No one knows the answer to these questions, because no one has studied the variation in traits of applied interest such as protein or isothiocyanate content across Moringa oleifera with a global perspective. And in addition to a lack of studies of traits of applied interest, no one has studied the global geographical distribution of genetic variation. Studying genetic variation is essential because variation in traits of interest almost always parallels genetic variation. The areas with highest genetic variation are also the places that are most likely to vary the most in the traits that we are interested in. Because selective breeding to improve a crop depends on variation, it is very important to detect these variational hotspots. By finding variants that start as close as possible to our breeding goals- say maximizing protein or cancer-preventive isothiocyanates—then we raise the chances of reaching our goals.
Trying to improve a crop without knowledge of its patterns of variation is just groping in the dark. Without a map of the geographical distribution of genetic variation, a breeder has no way of knowing whether he or she is sampling repeatedly from the same gene pool, or instead is sampling as widely as possible.
Because of the way that domestication usually affects genetic variation, I suspect that variation in the domestic Moringa oleifera that is cultivated worldwide is relatively low. This means that the variation that many researchers document in their local moringas is probably not very significant for breeding. The process of domestication involves selecting desirable variants from wild populations, and preferentially growing these. People then select the best variants from the progeny of these desirable wild plants. Over countless generations, the plants become molded according to human needs, and can depart markedly in their characteristics from the wild ancestor. Looking at a modern corn cob, with its row upon row of succulent kernels, you would never imagine the wild ancestor’s hard, nearly inedible seeds and tiny cobs. Eating a 300 gram avocado, you would never imagine the marble-sized, if tasty, wild ancestor.
These transformations are remarkable, and they occur because of a narrowing of genetic variation. Wild ancestral populations typically have a large amount of variation. In the space of variation in the traits of interest, most individuals in a population are very far from where humans would like them to be. For example, in a wild population of trees bearing edible fruit, some are usually sour, a few are very sweet, and most are somewhere in the middle. Humans like their fruit sweet, so breeders are usually not interested in the whole gamut from sour to pretty sweet. Breeders get rid of all of that unwanted variation by growing just the sweetest ones. In one step- taking seeds from the tree with the sweetest fruit and growing only those- the variation is greatly reduced. Over subsequent generations of selection for even greater sweetness, the variation is reduced even more. This reduction in variation is exactly what breeders want because it means that time after time the plants will dependably produce fruit of the desired quality. Moringa oleifera is quite different from its putative wild ancestor. It grows much faster, tastes different, and has leaves that are less tough and much more pleasant to eat. There is no wild Moringa that is identical to the cultivated M. oleifera, so this means that the moringa that we grow and eat has probably gone through a marked process of domestication. This strongly suggests that the variation in domestic Moringa oleifera is much lower than in the wild ancestor.
Given this reality, if a moringa breeder would like to maximize leaf protein content, then where would the best place to start be? Most researchers and agronomists working on moringa simply go out and use the moringas available locally. Many purchase seed of the long-fruited PKM variety, which was bred for edible fruit, not for leaves or for seed oil. It seems unlikely that these variants are always optimal for the breeding program at hand. If, instead, breeders had in hand a map showing where genetic variation in Moringa oleifera is high and where it is low, then they could carry out their sampling for breeding programs in an informed way. For example, to find the most potent cancer chemopreventive Moringa oleifera, it would be possible to go to the area where variation is highest, and sample intensively. There would be no point in surveying intensively across groups with low variation, but this is probably exactly what current moringa researchers are doing.
So this brings us back to the need for Garima’s study. Moringa oleifera is grown worldwide, so it is important to include at least a smattering of samples from the far-flung areas where moringa is grown. Accordingly, Garima’s study includes samples from South America, North America, Africa, Oceania, Madagascar, and various parts of Asia outside the Indian subcontinent. These are areas where Moringa oleifera is not native, so chances are that these areas together are rather low in moringa genetic diversity. It seems clear that Moringa oleifera is native to and was domesticated in India, and so it is here where the genetic diversity is almost certainly highest, and where the mapping of genetic diversity needs to be the most intensive. Also accordingly, Garima’s study emphasizes sampling across the Indian subcontinent, with emphasis on the putative ancestral populations.