at 320 bp for susceptable or at both 320 bp and 630 bp for heterozygous resistant or at 630 bp homozygous resistant [11]. The Ty-3a gene is more preferred due to the fact that the Ty-3 gene provides a wider durability, and many other features are undesirable with the gene.
Segregation ratios for resistant and susceptable individuals for F1 were checked with Chi-square test.
In this research it was determined that Ty-1 and Ty-3a genes did not segregate in the segregating populations and all individuals had both allels together. These results also provided that Ty-1 and Ty-3a were allels of the same gene [11-20].
Disease Assessment
Some breeders could obtain false data in negative and positive results because the they can’t calculate the distance of markers P6-25 stated [21]. Especially; emphasized that faulty results could be obtained from the sources transferred from different wild species of tomato to culture tomato. However, our results of the marker and biological testing were found to be compatible with each other.
The relationhsip between the characteristics of the lines and disease resistance
The length of stem at first inflorescence and stem length of internode directly affects the yield of tomato production. According to [22], the length of internode were determined by the addition effect. Indeterminate varieties have less cluster than determinate varieties so the yield is decrease in indeterminate varieties. For this reason, breeders have preferred the varieties which have short length of stem at first inflorescence and short stem length of internode. However, in this research we determined that as the stem length of internode and the length of inflorescence in tomato increased, the tomato individuals carried homozygous Ty-3a gene. Also the leaf size and the length of internode were determined to be significant in reduction at susceptable tomato plants [23]. Therefore, it can be stated that the length of internode can be used as selection criteria for resistant breeding programme in tomato.
Leaf attitude was evaluated at three different position (erect, horizontal, drooping) according to UPOV. There was a significant positive correlation between resistance to TLYCV and leaf attitude (Table 4). The individuals having leaf at dropping position was resistant to TLYCV indicating that these genotypes carried Ty-3a gene. The producers and breeders generally prefer the tomato variety with horizontal leaf position to prevent the transmission of fungal diseases. Because it believes that the horizontal leaf position can allow the plants to get better air. In contrast to this, we determined that the resistant tomato individuals had drooping leaf position.
Plant habitus was evaluated as weak, medium and strong type. The plant habitus of the resistant tomato individuals were weak type. Also the resistant tomato individuals had long length of inflorescence. Although not statistically significant, there was a negative correlation between resistance to TLYCV and fruit characteristics such as fruit weight and fruit length (Table 3). As the fruit weight decreased, the resistance to TYLCV increased. It was also determined that fruit size was effected with resistance gene and homozygous resistant gene resulted in the middle-small fruit group [15]. Two QTLs for fruit weight were identified on chromosomes 2 and the wild allels were associated with a reduction in fruit weight [24,25-26]. Five QTLs were identified for fruit length and similarly the most significant QTL for fruit length was detected on chromosome 2 [24]. The transfer of resistance genes from wild genotypes to culture forms were effected both the fruit and the morphological structure of the genotypes [27].
As [16-17] pointed, we determined that the resistant individuals had undesirable plant traits such as reduction of the number of fruits per plant and fruit traits. [15] also found a statistically significant and negative correlation between resistance to TLYCV and the number of fruits in the first 4 clusters, the number of branches per plant, the number of fruits per plant and yield per plant. It can be stated that in breeding programs for resistance which don’t use marker technology, resistant genotypes can be eliminated due to their undesirable fruit and plant characteristics such as small sized fruit, weak plant habitus, less number of fruit per plant.