Breeding synthetic varieties in annual caraway: observations on the outcrossing rate in a polycross using a high-throughput genotyping system

Abstract

Caraway (Carum carvi) is an economically important spice and medicinal plant of the Apiaceae family (syn. Umbelliferrae). Farmers often favor annual cultivation of caraway. However, the annual varieties, which are currently available, do not provide satisfying seed yields. Employing heterosis can be a promising approach to increase yield. Breeding of synthetic varieties utilizes heterosis and may be the method of choice for future caraway breeding. Knowledge of the outcrossing rate is important to evaluate the effectiveness of this breeding method. However, the outcrossing rate of caraway is unknown so far. We estimated the outcrossing rate of seven inbred lines under field conditions in a neighbor-balanced polycross design. For this purpose, we implemented a high-throughput genotyping system (PACE), accompanied by a high-throughput method for DNA extraction adapted to caraway. In total, more than 1300 individual plants were genotyped. We found a high variability of lines regarding outcrossing rate and other traits associated with flowering. The outcrossing rate was on average 66.5% and ranged from 51.6 to 82%. We discussed implications of our findings on the targeted breeding method.

On heterosis, inbreeding depression and general combining ability in annual caraway (Carum carvi)

“…They could be valuable traits to select for higher yield particularly in breeding stages that do not allow reliable yield estimations. The strong correlations with yield were already detected within the polycross data (von Maydell et al 2020). Probably, late developing genotypes will not play any role in future breeding processes because of the low seed yields of these genotypes.…”

“…The development of the breeding material used in this study was described in von Maydell et al (2020). Briefly, we used inbred material in the fourth and fifth inbred generation that originated from crossings between biennial and annual material.…”

“…The prior evaluation of the polycross revealed that we could not assume completely random pollination in the polycross. Furthermore, inbred lines had different outcrossing rates (von Maydell et al 2020). Without knowledge of the paternal side of the F 1 populations, we can compute neither mid-parent heterosis, nor better-parent heterosis for each line.…”

“…Recently, we revealed a mixed mating system with predominant outcrossing within a set of caraway inbred lines, which were placed in a polycross. The outcrossing rate was 66.5% on average and ranged from 51.6 to 82.0% (von Maydell et al 2020). Predominant outcrossing suggests that heterosis can be exploited in caraway.…”

“…In the year 2018, we conducted a polycross based on a set of 18 breeding lines of the fourth and fifth inbred generation. This polycross had already been used to investigate the outcrossing rate (von Maydell et al 2020). In this study as a consecutive step, we wanted to detect whether and to what extent heterosis can be exploited in caraway.…”