Recovery Resistance to Downy Mildew in Pearl Millet

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Abstract
The development of symptomless shoots from pearl millet [Pennisetum americanum] plants that show typical systemic symptoms of downy mildew (DM) disease is reported. This phenomenon, referred to here as "recovery", and the trait as "recovery resistance", was detected in 28 of the 33 pearl millet genotypes studied. These represent a wide range of breeding materials and cultivars. The genotypes showed considerable variability for the frequency of plants with recovery resistance and for the extent of sexual and asexual sporulation of Sclerospora graminicola in recovered plants before recovery. The levels of recovery resistance were substantially increased in several genotypes through pedigree selection under high disease pressure in the DM nursery. Injection of growing points of the symptomless shoots of recovered plants with a sporangial suspension, or clipping the stems and shoots of recovered plants growing under high disease pressure, generally did not result in subsequent disease development. Lines produced from recovered plants maintained their resistance at three locations in India. The phenomenon was also observed in Mali and Niger. It is suggested that recovery resistence may be an effective defense mechanism that should be exploited in breeding pearl millet for durable resistance to DM.