Cereals and Pseudocereals
Pearl Millet ‘HHB 67 Improved’ – Downy Mildew Resistance
THE IMPROVEMENT OF DOWNY MILDEW RESISTANCE IN PEARL MILLET (PENNISETUM GLAUCUM) HYBRID ‘HHB 67’
Stephen Gray; Anthony Mahama; and Walter Suza
Department of Agronomy, Iowa State University, Agronomy Hall 716 Farm House Ln, Ames, Iowa 50011.
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1. SUMMARY
Resistance to downy mildew disease caused by Sclerospora graminicola in pearl millet [Pennisetum glaucum (L.) R. Br.] is crucial due to dramatic yield loss that occurs as a result of downy mildew attacks. Resistance conferred by the original ‘HHB 67’ hybrid was quickly broken down. This led to the development of ‘HHB 67 Improved’, which was developed via marker-assisted and conventional backcrossing of disease resistance into original male and female parent lines. For the original male parent, line ‘H77/833-2’, disease resistance was conferred by marker-assisted selection from the donor line ‘ICMP 451’. The original female parent of HHB 67, line ‘843A/B’, had disease resistance transferred via conventional backcrossing from line ‘ICML 22’ at the International Crops Research Institute for Semi-Arid Tropics (ICRISAT) in India.
The goal was to improve downy mildew resistance in pearl millet hybrid HHB 67.
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2. PROBLEMS ADDRESSED
In the mid 1960’s the release of the first pearl millet hybrids ‘HB1’, ‘HB2’, and ‘HB3’ led to a significant increase in yield throughout India. In 1970-1971, with less than 20% of land being planted to HB3, India recorded a record pearl millet harvest of 8.2 million metric tons. However, this success was short lived as the following year a downy mildew attack reduced the harvest to 4.6 million metric tons (Singh, 1995). Subsequent hybrid releases with improved adaptability to growing conditions within India gradually raised production back to 6 million metric tons; however, disease resistance of these improved hybrids would fade quickly (Pray & Nagarajan, 2009). As a result, the success of pearl millet hybrids is short-lived and breeding efforts moved quickly to ensure the stability of pearl millet production.
The release of the popular pearl millet hybrid ‘HHB 67’, in the 1990’s provided farmers with the ability to capture high yields in a short duration providing the opportunity to double crop. While ‘HHB 67’ would raise production levels to 9 million tons, downy mildew disease would still inhibit ‘HHB 67’ from realizing maximum yield potential (Pray & Nagarajan, 2009). As a result, an emphasis was placed on transferring downy mildew disease resistance into ‘HHB 67’.
3. SOLUTIONS DEVELOPED
In order to confer resistance to ‘HHB 67’ elite donor lines ‘ICMP 451’ and ‘ICML 22’ were backcrossed onto parental lines ‘H 77/833-2’ and ‘843 A/B’ (Hash et al., 2006). Utilizing donor lines ‘ICMP 451’ and ‘ICML 22’ provided a great base for disease resistance; for example, ‘ICML 22’ demonstrated 95% resista