Correlation of Root Anatomical Components with Resistance in Sugar Beet Genotypes to Cyst Nematode Heterodera schachtii Schmidt 1871

Sugar beet cyst nematode (SBCN), Heterodera schachtii Schmidt 1871, marked as one of the most damaging disease of sugar beet worldwide. This is also an important disease pathogen of sugar beet which had an irreversible damage to this particular crop in Isfahan Province, Iran. Thus, the nematode - infested fields of sugarbeet in the province is to be threatened. This nematode has a wide host range, over 218 plant species from 95 genera, belonging to 23 families, including field crops, ornamentals and weeds as the hosts, which have been identified and introduced so far. The SBCN management's strategies are included as a long term crop rotation, use of catch crops, soil solarization, early planting and the use of nematicides. In general, the best method to control SBCN is use of resistant sugar beet cultivars.
In this study, the resistance and anatomical components of 70 sugar beet genotypes were screened against sugar beet cyst nematode (SBCN), Heterodera schachtii. Thus, the susceptibility of 70 sugar beet genotypes were assessed to sugar beet cyst nematode, H. schachtii in a completely randomized design in greenhouse and a complete randomized block design under the field conditions. The data were subjected to statistical analysis using SAS software and the means were compared using Duncan´s multiple test range. Cluster analysis was performed by the SPSS software. The initial population of SBCN in the infested soil was determined, before treating the selected field. Then, 200 g of soil were selected, out of which several samples collected from each plot and was air dried and in the file system, the cysts were extracted using Fenwick. Eggs and the second larvae in a 200 g of soil were calculated accordingly. Reproductive factors and the percent decrease and or increase in SBCN populations in each genotype were calculated relative to the initial population of the same treatment. Then, the comparison of means was done by Duncan tests. For the greenhouse experiments, the same treated soils from each treatment in field were poured into the clay pots with a capacity of 5 kg of soil. Initially, the genotypes based on sensitivity spectral to sugar beet cyst nematode were classified into 5 distinct groups of resistant, moderately resistant, tolerant, moderately susceptible and susceptible ones. Then, the root anatomical components of the sugar beet genotypes, such as the thickness of periderm, and skin parenchyma thickness were determined in microns.
The screening of sugar beet genotypes resulted in identifying the resistant and or susceptible ones to H. schachtii with a high significant difference under the field and greenhouse conditions. The combined results of greenhouse and field experiments coupled with cluster groups showed that, the genotypes 53 (SB-2), 69 (NE 0911), 16 (SB32-HSF-5) had the minimum number of cysts and the genotype of 16 (SB32-HSF-5) and 5 (SB31-HSF-2) had the lowest rates of eggs and larvae and reproductive factors. So, the two lines of 16 (SB32-HSF-5) and 5 (SB31-HSF-2), were identified as the most resistant genotypes and were located in the same cluster group in these studies. Therefore, it can be concluded that, these genotypes can be used as the nematode resistant genotypes and also, in breeding programs. The maximum thickness of the periderm was in the resistant genotype SB32 with 536.27 micron and was followed by resistant genotypes F-20747, F-20746, SB31-HSF-2, and SB27-HSF -10, with 480, 445.87, 436 and 419.47 microns respectively. The minimum thickness of the periderm was in susceptible genotypes SB35-HSF-8, F-20583 and SB35 with, 194.13, 258.67, and 319.47 microns, respectively. Also, the maximum thickness of the cortex parenchyma was in genotype F-20746 with 438.93 micron, followed by the genotypes 3 (SB27-HSF-10), 62 (F-20583), 29 ((7112 * SB36) * S1-11) and 8 (SB31-HSF-7) with 403.20, 402.40, 360.53, 344.27 and 323.73 microns, respectively. The minimum cortex parenchyma thickness was in susceptible genotypes SB32-HSF-10 and F-20603 with an average of 210.13 and 213.33 microns respectively. The other genotypes were located in between these two ranges. These results suggest a direct correlation coefficient between these characteristics of anatomical features and the resistance of some genotypes tested for the sugar beet cyst nematode disease.
1- It was found that, there are resistant genotypes among the tested sugar beet lines for cultivation and or breeding program.
2- It also was found that, there is certain and direct correlation coefficient between the sugar beet root anatomical features and the resistance of some genotypes.
3- The thickness of the periderm and cortex parenchyma as a physical barrier plays an important role in resistant of sugar beet to cyst nematode.