“Genomic Selection Strategies to Increase Genetic Gain in Tea Breeding Programs”, Nelson Lubanga, Festo Massawe, Sean Mayes, Gregor Gorjanc, Jon Bančič2022-11-09 (breeding, tea)⁠:

Tea [Camellia sinensis (L.) O. Kuntze] is mainly grown in low/middle-income countries (LMIC) and is a global commodity. Breeding programs in these countries face the challenge of increasing genetic gain because the accuracy of selecting superior genotypes is low and resources are limited. Phenotypic selection (PS) is traditionally the primary method of developing improved tea varieties and can take over 16 years. Genomic selection (GS) can be used to improve the efficiency of tea breeding by increasing selection accuracy and shortening the generation interval and breeding cycle.

Our main objective was to investigate the potential of implementing GS in tea-breeding programs to speed up genetic progress despite the low cost of PS in LMIC. We used stochastic simulations to compare 3 GS-breeding programs with a pedigree and PS program [maximizing a single trait, ‘tea yield’]. The PS program mimicked a practical commercial tea-breeding program over a 40-yr breeding period.

All the GS programs achieved at least 1.65× higher genetic gains than the PS program and 1.4× compared with Seed-Ped program. Seed-GSc was the most cost-effective strategy of implementing GS in tea-breeding programs. It introduces GS at the seedlings stage to increase selection accuracy early in the program and reduced the generation interval to 2 years. The Seed-Ped program outperformed PS by 1.2× and could be implemented where it is not possible to use GS.

Our results indicate that GS could be used to improve genetic gain per unit time and cost even in cost-constrained tea-breeding programs.

…conventional tea breeding is well established in the major tea-growing countries such as China, India, and Kenya and has led to the development of many superior varieties (Chen et al 2012_12ya). In Kenya, Tea Research Institute has in the past released high yielding and good quality varieties such as TRFK 31/8 and TRFK 303/577 and TRFK 6/8 (Kamunya et al 2012_12ya). These varieties are widely cultivated by most smallholders and the main multinational tea companies in Kenya. To sustain long-term tea production and the increasing demand for tea, breeders need to continuously bring new improved varieties to the market. Tea-breeding goals vary among the major tea-growing countries, depending on local needs. However, in the recent times, the most important tea-breeding objectives are to develop varieties with high yield and improved quality (ie. color, aroma, taste, and mouthfeel) (Kamunya et al 2012_12ya; Mondal2014). Currently, tea productivity is seriously threatened by climate change, which is already causing yield losses and decreased quality (Gunathilaka et al 2017). Climate change has led to extreme and unpredictable weather patterns, resulting in longer dry spells, heavy rainfall, more hail, higher temperatures, and increased attacks of pests and diseases (Marx et al 2017). Therefore, effective tea-breeding strategies that use genomic-assisted breeding are needed to develop high-yielding and high-quality tea varieties that are also tolerant to biotic and abiotic stresses (Mondal2011; Muoki et al 2020)…Tea-breeding programs traditionally use recurrent phenotypic selection (PS) to identify the best individuals based on phenotypic values estimated from the per se performance of clones in evaluation trials. This involves the creation of genetic variation through crossing, followed by many years of testing to determine the genetic value of promising genotypes, leading to the identification of genotypes that will serve as new parents for crossing and for the commercial release (Kamunya et al 2012_12ya). In the initial phase of the breeding program, new genotypes are first tested as seedlings in single bush (preliminary) trials. Then, selected seedlings are clonally propagated allowing the clones to be tested across multiple locations and years (Carr2018). The PS has been somewhat successful in delivering improved tea varieties over many years (Mondal2014). However, it is a time-consuming process as it takes about 16 yr to develop new varieties for commercial release (Figure 1).

See Also:

• Assessing the response to genomic selection by simulation

• Plant breeders should be determining economic weights for a selection index instead of using independent culling for choosing parents in breeding programs with genomic selection

• Using high-throughput phenotypes to enable genomic selection by inferring genotypes

• The value of early-stage phenotyping for wheat breeding in the age of genomic selection

• Genome-wide selection and genetic improvement during modern maize breeding

• Phenomic selection: a low-cost and high-throughput alternative to genomic selection

• Genetic architecture and genomic prediction accuracy of apple quantitative traits across environments