From 1998 to 1999, 15 early maturity and flint populations (belonging to INTA germplasm bank, Argentina) were planted in a completely random block design with four replications at the IFSC (Instituto Fitotécnico de Santa Catalina, Llavallol in Buenos Aires) experimental farm. Each plot consisted of 15 plants in a single row (3,5 m long), with 25 cm between plants and 80 cm between rows. Five corn ears randomly sampled from each row were harvested and their kernels were shelled and pooled. A subsample of 100 kernels per plot was taken to determine fungal contamination. Twenty-five kernels per Petri dish (9 cm diameter) were placed on filter paper watered with sterile distilled water. The Petri dishes were incubated at 24 C ± 2 C for 7 days under 12/12 h photoperiod and cold white and black fluorescent lamps (1). One hundred seeds per replication were evaluated by the blotter test, according to ISTA rules.
The fungi developed in those kernels were subcultured in PDA and then identified. The percentage of contaminated seeds by each genera of fungus in the different replicates was recorded. Data (arcsin transformed) were analyzed by ANOVA, through a mixed model of two factors in which genotypes were used as the fixed factor. Means were compared by LSD test at 0.05 probability level. Simple correlation between % of each fungus vs. passport data (origin, latitude, longitude, altitude) and characterization data (racial form, endosperm colour, heat units from planting to silking) were calculated. The coefficient of product-moment correlation, formulated by Pearson, was used. Furthermore, a "t" test for significance of this coefficient with n-2 degree of freedom was done (Sokal and Rohlf, 1995).
The external mycoflora identified included: 3 species of Fusarium (F) Genera of the Section Liseola: F. moniliforme, F. proliferatum and F. subglutinans; two species of Aspergillus Genera: A. flavus (Af), A. niger (An) and Penicilium spp. (P).
The maize populations didnít show dissimilar
behaviours for the presence of Af, An and P contaminants. However, genotypes
(populations) had a differential response to Fusarium. This could
indicate some sort of coadaptation between host-pathogen related with the
collection sites of accessions (longitudinal position) and with some characters
(highly heritable) such as heat units from planting to silking and endosperm
colour. Earlier maturity populations with white or yellow endosperm showed
a higher level of Fusarium. Genotype-environment interaction was
the most important source of variation for A. flavus, A. niger
and Penicilium spp. This possibly prevented the differences
among genotypes from showing. It would also indicate that the populations
of fungi would change their behaviour according to the environment. Possibly,
environmental factors related to grain storage were responsible for some
changes, but they were not controlled during this experiment.
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