Characterization of Maize Doubled Haploid and Varietal Hybrids under Low-nitrogen and Drought Stress Conditions

Mwangi, Damaris Wanjiru (2015) Characterization of Maize Doubled Haploid and Varietal Hybrids under Low-nitrogen and Drought Stress Conditions. Masters thesis, University of Nairobi.

[img] PDF (Characterization of Maize Doubled Haploid and Varietal Hybrids under Low-nitrogen and Drought Stress Conditions)
Mwangi_Characterization of maize doubled haploid.pdf - Accepted Version
Restricted to Repository staff only

Download (5MB) | Request a copy

Abstract

Drought and nitrogen (N) deficiency are important causes of low maize (Zea mays L.) yields in Eastern Africa. Breeders developing maize varieties use classical methods and little work has been done in sub-Sahara Africa using doubled haploid (DH) technology or the varietal hybrid (VH) methods which may confer enhanced efficiency in breeding for these stresses. This study was conducted in 24 locations across seven countries. The objectives of this study were to assess the heterosis for grain yield and secondary traits as well as yield stability in F1 VHs (Experiment 1) and also to determine the combining abilities for grain yield and its associated secondary traits in DH lines (Experiment 2). In Experiment 1, 10 F1 VHs, their parents and 4 checks were evaluated at 17 locations: 5 drought stressed and 12 optimal. The trials under managed drought stress were grown under irrigation during rain-free months until two weeks to flowering when water was withdrawn to impose stress. An Alpha lattice design replicated twice was employed. Plot size was 5 m long, spaced 0.75 m and 0.25 m between and within rows respectively. Fields were kept free of weeds and pests. Each trial received 90.0 Kg ha-1 N and 98 Kg/ha P as Diammonium Phosphate fertilizer at planting and 100 Kg ha-1 N as Calcium Ammonium Nitrate fertilizer top-dressed at 6 weeks after emergence. In Experiment 2, 46 DH lines were crossed to Tester 1 (CML312/CML442) and to Tester 2 (CML395/CML444), belonging to heterotic groups (HG) A and B respectively. The 92 DH hybrids and 4 classical hybrid checks were evaluated across 7 locations: 1 under managed drought, 1 under low-N and 5 under optimal conditions. An Alpha lattice design was used replicated twice. The sizes of plots, weeds, fertilizers application and pest control measures were similar to those in Experiment 1 but the plots under low N trial had been depleted of N until the yields were reduced to 30 % that of the estimated original optimal potential and no fertilizer was applied post-emergence. Results from Experiment 1, revealed that drought reduced broad heritability (H2) from 90 % to 30 %. Similarly, whereas heterosis for grain yield was significant (P≤0.05) under optimal conditions, drought stress xii reduced the magnitude of this trait to insignificant levels. On the other hand, heterosis for plant height and anthesis silking-interval were significant (P≤0.05) under drought and not under optimal conditions. Amongst the VHs significant (P≤0.05) differences for grain yield occurred under optimal conditions but not under drought environments. Surprisingly, the highest heterosis values (of >40 %) were expressed under drought, where the widest ranges for grain yield were also realized. The VHs yielded 40 % higher than the OPV and as much as the 3-way cross hybrid used as commercial checks. Overall, three VHs (2, 8 and 10) were exceptionally good performers exhibiting both high yields and stability. It was recommended that these three varieties should be evaluated further for possible release to farmers. Results from Experiment 2 revealed that highest H2 for grain yield was present under drought (at 77 %), and lowest under low N conditions; H2 under optimal conditions was in between these two extremes (at 60 %) amongst these DH materials. Variations amongst the DH lines were significant (P≤0.001) for grain yield and secondary traits under both stresses. Differences due to line x tester effects were significant (P≤0.05) for grain yield under drought stress and not significant (P≤0.05) under low N stress. Several DH lines (i.e. 29, 14 and 15) exhibited good GCAs for grain yield and secondary traits. The 46 DH lines were separated into 2 HGs: 24 fell into HG A and 22 into HG B; no lines were placed under HG AB. Although heterotic effects were important in the DH hybrids, GCA effects were more pronounced compared to SCA effects under all production environments. Whereas, across environments, yields under low N and drought stresses were respectively 45 % and 57 % lower than that under optimal conditions, yields of best line (DH Line 29) were consistently higher than those of the best classical-commercial hybrid checks. The findings of this study showed that both DH based hybrids and OPVs have great promise although DH-materials had much higher potential. They should therefore be assessed further for commercial exploitation in Eastern Africa.

Item Type: Thesis (Masters)
Subjects: S Agriculture > S Agriculture (General)
S Agriculture > SB Plant culture
Divisions: Africana
Depositing User: Mr. Senay Abate
Date Deposited: 27 Jul 2016 08:54
Last Modified: 27 Jul 2016 08:57
URI: http://thesisbank.jhia.ac.ke/id/eprint/1243

Actions (login required)

View Item View Item