Evaluation of early drought tolerant maize genotypes under low nitrogen conditions Nyasha E. Goredema1, Ms Nakai Goredema2, Ezekia Svotwa1, Gabriel Soropa1, and Arnold B. Mashingaidze1 1Department of Crop Science and Post Harvest Technology, Chinhoyi University of Technology 2Crop Breeding Institute, Department of Research and Specialist Services

Introduction Nitrogen is generally the most limiting mineral nutrient for crop production in the world (Blumenthal et al., 2008). Declining soil fertility, depleted soils and drought are the major constraints to maize production in East and Southern Africa, and N is considered to be the most limiting nutrient (Kikafunda et al., 2001) Smallholder (SH) farmers fail to apply adequate fertilizers and manures to replace nutrients exported out of the soil when the crop is harvested (Chitende, 2013).

Introduction N is required for the synthesis of proteins, enzymes and chlorophyll hence there is positive relationship between photosynthetic efficiency to produce dry matter and leaf N-content Being a component of proteins and cytoplasm, N is required for meristematic growth and leaf area expansion N-deficient plants are chlorotic and have low photosynthetic capacity and are stunted with low LAI to capture radiation and convert it to dry matter. They produce low economic yields

Introduction Most of the soils in sub-Saharan Africa (SSA) are N-deficient causing yield losses of up to 25% (www.global harvest initiative). Breeding and selecting for increased N-use efficiencies provides a low cost and sustainable solution to yield losses caused by N-deficiency for SH farmers in SSA.

Objectives of the study Main objective To screen maize hybrids for yield tolerance to low nitrogen soils so that they can be used in breeding programmes to confer high nitrogen use efficiency to commercial released varieties

Specific objectives To identify hybrids with the highest tolerance to low nitrogen soils To determine the relationship between variety agronomic performance and yield under low nitrogen

Materials and Methods Study site description Study was carried out at Harare Research Station that is located 2.7 km North East of Harare City Centre in Zimbabwe. It lies at cardinal points 17°48'21.63''S and 31°03'07.21''E. The soils in the experimental area are derived from granite. The field on the study site that was used for the experiment was depleted of nitrogen for the last 50 years.

Experimental design and layout Drought-tolerant maize varieties used in the study were selected from a set of EDT maize inbred lines from the Crop Breeding institute under the DRSS An alpha lattice design replicated three times was used to evaluate 25 maize breeding lines against 20 commercial check varieties. The plots used were 4 m long rows with inter-row spacing of 0.75 cm and in-row spacing of 0.25 cm.

Experimental Design The trial was located on long term N-depleted plots where crops have been grown without N application for the past 50 years. Irrigation was applied for crop establishment, however the crop was rain-fed, 650mm of rainfall, but poorly distributed, the season ended in January, 2016. The crop was top dressed with 75 kg AN at 3 WACE.

Data collection and analysis On the established trial data was collected for : Plant height Ear height Root lodging Stem lodging Number of ears harvested Number of plants per plot Grain weight   Plant height­ was determined by measuring the distance from the base of a plant to the insertion of the first tassel branch. The ear height was determined by measuring the distance from the base of the plant to the insertion of the top ear of the same plant. Root lodging was considered only when the plant had tilted 90 degrees from the root zone. Stem lodging was also considered only when the stem has dropped its cob. Number of the ears harvested and number of plants per plot were counted.

Data Analysis Data was checked for normality before Analysis of Variance was done. Analysis of variance for the measured parameters was done using Fieldbook Cimmyt Software and Meta R at P < 0.05. Mean separation was done using the Least Significant Difference (LSD) when treatment effects were significant at P<0.05.

Grain Yield SC301, PGS63, PGS61 and PAN53 had higher yields than breeding lines 103WH125, 103WH123, 103WH52, 113WH1438, 113WH1454 and 113WH637 surpassed the commercial varieties under low N 103WH123 had the highest yield of 0.79 tons per ha under low N 113WH856 had the lowest grain yield of 0.07 tons per ha (mean = 0.38 tons) (Figure 1)

Ranks for the relationship between variety agronomic performance and yield under low nitrogen. Table 1:Genotype ranking Name Grain Yield Plant Ear Lodging Ears/ Num   GW FW Rank Height Root Stem Plants 103WH123 0.79 0.78 1 124.3 52.1 0.0 0.72 15.9 PAN53 0.80 2 108.7 43.1 2.6 0.61 13.3 SC301 0.73 3 137.4 45.6 0.66 18.6 PGS63 0.62 0.68 4 140.1 49.0 0.54 16.8 103WH125 0.59 0.64 5 120.9 51.1 14.4 113WH1454 0.63 0.57 6 110.7 43.9 5.1 0.26 SC727 83.8 42.6 4.8 0.51 15.1 PGS61 0.50 0.52 8 132.6 54.3 0.46 17.6 113WH1438 0.53 9 144.6 59.3 1.96 11.0 103WH12 0.47 10 117.2 44.8 3.0 12.1 CZH1259 11 107.1 30.2 0.48 13.9 SC403 0.49 107.7 37.1 0.45 14.9 103WH52 13 101.6 33.6 3.3 5.6 12.7 113WH637 14 81.7 40.2 26.6 0.58 12.4 113WH1452 15 106.0 35.6 13.4

Conclusions BL’s 103WH123 (1), 103WH125 (5), 113WH1454 (6), 113WH1438 (9), 103WH12 (10) were ranked between 1 -10 in terms of yield and other desirable agronomic characteristics under low N 113WH637 (14) and 113WH1452 (15) were promising low N tolerant varieties and attained higher ranking than most commercial varieties already on market. 103WH123 and 103WH125 had zero root and stem lodging, an average stem and ear height,

Recommendations Breeding lines 103WH123 (1), 103WH125 (5), 113WH1454 (6), 113WH1438 (9), 103WH12 (10) should be tested in multi location trials for assessment for adaptations to various regions and production systems in Zimbabwe