واکنش برخی از ژنوتیپ های گندم نان آبی برنامه های ملی به نژادی اقلیم های معتدل و گرم و مرطوب شمال نسبت به زنگ‌های زرد و ساقه در مرحله گیاهچه‌ای و گیاه بالغ

Lack of durable resistance in wheat cultivars is a major cause of yellow rust (Puccinia striiformis f. sp. tritici, Pst) and stem rust (Puccinia graminis f. sp. tritici, Pgt) epidemics, which severely affecting global wheat production. This study identified resistance sources at the seedling and adult plant stages among 44 wheat genotypes adapted to temperate and northern warm and humid agro-climatic zones of Iran. Seedling evaluation carried-out at glassohuses at Cereal Research Department, Seed and Plant Improvement Institutie in Kataj, Iran. Field evaluations were conducted in
2018–19 and 2019–20 at the Ardabil Agricultural Research Station. Adult plant resistance was assessed using epidemiological parameters: coefficient of infection (CI), final rust severity (FRS), and relative area under the disease progress curve (rAUDPC). Seedling reactions were evaluated under controlled conditions against two Pst and four Pgt pathotypes. For yellow rust, 12 (27.2%), 20 (45.4%), and 12 (27.2%) genotypes exhibited slow-rusting resistance (SR), all-stage resistance (ASR), and adult plant resistance (APR), respectively. For stem rust, 12 (27.2%) showed SR, 2 (4.5%) had ASR, and 30 (68.2%) were susceptible. Genotypes susceptible at the seedling stage but resistant at the adult stage likely carry multiple APR or slow-rusting genes, offering valuable genetic resources for development of bread wheat cultivars with durable resistance.
 
Keywords: Bread wheat, race-specific resistance, non-race-specific resistance, slow rusting.
 
Introduction
Bread wheat is a staple food crop and essential for global food security, particularly in Mediterranean regions. In Iran, bread wheat production is consistently challenged by some biotic and abiotic stresses. Rust diseases are among the most devastating biotica stresses. The dynamic and rapid evolution of yellow rust (Pst) and stem rust (Pgt) populations may overcome race-specific resistance genes those are deployed in commercial cultivars. Periodic epidemics and substantial economic losses are possibly occurred subsequently (Chen, 2020). The emergence of virulent races such as the Ug99 lineage for stem rust has further highlighted the vulnerability of genetically similar commercial cultivars. In contrast, adult plant resistance (APR), often expressed as slow rusting, is typically polygenic and considered more durable (Huerta-Espino et al., 2020; Singh et al., 2011). This type of resistance slows disease development through mechanisms that are not pathogen race-specific. Therefore, the identification and employment of APR sources into breeding programs is a principal strategy to obtain sustainable bread wheat production. This study was designed to phenotypically characterize a collection of Iranian wheat genotypes for both seedling and adult plant resistance to stripe and stem rusts, with the goal of identifying potential donors of durable resistance.
 
Materials and Methods
The study consisted of controlled seedling tests and field evaluations. Forty-four wheat genotypes from the national bread wheat breeding programs for temperate and northern warm and humid agro-climatic zones were evaluated for their reaction to yellow rust and stem rust at the seedlingand adult plant resistances. For seedling resistance screening, plants were inoculated with two Pst pathotypes (174E150A+, Yr27 and 14E158A+, Yr27) and four Pgt pathotypes (TTTTF, PTRTF, TKTTF, TTKTK). Infection types (ITs) were assessed 14 days post-inoculation using a standardized 0–4 scale. Field evaluations were conducted at the Ardabil Agricultural Research Station over two cropping cycles (2018-19 and 2019-20). Stripe rust was evaluated under artificial epiphytotic conditions, while stem rust was assessed under natural infection. Resistance at the adult plant stage was quantified using three significant epidemiological parameters including final rust severity (FRS), coefficient of infection (CI = FRS × constant value of host response), and the relative area under the disease progress curve (rAUDPC). Genotypes were grouped into four resistance groups: all-stage resistance (ASR), adult plant resistance (APR), slow rusting resistance (SR), and susceptible, based on established thresholds for these parameters (Zeng et al., 2014). Correlation coefficients were calculated to understand the relationships between resistance parameters.
 
Results and Discussion
Seedling screening tests revealed that none of the bread wheat genotypes exhibited resistance to all pathotypes of both rust diseases under controlled conditions. However, significant levels of adult plant resistance were observed in field evaluations. For yellow rust, 12 (27.2%), 20 (45.4%), and 12 (27.2%) genotypes exhibited slow-rusting resistance (SR), all-stage resistance (ASR), and adult plant resistance (APR), respectively. For stem rust, 12 (27.2%) showed SR, 2 (4.5%) had ASR, and 30 (68.2%) were susceptible. Bread wheat genotypes M-97-7, M-97-14, M-97-15, N-97-4, and
N-97-7 demonstrated promising resistance against both diseases. A strong positive correlation were observed between the APR parameters (FRS, CI, rAUDPC), validating their reliability for assessing quantitative resistance (Hei et al., 2015). However, the correlations between seedling infection types (ITs) and adult plant parameters were non-significant. This finding indicated that APR is genetically independent from all-stage resistance (Singh et al., 2011). The superior performance of certain bread wheat genotypes suggests combinations of non-race-specific APR genes, such as Yr18/Lr34 or Yr46/Lr67, which are known for their durable and pleiotropic effects (Huerta-Espino et al., 2020; Chen, 2020). Consequently, gene pyramiding is highly recommended to develop new bread wheat cultivars with robust and long-lasting resistance. Therefore, reducing reliance on fungicides and mitigating the risk of future epidemics driven by emerging virulent pathogen populations (Singh et al., 2011).
 
References
Chen, X. 2020. Pathogens which threaten food security: Puccinia striiformis, the wheat stripe rust pathogen. Food Security, 12(2), pp.239–251. DOI: 10.1007/s12571-020-01016-z
Singh, R.P., Huerta-Espino, J., Bhavani, S., Herrera-Foessel, S.A., Singh, D., Singh, P.K., Velu, G., Mason, R.E., Jin, Y., Njau, P. and Crossa, J. 2011. Race non-specific resistance to rust diseases in CIMMYT spring wheats. Euphytica, 179(1), pp.175–186. DOI: 10.1007/s10681-010-0322-9
Huerta-Espino, J., Singh, R.P., Crespo-Herrera, L.A., Villaseñor-Mir, H.E., Rodriguez-Garcia, M.F., Dreisigacker, S., Barcenas-Santana, D. and Lagudah, E. 2020. Adult plant slow rusting genes confer high levels of resistance to rusts in bread wheat cultivars from Mexico. Frontiers in Plant Science, 11, 824. DOI: 10.3389/fpls.2020.00824
Zeng, Q.D., Han, D.J., Wang, Q.L., Yuan, F.P., Wu, J.H., Zhang, L., Liu, D.J. and Jin, S.L. 2014. Stripe rust resistance and genes in Chinese wheat cultivars and breeding lines. Euphytica, 196(2), pp.271-284. DOI: 10.1007/s10681-013-1029-5