Breeding of sweet potatoes | Indigenous/traditional African vegetables | Potatoes | Genebanks | Biotechnology | Agro-processing
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Dr AB Assefa
Project Team Leader


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​Roelene Pienaar
Research Technician
Phone: +27 (0)12 808 8000


Researcher

Onion

Onion is the third most important vegetable crop after tomato and watermelon globally. In South Africa, onion is the third largest vegetable crop, following potato and tomato, and the annual production exceeds 500 000 metric tons. In many African sauces, onion is an essential ingredient and a source vitamins, minerals, trace elements, phenolic compounds and antioxidantive flavonoids.  Onion breeding at the Agricultural Research Council started in 1947, with the aim of developing improved short-day onion cultivars.  In 1972, a breeding programme for intermediate-day onions initiated. Improved cultivars were developed by crossing short and intermediate-day lines, which inherently have multiple bulb scales, high bulb firmness and uniformity with adaptation to local conditions. Three open-pollinated short-day cultivars, namely Pyramid (1968), Bon Accord (1968), and Radium (1987), and five intermediate-day cultivars namely Roël (1987), Rion-1, Rion-2, Rion-3, and Rion-4 (all in 1992) were released.  In 1980, the breeding of male-sterile and maintainer lines for both day lengths was initiated. Since then several well-adapted male-sterile and maintainer lines for both day lengths were developed. Currently, the breeding program has been limited to maintenance of the available germplasm.

In South Africa, almost all the onion breeding activities have been done by private seed companies. The majority of onion cultivars on the market are hybrids, most of which are imported, and owned by a few seed companies. Smallholder farmers are not benefitting from the available technologies because of the high seed price and input requirements of the onion hybrids. To alleviate poverty and food insecurity in the rural community, priorities must be given to improve the livelihoods of smallholder farmers. In recent years, encouraging results have been observed on home gardening, especially in semi-urban and urban areas with small plots of vegetables. Farmers grow vegetables such as cabbages, onions, tomatoes, chilli peppers, carrots and potatoes in their homesteads for consumption and to earn income. Through a planned project, the ARC wishes to play a role in promoting small scale vegetable production by developing low input, improved cultivars, providing training and technical support. The main objectives of the onion breeding program will be to develop onion cultivars (new improved hybrids and open pollinated cultivars) with enhanced bulb yield and quality, tolerance to heat and drought, as well as resistance to pests and diseases for both commercial and smallholder farmers.

The onion project at the ARC makes use of molecular markers that facilitate the selection of male sterile and maintainer parental lines. Male sterility is important to prevent self-pollination and loss of the onion hybrid genotype. Classic methods (test crosses) require 4-8 years of progeny testing before the cytoplasm type can be determined. Accurate and time-saving PCR molecular markers and custom TaqMan® SNP genotyping assays were found to be efficient in screening the ARC onion lines rapidly for their cytoplasmic and nuclear male sterility genotype. The molecular marker methods are used in the production of the correct seed for commercialization of ARC onion lines.


Publications:

Gazendam I, Greyling MM, & Laurie SM. 2018. The application of molecular markers to accelerate the recovery of cytoplasmic and nuclear male sterility in South African onion hybrid parental lines. Journal of Agricultural Science 10(7): 95-109

Lodama, K.E., Gerrano, A.S, Laurie, SM., Mavengahama, S. & Adebola, P.O. 2018. Response of prolonged storage time and growth media on seedling emergence of onion (Allium cepa L.) in South Africa. Acta Horticulturae 1204: 33-39.


 ​Harvested onion bulbs

Onion flowers exhibiting male fertile (pollen-producing) phenotypes

Onion flowers exhibiting male-sterile phenotypes

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Multiplex PCR products of onion nuclear AcSKP1 (Huo et al. 2015) and cytoplasmic orfA501 (Engelke et al. 2003) male sterility markers on selected samples of onion breeding line R1201 B (seed lot S09-002), harvested from the open field in 2015. M: Molecular weight marker VI (Roche Diagnostics). Lanes 1-6: Individual plants from seed lot S09-002. Their nuclear (MsMs, Msms and msms) and cytoplasmic (S or N) genotypes are indicated below the numbers. Lane 7: negative water control. Expected fragment sizes are indicated on the left with black arrows. Msms: 898bp; Msms: 898+628bp; msms: 628bp; S cytoplasm: 473bp.


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