Breeding investigations of maize (Zea mays L.) genotypes for tolerance to low nitrogen and drought in Zambia.
Year: 2007
Type: dissertation
Abstract: Low soil nitrogen (N) and drought impede maize production in the small-scale farming \n \nsector in Zambia; and adoption of new cultivars with improved tolerance might enhance \n \nproduction. This study: a) assessed farmer preferences for maize cultivars; b) \n \ndetermined genotype x environment interaction effects among popular maize cultivars \n \nunder contrasting soil fertility levels and; c) investigated landraces for tolerance to low N \n \nand drought using S1 selection. The study was carried out in Zambia from 2004-07. \n \nFarmer preference influencing the adoption of maize cultivars was investigated using \n \nboth formal and informal surveys in Luangwa, Chibombo and Lufwanyama rural districts \n \nrepresenting the three agro-ecological regions of Zambia. Focus group discussions and \n \npersonal interviews were used to collect data on issues that affected maize production in \n \nthese areas. It has been found that although farmers perceived landraces to be low \n \nyielding, they believed that they were superior to improved cultivars for: tolerance to \n \ndrought; tolerance to low soil fertility; grain palatability; grain storability; and poundability. \n \nThe need for food security, their inability to apply fertiliser, and their need for drought \n \ntolerant cultivars significantly (p ≤ 0.05) influenced farmers in adopting cultivars. The \n \nfarmers would readily adopt cultivars that address these concerns. The predominant use \n \nof certain landraces (76%) reflected their superiority in meeting some of these needs. \n \nThe performance of nine popular cultivars (three for each of hybrids, OPVs and \n \nlandraces) under contrasting levels of soil fertility, across six environments (ENVs) in the \n \nthree agro-eological regions, was evaluated. An ENV was defined as season x location \n \ncombination. The fertilizer treatments were full fertilization, basal dressing, top dressing \n \nand nil fertilization. The cultivars exhibited significant non-crossover type of genotype x \n \nfertilisation interaction effects at three ENVs, while the genotype x fertilisation interaction \n \neffects, were non-significant at the other three ENVs. The cultivars exhibited dynamic \n \nstability by increasing grain yield (GY) when fertilization was increased. Landraces \n \nyielded higher than all open pollinated varieties and were generally higher yielding than \n \ntwo hybrids. Based on average rank for GY, the five highest yielding cultivars were \n \nMRI724, Gankata, MM603, Kazungula and Pandawe. Superiority of landraces revealed \n \ntheir genetic potential for GY under low soil fertility and they should be used as \n \ngermplasm in developing cultivars targeting such environments. \n \nNinety-six local landraces were selfed to generate S1 lines (2004/05 season) which were \n \ncrossed to a tester (2005/06 season). Testcrosses were evaluated under optimal, low N, \n \nand drought conditions (2006/07 season). Data on GY, anthesis-silking interval, number \n \nof ears per plant, leaf senescence, leaf rolling, tassel size and grain texture were \n \nrecorded in all the trials during the study period. Testcrosses, their S1 parents and \n \nlandraces that were superior under low N, drought, optimal conditions and across \n \nenvironments were identified; these should be used to develop varieties targeted to a \n \nparticular environment. Selection for tolerance to drought also selected for tolerance to \n \nlow N. Selection for low N tolerance also selected for GY under drought and optimal \n \nconditions. Therefore, in selecting for tolerance to abiotic stresses, use of optimal and \n \nmanaged stress environments was effective. The following landraces were superior at \n \n10% selection intensity: LR38, LR84 and LR86 (optimal, low N and drought conditions); \n \nLR11, LR35 and LR76 (low N and drought conditions); LR12 (optimal and drought \n \nconditions); LR40 and LR93 (low N conditions only); LR79 (drought conditions only) and; \n \nLR74 and LR85 (optimal conditions only). These landraces should be used as source \n \ngermplasm targeting respective environments. \n \nSignificant (p ≤ 0.05) positive general combining ability effects for GY under both low N \n \nand drought conditions were found implying that additive gene action conditioned GY \n \nunder the abiotic stresses. The heritability for GY under low N (0.38), and drought (0.17) \n \nconditions, was low suggesting that selection based on GY alone was not effective. The \n \ngenetic correlation for GY between optimal, and either low N (rG=0.458), or drought (rG = \n \n0.03) environments, was low (rG < 0.5) suggesting that indirect selection would not be \n \neffective either. Therefore, use of secondary traits for selection is discussed. \n \nThe study established that most farmers depended on local landraces for seed and \n \nwould adopt low input improved varieties that yield higher than the landraces. Some \n \nlandraces were found superior to some improved cultivars under contrasting fertilisation \n \nregimes. The study also found that landraces had genetic variation for tolerance to low N \n \nand drought. Landraces, S1 lines and testcrosses superior under low N, drought, optimal \n \nconditions and across environments were selected and they should be used to develop \n \ncultivars targeting respective environments. Policy implications of these results are \n \ndiscussed.
Author: Francisco Miti
Language: English
Topic: Genetics and Plant Breeding
Subfield: Plant Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W165446206