Combining Ability And Yield Performance Studies Of Tropical Maize (Zea Mays L.) Germplasm Under Drought Stress And Well-Watered Environments

ABSTRACT

Maize is increasingly consumed by Nigerien households. Limited studies have been conducted on the production and productivity of this crop in Niger and very few cultivars (mostly open pollinated varieties) are available to farmers. Knowledge and understanding of farmers’ preferences for new varieties would be invaluable in designing a successful maize breeding program. Maize cultivars grown in Niger are derived mainly from tropical yellow-grained extra-early and early-maturing lowland germplasm sources. Lack of availability of appropriate early and extra-early testers as well as information on the combining ability, the mode of gene action, and the heterotic patterns of the available early and extra-early inbreds impede the successful development and adoption of maize hybrids in West Africa.

Three activities were conducted in the present study. The first was a Rapid Rural Appraisal to assess the appropriateness of maize crop management practices used by farmers in Niger, to identify major factors limiting maize production and productivity, and to identify traits preferred by farmers. The study revealed that the production of maize in the country is carried out using few inputs and poor crop management practices. The current level of production is very low due to many factors including drought, low soil fertility, poor crop management and lack of availability of improved varieties. Yellow maize cultivars that combine earliness and high yield potential are desired by farmers.

The second activity consisted of two parts including an experiment to determine the right time to impose water stress in maize drought trials in Niger and a diallel study to explore the combining ability of grain yield and other traits of early maturing, yellow-grained maize inbreds under drought and well-watered conditions. The objectives of the this activity were to test the efficiency of the CIMMYT/IITA screening method for drought tolerance in Niger, examine the

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combining ability and the mode of gene action for drought tolerance among 15 early maturing inbred lines, classify the inbreds into contrasting heterotic groups using two different classification methods i.e. the SCA effects of grain yield and the HSGCA, and assess the yield performance and stability of hybrids under contrasting environments. The findings of the activity revealed that the drought screening method that involved (i) stopping irrigation 3 to 2 weeks before anthesis, (ii) applying a “rescue irrigation” 13 to 15 days after imposing drought stress, and (iii) resuming the normal irrigation 10 to 12 days later until crop maturity was the most appropriate for maize drought trials in Niger. A moderate yield reduction under drought of 36.84% of the yield under well-watered environment was observed.

Significant GCA and SCA effects for grain yield and most measured traits were detected with predominance of GCA effects over SCA effects, indicating that most traits were controlled predominantly by additive gene action. Two heterotic groups were identified based on the classification with the SCA_PY method. Inbreds ENT 13, TZEI1 124 and TZEI 129 displayed the highest GCA values in well- watered environments and were the best parents that are likely to contribute favorable alleles to progeny. Inbred ENT 13 was the best combiner under both drought and well-watered conditions suggesting its inclusion in population imporvement and in the development of hybrids and synthetics. Significant differences were observed among the single cross hybrids under the two water treatments. The single cross hybrids TZEI 124 x ENT 13; TZEI 160 x TZEI 157; TZEI 182 x ENT 13 and TZEI 167 x ENT 13 were the highest yielding hybrids across test environments and out-yielded all the checks.

In the third activity, three related single cross (RSC) parents, two single cross checks and 103 modified single crosses (MSCs) derived from crosses of the three RSCs to 36 inbreds of varying maturity groups were evaluated under drought and well-watered conditions to assess the yield

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performance of MSCs and examine the relationship between grain yield of MSCs and their maturity groups. Results revealed a moderate but adequate level of moisture stress (62.3% yield reduction). Significant differences were observed among the MSCs under the two moisture regimes. Under drought stress, the 3 highest yielding MSCs (TZEEI 76 x TZEEI 82) xCMK ENT 23; (TZEEI 76 x TZEEI 82) x CMZ ENT 8; and (TZEEI 95 x TZEEI 79) x CMK ENT 8 outyielded the best single cross check (ENT 13 x CamInbgp.1-17) by 91%, 67%, and 66%, respectively. Under well-watered conditions, the 3 top yielding MSCs (TZEEI 76 x TZEEI 82) x TZEI 124; (TZEEI 78 x TZEEI 79) x ENT 13 and (TZEEI 95 x TZEEI 79) x CMZ ENT 5 outyielded the best single cross check TZEI 124 x ENT13 by 19.3%, 17.8% and 17% respectively. Modified single cross hybrids developed from early and intermediate maturing inbreds yielded higher than those developed from extra-early inbreds indicating that extra-early germplasm is less advantageous in terms of grain yield potential particularly under optimal growing conditions.