Methodologies for hybridization in predominantly self-pollinating crops: a review

ABSTRACT

Reliable and effective hybridization methods are required in self-pollinating crops for genetic analysis, recurrent selection and large-scale production of hybrid seed. The objective of this review was to document the different methodologies available for hybrid seed production in predominantly self-pollinating crops. Various methods have been used for hybrid seed production, each with its own advantages and limitations. To obtain a limited quantity of hybrid seed, mechanical emasculation combined with hand pollination remain the most widely used technique. However, these methods are labor-intensive and expensive when a continuous supply of large quantities of hybrid seed is required. Genetic male-sterility systems provide opportunities for large-scale hybrid seed production. However, the occurrence of natural male sterility is rare, and when available, it may not always provide compatible combinations with desirable agronomic attributes. Temporal male sterility can be achieved by the application of chemical hybridizing agents (CHAs), which render the pollen non-viable but maintain female fertility. CHAs hold promise for hybrid seed production because they are easy to use, particularly for field crops that are predominantly self-fertilizing. The cost and variable response of different crops and genotypes to various concentrations of CHAs present technical challenges for their widespread adoption. The choice of crossing method in each breeding program is influenced by the amount of seed required, crop species, level of technical expertise required, availability of cytoplasmic male-sterile lines and access to cheap and effective CHAs. This review provides guidance to plant breeders and seed producers in selecting a suitable crossing method for hybrid seed production in self-pollinating crops.

KEYWORDS:

• Chemical hybridizing agents
• cytoplasmic male sterility
• manual emasculation
• hybrid breeding
• self-pollinating crops

Acknowledgments

The first author acknowledges the following: Ph.D. Scholarship granted by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) under the second phase of the ‘Harnessing Opportunities for Productivity Enhancement (HOPE II) for Sorghum and Millets in Sub-Saharan Africa’ project funded by the Bill & Melinda Gates Foundation (BMGF); study fellowship granted by the Institute for Agricultural Research Samaru, Ahmadu Bello University Zaria Nigeria and; the technical support provided by the African Centre for Crop Improvement (ACCI) of the University of KwaZulu-Natal (UKZN) South Africa.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the The International Crops Research Institute for the Semi-Arids Tropics [(RDWCA/BKO/RD/RT-AG/2018/00102)].