Phenotypic characterization of mycotoxins resistant maize inbred families and regional hybrids under Aspergillus flavus and Fusarium verticillioides infestation.
Masemola, Bogaleng Milcah.
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Most South African households depend on maize as source of their staple food and daily calories intake, especially the rural communities which depend on the crop to maintain their livelihood. Despite the importance of maize, numerous factors either biotic or abiotic factors affect its production worldwide. Ear rot is one of the common diseases that affect maize production and productivity worldwide. Aspergillus flavus (Raper and Fennel) and Fusarium verticillioides (Sacc.) are two of the serious ear rot-causing maize fungi. These fungi secrete mycotoxins which are hazardous when consumed by humans or animals. The study was executed to characterize mycotoxins resistant maize inbred families at the phenotypic level and to determine the level of natural incidences of ear rot diseases which are associated with mycotoxins contamination. Understanding architecture of genetic of these resistant maize inbred families would greatly aid in breeding high yielding and stable ear rot and mycotoxins resistant hybrids. Experimental trials were conducted at Ukulinga and Cedara Research Stations, during the 2014 to 2015 growing seasons. Further evaluation was conducted at the Makhathini Research Station during the winter season of 2015. The study was conducted using two experiments. The first experiment was assessment of natural ear rot incidences on regional maize hybrids. These hybrids represented a sample of varieties which are grown in the Southern African region. In the second experiment, S3:4 families, which were derived from three way crosses among, A. flavus and F. verticillioides resistant maize families, were artificially inoculated with A. flavus and F. verticillioides. Grain yield and agronomic traits were measured in both experiments. The grains were evaluated for ear rot infection at harvest. The analysis of variance and correlation analysis were conducted using Genstat 14th edition (Payne et al 2007) and Agronomix Generation II (2000), while the multivariate analyses were conducted using the NCSS (2004) statistical computer program. The assessment of natural ear rot incidences on regional hybrids revealed that ear rot causing fungi is a challenge. The results revealed four fungi that were responsible for the natural incidences of ear rots. The fungi included A. flavus (Raper and Fennel), Stenocarpella maydis (Berk.), Fusarium graminearum (Schwein.) and F. verticillioides (Sacc.). Incidences of F. verticillioides were the highest during the two seasons. This might be due to hot dry weather conditions that occurred after flowering. Early maturing hybrids showed lower incidences of ear rots than hybrids that matured late. Although early maturing hybrids encountered less incidences of mycotoxin causing fungi, the results revealed early maturity period had a significant strong negative correlation with grain yield. This trend was consistent with previous studies. Phenotypic characterization study revealed a significant variability among the mycotoxins resistant maize inbred families for resistance to Aspergillus ear rot, Fusarium ear rot and other selected secondary traits except husk cover, insect damage and days to mid maturity. Generally heritability (H2) estimates were large for most traits, indicating an opportunity for selection of the best inbred families for advancement in the breeding programme. Plant height, ear height and primary tassel branches recorded higher heritability values (>80%) compared to the other traits. This was followed by Fusarium ear rot and Aspergillus ear rot resistance scores (≥77%) and grain yield (73%). The results revealed five principal components contributing more than 69% of the total variation and the traits responsible to this variation are Fusarium ear rot, Aspergillus ear rot, plant height, ear height, days to mid maturity, husk cover, insect damage and primary tassel branches. The inbred families were grouped into five principal component groups based on their phenotypic characteristics. Lines to be derived from these grouped families would be exploited to make heterotic combinations by crossing lines from the different phenotypic clusters.