Genetic variability and inheritance studies for low pH tolerance in tropical and sub-tropical maize germplasm

English: In Malawi maize is grown even in marginal lands, on steep slopes, wet lands, rocky areas and low pH soils due to the high human population which excert pressure on the land. The objectives of this study were to investigate genetically diverse maize genotypes for tolerance to low pH soil conditions. In the hydroponic experiment genotypes IWDC3SYNF2-B, VPO52, and LPHpop 4 had relatively higher nett seminal root length and were considered tolerant, and DT-YSTR SYNTHETIC-B, TZE-WPOPDTC2STR-B, TZE-YDTSTRC4-B, LPHpop3, LPHpop13, and LPHpop14 were sensitive or susceptible to Al toxicity. Under field conditions, genotypes LPHpop16, LPHpop3, VPO739, VPO5173 and LOW N POOL C3-B were identified to be relatively tolerant to low pH soil conditions. SYNDTE–STY-W-B ranked first in terms of root tolerant index (RTi) with a good NSRL in the glasshouse hydroponic experiment and this was followed by VPO717 which also had a relatively a better root tolerance index and nett seminal root length. Phenotypic traits associated with grain yield, such as plant vigour, seed size (100 seed weight), shelling percentage, number of ears per plant, ear height and plant height can be used alongside grain yield when selecting germplasm for tolerance to low pH stress. In general, the effects of low pH soil conditions contributed to reduction in grain yields and yield components. The combined mean yield reduction due to low pH soil in this study was 69.9%. From AMMI and GGE analysis, genotypes LPHpop21, VPO52, VPO72, VPO744 and VPO96 were identified as the most stable. VPO097 was identified as an unstable genotype. Chitala low-land optimal site was identified as the most discriminating environment in terms of genotypes while Chitedze mid-altitude optimal environment was identified as a stable environment. The diallel study revealed that additive and non-additive gene actions were at play in the expression of some of the traits like grain yield, number ears per plant, shelling percentage, 100 seed weight and plant vigour, while non-additive gene action was predominant in the inheritance of characteristics such as anthesis-silking interval, plant and ear height, grain texture, stem and root lodging and gray leaf spot disease. Positive and highly significant GCA effects for grain yield were observed for inbred line CZL999601 across low pH and optimal conditions. While negative and significant GCA effects for grain yield were observed for inbred line CML161 across low pH and optimal conditions. SCA results indicated that single-cross hybrids CML999601/CML144, CML144/CML202, CML481/CML288 and CML161/CM172 were best for grain yield across low pH and optimal conditions. At a cut-off point of 1.0 with a cophenetic correlation of rcop = 0.87, the UPGMA clustered the inbred lines based on GCA for grain yield into two main clusters through use of Euclidean distance and standard deviation as type of scale. The pattern mostly followed the origin of the maize inbred lines such that six out of seven inbred lines from CIMMYT-Colombia (tropical) were grouped in the second cluster. The open pollinated inbred line varieties and specific combinations (single-crosses generated) identified in this study will be used in the National Maize Breeding Programme for development of genotypes tolerant to low pH and diseases for yield improvement and subsequent food security in the country.