Evidence for the Application of Emerging Technologies to Accelerate Crop Improvement – A Collaborative Pipeline to Introgress Herbicide Tolerance Into Chickpea

Abstract

Accelerating genetic gain in crop improvement is required to ensure improved yield and yield stability under increasingly challenging climatic conditions. This case study demonstrates the effective confluence of innovative breeding technologies within a collaborative breeding framework to develop and rapidly introgress imidazolinone Group 2 herbicide tolerance into an adapted Australian chickpea genetic background. A well-adapted, high-yielding desi cultivar PBA HatTrick was treated with ethyl methanesulfonate to generate mutations in the ACETOHYDROXYACID SYNTHASE 1 (CaAHAS1) gene. After 2 years of field screening with imidazolinone herbicide across >20 ha and controlled environment progeny screening, two selections were identified which exhibited putative herbicide tolerance. Both selections contained the same single amino acid substitution, from alanine to valine at position 205 (A205V) in the AHAS1 protein, and KASP™ markers were developed to discriminate between tolerant and intolerant genotypes. A pipeline combining conventional crossing and F2 production with accelerated single seed descent from F2:4 and marker-assisted selection at F2 rapidly introgressed the herbicide tolerance trait from one of the mutant selections, D15PAHI002, into PBA Seamer, a desi cultivar adapted to Australian cropping areas. Field evaluation of the derivatives of the D15PAHI002 × PBA Seamer cross was analyzed using a factor analytic mixed model statistical approach designed to accommodate low seed numbers resulting from accelerated single seed descent. To further accelerate trait introgression, field evaluation trials were undertaken concurrent with crop safety testing trials. In 2020, 4 years after the initial cross, an advanced line selection CBA2061, bearing acetohydroxyacid synthase (AHAS) inhibitor tolerance and agronomic and disease resistance traits comparable to parent PBA Seamer, was entered into Australian National Variety Trials as a precursor to cultivar registration. The combination of cross-institutional collaboration and the application of novel pre-breeding platforms and statistical technologies facilitated a 3-year saving compared to a traditional breeding approach. This breeding pipeline can be used as a model to accelerate genetic gain in other self-pollinating species, particularly food legumes.

Breeding More Crops in Less Time: A Perspective on Speed Breeding

“…Applications of SB include the development of biparental and more complex mapping populations, pyramiding traits, hastening backcrosses, phenotyping adult plant traits, mutant studies, and genetic transformation experiments [ 7 , 29 ]. Recent research has shown the power of combining emerging techniques, such as gene editing, high-throughput phenotyping and genotyping, genomic selection (GS), and MAS, with SB for accelerating crop improvement [ 30 , 40 , 42 , 43 , 44 , 45 , 46 ]. Furthermore, the cost and space requirements for producing a large number of inbred lines can be minimized by planting them at high plant densities [ 47 ].…”

“…Since 2016, SB has been integrated within all cool-season legume public breeding programs in Australia, with more than 45,000 individuals processed through an aSSD platform at the University of Western Australia. The resulting RILs have been used for gene-trait associations [ 43 , 44 , 45 , 46 ], and SB has been integrated with other technologies to accelerate cultivar development pipelines [ 40 ].…”

“…The method illustrates efficient exploitation of resources by analyzing multiple traits for the same group of plants. Selection in the early generation under SB improves genetic gain in breeding programs, as well as curtailing the time required to incorporate desirable traits in breeding populations [ 40 , 49 ]. Phenotyping of wheat or other important crops under SB conditions can be further improved through MAS.…”

“…SB technology has facilitated rapid phenotyping in wheat and the analysis of multiple disease-resistance traits in European two-rowed barley [ 15 , 30 ]. A combination of SB technology and marker-assisted selection (MAS) has accelerated development of herbicide-tolerant chickpea [ 40 ] and the introgression of valuable allelic variation from wild relatives in lentil [ 41 ]. These practical breeding outcomes highlight the potential of the global suite of SB techniques to substantially accelerate genetic gain.…”

Biotechnological Road Map for Innovative Weed Management

“…Similarly, novel genetic variation can be induced using chemical mutagenesis to create mutant populations, in turn producing new allelic variants and/or discovering new modes of action for weed control. Implementation of this method can be seen where imidazolidinone tolerance in wheat ( Newhouse et al, 1992 ) and chickpea ( Croser et al, 2021 ) was produced using ethyl methanesulfonate (EMS) mutant population. Leucaena leucocephala is another example of the implementation of chemical mutagenesis for weed management.…”