Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
5 Limitations and Uncertainties Quality-protein maize (QPM) has been produced, and its advance- ment is under way. However, despite its outstanding potential, uncer- tainties over its performance in general practice still exist. Although QPM has performed well in test plots and in some progressive farmers' fields, it hasn't yet been widely exposed to unsupervised farm use in subsistence settings. Research is still needed to support the steady and orderly development of what promises to become an important new food crop. CUSTOMIZING Overall, the next requirement is to intensify testing and selection in areas suitable for commercial production, and to test its acceptability for human consumption and industrial use, not just in laboratories but in the unforgiving world of commerce. The QPM varieties developed by Centro Internacional de Mejora- miento de Maiz y Trigo (CIMMYT) have performed as well as common maize in trials and seem to have good adaptability. However, maize needs many varietiesâeach adapted to the soil type, growing season, altitude, latitude, pests, diseases, and human preferences of its own locality. It is QPM types for these localized situations that must now be perfected. Today's germplasm should be regarded as an intermediate product. In some locations it may perform well, but in others it will have to be locally refined and adapted before being released to farmers. GENETIC STABILITY Although the agronomic traits of QPM have been brought up to levels essentially equal to those of their common-maize counterparts, their stability has not been confirmed as yet. It is not certain, for 41
42 QUALITY-PROTEIN MAIZE example, that high yields and nutritional quality can be maintained with seed collected and resown in the same location year after year. The limited trials carried out so far show that the high yield is generally stable over two or three generations, but how many more years this will continue is not known. Also uncertain is the stability of yield over different locationsâthat is, whether the same seed will give similar yields when planted in different places, even those with similar environments. Although there is no reason to expect that QPM varieties will be disastrously unstable, the crop has not been tested widely enough to quantify the consistency of its performance, and some types have proved unpredictable. DELIVERY SYSTEMS The introduction of any new crop variety brings a host of operational complications. No matter how good the material and how great the need in the countryside, if there is no "delivery system" to multiply and distribute seed and ensure a reasonable degree of purity, it will fail. QPM is no more demanding than any other new maize variety, but its organized introduction is nonetheless an important requirement. CREDIBILITY Trying to introduce a new version of a crop that once failed could encounter psychological hurdles. For those who remember the enthu- siasm for opaque-2 maize in the 1970s, QPM suffers a "credibility gap." Researchers could be hesitant to undertake QPM studies because of the lingering memories of the earlier form that did not live up to its billing. LACK OF DISTINGUISHING FEATURES The fact that QPM is now indistinguishable in appearance from common commercial maize is also a potential limitation. (It is ironic that such a beneficial feature is also a weakness.) People could easily identify opaque-2 maize's soft, chalky kernels, but only in a laboratory can QPM be distinguished (by measurement of its lysine and tryptophan levels). This is a particular concern because genetic contamination is a potential problem, and even deliberate adulteration could occur. Unscrupulous farmers or dealers could adulterate QPM with common
LIMITATIONS AND UNCERTAINTIES 43 maizeâa particular temptation if QPM is allowed to sell at a premium price.1 SOCIAL FACTORS The nutritional advantages of QPM appear to be documented in laboratory experiments. However, they are not adequately authenti- cated in local diets of actual populations. QPM has outstanding promise where maize is a preferred item in the diet, but unforeseen factors may arise. People who have used maize all their lives may recognize subtle differences and may suspiciously reject QPM as "alien." SPECIAL HANDLING QPM seed plots must be isolated from the pollen of other maize types. This is true for any quality maize, but with QPM it is even more necessary because cross-pollination reduces both yield and nutritional value. Around the edges of the fields, cross-pollination with nearby common maize causes genetic contamination. (About 10 percent contamination has been measured in Guatemala.) To maintain the nutritional quality, farmers must save seed from the center of their fields and (for safety) replenish their seed from certified stocks every few growing seasons. PESTS AND DISEASES Because pests also benefit from good nutrition, commercially avail- able QPM may prove somewhat more susceptible to storage problems than will normal maize. So far, there is no unequivocal evidence that this will occur, but QPM has shown some storage damage under experimental conditions. A problem of particular concern is aflatoxin. Again, there is no unequivocal evidence that QPM is any more susceptible than normal maize to this toxin-producing fungus, but, like people, fungi respond to better nutrition. In two experiments comparing aflatoxin infections in QPM and normal maize, one showed no difference and the other was inconclusive because it showed both higher and lower levels of infection. 1 One way to avoid this is to introduce QPM of a different color from the local common maize: yellow QPM where white maize is now standard and vice versa. Another method is to introduce hybrids, which must of necessity be sown using fresh seed.
44 QUALITY-PROTEIN MAIZE SPECIAL ENVIRONMENTS Because varieties are not yet selected for all sites, current QPM varieties have not performed well in a few select environments, especially those with specific disease or insect problems. In Thailand, for example, one test plot was wiped out by downy mildew fungus.2 Thus, although current QPM varieties can approach normal yields, this is not yet necessarily true for every part of the world. The current materials seem best adapted to drier areas. A project under way to adapt QPM to wetter areas is now developing strains in which the husks cover and cling to the ears, thereby hindering the entry of pest and disease organisms. Work is also under way in promising QPM materials to develop resistance to maize streak virus, a serious disease in Africa. HYBRIDS The work so far has concentrated on open-pollinated varieties, but QPM is also promising for hybrid maize. Hybrids generally yield better and maintain their genetic qualities more consistently. For this, separate QPM lines must be generated and then joined to form hybrid combi- nations. A beginning has already been made; CIMMYT expects to test hybrids at farm level within a few years. Moreover, researchers at Texas A & M and other universities also have QPM hybrids in preparation.3 Although hybrids are a way of stabilizing the purity of the QPM traits, they have to be produced centrally, farmers must buy new seed each year, and hybrid seeds cost appreciably more than those of traditional, open-pollinated varieties. MALNUTRITION QPM is a quality food that is potentially within the financial reach of a vast population of malnourished people, but it is no panacea. Quality protein is not the only requirement for overcoming malnutrition. Building a person's body protein depends also on the supply of calories from carbohydrates and fats in the diet. (If these are not adequate, 2 However, downy mildew resistance can be developed in QPM materials rather quickly, and this is currently being done with some populations of normal maize in Thailand. 3 Information from A.J. Bockholt. It should be noted that these are hard-endosperm hybrids, not the soft-endosperm opaque-2 types (see appendix A).
LIMITATIONS AND UNCERTAINTIES 45 the body wastefully burns up food proteins for energy.) Indeed, QPM may be unable to solve the problem in its worst case scenario. Calories are possibly the limiting problem for people that most desperately need it, and some nutritionists claim that the calorie problem must first be solved. In addition, diets of the destitute are likely to be insufficient in critical minerals and vitamins (for example, calcium and riboflavin). Also, malnutrition will persist because it is associated with medical problemsâinfections and diarrhea, for example. Its eradication will thus require the inputs of preventive medicine and medical care. In addition, any nutrition-improvement program should be a component of other interventions such as those that modify living conditions, improve water supplies and food storage, and increase income. It would be a mistake to infer from this report that nations need only feed QPM to their malnourished populations to overcome all malnu- trition.
