نوع مقاله : مقاله پژوهشی
نویسندگان
1 موسسه تحقیقات اصلاح و تهیه نهال و بذر، سازمان تحقیقات، آموزش و ترویج کشاورزی، کرج، ایران
2 مؤسسه تحقیقات اصلاح و تهیه نهال و بذر، سازمان تحقیقات، آموزش و ترویج کشاورزی، کرج، ایران
چکیده
کلیدواژه‌ها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Introduction[1]
The pathogenic fungus, Fusarium oxysporum f.sp. carthami (FOC) is one of the main causal agent of safflower damping-off in Iran and worldwide. Climate change and extending of safflower farming area, specifically in rainfed systems have caused considerable crop loss in recent years. This pathogen can cause damping-off in any growth stage.
Materials and Methods
The pathogen FOC was isolated from infected plants, purified by single sporing, identified to species level, followed by the pathogenicity test in the lab condition on the Petri plates containing SNA media using Soffeh, a cultivar of safflower. A high pathogenic isolate of FOC was selected for further investigation for disease resistance evaluation test in greenhouse condition. Resistance level of 16 safflower genotypes was determined using inoculum layer test method in which infestation of sterile soil was implemented using fungal mycelial mat cultured on agar disk. Each genotypes comprised of six replications. Three pots inoculated and three un-inoculated as the mock. 45 days later, the plants uprooted and washed. Since disease scoring might vary a lot in replications, three more traits including plant height, aboveground biomass weight and root weight were recorded in inoculated and un-inoculated pots and then compared with each other. In addition, disease severity (DS) using a 0-5 scale were recorded for each plant. Reduction percent of plant height (PHR), root weight reduction percent (RWR) and biomass reduction percent weight (PBR) were calculated using data obtained from inoculated and un-inoculated pots and subjected to statistical analysis using R programming software. Since dwarfing of the inoculated plants was an important symptom in the field and greenhouse, a disease index (DI) was identified by multiplication of PHR and DS for each genotype. All the traits were subjected to analysis of variance and comparison of means by least significant difference (LSD) method. Correlation test was conducted between all the traits to find if there is any statistically significant correlation between them. Reaction of genotypes to the disease was shown by a partitional cluster plot using k-means algorithm.
Results and Discussion
Different Fusarium species were isolated from infected root and crown of safflower. Fusarium spp. and Macrophomina phaseolina were the top two main agents of damping-off isolated from safflower farms in Karaj and Zabol. Three different pathogenic Fusarium species including F. oxysporum, F. solani and F. verticillioides were isolated out of 30 infected samples. G186 as a very aggressive isolate of FOC was selected in order to screen the genotypes in the greenhouse. Analysis of variance of the traits which measured in greenhouse showed that all of them are statistically different at 1% level. Least square difference (LSD) multiple comparison of the RWR trait showed that the cultivar Goldasht has the lowest decrease in root weight compared to the control. This cultivar had the lowest decrease in PBR and PHR traits among the genotypes as well. Comparing DI of 16 genotypes indicated that Goldasht had the lowest index followed by L160 and L136. Therefore, they can be considered the most tolerant ones to FOC. The Pearson correlation test suggested a statistically significant difference between the traits RWR and PBR. PHR had a stronger correlation with PBR, as well. Partitional clustering revealed 4 different clusters in which resistant genotypes including Goldasht, L160 and L136 grouped in the same cluster while the susceptible ones including Padideh, Ghazzaghi, L72 and L111 grouped together in another cluster.
Conclusion
Fusarium oxysporum was frequently isolated in Karaj and Zabol fields and is expected to be a major pathogen of safflower in other safflower growing areas that needs to be verified by collecting more samples. The inoculum layer test method of inoculation seems to be an effective method to cause disease symptoms on safflower genotypes. However, there should be more tests on safflower-Fusarium interaction using different Fusarium species., i.e. F. solani and F. verticillioides to find more sources of resistance using different methods of inoculations. Most of the worldwide researches on pathobreeding of safflower to Fusarium are conducting using FOC isolates. Isolation of F. verticillioides frequently in this research might indicate that this species can be an important threat to this crop in the coming years. This species is known to cause crop loss mainly in aboveground parts of corn and sorghum farms but now it is frequently observed in safflower fields. Application of machine learning techniques to cluster different genotypes based on their reaction to the disease might be regarded as a useful method to find reaction of each genotype to the disease more accurately.
کلیدواژه‌ها [English]
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