This is all well and good, but it is in the prevention of future difficulties that top-cross hybrids really shine. Should one of them ever succumb to disease, plant breeders can introduce resistance through the open-pollinated parent in just a generation or two (in, say, not more than 2 years). It is possible, therefore, to keep a hybrid strong and secure by performing parallel breeding on the open-pollinated parent as a sort of ongoing genetic preventive maintenance.
The ICRISAT plant breeders are now taking the strategy a stage further and replacing even the sole remaining inbred parent with a hybrid of broad genetic background. This means that the resulting hybrid has even more genetic variability within it. This method helps, too, in reducing the cost of seed production.
Pearl millet (that is, Pennisetum glaucum) will hybridize with a few wild Pennisetum species, some of them very distantly related. Crosses with close relatives produce fertile hybrids, thus permitting extensive modifications to the genomes of both. Some hybridization work has already been done involving napier grass (Pennisetum purpureum ). Pearl millet x napier grass hybrids have been released for perennial fodder supplies in India. the United States, and various other nations.
Two wild and weedy subspecies (Pennisetum glaucum subspecies monodii and Pennisetum glaucum subspecies stenostachyum) also readily cross with pearl millet. The useful characteristics they can confer include disease- and insect resistance, genes for fertility restoration of the A1 cytoplasm, cytoplasmic diversity, high yield under adverse conditions, apomixis, early maturity, and many inflorescence and plant morphological characteristics.
Among other possibly useful wild species are Pennisetum squamulatum, Pennisetum orientale, Pennisetum faccidum, and Pennisetum setaceum.
Pearl millet has also been crossed with species of completely different genera, including buffel grass (Cenchrus ciliaris).13
In an approach that turns normal practice on its head, at least one researcher is using pearl millet to "improve" its wild relatives. The resulting tough, resilient, almost-wild Pennisetum hybrids appear useful for stabilizing desertifying environments, while giving those who live there a chance to get some food.14