Document Type : Original Article
Authors
1
PhD, Department of Plant Production and Genetics, Shahid Bahonar University of Kerman, Kerman, Iran.
2
Assistant Professor, Department of Plant Production and Genetics, Shahid Bahonar University of Kerman, Kerman, Iran.
3
Professor, Research and Technology Institute of Plant Production (RTIPP), Afzalipour Research Institute, Shahid Bahonar University of Kerman, Kerman, Iran.
4
Professor, Department of Plant Production and Genetics, Shahid Bahonar University of Kerman, Kerman, Iran.
5
Associate Professor, Research and Technology Institute of Plant Production (RTIPP), Afzalipour Research Institute and Department of Plant Production and Genetics, Faculty of Agriculture, Shahid Bahonar University of Kerman, Kerman, Iran.
Abstract
Objective
Achieving isogenic lines is a limitation in breeding programs due to the time-consuming nature of the process. The present study aims to optimize a speed breeding method concurrent with the production of isogenic lines derived from a backcross of bread wheat (cultivars Roshan and Kalheydari) with the early heading Australian cultivar Excalibur. This is to investigate the genetic status and effects of vernalization and photoperiod genes on earliness, yield, and yield components.
Materials and Methods
In the current study, early heading BC3F2 generation plants, obtained through a backcrossing method from the Excalibur cultivar to the Roshan and Kalheydari cultivars in previous studies, were crossed with the recurrent parent (Roshan/Kalheydari) to obtain the BC4F1 generation. Both parents and progeny were evaluated for vernalization and photoperiod genes using specific markers. Before planting, seeds of each generation were dried in an oven (29°C) for 120 hours, then stored for 72 hours in a refrigerator (4°C) after a 0.5 ppm gibberellic acid treatment. Subsequently, they were sown in an optimized medium consisting of cocopeat, decomposed manure, sand, and field soil. Lighting racks equipped with 18 LED lamps and timers provided 16:8 (darkness/light) photoperiod cycles. The greenhouse temperature was controlled at 21-24°C. The development of BC5F1 to BC5F4 generations under greenhouse conditions using this method allowed for speed breeding in a year. Throughout these generations, only heterozygous plants were selected using specific markers. In the BC5F5 generation, based on molecular test results, homozygous lines were chosen for final field trials.
Results
In this research, through optimized greenhouse-based speed breeding and the development of five backcross generations and four selfing generations, the Ppd-D1b/Ppd-D1b and Ppd-D1a/Ppd-D1a isogenic lines were obtained within the genetic background of the Roshan and Kalheydari cultivars. Additionally, Vrn-B1a/Vrn-D1a, Vrn-B1a/vrn-D1, vrn-B1/Vrn-D1a, and vrn-B1/vrn-D1 isogenic lines were obtained within the genetic background of Roshan. The results indicated that marker-assisted selection for a combination of the Vrn-B1 and Vrn-D1a vernalization alleles could reduce the number of days to heading by approximately ten days. In contrast, within a backcross breeding program for heading (phenotypic selection) in the same genetic background (Roshan), heading was 14 days earlier. The vrn-B1/Vrn-D1a was the isogenic line exhibiting the fewest days to ripening in both trials. The Vrn-B1a/Vrn-D1 and Vrn-B1a/Vrn-D1a isogenic lines, respectively, showed the highest number of days to ripening under well-watered and rainfed conditions. The selection of the Ppd-D1a allele in the current study indirectly improved heading in the Roshan and Kalheydari genetic backgrounds by 4.25 and 6.03 days, respectively. The production of the BC5F1 generation within a 65-day timeframe from planting, with the genotypes entering the heading stage, facilitated the cross-pollination.
Conclusion
Year-round marker-assisted backcrossing in a greenhouse is feasible without requiring phenotypic selection. Given the recovery of a significant portion of the recurrent parent's genome over generations, shortening the breeding cycle using new technologies like accelerated breeding methods can increase genetic progress without a substantial increase in population size.
Keywords
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