# Evaluation of Fire Blight Resistance of Eleven Apple Rootstocks Grown in Kazakhstan Fields
## 3 Results  
### Observing and Tracking the Occurrence of Fire Blight in Rootstock Fields  
Disease monitoring was conducted in four different fields of eleven rootstock types for two years (2021-2022), considering the weather conditions. The DDI in 2021 was slightly higher in the 'B.9' and 'Zh.5' fields compared to other rootstocks, with the index of 7.1% and 6.3% respectively. Less than 5% of disease distribution was observed in remaining rootstock types. Considering the results of DDI in 2022, the highest DDI was observed in the 'B.9' field, with a disease prevalence of 16.9%. According to the DDI scale, the field received a rating of 2, which corresponded to the brown polygon (Figure 1, Table 4). '62-396', 'G.41', and 'G.16' showed zero prevalence of disease and corresponded to light green polygons. The DDI among other rootstocks remained below 10% and indicated green-brown polygons (Figure 1). \begin{table}
\begin{tabular}{l c c} \hline \hline
**Region** & **Rootstock** & **2021** & **2022** \\ \hline \multirow{6}{*}{Almaty} & 62-396 & 0 & 0 \\ \cline{2-3}  & M9 & 1 (3.2\%) & 1 (7.1\%) \\ \cline{2-3}  & Apm 18 & 1 (5.4\%) & 1 (8.5\%) \\ \cline{2-3}  & G.41 & 0 & 0 \\ \cline{2-3}  & G.16 & 0 & 0 \\ \cline{2-3}  & B.9 & 1 (7.1\%) & 2 (16.9\%) \\ \cline{2-3}  & Zh.5 & 1 (6.3\%) & 1 (9.7\%) \\ \cline{2-3}  & B.7-35 & 1 (4.1\%) & 1 (7.4\%) \\ \cline{2-3}  & B.16-20 & 1 (2.7\%) & 1 (5.2\%) \\ \cline{2-3}  & _M. siversii_ & 1 (3.1\%) & 1 (6.8\%) \\ \hline Almaty, Turkistan & MM106 & 1 (2.2\%) & 1 (5.0\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Disease distribution index values in 2021 and 2022. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**SNP Marker** & **LG \({}^{*}\)** & \begin{tabular}{c} **Gene/Locus** \\ **Name** \\ \end{tabular} & \begin{tabular}{c} **SNP ID** \\ \end{tabular} & \begin{tabular}{c} **Taqman Assay** \\ **ID** \\ \end{tabular} & \begin{tabular}{c} **SNP** \\ **Type** \\ \end{tabular} & \begin{tabular}{c} **Reference** \\ \end{tabular} \\ \hline FB-MR5-K35 & 3 & MR5 & \
\begin{tabular}{c} FB-MR5- \\ NZsneH034548\_K35 \\ \end{tabular} & AH0 JFXM & G/T & [35] \\ \hline FB-MR5-R249 & 3 & MR5 &
\begin{tabular}{c} FB-MR5- \\ NZsneH034548\_R249 \\ \end{tabular} & AH21B92 & A/G & [35] \\ \hline FB-MR5-rp16k15\_M106 & 3 & MR5 & FB-MR5-rp16k15\_M106 & AH4 AAGA & A/C & [35] \\ \hline RLP1a & 3 & RLP1 & RLP1a & AH5I8 MI & C/A & [9] \\ \hline RLP1b & 3 & RLP1 & RLP1b & AH6R6 SQ & A/T & [9] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Description of the five single-nucleotide polymorphisms (SNPs) analyzed in rootstock types. Evaluation of the DDI results showed that fire blight occurrence was nearly twice as high in 2022 than in 2021 (Table 4). However, no severe infection was detected in any of the fields in 2022 because any trees identified as pathogen-positive based on qPCR testing were immediately eliminated. The maximum DSI was less than 5%. Real-time PCR analysis was conducted using the primers hpEaF and hpEaR and the probe hpEaP targeting _E. amylovora_ chromosomal DNA [33]. All apple rootstocks exhibiting fire blight symptoms were analyzed by qPCR testing. The maximum DSI value of 1.87 was recorded for the B9 rootstock in the AIL field. DDI values of 1 were obtained for eight rootstocks except 62-396, G.41, and G.16, all of which showed zero DDI (Figure 1). A strong correlation between levels of infection and weather conditions has previously been demonstrated. Researchers have found that temperature, humidity, and precipitation are the most important factors for disease development [37; 38]. The temperature and air humidity in early spring are crucial because bacteria overwintering in cankers begin to spread by insects, birds, rain, wind, and equipment. Wounds in shoots occur during mechanical treatments of trees, and roots act as a gateway for the entrance of pathogens into rootstocks [16; 39].