Abstract
Yam (Dioscorea spp.) is a staple crop for millions of people in the tropics and subtropics. Its genetic improvement through breeding is being challenged by pre-zygotic and post-zygotic cross-compatibility barriers within and among species. Studies dissecting hybridization barriers on yam for improving the crossability rates are limited. This study aimed to assess the cross-compatibility, which yielded fruit set, viable seeds and progeny plants in an extensive intraspecific and interspecific crossing combinations in a yam genetic improvement effort to understand the internal and exogenous factors influencing pollination success. Cross-compatability was analyzed at the individual genotype or family level using historical data from crossing blocks and seedling nurseries from 2010 to 2020 at the International Institute of Tropical Agriculture (IITA). The average crossability rate (ACR) was lower in interspecific crossing combinations (6.1%) than intraspecific ones (27.6%). The seed production efficiency (SPE) values were 1.1 and 9.3% for interspecific and intraspecific crosses, respectively. Weather conditions and pollinator's skills are the main contributors to the low success rate in the intraspecific cross combinations in yam breeding. At the same time, genetic distance and heterozygosity played little role. Interspecific cross barriers were both pre-zygotic and post-zygotic, resulting from the evolutionary divergence among the yam species. Dioscorea rotundata had higher interspecific cross-compatibility indices than D. alata. Distant parents produced intraspecific crossbred seeds with higher germination rates compared to closest parents (r = 0.21, p = 0.033). This work provided important insights into interspecific and intraspecific cross-compatibility in yam and suggested actions for improving hybridization practices in yam breeding programs.
Highlights
Yam (Dioscorea spp.) is a staple crop for millions of people in the tropics and subtropics
Yam breeding is instrumental in developing improved varieties, packaged in the form of seed, possessing superior yield and food quality attributes for different market segments and production environments
At the Ibadan station, the temperature was stable across years while the rainfall was erratic and significantly fluctuated from year to year (Fig. S1a)
Summary
Yam (Dioscorea spp.) is a staple crop for millions of people in the tropics and subtropics. This study aimed to assess the cross-compatibility, which yielded fruit set, viable seeds and progeny plants in an extensive intraspecific and interspecific crossing combinations in a yam genetic improvement effort to understand the internal and exogenous factors influencing pollination success. Yam breeding is instrumental in developing improved varieties, packaged in the form of seed, possessing superior yield and food quality attributes for different market segments and production environments. Breeding objectives are diverse and include high and stable tuber yield, outstanding nutritional and processing qualities, pest and disease resistance, and ecological adaptation traits[2] To achieve these objectives, crop breeding relies on identifying desirable genes in source germplasm: landrace, breeding line, wild relatives, and their successful transfer to the agronomically and nutritionally preferred background. The domesticated yam species primarily propagate vegetatively via tubers or bulbils than the botanical seeds
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