Estimation of Combining Ability of Maize Inbred Lines for High Plant Density Tolerance in Medium Altitudes of Kenya
Authors: Ndungu J , Danga Benjamin , Henga Silvia , Makumbi Dan 
Published: August 2023

Purpose: The primary objective of any breeding program is to increase yields, thus superior lines based on yields are used as parents. After parents’ selection, hybrids may not perform as expected because the performance is influenced by the interactions of genotypes used, which the breeder must be well conversant with for accurate prediction of the ultimate hybrids.
Methodology: This study aimed at characterizing tropical maize germplasm on plant density tolerance and comparing combining abilities for grain yield on 120 hybrids obtained by crossing 24 males with 30 female lines using North Carolina design 2 (sets option). This was done under low (53,333), medium (66,666), and high density (88,888) plants per ha in three different zones; Kiboko (marginal zone), Embu (transitional medium), and Kakamega (upper medium). General combining ability (GCA) of 54 maize inbred lines was estimated and specific combining ability (SCA) established for 120 hybrids in 6 sets of 20 each based on family decent. They were evaluated under optimal conditions in the 3 sites named above. Evaluation was done at low, medium and high plant densities under study. The hybrids were planted in a 31*8 alpha lattice design, four local commercial varieties incorporated as checks, and the experiment replicated twice. Data collected included various agronomical traits associated with tolerance to high plant density. Field book software (CIMMYT) was used to organize data and perform preliminary analysis while SAS program (Frederick, 1999) was used to compute analysis of variance (ANOVA) for North Carolina design 2 (NC2).
Findings: Observation revealed increase in plant height, grain yield, ear height, anthesis silking interval, days to 50% silking but lead to reduction in leaf angle with increase in plant density from 53,333 to 66,666 and then to 88,888. Six hybrids were significantly earlier than the check hybrids CKH10717, H517, WH505 and PHB30G19 under the 3 densities. In contrast, 6 varieties were later than all the above checks for the 3 densities. Line CKL15276 had the highest GCA effects for anthesis and days to silking at the three plant densities and highest grain yield at 66,666 plant density. In contrast female line CKL15303 had the highest negative GCA effects for anthesis and days to silking at the three plant densities revealing earliness traits. Likewise, lines CML444, CML 436 and CKL151431 had highly significant GCA effects for field and grain weights. The hybrid CKH 156598 had the highest significant SCA effects for grain yield at 66,666 plant density and for field weight at the three plant densities.
Unique Contribution to Theory, Practice and Policy: The study was informed by Diallel Crossing Theory and conducting systematic field trials, researchers can gain insights into the genetic effects of combining different maize inbred lines and identify potential candidates for developing maize varieties with improved high plant density tolerance in the specified region. This reveals presence of superior alleles and desirable SCA effects and thus can be utilized as parents in hybrid formation and further breeding work. The study also recommends that support should be garnered from relevant government agencies and policymakers to allocate resources for the collaborative network's activities. Advocate for policies that promote research and development in maize breeding for high plant density tolerance.