STUDY AND DEVELOPMENT OF MAIZE CULTIVARS RICH IN FLAVONOIDS

Maize is one of the most consumed and appreciated cereals in the world, representing a staple food for many populations; during its diffusion the process of adaptation to different environments and growing conditions, together with human selection, led to the diversification of hundreds different landraces. Nowadays the preservation of maize biodiversity appears crucial given the importance of this species for global food security. Even if the great part of maize varieties cultivated worldwide has white or yellow kernel, several flavonoids compounds such as anthocyanins and phlobaphenes can be accumulated in seeds and in other plant tissues, conferring them a red-purple, blue or brown pigmentation. A few regulatory genes are involved in flavonoids accumulation, inducing a tissue specific pattern of pigmentation. Flavonoids consumption is known to be associated to many beneficial effects on health, especially in the prevention of cancer, cardiovascular diseases, myocardial infarction, age-related neurodegenerative diseases, obesity and type 2 diabetes, mainly due to their antioxidant activity. Considering the interest for pigmented maize varieties as source of antioxidants in the diet and natural food colorants, in this PhD project we studied the heritability of the main regulatory genes involved in seeds pigmentation. Improved maize varieties able to exert beneficial effects on human health could be developed through a breeding approach, using pigmented maize varieties as donors of the main regulatory genes, thus developing real functional foods that could be introduced in the diet of many people. Three strategies can be followed to develop colored maize varieties rich in flavonoids adapt to the European growing conditions without recurring to a biotechnological approach: the easiest strategy is represented by the rediscovery of the ancient colored landraces still cultivated in restricted areas that could also represent a starting point for future breeding programs. A second strategy can be adopted using colored maize varieties already adapted to the European growing conditions as source of the dominant alleles of the regulatory genes of the flavonoids biosynthetic pathway: booster1 (b1) and purple plant1 (pl1), inducing the accumulation of anthocyanins in the seeds pericarp layer. A third strategy is represented by the use of tropical or subtropical materials as source of dominant alleles of the regulatory genes, in fact the “strong” dominant alleles of the purple plant1 gene inducing the accumulation of very high amounts of anthocyanins, have not been yet discovered in varieties already adapted to our photoperiod. According to the first strategy, in this project two ancient European colored landraces were studied and characterized. The Spanish blue maize variety Millo Corvo was found to accumulate anthocyanins (mainly cyanidin) in the seed aleurone layer, due to the presence of a dominant allele of the red colour1 (r1) gene, as confirmed by mapping and sequencing data. The Italian Nero Spinoso variety was also characterized founding that its dark pigmentation is due to the accumulation of phlobaphenes in the pericarp layer, due to the pericarp colour1 (p1) gene. In collaboration with the municipalities of Esine and Piancogno (BS) and with the “Università della Montagna” (Edolo, BS), the Nero Spinoso has also been included in the “National Register of Varieties of Agricultural and Horticultural Species” as a “Variety of Conservation”. Following the second strategy we performed a breeding program based on backcrossing and selection, using the colored inbreed line Reduno (included in the CPVO register, N° EU 33449), as pollen donor (source of the dominant alleles of the regulatory genes booster1 and purple plant1), and a colourless sweet corn line as recurrent parent, thus obtaining a colored sweet corn rich in anthocyanins and characterized by an higher antioxidant power with respect to the recurrent parent. Regarding the third strategy, considering that colourless varieties, even if lacking in anthocyanins and phlobaphenes, can contain high amounts of other flavonoids, we sampled two South African varieties characterizing them for the first time from the phenotypical and nutritional points of view, in collaboration with the Vaal University of Technology (Vanderbijlpark, Guateng, South Africa). Our results showed a low nutritional value and also a low content of flavonoids, suggesting the possibility of using these varieties in a breeding program aimed to develop improved maize varieties that could represent functional foods for the local population.