Breeding approaches in simultaneous selection for multiple stress tolerance of maize in tropical environments

Abstract

Maize is the principal crop and major staple food in the most countries of Sub-Saharan Africa. However, due to the influence of abiotic and biotic stress factors, maize production faces serious constraints. Among the agro-ecological conditions, the main constraints are: lack and poor distribution of rainfall; low soil fertility; diseases (maize streak virus, downy mildew, leaf blights, rusts, gray leaf spot, stem/cob rots) and pests (borers and storage pests). Among the socio-economic production constraints are: poor economy, serious shortage of trained manpower; insufficient management expertise, lack of use of improved varieties and poor cultivation practices. To develop desirable varieties, and thus consequently alleviate some of these constraints, appropriate breeding approaches and field-based methodologies in selection for multiple stress tolerance, were implemented. These approaches are mainly based on: a) Crossing selected genotypes with more desirable stress tolerant and other agronomic traits; b) Using the disease/pest spreader row method, combined with testing and selection of created progenies under strong to intermediate pressure of drought and low soil fertility in nurseries; and c) Evaluation of the varieties developed in multi-location trials under low and "normal" inputs. These approaches provide testing and selection of large number of progenies, which is required for simultaneous selection for multiple stress tolerance. Data obtained revealed that remarkable improvement of the traits under selection was achieved. Biggest progress was obtained in selection for maize streak virus and downy mildew resistance, flintiness and earliness. In the case of drought stress, statistical analyses revealed significant negative correlation between yield and anthesis-silking interval, and between yield and days to silk, but positive correlation between yield and grain weight per ear.Kukuruz je glavni usev i osnovna komponenta u ishrani ljudi u vecini zemalja Afrike ispod Sahare. Medjutim, zbog uticaja abiotskih i biotskih stres faktora, proizvodnja kukuruza je limitirana u velikoj meri. Medju agro-ekoloskim uslovima glavni cinioci su; nedovoljna kolicina i los raspored padavina, neplodna zemljista, bolesti (crticavost lista, plamenjaca, pegavost lisca, rdja, trulez stabljike i korena) i stetocine (busaci i stetocine skladista). Medju socio-ekonomske faktore ogranicavanja proizvodnje kukuruza su: siromasna ekonomija, nedovoljno strucnih kadrova i neobucenost radne snage, lose agrotehnicke mere i odsustvo koriscenja novih sorata. Da bi se stvorile odgovarajuce sorte, i time umanjilo delovanje veceg broja stres faktora, primenjeni su odredjeni pristupi u odabiranju roditeljskih parova i metoda rada u laboratorijskim i poljskim uslovima. Ovi pristupi se uglavnom zasnovani na: a) Ukrstanje odabranih genotipova sa vise pozeljnih agronomskih osobina, a posebno onih koje uticu na otpornost prema faktorima stresa, b) Kombinovano koriscenje metoda zarazenih redova sa bolestima i stetocinama i metoda testiranja i odabiranja kreiranih genotipova u uslovima suse i niske plodnosti zemljista. Ovakvi pristupi omogucavaju testiraje i odabiranje velikog broja potomstava, koje je neophodno u simultanoj selekciji na otpornost prema vise faktora stresa. Dobiveni podaci pokazuju da je dobiveno znacajno poboljsanje osobina koje su bile predmet selekcije. Najvece poboljsanje osobina je postignuto na otpornost prema crticavosti lisca i plamenjace, tvrdoci zrna i ranostasnosti. U slucaju otpornosti na susu, statisticki podaci pokazuju negativnu korelaciju izmedju prinosa i svilanja i intervala izmedju prasenja polena i svilanja, ali i znacajnu pozitivnu korelaciju izmedju prinosa i tezine zrna po klipu. .